A new class of functionalized terpyridyl ligands as building blocks for photosensitized supramolecular architectures. Synthesis, structural, and electronic characterizations

DOI: 10.1021/ja011069p

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Journal of the American Chemical Society p. 1364 - 1377 (2002)

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Authors:

Laine, Philippe

Bedioui, Fethi

Ochsenbein, Philippe

Marvaud, Valerie

Bonin, Michel

Amouyal, Edmond

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Article abstract of DOI:10.1021/ja011069p

A new class of triarylpyridinio-derivatized [4′-(p- phenyl)_n]terpyridyl ligands, R¹₂R²TP⁺-(p)_ntpy, was designed as a novel category of electron-acceptor (A)-substituted proto-photosensitizi

Full text of DOI:10.1021/ja011069p

Published on Web 01/26/2002

A New Class of Functionalized Terpyridyl Ligands as Building

Blocks for Photosensitized Supramolecular Architectures.

Synthesis, Structural, and Electronic Characterizations

,§

Philippe Laine´,*^,†Fethi Bedioui,^‡Philippe Ochsenbein, Vale´rie Marvaud,^|

Michel Bonin,^§and Edmond Amouyal^†

Contribution from the Laboratoire de Chimie Physique, CNRS UMR 8000, UniVersite´ Paris-Sud,

Baˆtiment 350, 91405 Orsay Cedex, France, Laboratoire d’EÄ lectrochimie et Chimie Analytique,

CNRS UMR 7575, EÄ cole Nationale Supe´rieure de Chimie de Paris, 11 rue Pierre et Marie

Curie, 75231 Paris Cedex 05, France, Sanofi-Synthe´labo Recherche, 371 rue du Professeur

Blayac, 34184 Montpellier Cedex 04, France, Laboratoire de Chimie Inorganique et Mate´riaux

Mole´culaires, CNRS UMR 7071, UniVersite´ Pierre et Marie Curie, 4 Place Jussieu,

F-75252 Paris Cedex 05, France, and Institute of Crystallography,

UniVersity of Lausanne, BSP, 1015 Lausanne, Switzerland

Received April 27, 2001

Abstract: A new class of triarylpyridinio-derivatized [4′-(p-phenyl)_n]terpyridyl ligands, R¹R²TP⁺-(p)_ntpy, was

designed as a novel category of electron-acceptor (A)-substituted proto-photosensitizing molecules. The

first elements of this versatile family of ligands (i.e., n ) 0, 1 and R¹) R²) H), H₃TP⁺-tpy and H₃TP⁺-ptpy,

were synthesized as well as their Ru(II) and Os(II) complexes to form the related acceptor-functionalized

M(tpy)₂²⁺and M(ptpy)₂²⁺photosensitizer components denoted P0 and P1, respectively. Within the P1 series

of compounds, an electron-donor (D)-substituted ligand, Me₂N-ptpy, was also involved and associated

with H₃TP⁺-ptpy, giving rise to various combinations (up to 10 polyad systems). The two resulting series

of nanometer-scale rigid rod-like photosensitized supramolecular architectures are of potential interest for

long-range photoinduced electron transfer purposes. The main structural features of such supermolecules

were determined by comparing the results obtained from (i) single-crystal X-ray analysis of the two free

ligands together with that of the P0A/Ru and P1A₂/Ru complexes and (ii) a detailed solution ¹H NMR

study of the P0 series and, more specifically, of the P0A/Ru dyad (ROESY experiment). It is shown that

the pseudoperpendicular conformation of the covalently linked A and P subunits found in the solid state is

persistent in fluid medium; i.e., A is not conjugated with P (P0 and P1). The first insights regarding the

consequences upon intercomponent couplings of combined substituent effects and conjugation (case of

D-based polyads)sor absence of conjugationsare discussed in the light of ground-state electronic properties

of the compounds.

1. Introduction

the latter “molecules” being therefore viewed as the full building

blocks of a final supermolecule.^1aFrom the point of view of

physical chemists, the supermolecule is thus proposed to be a

multicomponent system (polyad) which behaves as a small

device capable of performing a predetermined function, i.e., of

receiving an external stimulus (input) and specifically reacting

(output). A significant feature of such supermolecules, examined

in the ground state, stems from the fact that the parentage of

each component remains identifiable with respect to the

corresponding isolated entities. In other words, the constitutive

subunits are not being too strongly coupled one to the others.^4,5

Thus, depending on the intrinsic properties of the associated

units, the resulting assembly may achieve various functions.

Molecular electronics and artificial photosynthesis are closely

related challenging fields of research that have experienced a

considerable rise during the last few decades. These noticeable

advances partly originated in the advent of new insights in

molecular chemistry,¹along with the revival of inorganic

photochemistry.²

Originally concerned with weakly interacting individual

molecules, the concepts of supramolecular chemistry³have

readily spread around toward coValently assembled architectures,

^†Universite´ Paris-Sud.

^‡EÄ cole Nationale Supe´rieure de Chimie de Paris.

Present address: Sanofi-Synthe´labo Recherche.

^|Universite´ Pierre et Marie Curie.

(4) (a) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem.

ReV. 1996, 96, 759-833. (b) Balzani, V.; Moggi, L.; Scandola, F. In

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F. Supramolecular Photochemistry; Ellis Horwood: Chichester, 1991.

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^§University of Lausanne.

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1364 VOL. 124, NO. 7, 2002 J. AM. CHEM. SOC.

Terpyridyl Ligands as Photosensitized Supermolecules

A R T I C L E S

Chart 1

When light is the primary efficient stimulus (photosensitized

species), photochemical molecular devices (PMDs)^4b,c,5,6are

concerned, and one of the most investigated light-triggered

functions at the molecular level is undoubtedly the monitoring

of photoinduced electron transfer (PET) processes. These

phenomena are of fundamental importance within the framework

of research devoted to molecular electronics^4-7and solar energy

photoconversion and storage.^2a,8A typical composition of

supramolecular species built for such purposes consists of

electron-donating (D) and/or -accepting (A) units, associated

with a photosensitizer (P) that exhibits substantial redox activity

at the excited state. When designed more specifically for

artificial photosynthesis, these electroactive entities are as-

sembled within the polyad systems in such a manner that

sequential intramolecular electron transfers (ETs) following the

excitation of P lead to a charge-separated (CS) state (e.g., D⁺-

P-A^-). This CS state actually corresponds to the transient

conversion of light into an electrochemical potential that may

be subsequently usedsunder appropriate conditionssfor per-

forming chemistry (fuel, energy storage) or producing electric-

ity.⁹Depending on whether the final goal is related to molecular

electronics or artificial photosynthesis, the supramolecular

species will be rather tuned in order to get a fast and long-

range ET (e.g., nanometer-scale electron wires) or long-life CS

state, respectively. Hence, it is of determining importance to

design supramolecular architectures allowing fine control over

both the properties of their components and their overall

geometrical features.

Over the years, topological, thermodynamic, and kinetic

criteria that govern PET processes within polyad systems have

been determined and the components satisfying these require-

ments progressively selected.^4a,c,5Metalated and nonmetalated

porphyrins together with d⁶transition metal complexes (second

and third rows) with oligopyridyl ligands are among the most

popular chromophoric photosensitizers, P.^2b,4,5,10Concerning the

other ingredients (D, A) of the multicomponent systems,

substituted amines, phenothiazines, and carotenoid polyenes are

commonly employed as electron-releasing elements, whereas

naphthalenediimide fragments, dicyanovinyl groups, fullerenes,

and more notably quinones and bipyridinium (viologens) species

generally play the role of electron-withdrawing units.^2a,5,8,11

Although viologens are somewhat archetypal as organic electron-

acceptor building blocks, there exists, however, a class of

pyridinium species less frequently used, namely the N-aryl-

substituted pyridinio derivatives. Interestingly, this type of

monopyridinium fragment has already been involved as the

electron-acceptor moiety in a family of purely organic bipartite

molecules which undergo intramolecular charge transfers. These

zwitterionic compounds are the solvatochromic pyridinium

N-phenolate betaine dyes (so-called Reichardt’s salt), widely

adopted as solvent polarity indicators.¹²In addition, the structure

of such a pyridinium moiety can be extensively varied in order

to give differentsbut affiliatedsdyes, thus allowing the probing

of almost all solvents at our disposal.¹³It is worth noting that

this synthetic versatility of N-aryl pyridinio molecules actually

originates from that of their pyrylium precursors (Chart 1).

Indeed, the pyrylium ring can be substituted almost on demand;

fortunately, its chemistry is also well-established and docu-

mented.¹⁴

(6) Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304-1319.

(7) (a) Joachim, C.; Gimzeswski, J. K.; Aviram, A. Nature 2000, 408, 541-

548. (b) Molecular Electronics, Science and Technology; Aviram, A., Ed.;

American Institute of Physics: New York, 1992. (c) Molecular Electronics;

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48. (b) Amouyal, E. In Homogeneous Photocatalysis; Chanon, M., Ed.;

John Wiley: Chichester, 1997; Chapter 8, pp 263-307. (c) Barbara, P. F.;

Meyer, T. J.; Ratner, M. A. J. Phys. Chem. 1996, 100, 13148-13168. (d)

Hagfeldt, A.; Gra¨tzel, M. Chem. ReV. 1995, 95, 49-68. (e) Bard, A. J.;

Fox, M. A. Acc. Chem. Res. 1995, 28, 141-145. (f) Amouyal, E. Sol.

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Chanon, M., Eds.; Elsevier: Amsterdam, 1988.

As part of our work devoted to the search for new building

blocks for inorganic PMDs of potential interest for energy

conversion or information storage purposes, our proposal is thus

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Sakata, Y.; Fukuzumi, S. J. Am. Chem. Soc. 2001, 123, 100-110. (b)

Hagfeldt, A.; Gra¨tzel, M. Acc. Chem. Res. 2000, 33, 269-277. (c) Bignozzi,

C. A.; Argazzi, R.; Indelli, M. T.; Scandola, F. Sol. Energy Mater. Sol.

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737-740.

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(b) Chen, P.; Meyer, T. J. Chem. ReV. 1998, 98, 1439-1477.

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1963, 661, 1-37.

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V. V.; Mezheritskii, A. V.; Schroth, W. In Pyrylium Salts: Synthesis,

Reactions and Physical Properties. AdVances in Heterocyclic Chemistry;

Katritzky, A. R., Ed.; Academic Press: New York, 1982; Suppl. 2.

(10) Kalyanasundaram, K. Photochemistry of Polypyridine and Porphyrin

Complexes; Academic Press: London, 1992.

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therein.

J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002 1365

A R T I C L E S

Laine´ et al.

to take advantage of the properties of these latter N-aryl-

substituted pyridinio electron-accepting groups by replacing, in

the case of polypyridyl complexes of Ru(II) and Os(II), the

phenolate organic moiety of betaine dyes by light-triggered

electron donors. Based on hitherto established structural and

energetic requirements, the new 4′-[4-N-(2,4,6-triarylpyridinio)-

analysis of the influence of the novel acceptor-derivatized

ligands upon P, the effects of the donor ligand being also

investigated as they give some insights (especially concerning

the electronic coupling between P and D) that remain valid for

the other elements of the R₂N-ptpy family. Of importance, the

structural aspect is more specifically addressed here, as it is

related to the actual electronic coupling between P and A.

Indeed, the cost for the rigidity of the overall architecture is

potentially the partial conjugation of A with P, which can be

considered as a drawback for charge-separation purposes and

for PMDs, as defined within the framework of supramolecular

photochemistry.

phenyl]-2,2′:6′,2′′-terpyridine ligand (R¹R²TP⁺-ptpy) has been

designed,¹⁵as well as the directly functionalized analogue 4′-

N-(2,4,6-triarylpyridinio)-2,2′:6′,2′′-terpyridine (R¹R²TP⁺-tpy)

depicted in Chart 1. The only difference between these two

ligands stems from the presence of a phenyl spacer (p) that

allows an increase of the intercomponent distance without any

loss regarding the main topological features (axial symmetry,

rigidity, ...) of the resulting complexes. In addition, such a

connector can be equally intercalated between P and A/D

electroactive units for both the triarylpyridinio electron-acceptor

moiety and electron-releasing groups such as NR₂(R ) alkyl,

aryl) to form donor-substituted ligands of the type of 4′-(4-

N,N-disubstituted-aminophenyl)tpy (R₂N-ptpy, R ) alkyl, aryl)

(Chart 1).¹⁵When these two types of ligands are associated

within the same heteroleptic complexes, the resulting triads,

D-P-A, exhibit a supplementary interesting characteristic for

CS purposes. Indeed, both pyridinio and amino nitrogen atoms

are located at equal distances d_MNfrom the metal center (M)

(Chart 1), which may favor a competition between intramo-

lecular ETs, thus retarding the charge recombination.^5,15

The main features of these novel triarylpyridinium-derivatized

terpyridyl ligands are their well-defined topology (rigid struc-

tures) and their chemical flexibility. Thus, it is expected that

the electronic and redox properties of the acceptor moieties could

be tuned via peripheral substituents (R¹and R²). Regarding the

connectivity of the complexes, the structure could be expanded

either via R²to give rise to singly linked axial rods of adjustable

length,^5,16so as to generate long-range vectorial ET (electron

wires) and long-lived CS, or via both R¹and R²in order to

build branched architectures (antenna effects, multielectron

catalysis, “molecular batteries”).¹⁷

2. Results and Discussion

2.1. Synthesis. The key intermediate for the synthesis of

R¹R²TP⁺-substituted ligands is the amino derivative of their

chelating fragment. Actually, despite the wide variety of

reactions that may be subsequently performed on such a starting

material, the synthesis of amino-terpyridine ligands has only

recently attracted its merited interest. In an effort to synthesize

the H₃TP⁺-tpy ligand, we have thus undertaken the preparation

of the 4′-amino-2,2′:6′,2′′-terpyridine (H₂N-tpy), by using the

Stille coupling reaction,¹⁸in accordance with a strategy adapted

from that first reported by Yamamoto et al. for the synthesis of

some other terpyridines (Scheme 1).¹⁹In the meantime, Fal-

lahpour and co-workers²⁰described a synthesis of the target

amino precursor, following a procedure very similar to ours.

We will therefore refer to their published synthetic route for

the preparation of the key H₂N-tpy molecule.

Regarding the 4′-[p-aminophenyl]-2,2′:6′,2′′-terpyridine (H₂N-

ptpy) precursor, syntheses different from that we have selected

were also recently reported in the literature.²¹Instead of directly

synthesizing the H₂N-ptpy ligand from polymerized p-ami-

nobenzaldehyde and 2-acetylpyridine, a two-step synthesis via

the nitro intermediate was preferred (also because of our need

of this latter compound for other purposes). Thus, the synthetic

route (Scheme 1) consists first of preparing the 4′-[p-nitrophe-

nyl]terpy according to a procedure adapted from that reported

by Collin et al. for making the 4′-p-tolyl-terpy (ttpy or Me-

ptpy)²²and based on the conventional one-pot synthesis of 4′-

[para-substituted phenyl]-terpy ligands.²³The purification was

then performed by the method of Constable et al.^22,24The nitro

species was subsequently converted into the corresponding

amino derivative with hydrazine over palladium charcoal²⁵

(quantitative reaction) with an overall yield of ca. 10.5% (steps

viii and vi, Scheme 1). Note that the reduction of the nitro group

was in fine preferably performed with hydrazine on palladium

charcoal rather than with sodium dithionite¹⁵of irregular and

lower efficiency. Moreover, high yields for the reduction

reaction are of crucial importance when several nitro groups

belonging to the same molecule have to be transformed to obtain

branched species.

As a prerequisite for manipulating such potentially complex

supramolecular architectures, a detailed study of the original

skeleton (R¹R²TP⁺-(p)_ntpy, R¹) R²) H and n ) 0, 1) is

required in order to establish forthcoming and possibly related

complicated chemistry. Our approach is aimed at reporting on

the very basic properties and main features of the native building

blocks, before their modification to explore new potentialities.¹⁵

In this work, the new families of ruthenium(II) and osmium(II)

complexes with triphenylpyridinio-derivatized electron-acceptor

ligands are presented and fully characterized. The dimethy-

lamino-substituted p-phenyl-terpy is also described. It has been

used for illustration purposes as a representative element of the

family of the donor ligands (R₂N-ptpy) that may be suitably

associated with the R¹R²TP⁺-ptpy partners, although such

dimethyl derivative may not be the best candidate as electron-

donor (vs *P). This study is indeed mainly focused on the

(18) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508-524.

(19) Yamamoto, Y.; Azuma, Y.; Mitoh, H. Synthesis 1986, 564-565.

(20) (a) Fallahpour, R.-A. Eur. J. Inorg. Chem. 1998, 1205-1207. (b) Fallahpour,

R.-A.; Neuburger, M.; Zehnder, M. New J. Chem. 1999, 53-61 and

references therein.

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1997, 3011-3028.

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Chem. 1998, 1-14. (d) Barigelletti, F.; Flamigni, L.; Collin, J.-P.; Sauvage,

J.-P. Chem. Commun. 1997, 333-338.

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Flamigni, L.; Balzani, V. Inorg. Chem. 1991, 30, 4230-4238.

(23) Spahni, W.; Calzaferri, G. HelV. Chim. Acta 1984, 67, 450-454.

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203.

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1366 J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002

Terpyridyl Ligands as Photosensitized Supermolecules

A R T I C L E S

Scheme 1. Synthetic Routes for the Novel Triphenylpyridinio-Substituted Terpyridyl Ligands and Numbering Scheme Adopted for ¹H and

¹³C NMR Assignments^a

^aReagents and conditions: (i) H₂O₂/TFA. (ii) HNO₃/H₂SO₄. (iii) CHCl₃/PCl₃. (iv) nBuLi, Bu₃SnCl, THF, -78 °C. (v) Pd(PPh₃)₄, toluene, T°. (vi) Pd/C

(10%), EtOH, H₂NNH₂‚H₂O, T°. (vii) pyrylium salt, NaOAc/EtOH, T°. (viii) NH₄OAc, CH₃CONH₂, T°; NaOH aq, T°; [Fe²⁺], NaOH/H₂O₂.

Chart 2. Schematic Structures of the Polyad Systems with Their

The last step for the preparation of the pyridinium moieties

Corresponding Label (In All Cases the Counterions Are PF₆

)

was adapted from the synthesis of the Betaine 30 solvatochromic

dye.^13,26H₃TP⁺-tpy and H₃TP⁺-ptpy ligands were synthesized

by reacting the related amino precursor with the commercially

available triphenylpyrylium salt, affording the target molecules

as salts (Scheme 1). It is worth emphasizing, in view of

forthcoming works, that the very well documented chemistry

of triarylpyrylium organic material¹⁴is such that it offers a wide

variety of possible designs for pyridinio-derivatized ligands.²⁷

One should also underline the stability of the new synthesized

ligands. Indeed, although triphenylpyrylium salts are often used

for functional group conversion purposes,²⁸as is the case for

primary alkyl and benzylamines which are converted into their

corresponding pyridinium leaving groups,²⁹N-arylpyridinium

salts normally do not undergo nucleophilic displacement

reactions.²⁹The two reported exceptions are dealing with cases

where pyrolysis at a temperature above 200 °C or thermolysis

above 220 °C was performed.³⁰The chemical inertness of the

N-arylpyridinio derivatives is explained by the fact that stereo-

electronic requirements for intermolecular nucleophilic displace-

ments of N-aryl groups are not favorable (steric protection of

the R substituents of the pyridinium ring).³⁰

with a slight excess for L). The syntheses were performed in

the presence of sodium ascorbate as a reducing agent, instead

of the generally used N-ethylmorpholine or triethylamine,

because of the additional moderate complexing property of

ascorbate that may help in the displacement of chloride anions

from MCl₃. Heteroleptic complexes, [(L¹)M(L²)]ⁿ⁺(n ) 2, 3),

were obtained in two steps by reacting first the ligand L¹with

the metal trichloride to get the poorly soluble neutral complex

(L¹)MCl₃, and then this latter precursor with the second ligand

(L²) in the same conditions as for the synthesis of the homoleptic

compounds. All cationic complexes were first purified by

counteranion metathesis (Cl^-f PF₆^-) and then by column

chromatography over basic alumina. The final recrystallization

of the pure product was usually accomplished by slow vapor

diffusion of diethyl ether into an acetonitrile solution of the

complex. All complexes synthesized, along with their corre-

sponding labels, are schematically gathered in Chart 2. Homo-

leptic complexes have been synthesized as reference compounds

for comparison purposes.

The synthetic route for the model electron-donor ligand,

Me₂N-ptpy, was adapted from that previously mentioned for

NO₂-ptpy,²²by reacting 2-acetylpyridine with the conveniently

substituted aldehyde, i.e., p-N,N-dimethylamino benzaldehyde.

Homoleptic complexes, [(L)₂M]ⁿ⁺(n ) 2, 4), were directly

synthesized by reacting the transition metal chloride (MCl₃‚

3H₂O, M ) Ru, Os) with the corresponding ligand (L) in

approximately stoichiometric proportions (i.e., 1:2 respectively,

(26) (a) Kessler, M. A.; Wolfbeis, O. S. Synthesis 1988, 635-636. (b) Osterby,

B. R.; McKelvey, R. D. J. Chem. Educ. 1996, 73, 260-261.

(27) Work in progress.

(28) Vogel’s Textbook of Practical Organic Chemistry, 5th ed; Furniss, B. S.,

Hannaford, A. J., Smith, P. W. G., Tatchell, A. R., Eds.; John Wiley &

Sons: New York, 1989.

(29) Katritzky, A. R. Tetrahedron 1980, 36, 679-699.

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429.

J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002 1367

A R T I C L E S

Laine´ et al.

Figure 2. ORTEP drawing of the [(tpy)Ru(tpy-TPH₃⁺)]³⁺complex, P0A/

Ru, with thermal ellipsoids (30% probability). The hydrogen atoms, PF₆

counterions, and cocrystallized solvent molecules are omitted for clarity.

Figure 1. ORTEP drawing of the H₃TP⁺-tpy ligand with thermal ellipsoids

(50% probability). The BF₄counterion and the cocrystallized solvent

molecule are omitted for clarity.

solution of the compound in acetonitrile. The molecular structure

of the complex P0A/Ru within [(tpy)Ru(tpy-TPH₃⁺)](PF₆)₃‚

0.8CH₃CN‚0.5H₂O is depicted in Figure 2.

Single crystals of [Ru(ptpy-TPH₃⁺)₂](PF₆)₄suitable for X-ray

structure analysis were obtained by slow vapor diffusion of

diethyl ether into an acetonitrile solution of the complex. The

molecular structure of the complex P1A₂/Ru is given in Figure

3. The length of this rigid rod-like complex is 34.4 Å edge-to-

The purity of all compounds and their identity (for the new

species) were checked by elemental analysis, ¹H and ¹³C NMR,

and CI and ES mass spectrometry, and they are in good agree-

ment with the expected structures. However, it should be noted

that the elemental analysis of H₃TP⁺-phenyl and -ptpy deriva-

tives indicates that partial to almost complete anion-exchange

did take place between that coming from the pyrylium source

(HSO₄^-) and that coming from the sodium salt (OAc^-) present

in excess in the reaction medium during the last step of

pyridinium formation. This may account for the poor crystal

quality of the H₃TP⁺-ptpy ligand, which showed unresolved

disorder regarding the counterion (see below). We did not per-

form any further metathesis on the mixed (HSO₄^-/OAc^-) salts

of the ligands, which were used as obtained for the following

step of complexation, affording pure PF₆^-salts after purification.

Fortunately, this untimely ion exchange did not occur when the

edge (terminal hydrogen atoms not included). The distance, d_MN

between the metal center of P1 and the N_pyridinioatoms of the

acceptor moieties (A), was determined as 10.4 Å.

Classical features, regarding the 2,2′:6′,2′′-terpyridyl chelating

part (tpy) of the ligands, are the changing conformations of the

pyridines with respect to their interannular C-C bonds observed

on passing from the free ligand (anti-anti, i.e., transoid

conformation) to the complexed form.³²Indeed, for chelating

purposes, the two terpyridyl fragments that participate in the

inorganic core within the P0- and P1-based complexes have

adopted a syn-syn (i.e., cisoid) conformation. These two ligands

are mutually arranged about each metal center in an almost

orthogonal fashion. The resulting local environment around the

Ru²⁺cation is therefore pseudo-octahedral (D_2d), with shortened

Ru-N bonds (d_Ru-N, mean ) 1.977 Å) along the main

molecular axis (i.e., the bond that connects the Ru²⁺to the

central pyridine ring of each tpy ligand). The average value

over P0A/Ru and P1A₂/Ru complexes of d_Ru-Nwhen lateral

pyridines of the tpy ligands are involved is 2.068 Å.

BF₄salt of the pyrylium precursor was used, as was the case

for the [H₃TP⁺-tpy](BF₄) ligand, which was readily crystallized

in a pure form. Concerning the microanalytical results for the

inorganic compounds, it was observed that the experimentally

determined carbon abundance was, from time to time, lower

than that expected theoretically. This finding has already been

reported and ascribed to the propensity of Ru (and Os) transition

metals to form carbides species upon combustion.³¹

2.2. Structural Characterizations. 2.2.1. Crystallography.

H₃TP⁺-tpy crystallizes readily as the tetrafluoroborate salt from

a dichloromethane/ethyl acetate mixture to give colorless

plates. The molecular structure of the ligand in [H₃TP⁺-tpy]-

(BF₄)‚0.5CH₃CO₂C₂H₅is given in Figure 1.

An important structural feature of these triphenylpyridinio-

derivatized molecules (ligands and complexes), that actually

motivates the present crystallographic study, is related to the

local topology about the acceptor moiety, which has to do with

the electronic communication between P and A subunits. More

precisely, the conformations adopted by bulky aryl groups

situated on either side of the pyridinio nitrogen atom, as well

as that of the aromatic N-group Ar¹(Figures 2 and 3), are under

investigation. Significant geometrical data collected out of this

work and retrieved from the Cambridge Structural Database,³³

for 1,2,4,6-tetraarylpyridinium and related molecules (Figure

4), are gathered in Table 1.

Slightly yellow colored crystals of H₃TP⁺-ptpy of poor quality

were obtained from ethanol/diethyl ether solution. An ORTEP

drawing of the molecular structure of the ligand in [H₃TP⁺-

ptpy](anion)‚solvent is available as Supporting Information. Due

to the nondetermination of the cocrystallized molecules (coun-

teranion and possibly solvent), we have no deposited data for

this structure (see Experimental Section). Nevertheless, atomic

coordinates of the organic ligand itself have been satisfactory

localized, and a two-fold orientational disorder of the terminal

phenyl ring could even be successfully modeled.

Single crystals of the P0A/Ru complex suitable for X-ray

structure analysis were obtained by slow evaporation of a

(32) Thummel, R. P.; Jahng, Y. Inorg. Chem. 1986, 25, 2527-2534.

(33) Allen, F. H.; Davies, J. E.; Johnson, O. J.; Kennard, O.; Macrae, C. F.;

Mitchell, E. M.; Mitchell, G. F.; Smith, J. M.; Watson, D. G. J. Chem. Inf.

Comput. Sci. 1991, 31, 187-204.

(31) Constable, E. C.; Cargill Thompson, A. M. W.; Tocher, D. A.; Daniels,

M. A. M. New J. Chem. 1992, 16, 855-867.

1368 J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002

Terpyridyl Ligands as Photosensitized Supermolecules

A R T I C L E S

Figure 3. ORTEP drawing of the [(H₃TP⁺-ptpy)Ru(ptpy-TPH₃⁺)]⁴⁺complex, P1A₂/Ru, with thermal ellipsoids (30% probability). The hydrogen atoms

and PF₆counterions are omitted for clarity.

Table 1. Selected Bond Lengths and Dihedral Angles (θ) between the Central Pyridinium Ring and Peripheral Aryl Mean Planes

Ar¹

d(C_Ar−N

)

(θ1°)

R (θ2°)

R (θ4°)

R (θ6°)

entry

H₃TP⁺-tpy

1.4659(10)

1.440(3)

(78.71)

(72.60)

H(55.92)

H(62.42)

H(25.14)

H(16.45)

H(37.03)

H(24.29)

H(46.93)

H(2.13)

H(20)

H(25)

H(20)

H(22)

p-Br(18)

H(53)

H(71.18)

H(65.11)

H₃TP⁺-ptpy

P0A/Ru

P1A₂/Ru

1.439(6)

1.431(3)

1.420(3)

1.459

1.460

1.463

1.459

1.479(8)

1.470

(79.38)

(87.42)

(89.21)

(77)

(78)

(70)

(65)

(73)

H(85.48)

H(72.85)

H(65.32)

H(84)

H(72)

H(51)

H(53)

H(54)

H(59)

O-

H(78.31)

H(87.42)

H(73.81)

H(72)

H(59)

H(50)

H(66)

H(70)

H(47)

p-O₂SCH₂ph

p-HOph

p-^-Oph

p-HOph

^aReference 34. ^bReference 35. ^cReference 36. ^dReference 37. ^eReference 38. ^fReference 39. ^gReference 40.

photosensitizer, P, in the solid state because of localized

intraligand constraints.³⁴

2.2.2. NMR Study. ¹H and ¹³C NMR techniques performed

on diamagnetic coordination compounds gave expected results

in regard to what is known in the literature for bis(phenyl)-

terpyridyl transition metal complexes.^22,31,42Where necessary,

assignments were checked by performing 2D homonuclear (¹H-

¹H) and heteronuclear (¹H-¹³C) COSY experiments. Thus,

classically, NMR signatures of heteroleptic compounds are

roughly the superposition of those of the corresponding reference

homoleptic complexes,³¹indicating that two tpy ligands as-

sembled around a metal ion are structurally independent.

However, this is no longer true when considering more subtle

phenomena related to electronic effects, as is the shielding/

deshielding of proton resonance that originates from the so-

Figure 4. Parameters for Table 1.

Taking into account the overall set of data (Table 1), the main

topological features may be summarized as follows. On one

hand, the two aromatic substituents in ortho (i.e., 2,6-) positions

of the pyridinium rings (Figure 4) are found to be tilted with

respect to their supporting plane ((θ2 + θ6)/2, mean ) 66.13°).

On the other hand, these latter pyridinium rings are observed

to be oriented almost perpendicularly to the plane of the Ar¹

moiety they are attached to (θ1, mean ) 76.39°). These general

trends are even more striking when considering the complexes

only. Indeed, the average value of (θ2 + θ6)/2 is 77.20°, and

that of the dihedral angle θ1, between the pyridinium rings and

the connected coordination plane of the tpy (P0 series) or the

plane of the phenyl spacer (for P1), is 85.34°. These particular

conformations result from internal steric hindrance about the

interannular bond that connects Ar¹and the pyridinium part

(Figures 2 and 3), i.e., between hydrogen atoms facing the

N_pyridinioatom and the two latter 2,6-aryl substituents of the

pyridinium ring. In the present case, these hydrogen atoms are

H(3′A) and H(9A) from the central pyridine ring of the tpy

ligand (P0 series) and from the phenyl spacer (P1 series),

respectively (Scheme 1). In other words, the acceptor fragment,

A, is shown to be geometrically almost “decoupled” ⁴¹from the

(34) Farag, I. S. A.; El-Shora, A. I.; Rybakov, V. B. Cryst. Res. Technol. 1990,

25, 519-524.

(35) Othman, A. H.; Zakaria, Z.; Ng, S. W. J. Crystallogr. Spectrosc. Res. 1993,

23, 921.

(36) Milart, P.; Stadnicka, K. Liebigs Ann./Recueil 1997, 2607-2611.

(37) Milart, P.; Mucha, D.; Stadnicka, K. Liebigs Ann. 1995, 2049-2051.

(38) Allmann, R. Z. Kristallogr. 1969, 128, 115-132.

(39) Katritzky, A. R.; Ramsden, C. A.; Zakaria, Z.; Harlow, R. L.; Simonsen,

S. J. Chem. Soc., Perkin Trans. 1 1980, 1870-1878.

(40) Surprisingly, it is worth noting that the length, d(C_Ar-N_py), of the bond

connecting the pyridinio nitrogen atom to its substituent (Ar¹) carbon atom

(independently of whether an aryl or pyridine ring is involved, Table 1) is

slightly, but sizably, diminishing as the dihedral angle θ1 gets closer to

90° (d(C_Ar-N_py), mean ) 1.453 Å), as evidenced by the plot of d(C_Ar

N_py) as a function of θ1 (Supporting Information). A theoretical study

has been undertaken in order to explain this not straightforwardly

understandable finding, that apparently correctly models this behavior (Prof.

F. Volatron, private communication).

(41) In this paper, the term “geometrical decoupling” refers to the marked twist

angle (i.e., pseudo-orthogonal conformation) between the planes of two

components directly linked by a single bond.

(42) Collin, J.-P.; Guillerez, S.; Sauvage, J.-P.; Barigelletti, F.; De Cola, L.;

Flamigni, L.; Balzani, V. Inorg. Chem. 1992, 31, 4112-4117.

J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002 1369

A R T I C L E S

Laine´ et al.

coming from the phenyl groups adjacent to the N_pyridinioatom,

making the shielding measured for H(3′A) apparently smaller

than that for H(3A).

Finally, a direct proof of the pronounced tilt between P and

A is provided by NMR experiments based on the nuclear

Overhauser effect (NOE), allowing the measurement of through-

space couplings between protons.⁴³Indeed, NOESY and

ROESY (see Supporting Information) experiments carried out

on P0A/Ru evidenced that through-space interligand couplings

do take place between the probe H(6) of the tpy ligand and

protons H(21A), H(20A), and eVen H(19A) from the tilted phenyl

substituents adjacent to the N_pyridinioatom of the other ligand

(H₃TP⁺-tpy). Furthermore, these couplings are found to be of

the same order of magnitude assand even stronger thansthat

of H(6) with H(3′A), which are geometrically fixed within the

rigid coordination sphere at a distance ranging from 4.482 to

4.786 Å (X-ray data). Owing to the intrinsic limitation of the

method that allows the detection of couplings between protons

separated by a distance ranging from 2 to ca. 4.5 Å, the

occurrence of these couplings is only compatible with a dihedral

angle θ1 (Figure 4) between the tpy and pyridinium mean planes

very close to 90°. The phenyl rings in the 2,6-positions of the

pyridinium ring are then also assumed to be tilted with respect

to their supporting pyridinium fragment,⁴⁴due to an internal

and local steric hindrance. Hence, one may consider that the

actual conformation of P0A/Ru in solution is very similar to

that determined in the solid state by X-ray structure analysis,

confirming the “geometrical decoupling” ⁴¹already asserted by

Sun et al. for purely organic oligomeric analogues.⁴⁵

2.3. Shared Structural Features and Consequences. The

present work is related to strongly anisotropic molecules,

showing a pronounced axial symmetry, that are expectedly

suitable for directional and possibly vectorial PET. These

compounds may be classified as polyad systems, as they are

made of covalently linked building blocks such as electron-

acceptor (A) and -donor (D) entities, which are linearly

assembled on both sides of a photosensitizer (P). With the help

of phenyl spacers (p) inserted between the P and D/A units,

this particular arrangement allows the optimal remote location

of the redox-active sites. Such a geometrical disposition actually

results from the intrinsic nature of the central chromophore,

which consists of two terdentate terpyridyl ligands complexed

around an octahedral transition metal cation (M), Ru(II) or Os-

(II), in a trans-meridional fashion. Indeed, attachment of

electroactive components at the 4′-position of both tpy ligandss

in some cases via phenyl spacerssgives rise to rigid rod-like

complexes that roughly have the rotation motion along their

main axis as the only degree of freedom.

Figure 5. Pictorial representation of the ring current effects on H(6) (1D

¹H NMR, top) and of through-space proton-proton interaction between

H(6) and the facing ligand (ROESY experiment, bottom) within P0A/Ru

(X-ray structure).

called ring-current effects. A known example of such a through-

space interligand interactionsfor bis-terpyridyl compoundss

is the pronounced shielding of H(6) (Scheme 1 and Figure 5)

when complexed as compared to the related chemical shift for

the free ligand. This shielding is ascribed to the proton lying

over the π-cloud of the nearby central pyridine ring belonging

to the other tpy ligand.^31,32In the present work, it was found

that such a through-space effect enables us to get precious

structural information regarding the topology of the ligand about

the acceptor fragment, i.e., concerning the actual degree of

conjugation between P and A moieties. Indeed, in the case of

the P0-based polyads and contrary to the P1 series of com-

pounds, fixedly positioned H(6) protonssdirectly adjacent to

the nitrogen atom of the external pyridines of the tpy ligand

(Scheme 1 and Figure 5)sgive the unique opportunity to probe

the questioned planarity of the H₃TP⁺-tpy ligand (see Figures

2 and 5). As a matter of fact, when comparing ¹H NMR spectra

of P0A/Ru and P0A₂/Ru with the H NMR spectrum of the

reference P0/Ru (Figure 6), an interesting feature appears: the

exceptional upfield-shifted signal of these latter H(6) protons.

The reason put forward to explain such a behavior is that proton

H(6) is not only surrounded by the shielding cone of the central

pyridine ring of the opposite H₃TP⁺-tpy ligand^31,32but is also

allowed to experience the ring current effects of the tilted phenyl

ortho substituents of its 4′-attached pyridinium ring (Figure 5).

The existence of the latter supplementary shielding effect (∆δ

≈ -0.6 ppm) clearly indicates that the pyridinium ring of the

acceptor component is almost perpendicular to the plane of the

connected tpy moiety.

Besides the reported interligand ring current effect, additional

evidence for the “geometrical decoupling” ⁴¹of P and A may

be obtained from the study of the intraligand-related phenom-

enon within the same H₃TP⁺-tpy series of compounds. Indeed,

one may notice that (i) H(3′A) appears to be significantly

shielded by -0.3 ppm with respect to H(3′) of the reference

coordinated tpy (Figure 5) and (ii) a similar upfield shift is also

observed when comparing resonances of H(3) and H(3A)

detected at 8.47 and 8.10 ppm, respectively. These behaviors

suggest, in accordance with previous conclusions, that either

or both dihedral angles θ1 and θ2/θ6 (Figure 4, Table 1) slightly

deviate from the strict orthogonality, allowing H(3′A) and H(3A)

to experience the above-mentioned ring current effects. It is

worth noting that the chemical shift of H(3′A) actually results

from the balance between various contributions which are

mainly the electron-withdrawing effect originating from the

pyridinium (deshielding) and the ring current effect (shielding)

First, the status of phenyl spacers (p) between P and D/A,

when present, deserves to be discussed. Their original role is

actually dual. On one hand, it consists of locating D/A groups

away from P so as to retard charge recombination and draw

out CS-state lifetimes when formed (charge separation purposes)

without altering the rigidity of the overall system. On the other

(43) Sanders, J. K. M.; Hunter, B. K. Modern NMR spectroscopy, 2nd ed; Oxford

University Press: Oxford, 1993.

(44) Typically, the X-ray analysis of P0A/Ru gives the following distances

between the probe H(6) and the through-space coupled protons of the facing

acceptor ligand: 3.727 and 4.093 Å for H(6)-H(21A); 3.564, 3.895, 4.439,

and 5.024 Å for H(6)-H(20A); 4.210, 4.746, 5.186, and 5.638 Å for H(6)-

H(19A).

(45) Sun, X.; Yang, Y.-K.; Lu, F. Macromolecules 1998, 31, 4291-4296.

1370 J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002

Terpyridyl Ligands as Photosensitized Supermolecules

A R T I C L E S

Figure 6. ¹H NMR spectra of CD₃CN solutions of P0/Ru (a), P0A/Ru (b), and P0A₂/Ru (c).

hand, it contributes to the improvement of the photophysical

properties of the M(II)-bisterpyridyl chromophoric core (P).

Indeed, the dihedral angle (θ) between this latter phenyl moiety

and the central pyridine ring of the tpy ligand is rather small

(θ, mean ) 24.81°, range ) 2.47-43.30°).⁴⁶This allows an

extension of the conjugation and thus an electronic delocalization

over the entire phenyl-terpy (ptpy) skeleton.^5,22Therefore, these

issues legitimate (i) the distinction we have made between the

various polyad systems depending on the absence, P0, or the

presence, P1, of phenyl spacers (i.e., P1 rather than p-P0-p, see

Chart 2) and (ii) our choice of different related model photo-

sensitizer for each series.

As previously emphasized, an important question to be

answered within the framework of this work is the actual degree

of conjugation of A and D with P that determines, to a large

extent, the strength of the intercomponent electronic coupling.

Regarding the P/A couple, the situation is tightly connected to

the value of the dihedral angle (θ1)^47,48between the acceptor

pyridinium ring of H₃TP⁺and the plane of the N-group, Ar¹,

that belongs to the photosensitizer P (Figure 4). What is known

from X-ray analysis is that the internal steric hindrance around

the N_pyridinioatom is such that both aryl groups in 2- and

6-positions for the pyridinium ring are tilted with respect to

the ring bearing them. The steric constraints about the interan-

nular bond that connects the pyridinium ring and its N-aryl

substituent (phenyl or pyridyl) is sufficient to produce the

“geometrical decoupling” ⁴¹of the components (Table 1, θ1 ≈

90°).^34,45Moreover, this resulting steric interaction between P

and A within the P0 series of complexes is not appreciably

different from that within the P1 family of compounds. Hence,

conclusions drawn out of the structural study of P0 species may

therefore be extrapolated to the P1 analogues.

However, beyond these solid-state issues, it remains of crucial

importance to get insights regarding the actual conformation

of molecules in solution, i.e., in the real conditions for which

their physical properties are investigated. This allows one to

establish a possible structure vs properties correlation. For the

present purposes and beyond its routine use for the structural

characterization, the ¹H NMR technique was revealed to be very

well adapted and informative. First, the local topology about

the acceptor moiety within polyad compounds in solution has

to be elucidated. Interestingly, in the particular case of P0A/

Ru, protons H(6) and H(6′′) from the native tpy ligand are

fixedly positioned in such a manner that the direct surrounding

of the N_pyridinioatom of the acceptor moietysattached to the

opposite tpy ligandsmay be directly probed by taking advantage

of both ring current and the through-space Overhauser nuclear

effects. Indeed, we have unambiguously shown that, in solution,

the pyridinium ring of the electron acceptor center remains

almost perpendicular to the plane of the supporting tpy fragment,

as it is evidenced in the solid state (X-ray analysis). Thus, in

accordance with our previous reasoning about the structural

similarities between P0-A and P1-A, and based on other

indirect NMR considerations, the “geometrical decoupling” of

H₃TP⁺from P is also established for the P1 series of complexes.

Moreover, notice that theoretical calculations performed for the

organic analogous pyridinium N-phenolate dye, Betaine-30, have

shown that the more stable conformation of such a molecule in

(46) Cambridge Structural Database statistical search,³³40 entries.

(47) (a) Fisher, H.; Tom, G. M.; Taube, H. J. Am. Chem. Soc. 1976, 98, 5512-

5517. (b) Larson, S. J. Am. Chem. Soc. 1981, 103, 4034-4040. (c) Joachim,

C.; Launay, J.-P. Chem. Phys. 1986, 109, 93-99. (d) Woitellier, S.; Launay,

J.-P.; Joachim, C. Chem. Phys. 1989, 131, 481-488. (e) Gourdon, A. New

J. Chem. 1992, 16, 953-957. (f) Dong, T.-Y.; Huang, C.-H.; Chang, C.-

K.; Wen, Y.-S.; Lee, S.-L.; Chen, J.-A.; Yeh, W.-Y.; Yeh, A. J. Am. Chem.

Soc. 1993, 115, 6357-6368. (g) Pierce, D. T.; Geiger, W. E. Inorg. Chem.

1994, 33, 373-381. (h) Das, A.; Maher, J. P.; McCleverty, J. A.; Navas

Badiola, J. A.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1993, 681-686.

(i) Beer, P. D.; Chen, Z.; Grieve, A.; Haggitt, J. J. Chem. Soc., Chem.

Commun. 1994, 2413-2414.

(48) (a) Chen, P.; Curry, M.; Meyer, T. J. Inorg. Chem. 1989, 28, 2271-2280.

(b) Berg-Brennan, C.; Subramanian, P.; Absi, M.; Stern, C.; Hupp, J. T.

Inorg. Chem. 1996, 35, 3719-3722. (c) Damrauer, N. H.; Boussie, T. R.;

Devenney, M.; McCusker, J. K. J. Am. Chem. Soc. 1997, 119, 8253-8268.

(d) Liard, D. J.; Vlcek, A., Jr. Inorg. Chem. 2000, 39, 485-490.

J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002 1371

A R T I C L E S

Laine´ et al.

Table 2. Electronic Absorption Data and Assignments

_max[nm] (ꢀ [10⁴M^-1cm^-1])

¹MLCT

³MLCT

P0/Ru

271 (3.87), 308 (6.42)

271.5 (5.13), 309 (8.59)

274 (5.11), 313 (9.94)

285 (7.86), 310 (8.77)

312 (11.65)

312.5 (14.64)

232 (4.39), 286 (6.40), 309 (9.22), 382 (1.32)

238.5 (4.84), 275 (5.13), 287 (5.32), 309.5 (10.53), 388 (2.95)

287 (7.62), 310 (11.33)

286 (7.64), 314.5 (8.64)

290 (7.82), 315 (11.22)

315.5 (14.59)

231 (4.98), 287.5 (6.47), 313 (9.90), 386 sh (2.15)

238 (4.95), 276 (5.19), 313 (10.62), 349 (4.62), 380 sh (3.54)

313 (11.94)

475.5 (1.48)

488 (2.09)

491 (2.86)

490 (3.39)

491.5 (3.63)

493 (4.13)

499.5 (4.05)

514 (5.46)

497 (4.10)

490 (3.01)

491 (3.32)

491 (3.90)

501 (4.07)

512 (4.84)

503 (4.21)

P0A/Ru

P0A₂/Ru

P1/Ru

P1A/Ru

P1A₂/Ru

DP1/Ru

D₂P1/Ru

DP1A/Ru

P1/Os

P1A/Os

P1A₂/Os

DP1/Os

D₂P1/Os

DP1A/Os

645 (0.67), 668 (0.77)

642 (0.68), 668 (0.77)

645 (0.78), 671 (0.93)

648 (0.96), 672 (1.05)

653 (1.20), 676 (1.35)

644 (0.92), 674 (0.92)

solution in polar solvents corresponds to a value of θ1 close to

90°.⁴⁹

Concerning the P1/D couple, when borne by an aryl group,

the geometry around the N_aminoatom of a D fragment of the

4-N,N-disubstituted amino type is known to be that of a flattened

pyramid,⁵⁰almost coplanar with the latter supporting ring with

the nitrogen lone pair being delocalized over it (when no steric

hindrance interferes). In other words, such electron-releasing

substituents behave as conjugated aromatic amines, strongly

coupled to P (P0 and P1). This is, for instance, the case for the

D₂P0/Ru complex (D ) NMe₂), as previously reported by

Constable et al.³¹

2.4. Electronic Behaviors. Ground-state absorption spectra

of all polyads and reference compounds were recorded; the

corresponding data are collected in Table 2. The main features

obtained are classical for Ru(II)- and Os(II)-bisterpyridyl

complexes.⁵In the near-UV part of the spectra, ligand-centered

(LC) transitions originating from both tpy/ptpy fragments and

the organic acceptor subunit, H₃TP⁺, are observed. Spin-allowed

dπ(M^II) f π*(L) metal-to-ligand charge transfer (¹MLCT)

transitions are detected in the visible region around 500 nm.

The strong spin-orbit coupling of the Os(II) metal cation

partially allows the normally spin-forbidden ³MLCT transitions.

These are therefore observed in the far-visible-near-IR region

as poorly resolved bands of weak intensity.

Classical behaviors are also the bathochromic shift and the

hyperchromic effect of the photosensitizer-centered ¹MLCT

transition (mainly) that accompany its electronic coupling with

substituents, regardless of their electron-withdrawing or -releas-

ing nature.^5,31,51Indeed, obvious perturbations of the chro-

mophores are evidenced within (i) the P0/Ru-based series of

complexes where the H₃TP⁺moiety is directly connected to

the tpy ligand (red-shift up to ca. 15 nm associated with a molar

extinction coefficient enhancement of ca. 100%) and (ii) the

P1-based polyads that involve the dimethylamino electron-donor

substituent (red-shift of at least 10 nm associated with an ꢀ

enhancement and a new band rising at ca. 380 nm). Besides,

the latter finding is observed independently of whether the metal

cation is Ru(II) (see Figure 7a) or Os(II).

Figure 7. Absorption spectra (room temperature, acetonitrile solution). (a)

P1/Ru (solid), DP1/Ru (dashed), and D₂P1/Ru (dotted). Inset: Overall

representation. (b) P1/Ru (solid), P1A/Ru (dashed), and P1A₂/Ru (dotted).

Inset: Overall representation.

Bathochromic shifts and hyperchromic effects that normally

account for the extension of conjugation (π delocalization) and

the mediation of electronic effects (electron-withdrawing or

-releasing substituent effects) are both indicative of strong

intercomponent electronic couplings.⁵These trends follow a

progressive variation upon increasing the number of electron-

donating or -withdrawing substituents, i.e., on passing from

dyads (DP1 and P0A heteroleptic compounds) to reference triads

(D₂P1 and P0A₂homoleptic species). Such behaviors have been

rationalized by Maestri et al.⁵¹in terms of differential acceptor-

induced stabilization and donor-induced destabilization of the

frontier HOMO (π_M) and LUMO (π*_L) orbitals.

(49) (a) Mente, S. R.; Maroncelli, M. J. Phys. Chem. B 1999, 103, 7704-7719.

(b) Bartkowiak, W.; Lipinski, J. J. Phys. Chem. A 1998, 102, 5236-5240.

(50) Gourdon, A.; Launay, J.-P.; Bujoli-Doeuff, M.; Heisel, F.; Miehe´, J. A.;

Amouyal, E.; Boillot, M.-L. J. Photochem. Photobiol. A: Chem. 1993,

71, 13-25.

(51) Maestri, M.; Armaroli, N.; Balzani, V.; Constable, E. C.; Cargill Thompson,

A. M. W. Inorg. Chem. 1995, 34, 2759-2767.

A careful analysis of the electronic properties of the ptpy-

1372 J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002

Terpyridyl Ligands as Photosensitized Supermolecules

A R T I C L E S

Table 3. Summary of Crystallographic Data for [H₃TP⁺-tpy](BF₄)‚0.5CH₃CO₂C₂H₅, [H₃TP⁺-ptpy](Anion)‚Solvent,

[(tpy)Ru(tpy-TPH₃⁺)](PF₆)₃‚0.8CH₃CN‚0.5H₂O, and [Ru(ptpy-TPH₃⁺)₂](PF₆)₄

[H TP -tpy](BF )‚

[H TP -ptpy](anion)‚

P0A/Ru‚0.8CH CN‚

compound

0.5CH CO C H

solvent

0.5H O

P1A /Ru

empirical formula

C₃₈H₂₇N₄‚BF₄‚

CH₃CO₂C₂H₅

714.550

C₄₄H₃₁N₄‚Cl/anion‚

solvent

615.728‚Cl/anion‚solvent

293(2)

1.54178

monoclinic

P2₁/c

pale yellow

0.35 × 0.12 × 0.10

13.469(2)

9.530(2)

30.088(3)

C₅₃H₃₈N₇Ru‚3PF₆‚

0.8CH₃CN‚0.5H₂O

1350.735

293(2)

0.71073

triclinic

P1h

orange

0.32 × 0.15 × 0.05

14.366(3)

14.570(3)

14.677(3)

82.82(3)

75.68(3)

82.19(3)

2935.6(10)

1.524

C₈₈H₆₂N₈Ru‚4PF₆

formula weight

T, K

wavelength, Å

crystal system

space group

color

crystal size, mm

a, Å

b, Å

1912.406

293(2)

0.71073

orthorhombic

Pbca

orange-red

0.30 × 0.09 × 0.03

16.355(3)

16.690(3)

60.729(12)

16577(6)

1.533

293(2)

1.54178

triclinic

P1h

colorless

0.34 × 0.32 × 0.24

10.446(2)

13.750(2)

14.169(4)

116.59(3)

105.55(3)

93.46(3)

1714.4(6)

1.303

c, Å

R, deg

â, deg

94.16(3)

3851.8(11)

1.196

γ, deg

V, Å³

_calc, g cm^-3

µ, mm^-1

0.780

694

1.196

1435

0.451

1350

0.373

7728

F(000)

θ range, deg

3.68-66.94

-12 e h e 12,

-16 e k e 14,

0 e l e 16

6370

2.95-45.65

0 e h e 12,

0 e k e 8,

-27 e l e 27

3407

2.47-22.49

-18 e h e 19,

-19 e k e 18,

-19 e l e 19

18 176

1.39-20.96

-16 e h e 16,

-16 e k e 16,

-60 e l e 60

64 871

limiting indices

reflns collected

independent reflns

refinement method

data/restraints/params

goodness-of-fit on F²

final R indices

6103 [R(int) ) 0.0239]

3221 [R(int) ) 0.1165]

7203 [R(int) ) 0.0864]

8774 [R(int) ) 0.2628]

full-matrix least-squares on F²

4953/0/458

1.784

R1 ) 0.0599, wR2 ) 0.2037

2068/1760/449

1.452

R1 ) 0.1405, wR2 ) 0.3574

6722/534/775

1.165

R1 ) 0.0618, wR2 ) 0.1385

7386/6094/1127

1.641

R1 ) 0.1304, wR2 ) 0.2745

[I>2σ(I)]

R indices (all data)

R1 ) 0.0965, wR2 ) 0.2382

0.451/-0.232

R1 ) 0.3725, wR2 ) 0.5534

0.503/ -0.479

R1 ) 0.0915, wR2 ) 0.1504

0.776/-0.340

R1 ) 0.2087, wR2 ) 0.3480

3.435/ -0.711

peak/hole (e‚Å^-3

)

based chromophores (P1) shows that, in the case of polyad

systems made of P1 and H₃TP⁺components only (and contrary

to the P1/D family), the influence of the triphenylpyridinio

moiety upon the MLCT absorption transitions is barely detected,

except for a slight hyperchromic effect, as exemplified in Figure

7b. In light of the previous reasoning, this behavior is then

considered as indicative of an extremely moderate intercom-

ponent coupling.⁵²

with the photosensitizer. However, a substituent effect (electron-

withdrawing) exists in the case of the direct attachment of A to

the tpy ligand (P0 series, H₃TP⁺-tpy family of ligand) as well

as for D-substituted P1 luminophores (electron-releasing effect).

Based on these findings, the intercomponent coupling within

the polyad systems, as a key parameter accounting for the

interesting photophysical behaviors, will be discussed in further

detail in a forthcoming paper.

3. Summary

4. Experimental Section

In this work, the first elements of a novel family of

triarylpyridinio-derivatized terpyridyl ligands, i.e., H₃TP⁺-tpy

and H₃TP⁺-ptpy have been synthesized and fully characterized.

When complexed with ruthenium(II) and osmium(II) transition

metal cations, nanometer-scale rigid rod-like supermolecules

with a unique axis and variable length (up to ca. 34.5 Å) have

been obtained. Moreover, it has been shown that, due to their

particular nature as chromophoric entities and their differential

electronic sensitivity toward covalently linked redox-active units,

P0 and P1 are actually distinct photosensitizers.

Combined X-ray structural analysis and NMR studies have

demonstrated that the rotation motion is not completely free

along the main molecular axis, even in solution. Indeed, a

pronounced twist angle between the photosensitizer and the

pyridinium ring of the acceptor has been evidenced, originating

from internal steric hindrance. As a result, concerning the P0

and P1 series of compounds, A (contrary to D) is not conjugated

4.1. General Experimental Details. Electronic spectra were recorded

on a Perkin-Elmer Lambda 9 spectrophotometer. The CI and ES

(solvent, acetonitrile) mass spectra were recorded with a modified

Nermag R10-10 quadrupole mass spectrometer.

4.2. Crystal Structure Determinations. Crystal data and data

collection and refinement parameters for [H₃TP⁺-tpy](BF₄)‚

0.5CH₃CO₂C₂H₅, [H₃TP⁺-ptpy](anion)‚solvent, [(tpy)Ru(tpy-TPH₃⁺)]-

(PF₆)₃‚0.8CH₃CN‚0.5H₂O, and [Ru(ptpy-TPH₃⁺)₂](PF₆)₄are sum-

marized in Table 3.

4.2.1. Organic Ligands. A single crystal of each species was

mounted on an automated Enraf-Nonius CAD4 diffractometer.⁵³The

unit cells were determined on the basis of 25 indexed and centered

reflections. Intensities were collected at room temperature with the use

of graphite-monochromated Cu KR radiation (1.54178 Å) in ω/2θ scan

mode. The data were corrected for Lorentz and polarization effects,

without being corrected for absorption. The intensities of three

reflections were monitored during the data collection and showed no

(53) Frenz, B. A. The Enraf-Nonius CAD4-SDP. In Computing in Crystal-

lography; Shenk, H., Olthof-Hazenkamp, R., Van Koningveld, H., Bassi,

G. C., Eds.; Delftse Universitaire Pers: Delft, The Netherlands, 1978; pp

64-71.

(52) Laine´, P.; Bedioui, F.; Amouyal, E.; Albin, V.; Berruyer-Penaud, F.

Submitted.

J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002 1373

A R T I C L E S

Laine´ et al.

systematic variation throughout. The structures were solved by direct

Structure of [(tpy)Ru(tpy-TPH₃⁺)](PF₆)₃‚0.8CH₃CN‚0.5H₂O. The

asymmetric unit is made up of one tricationic heteroleptic complex,

three hexafluorophosphate anions, and one acetonitrile plus one water

solvent molecules. The ruthenium(II) cation exhibits a pseudo-

octahedral environment. The two terdentate ligands complexing the

metal center display the expected cisoid conformation about the

interannular C-C bonds. All non-hydrogen atoms were refined

anisotropically. Hydrogen atoms were geometrically positioned; no

hydrogen atom was generated for the solvents. The populations of the

acetonitrile solvent and of the water molecule were refined to values

of 0.80 and 0.50, respectively. Similarity restraints were applied to the

ligands; acetonitrile bond distances/lengths were also restrained to the

standard target values. The maximum of residual electronic density

(0.78 e/Å³) is located close (ca. 1 Å) to the ruthenium coordinates.

Structure of [Ru(ptpy-TPH₃⁺)₂](PF₆)₄. Only tiny needles could be

grown, and the resulting lack of observed data leads to a rather poor

internal R value. The asymmetric unit is made up of one tetracationic

homoleptic complex associated with four hexafluorophosphate anions.

Two terpyridyl fragments achieve the completion of the coordination

of the metal center, each adopting a cisoid conformation about its

interannular C-C bonds. The resulting local symmetry about the Ru²⁺

cation is that of a distorted octahedron. All non-hydrogen atoms were

refined anisotropically, hydrogen atoms were geometrically positioned,

and a riding model was used. Restraints for planarity and similarity of

geometry and of displacement parameters were applied to the two

ligands. Geometrical and displacement parameter restraints were also

applied to the hexafluorophosphate moieties. Final difference Fourier

synthesis shows an unexpectedly high residual electronic density (3.43

e/Å³) close (ca. 1.35 Å) to the Ru atom. Improvements of the data

reduction were tried by checking the significance of integration

parameters (profile function, effective mosaic spread, and pixel-

overlapping tolerance). Moreover, refinements were performed in lower

crystal class (mm2), and the monoclinic symmetry was also considered.

None of the trials resulted in the elimination or the intensity weakening

of this spurious peak. Thus, it may be concluded that this feature is

due to the crystal specimen; i.e., a minor twin component is probably

attached to the major one. The small angular deviation between the

two crystal components precludes the collection of proper Bragg’s

peaks, especially along the very dense reciprocal direction c* (c )

60.73 Å). Notice that the second maximum of residual electronic density

stands in the expected range (0.78 e/Å³).

methods (SIR92)⁵⁴and refined on F²with the help of SHELX93.⁵⁵

Structure of [H₃TP⁺-tpy](BF₄)‚0.5CH₃CO₂C₂H₅. One cationic

molecule associated with a counteranion (BF₄^-) is present in the

asymmetric unit of the triclinic space group. Localization of the nitrogen

atoms showed a transoid conformation for the three pyridine rings about

the interannular C-C bonds, as least-squares calculations considering

a cisoid conformation led to clearly poorer values of the agreement

factors (wR2 ) 0.270). Hydrogen atoms were geometrically positioned,

except for the two hydrogen atoms attached to the ortho carbons

belonging to the lateral pyridine moieties, found on Fourier difference

maps. All hydrogen atoms were constrained with a riding model during

refinements; all non-hydrogen atoms were refined anisotropically. A

solvent region was found by Fourier synthesis, which should correspond

to an ethyl acetate molecule. This solvent molecule, which contains

one atom located on an inversion center, is disordered in a manner

that could not be readily resolved. All attempts to constrain interatomic

distances to expected values were unsuccessful. The final model is the

best fit to residual density. The two maxima of residual electronic

density (0.45 and 0.32 e/Å³, respectively) were found in the solvent

region.

Structure of [H₃TP⁺-ptpy](Anion)‚Solvent. Only aggregates of

poorly shaped crystals could be grown. As a consequence, the structure

is of rather poor quality. The asymmetric unit contains one monocationic

ligand molecule and a severely disordered region. Owing to the lack

of observed data, restraints for planarity and similarity of geometry

and of displacement parameters were applied to the ligand. A two-

fold orientational disorder of the terminal phenyl was resolved, and

populations were refined to a ratio of 60/40. Least-squares refinements

only suggest the expected transoid conformation of the terpyridine

(found in the previous structure), which was therefore imposed to the

model. Hydrogen atoms were geometrically positioned; no hydrogen

was generated for the disordered phenyl. All non-hydrogen atoms were

refined anisotropically, except for the carbon atoms belonging to the

terminal phenyl, which were refined isotropically. The disordered region

consists of a strong isolated peak, which wassarbitrarilysbest assigned

as a chemically not relevant chloride anion (A), and a region of residual

electronic density resembling a diethyl ether molecule. Examination

of X-ray diffraction patterns recorded with a STOE IPDS imaging plate

system⁵⁶(see below) led us to conclude that the assignment of the space

group of [H₃TP⁺-ptpy](anion) is problematic. Two triclinic twin

domains were evidenced, these domains being twinned along the

monoclinic axis. The triclinic cell parameters are very similar to the

monoclinic one: a ) 13.412(3) Å, b ) 9.214(2) Å, c ) 30.269(5) Å;

R ) 92.28(3)°, â ) 95.25(3)°, γ ) 92.93(3)°. A full sphere of data

was collected on the image plate, and a unique set of data could be

extracted and reduced in the triclinic symmetry. Investigations on the

crystal structure were performed either by direct methods or by

molecular replacement, but no solution was found. Attempts to refine,

in the triclinic symmetry, the structural model previously obtained from

thestwinnedsmonoclinic set of data also failed. The structure could

be again solved in the monoclinic space group by using the overall

twinned data from the image plate, but it was not possible to further

explain the unresolved electronic density. For these reasons, we have

not deposited the coordinates for this structure.

4.3. NMR Experiments. Routine H and ¹³C NMR spectra were

recorded on a Bruker AC-300 (300 MHz) spectrometer. Chemical shifts

are reported in parts per million (ppm) downfield from tetramethylsilane

(TMS) with reference to internal solvent. Multiplicities are abbreviated

as follows: singlet (s), doublet (d), triplet (t), and multiplet (m). Unless

otherwise specified (i.e., labels A and D refer to the acceptor and donor

ligands, respectively), H and ¹³C NMR assignments refer to the tpy

(P0 series) or Me-ptpy (P1 family) terminal ligands. NOESY and

ROESY experiments were performed with a Bruker DMX 500 (500

MHz) spectrometer on a concentrated and deoxygenated (argon

bubbling) CD₃CN solution of [(tpy)Ru(tpy-TPH₃⁺)](PF₆)₃. NOESY

experiments gave expected features for a medium-size molecule (M_r

) 1308.88 g mol^-1), i.e., slightly positive NOE signals at 300 MHz

that vanish when measured with the 500 MHz spectrometer. The

ROESY spectrum of P0A/Ru was recorded with a mixing period τ_m

) 400 ms and a strong off-resonance spin-lock (8400 Hz) pulse using

an adiabatic rotation angle of 54.7°.⁵⁷

4.2.2. Inorganic Compounds. A single crystal of each species was

mounted on a STOE IPDS.⁵⁶Intensities were collected at room

temperature with the use of graphite-monochromated Mo KR radiation

(0.71073 Å). The structures were solved by direct methods and refined

on F²with the SHELXTL V5.03 package. The data were corrected for

Lorentz and polarization effects as well as for absorption.

4.4. Syntheses. Chemicals. High-purity commercial reagent grade

products were used without further purification. The ligand Me-ptpy²²

and the complexes (tpy)RuCl₃,^31,58b(Me-ptpy)RuCl₃,^22,58(Me-ptpy)-

(54) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla, M.

C.; Polidori, G.; Cavalli, A. J. Appl Crystallogr. 1994, 27, 435-436.

(55) Sheldrick, G. M. SHELXTL-Plus, Rel. 5.03; Siemens Analytical X-ray

Instruments Inc.: Madison, WI, 1995.

(57) Desvaux, H.; Berthault, P.; Birlirakis, N.; Goldman, M.; Piotto, M. J. Magn.

Reson. A 1995, 113, 47-52.

(58) (a) Collin, J.-P.; Guillerez, S.; Sauvage, J.-P. J. Chem. Soc., Chem. Commun.

1989, 776-778. (b) Sullivan, B. P.; Calvert, J. M.; Meyer, T. J. Inorg.

Chem. 1980, 19, 1404-1407.

(56) STOE IPDS, STOE &CIE GmbH, 1997.

1374 J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002

Terpyridyl Ligands as Photosensitized Supermolecules

A R T I C L E S

OsCl₃,^58a[Ru(tpy)₂](PF₆)₂,³¹[Ru(ptpy-Me)₂](PF₆)₂,^22,58aand [Os(ptpy-

(C⁸); 128.00 (C⁷); 123.53 (C⁵); 121.20 (C³); 117.62 (C^3′); 115.05 (C⁹).

These data are in agreement with those reported in the literature.²¹

1,2,4,6-Tetraphenylpyridinium, [H₃TP⁺-p](0.5HSO₄, 0.5OAc). A

mixture of aniline (0.25 g, 2.68 mmol), 2,4,6-triphenylpyrylium

hydrogen sulfate (1.636 g, 4.026 mmol, 1.5 equiv), and anhydrous

sodium acetate (1 g) in EtOH (25 mL) was heated overnight under

reflux. Once the reaction medium was cooled to room temperature,

the solvent was removed and the product extracted with CH₂Cl₂. The

compound was subsequently purified by column chromatography over

basic alumina with a gradient mixture of eluent varying from pure

EtOAc to pure CH₂Cl₂. The pure product was obtained as white crystals

after recrystallization from a mixture of EtOAc and CH₂Cl₂(0.55 g;

yield 44.4%). ¹H NMR (300 MHz, CDCl₃, ppm): δ 8.39 (s, 2H; H^12A);

8.12 (dd, 2H, J ) 8.0, 1.3 Hz; H^15A); 7.67 (m, 3H; H^16A, H^17A); 7.43

(m, 4H; H^19A); 7.35 (m, 8H; H^9A, H^20A, H^21A); 7.19 (m, 3H; H^7A, H^8A).

¹³C NMR: δ 152.41 (C^11A); 152.25 (C^13A); 134.59 (C^18A); 129.64 (C^14A);

58a

Me)₂](PF₆)₂

were synthesized following the literature methods.

Concerning all synthesized inorganic compounds,¹H and ¹³C NMR data

along with full assignments are available as Supporting Information.

4′-(p-N,N-Dimethylaminophenyl)-2,2′:6′,2′′-terpyridine, (Me₂N-

ptpy). The procedure was derived from that of Collin et al. for Me-

ptpy,²²using the conveniently substituted aldehyde reactant, i.e., p-N,N-

dimethylaminobenzaldehyde. The black gummy solid obtained was

collected by decantation, thoroughly washed with H₂O, and dissolved

in CH₂Cl₂instead of being treated with HBr. The organic phase was

washed several times with H₂O until the aqueous phase was colorless

and neutral. After evaporation of the solvent, the solid was redissolved

in a CH₂Cl₂:EtOH mixture (1:1, 500 mL), and an aqueous solution of

Fe²⁺(Mohr salt, 10 g in 100 mL of H₂O) was added to give immediately

a dark purple medium, which was vigorously stirred for an additional

0.25 h. The phase separation of the reaction medium was then completed

by addition of CH₂Cl₂(200 mL) and H₂O (200 mL). The purple aqueous

phase was washed several times with CH₂Cl₂until the organic phase

was colorless. Afterward, the classical method of purification²⁴(anion

metathesis and precipitation of the complex followed by the decom-

plexation step) was performed (yield: 14%). ¹H NMR (300 MHz,

CDCl₃, ppm): δ 8.74 (dd, 2H, J ) 4.8, 1.6 Hz; H^6D); 8.72 (s, 2H;

H^3′D); 8.67 (d, 2H, J ) 7.8 Hz; H^3D); 7.88 (d, 2H, J ) 8.7 Hz; H^8D);

7.87 (dd, 2H, J ) 7.0, 1.8 Hz; H^4D); 7.34 (ddd, 2H, J ) 7.7, 4.8, 1.2

Hz; H^5D); 6.82 (d, 2H, J ) 8.9 Hz; H^9D); 3.02 (s, 6H; H^Me/D). ¹³C

NMR: δ 156.92 (C^2′D); 155.92 (C^2D); 151.34 (C^10D); 150.24 (C^4′D);

149.31 (C^6D); 137.03 (C^4D); 128.30 (C^8D); 125.75 (C^7D); 123.85 (C^5D);

121.60 (C^3D); 117.75 (C^3′D); 112.51 (C^9D); 40.59 (C^Me/D). UV-vis (CH₃-

CN) λ_max/nm (ꢀ/M^-1cm^-1): 234 (23 120), 290 (22 990), 346 (19 830).

Anal. Calcd for C₂₃H₂₀N₄: C, 78.38; H, 5.72; N, 15.90. Found: C,

78.38; H, 5.65; N, 15.75.

128.50 (C^17A); 127.98 (C^10A); 125.79 (C^21A); 125.52 (C^19A); 125.35 (C^8A

C^16A); 124.49 (C^12A); 124.34 (C^9A); 124.0 (C^15A, C^20A); 121.57 (C^7A).

UV-vis (CH₃CN) λ_max/nm (ꢀ/M^-1cm^-1): 237sh (32 620), 308

(33 190). Anal. Calcd for C₂₉H₂₂N₁(0.5HSO₄^-, 0.5CH₃CO₂^-): C, 77.89;

H, 5.23; N, 3.03. Found: C, 77.79; H, 5.34; N, 3.00.

4′-N-(2,4,6-Triphenylpyridinio)-2,2′:6′,2′′-terpyridine, [H₃TP⁺-

tpy](BF₄). A mixture of H₂N-tpy (0.372 g, 1.498 mmol), 2,4,6-

triphenylpyrylium tetrafluoroborate (0.89 g, 2.247 mmol, 1.5 equiv),

and anhydrous sodium acetate (1.2 g) in EtOH (30 mL) was refluxed

14 h. After evaporation of the solvent in a Rotavapor, the product was

extracted from the solid with CH₂Cl₂and purified by column chroma-

tography over basic alumina using a mixture of eluents with an

increasing gradient of polarity. The elution was performed with EtOAc/

CH₂Cl₂, 100:0 to 0:100, and then with CH₂Cl₂/EtOH, 99:1 to 50:50.

After recrystallization from a mixture CH₂Cl₂/EtOAc, the pure product

was obtained as colorless prismatic crystals (0.659 g; yield 65.6%). ¹H

NMR (300 MHz, CDCl₃, ppm): δ 8.61 (d, 2H, J ) 4.7 Hz; H^6A); 8.36

(s, 2H; H^3′A); 8.35 (d, 2H, J ) 7.9 Hz; H^3A); 8.11 (s, 2H; H^12A); 7.89

(dd, 2H, J ) 8.1, 1.3 Hz; H^15A); 7.78 (ddd, 2H, J ) 7.8, 7.7, 1.6 Hz;

H^4A); 7.57 (m, 4H; H^19A); 7.51 (m, 3H; H^16A, H^17A); 7.29 (dd, 2H, J )

7.5, 4.8 Hz; H^5A); 7.22 (m, 6H; H^20A, H^21A). ¹³C NMR: δ 158.73 (C^13A);

157.47 (C^2′A); 156.37 (C^2A); 153.94 (C^11A); 149.80 (C^6A); 148.51 (C^4′A);

137.18 (C^4A); 134.69 (C^14A); 132.55 (C^18A); 132.46 (C^17A); 130.81

(C^21A); 130.00 (C^16A, C^19A); 128.93 (C^15A, C^20A); 126.76 (C^12A); 124.92

(C^5A); 121.59 (C^3A); 120.21 (C^3′A). UV-vis (CH₃CN) λ_max/nm (ꢀ/M^-1

cm^-1): 308 (50 800). Anal. Calcd for C₃₈H₂₇N₄BF₄‚0.5CH₃CO₂C₂H₅:

C, 71.65; H, 4.66; N, 8.35. Found: C, 71.19; H, 4.44; N, 8.14.

4′-[4-N-(2,4,6-Triphenylpyridinio)phenyl]-2,2′:6′,2′′-terpyri-

dine, [H₃TP⁺-ptpy](0.1HSO₄, 0.9OAc). The procedure was similar

to that described for H₃TP⁺-tpy, using H₂N-ptpy (0.426 g, 1.313 mmol),

2,4,6-triphenylpyrylium hydrogen sulfate (0.8 g, 1.97 mmol, 1.5 equiv),

and anhydrous sodium acetate (1.0 g) in EtOH (25 mL) heated to reflux

for 20 h. The final recrystallization was performed in pure Et₂O, leading

to yellowish-ochre aggregated crystals (0.665 g; yield 74.6%). ¹H NMR

(300 MHz, CDCl₃, ppm): δ 8.65 (d, 2H, J ) 4.8 Hz; H^6A); 8.57 (d,

2H, J ) 7.9 Hz; H^3A); 8.46 (s, 2H; H^3′A); 8.15 (s, 2H; H^12A); 7.94 (d,

2H, J ) 8.0 Hz; H^15A); 7.83 (dd, 2H, J ) 7.9, 7.6 Hz; H^4A); 7.75 (d,

2H, J ) 8.7 Hz; H^8A); 7.62 (m, 4H; H^19A); 7.59 (d, 2H, J ) 8.7 Hz;

H^9A); 7.54 (m, 3H; H^16A, H^17A); 7.33 (dd, 2H, J ) 4.8 Hz; H^5A); 7.29

(m, 6H; H^20A, H^21A). ¹³C NMR: δ 156.73 (C^2′A); 156.58 (C^13A); 155.82

(C^2A); 155.46 (C^11A); 148.85 (C^6A); 147.74 (C^4′A); 139.59 and 139.50

(C^7A, C^10A); 136.91 (C^4A); 133.90 (C^14A); 132.70 (C^18A); 132.20 (C^17A);

130.24 (C^21A); 129.75 (C^19A); 129.58 (C^16A); 129.27 (C^8A); 128.39

(C^20A); 128.26 (C^15A); 127.35 (C^9A); 125.90 (C^12A); 123.94 (C^5A); 121.25

(C^3A); 118.44 (C^3′A). UV-vis (CH₃CN) λ_max/nm (ꢀ/M^-1cm^-1): 252

(43 700), 296 (44 980), 309 (45 570). Anal. Calcd for C₄₄H₃₁N₄(0.1HSO₄^-,

0.9CH₃CO₂^-): C, 81.06; H, 5.02; N, 8.26. Found: C, 80.82; H, 4.84;

N, 8.51. CI-MS data: m/z 615 [M⁺].

4′-(p-Nitrophenyl)-2,2′:6′,2′′-terpyridine, (O₂N-ptpy). The ligand

was made by following a modification of the literature method for the

synthesis of Me-ptpy,²²using the conveniently substituted aldehyde

reactant, i.e., p-nitrobenzaldehyde, except that no bromhydrate was

precipitated. As described above for the Me₂N-ptpy ligand, the ligand

was directly extracted with iron(II) as its homoleptic complex [Fe-

(ptpy-NO₂)₂]²⁺and purified. The final recrystallization of the O₂N-

ptpy ligand was carried out in a mixture EtOH/H₂O, affording the pure

product as beige needles (yield: 11%). H NMR (300 MHz, CDCl₃,

ppm): δ 8.76 (s, 2H; H^3′); 8.73 (dd, 2H, J ) 4.8, 1.6 Hz; H⁶); 8.68 (d,

2H, J ) 7.9 Hz; H³); 8.35 (d, 2H, J ) 8.8 Hz; H⁹); 8.04 (d, 2H, J )

8.8 Hz; H⁸); 7.91 (dd, 2H, J ) 7.8, 7.7 Hz; H⁴); 7.39 (dd, 2H, J ) 7.4,

4.8 Hz; H⁵). ¹³C NMR: δ 156.92 (C^2′D); 155.92 (C^2D); 151.34 (C^10D);

150.24 (C^4′D); 149.18 (C⁶); 137.04 (C⁴); 128.28 (C⁸); 125.75 (C^7D);

124.19 (C⁵); 121.41 (C³); 117.75 (C^3′D); 118.92 (C⁹). UV-vis (CH₂-

Cl₂) λ_max/nm (ꢀ/M^-1cm^-1): 245 (29 970), 252 (29 460), 286 (43 220).

Anal. Calcd for C₂₁H₁₄N₄O₂‚H₂O: C, 67.73; H, 4.33; N, 15.05.

Found: C, 67.67; H, 4.33; N, 15.29.

4′-(p-Aminophenyl)-2,2′:6′,2′′-terpyridine, (H₂N-ptpy). To a solu-

tion of O₂N-ptpy monohydrate (0.5 g, 1.34 mmol) in EtOH (100 mL)

was added Pd/C 10% (0.15 g), and the suspension was heated to reflux

for 1 h under Ar. Hydrazine hydrate solution (N₂H₄55%, 1.6 mL, 28.2

mmol, 21 equiv) was then added dropwise using a syringe and the

reflux carried on for an additional 0.5 h. The reaction mixture was

cooled to room temperature and filtered over cotton-wool, and the

catalyst was washed with CH₂Cl₂(150 mL). The combined organic

filtrates were washed several times with H₂O (5 × 100 mL) until the

aqueous phase was almost neutral. The organic phase was then dried

over magnesium sulfate and filtered, and the solvent was evaporated,

affording a pale yellow microcrystalline product (0.426 g; yield 97.7%).

¹H NMR (300 MHz, CDCl₃, ppm): δ 8.72 (dd, 2H, J ) 4.8, 1.6 Hz;

H⁶); 8.68 (s, 2H; H^3′); 8.65 (d, 2H, J ) 7.9 Hz; H³); 7.87 (dd, 2H, J )

7.8, 7.7 Hz; H⁴); 7.78 (d, 2H, J ) 8.6 Hz; H⁸); 7.33 (dd, 2H, J ) 7.4,

4.7 Hz; H⁵); 6.79 (d, 2H, J ) 8.6 Hz; H⁹). ¹³C NMR: δ 156.33 (C^2′);

155.52 (C²); 149.83 (C¹⁰); 148.89 (C⁶); 147.37 (C^4′); 136.69 (C⁴); 128.22

[Ru(tpy-TPH₃⁺)₂](PF₆)₄, (P0A₂/Ru). RuCl₃‚3H₂O (16 mg, 0.061

mmol) and [H₃TP⁺-tpy](BF₄) (87 mg, 0.13 mmol, 2.1 equiv) were

J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002 1375

A R T I C L E S

Laine´ et al.

dissolved in absolute EtOH (10 mL) and heated for 0.5 h. 1,2-Ethanediol

(20 mL) and sodium ascorbate (121 mg, 0.612 mmol, 10 equiv/Ru)

were then added, and the resulting mixture was heated at 110 °C for

21 h under an inert atmosphere. At room temperature, while stirring,

a solution of NH₄PF₆(199 mg, 1.22 mmol, 20 equiv/Ru) in distilled

H₂O (25 mL) was added to precipitate the complex, which was then

filtered off and washed successively with H₂O, EtOH, and Et₂O. The

orange product was purified by column chromatography over basic

alumina using an eluent mixture of CH₂Cl₂/acetone from 100:0 to 0:100.

A recrystallization from acetone/CHCl₃mixture led to red-orange

crystals (85 mg; yield 78%). Anal. Calcd for C₇₆H₅₄N₈RuP₄F₂₄‚H₂O:

C, 51.33; H, 3.17; N, 6.30. Found: C, 51.30; H, 3.02; N, 6.24.

[(tpy)Ru(tpy-TPH₃⁺)](PF₆)₃, (P0A/Ru). (tpy)RuCl₃(65 mg, 0.147

mmol) and [H₃TP⁺-tpy](BF₄) (118 mg, 0.177 mmol, 1.2 equiv) were

suspended in 1,2-ethanediol (20 mL) in the presence of sodium

ascorbate (292 mg, 1.47 mmol, 10 equiv/Ru) and heated at 120 °C for

17 h under an inert atmosphere (Ar). Afterward, while vigorously

stirring, EtOH (10 mL) and H₂O (20 mL) were added together with

NH₄PF₆(481 mg, 2.95 mmol, 20 equiv/Ru) for the precipitation of the

complex. The product was filtered off and washed successively with

H₂O, EtOH, and Et₂O to give an orange product which was purified

by column chromatography over basic alumina using an eluent of

increasing polarity, i.e., a mixture of CH₂Cl₂/acetone from 100:0 to

0:100. Recrystallization in acetone/CHCl₃afforded a dirty orange

microcrystallized product (148 mg; yield 77%). Anal. Calcd for

C₅₃H₃₈N₇RuP₃F₁₈: C, 48.63; H, 2.93; N, 7.49. Found: C, 48.66; H,

2.93; N, 7.34.

[Ru(ptpy-TPH₃⁺)₂](PF₆)₄, (P1A₂/Ru). A mixture of RuCl₃‚3H₂O

(18 mg, 0.069 mmol), [H₃TP⁺-ptpy](0.1HSO₄^-, 0.9OAc^-) (98 mg,

0.145 mmol, 2.1 equiv, dissolved in 5 mL of CH₂Cl₂), sodium ascorbate

(136 mg, 0.688 mmol, 10 equiv/Ru), and 1,2-ethanediol (15 mL) was

heated to 110 °C for 18 h under an Ar atmosphere. The reaction medium

was cooled to room temperature, and then EtOH (10 mL), distilled

H₂O (25 mL), and a large excess of NH₄PF₆(225 mg, 1.376 mmol, 20

equiv/Ru) were added while vigorously stirring, resulting in the

precipitation of the complex which was filtered off, successively washed

with H₂O, EtOH, and Et₂O, and air-dried. The crude orange powder

was subsequently purified by column chromatography over basic

alumina, eluting first with CH₂Cl₂/acetone using a gradient of acetone

(up to 100%), second with CH₃CN, and finally with a saturated CH₃-

CN solution of NH₄PF₆. After removal of the salt by precipitating twice

the complex in EtOH, the product was recrystallized by slow vapor

diffusion of Et₂O in a solution of the product in CH₃CN, giving fine

orange needles (48 mg; yield 36.5%). Anal. Calcd for C₈₈H₆₂N₈-

crude orange powder was subsequently purified accordingly to the

procedure described for P1A₂/Ru, affording the product as fine orange

needles (130 mg; yield 89%). Anal. Calcd for C₆₆H₄₈N₇RuP₃F₁₈‚H₂O:

C, 53.08; H, 3.37; N, 6.57. Found: C, 52.98; H, 3.32; N, 6.49. HRMS

- 3+

(ES) data: m/z 592.91 [M - 2PF₆] ] .

²⁺; 346.98 [M - 3PF₆

[(Me-ptpy)Os(ptpy-TPH₃⁺)](PF₆)₃, (P1A/Os). A procedure similar

to that reported for the Ru²⁺analogue, P1A/Ru, was followed. A

mixture of (Me-ptpy)OsCl₃(55 mg, 0.089 mmol), [H₃TP⁺-ptpy]-

(0.1HSO₄^-, 0.9OAc^-) (72 mg, 0.106 mmol, 1.2 equiv), and sodium

ascorbate (176 mg, 0.887 mmol, 10 equiv/Os) in 1,2-ethanediol (15

mL) was heated at 110 °C for 24 h under Ar. The product was finally

obtained as thin brown needles (100 mg; yield 69.6%). Anal. Calcd

for C₆₆H₄₈N₇OsP₃F₁₈‚3H₂O: C, 48.98; H, 3.36; N, 6.06. Found: C,

48.92; H, 3.30; N, 6.06. ES-MS data: m/z 1421 (¹⁹²Os) and 1419 (¹⁹⁰

Os), [M - PF₆^-]⁺; 638 [M - 2PF₆²⁺; 376 [M - 3PF₆

] ] .

- 3+

[(Me₂N-ptpy)₂Ru](PF₆)₂, (D₂P1/Ru). Under Ar, a mixture of RuCl₃‚

3H₂O (56 mg, 0.214 mmol), Me₂N-ptpy (166 mg, 0.471 mmol, 2.2

equiv), and a large excess of sodium ascorbate (424 mg, 2.14 mmol,

10 equiv/Ru) in 1,2-ethanediol (20 mL) was heated at 100 °C for 3 h.

To the dark red-violet solution were then added EtOH (20 mL) and

NH₄PF₆(698 mg, 4.28 mmol, 20 equiv/Ru) to precipitate the complex.

The solid was filtered off and washed with H₂O, EtOH, and Et₂O. To

eliminate highly fluorescent impurities of different solubility, the crude

violet powder was first extracted with acetone and the solution poured

into a large excess of EtOAc. One of the strongly emitting impurities

remained in solution, whereas the complex precipitated as a brown-

orange and shimmering microcrystallized compound. The solid thus

obtained was filtered off and washed with EtOAc and Et₂O. In a second

step, the solid collected was dissolved in a minimum volume of acetone

and poured while vigorously stirring into a large volume of EtOH. A

precipitate was formed that was filtered off and washed with EtOH

and Et₂O. The final recrystallization was achieved by slow vapor

diffusion of Et₂O in a solution of the product in CH₃CN, giving dark

violet and microcrystallized powder (167 mg; yield 70.6%). Anal. Calcd

for C₄₆H₄₀N₈RuP₂F₁₂‚0.5H₂O: C, 50.00; H, 3.74; N, 10.14. Found: C,

49.74; H, 3.69; N, 10.12. ES-MS data: m/z 403 [M - 2PF₆

] .

[(Me₂N-ptpy)₂Os](PF₆)₂, (D₂P1/Os). A mixture of OsCl₃‚3H₂O (100

mg, 0.285 mmol), Me₂N-ptpy (221 mg, 0.627 mmol, 2.2 equiv), and a

large excess of sodium ascorbate (565 mg, 2.85 mmol, 10 equiv/Os)

in 1,2-ethanediol (20 mL) was heated at 100 °C for 14 h under Ar. To

the dark brown-violet solution at room temperature were then added

EtOH (20 mL) and NH₄PF₆(930 mg, 5.70 mmol, 20 equiv/Os) to

precipitate the complex. The solid was filtered off and washed with

H₂O, EtOH, and Et₂O. The product was subsequently purified by

column chromatography over basic alumina, eluting with a mixture of

CH₂Cl₂/acetone using a gradient of acetone (up to 100%) and finally

recrystallized by slow vapor diffusion of Et₂O in a solution of the

product in CH₃CN (deep violet color), giving glistening greenish crystals

(97 mg; yield 28.7%). Anal. Calcd for C₄₆H₄₀N₈OsP₂F₁₂: C, 46.62; H,

3.40; N, 9.46. Found: C, 46.58; H, 3.46; N, 9.58. ES-MS data: m/z

RuP₄F₂₄: C, 55.26; H, 3.27; N, 5.86. Found: C, 55.23; H, 3.23; N,

²⁺; 492.66 [M -

6.05. HRMS (ES) data: m/z 811.62 [M - 2PF₆

]

3PF₆] ] .

³⁺; 333.31 [M - 4PF₆

- 4+

[Os(ptpy-TPH₃⁺)₂](PF₆)₄, (P1A₂/Os). The complex was synthesized

and purified following a procedure similar to the one described for the

Ru²⁺analogue, P1A₂/Ru. A mixture of OsCl₃‚3H₂O (24 mg, 0.068

mmol), [H₃TP⁺-ptpy](0.1HSO₄^-, 0.9OAc^-) (98 mg, 0.144 mmol, 2.1

equiv in 5 mL of CH₂Cl₂), sodium ascorbate (136 mg, 0.685 mmol, 10

equiv/Os), and 1,2-ethanediol (15 mL) was heated to 110 °C for 20 h

under inert atmosphere. The final recrystallization gave thin brown

needles (50 mg; yield 36.2%). Anal. Calcd for C₈₈H₆₂N₈OsP₄F₂₄‚H₂O:

C, 52.33; H, 3.19; N, 5.55. Found: C, 51.92; H, 2.98; N, 5.55. ES-MS

1041 (¹⁹²Os) and 1039 (¹⁹⁰Os), [M - PF₆^-]⁺; 448 [M - 2PF₆

] .

[(Me₂N-ptpy)Ru(ptpy-Me)](PF₆)₂, (DP1/Ru). Under Ar, a mixture

of (Me-ptpy)RuCl₃(100 mg, 0.188 mmol), Me₂N-ptpy (80 mg, 0.227

mmol, 1.2 equiv), and sodium ascorbate (373 mg, 1.88 mmol, 10 equiv/

Ru) in 1,2-ethanediol (20 mL) was heated at 100 °C for 3 h. To the

red-violet solution were then added EtOH (20 mL) and NH₄PF₆(614

mg, 3.77 mmol, 20 equiv/Ru) to precipitate the complex. The solid

was filtered off and washed with H₂O, EtOH, and Et₂O. The same

purification workup as for D₂P1/Ru was then performed, with an

additional step consisting of column chromatography over basic

alumina, eluting with CH₂Cl₂and acetone and using a gradient of

acetone (up to 100%). Recrystallization by slow vapor diffusion of Et₂O

in a solution of the product in CH₃CN gave a violet and microcrys-

tallized powder (150 mg; yield 74.6%). Anal. Calcd for C₄₅H₃₇N₇-

RuP₂F₁₂: C, 50.66; H, 3.49; N, 9.19. Found: C, 50.56; H, 3.43; N,

data: m/z 1857 [M - PF₆^-]⁺; 856 [M - 2PF₆²⁺; 522 [M - 3PF₆

] ] ;

- 3+

355 [M - 4PF₆

] .

[(Me-ptpy)Ru(ptpy-TPH₃⁺)](PF₆)₃, (P1A/Ru). Under Ar, a mixture

of (Me-ptpy)RuCl₃(52 mg, 0.098 mmol), [H₃TP⁺-ptpy](0.1HSO₄

0.9OAc^-) (80 mg, 0.118 mmol, 1.2 equiv), and sodium ascorbate (194

mg, 0.979 mmol, 10 equiv/Ru) in 1,2-ethanediol (15 mL) was heated

at 110 °C for 14 h. To the red-violet solution at room temperature

were then added EtOH (15 mL), H₂O (20 mL), and NH₄PF₆(319 mg,

1.96 mmol, 20 equiv/Ru) so as to precipitate the complex. The solid

was filtered off, washed with H₂O, EtOH, and Et₂O, and air-dried. The

9.04. ES-MS data: m/z 921 [M - PF₆^-]⁺; 389 [M - 2PF₆

] .

1376 J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002

Terpyridyl Ligands as Photosensitized Supermolecules

A R T I C L E S

[(Me₂N-ptpy)Os(ptpy-Me)](PF₆)₂, (DP1/Os). A mixture of (Me-

ptpy)OsCl₃(150 mg, 0.242 mmol), Me₂N-ptpy (102 mg, 0.29 mmol,

1.2 equiv), and sodium ascorbate (479 mg, 2.42 mmol, 10 equiv/Os)

in 1,2-ethanediol (20 mL) was heated at 100 °C for 14 h under inert

atmosphere. To the dark brown-violet solution were then added EtOH

(20 mL) and NH₄PF₆(789 mg, 4.84 mmol, 20 equiv/Os), leading to

the precipitation of the complex. The solid was filtered off and washed

with H₂O, EtOH, and Et₂O. The product was subsequently purified by

column chromatography over basic alumina. Elution was performed

with CH₂Cl₂and acetone using a gradient of acetone (up to 100%).

Finally, recrystallization by slow vapor diffusion of Et₂O in a solution

of the product in CH₃CN gave a dark brown and microcrystallized

powder (125 mg; yield 44.7%). Anal. Calcd for C₄₅H₃₇N₇OsP₂F₁₂: C,

46.75; H, 3.23; N, 8.48. Found: C, 46.72; H, 3.27; N, 8.51. ES-MS

data: m/z 1012 (¹⁹²Os) and 1010 (¹⁹⁰Os), [M - PF₆^-]⁺; 448 [M -

of acetone (up to 100%), second with CH₃CN, and finally with a

saturated solution of NH₄PF₆in CH₃CN. After removal of the salt by

precipitating twice the complex in EtOH, the product was recrystallized

by slow vapor diffusion of Et₂O in a solution of the product in CH₃-

CN, giving a red-violet microcrystalline solid (173 mg; yield 64%).

Anal. Calcd for C₆₇H₅₁N₈RuP₃F₁₈‚0.5H₂O: C, 53.18; H, 3.46; N, 7.41.

Found: C, 53.06; H, 3.46; N, 7.39. ES-MS data: m/z 357 [M -

3PF₆

] .

[(Me₂N-ptpy)Os(ptpy-TPH₃⁺)](PF₆)₃, (DP1A/Os). Under Ar, (Me₂N-

ptpy)OsCl₃(145 mg, 0.223 mmol), [H₃TP⁺-ptpy](0.1HSO₄^-, 0.9OAc^-)

(167 mg, 0.246 mmol, 1.1 equiv), and sodium ascorbate (443 mg, 2.23

mmol, 10 equiv/Os) in 1,2-ethanediol (20 mL) were heated at 100 °C

for 14 h. The purification was performed as for DP1A/Ru, giving a

brown-violet microcrystallized solid (143 mg; yield 39.5%). Anal. Calcd

for C₆₇H₅₁N₈OsP₃F₁₈‚1.5H₂O: C, 49.66; H, 3.36; N, 6.92. Found: C,

49.59; H, 3.34; N, 6.95. ES-MS data: m/z 1450 (¹⁹²Os) and 1448 (¹⁹⁰

2PF₆

] .

- 3+

Os), [M - PF₆^-]⁺; 652 [M - 2PF₆²⁺; 386 [M - 3PF₆

] ] .

(Me₂N-ptpy)RuCl₃. A mixture of RuCl₃‚3H₂O (200 mg, 0.765

mmol) and Me₂N-ptpy (275 mg in CH₂Cl₂, 1 mL, 0.78 mmol, 1.02

equiv) in EtOH (30 mL) was refluxed for 1 h. At room temperature,

the dark precipitate was filtered off, thoroughly washed with H₂O,

EtOH, CH₂Cl₂, and Et₂O, and air-dried, giving (Me₂N-ptpy)RuCl₃as

a dark brown powder (395 mg; yield 92.2%).

Acknowledgment. We are indebted to Dr. Kurt Schenk for

his support regarding X-ray crystallography and Dr. Isabelle

Corriera for ROESY experiments.

(Me₂N-ptpy)OsCl₃. The compound was prepared following the

procedure described for (Me₂N-ptpy)RuCl₃, with OsCl₃‚3H₂O (200

mg, 0.57 mmol) and Me₂N-ptpy (205 mg in CH₂Cl₂, 1 mL, 0.58 mmol,

1.02 equiv) in EtOH (30 mL), refluxed for 1 h. (Me₂N-ptpy)OsCl₃was

obtained as a dark brown powder (240 mg; yield 65%).

[(Me₂N-ptpy)Ru(ptpy-TPH₃⁺)](PF₆)₃, (DP1A/Ru). Under Ar, (Me₂N-

ptpy)RuCl₃(100 mg, 0.179 mmol), [H₃TP⁺-ptpy](0.1HSO₄^-, 0.9OAc^-)

(133 mg, 0.197 mmol, 1.1 equiv), and sodium ascorbate (354 mg, 1.786

mmol, 10 equiv/Ru) in 1,2-ethanediol (18 mL) were heated at 80 °C

for 18 h. The complex was precipitated at room temperature by adding

to the dark violet solution of EtOH (15 mL), H₂O (20 mL), and NH₄-

PF₆(582 mg, 3.57 mmol, 20 equiv/Ru). The solid was filtered off and

washed with H₂O, EtOH, and Et₂O. The crude powder in solution in

acetone was adsorbed over basic alumina and subsequently column

chromatographed, eluting first with CH₂Cl₂and acetone using a gradient

Supporting Information Available: ORTEP drawings along

with related numbering schemes, tables of crystal data, structure

solution and refinement, atomic coordinates, bond lengths and

angles, and anisotropic thermal parameters for [H₃TP⁺-tpy]-

(BF₄)‚0.5CH₃CO₂C₂H₅, [H₃TP⁺-ptpy](anion)‚solvent, P0A/Ru‚

0.8CH₃CN‚0.5H₂O, and P1A₂/Ru; plot of d(C_Ar1-N_py+) as a

function of θ1; ¹H and ¹³C NMR data along with related

assignments for all inorganic compounds as well as a selected

part of the ROESY spectrum of a CD₃CN solution of P0A/Ru;

figure showing the ground-state electronic spectra of the P0/

Ru series of complexes (PDF). This material is available free

of charge via the Internet at http://pubs.acs.org.

JA011069P

J. AM. CHEM. SOC. VOL. 124, NO. 7, 2002 1377

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