Homoleptic bis(aryl)acenaphthenequinonediimine-CuI complexes-Synthesis and characterization of a family of compounds with improved light-gathering characteristics

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DOI:10.1002/ejic.201201507

Homoleptic Bis(aryl)acenaphthenequinonediimine–Cu^I

Complexes – Synthesis and Characterization of a Family

of Compounds with Improved Light-Gathering

Characteristics

Panagiotis Papanikolaou,*^[a,b]Pericles D. Akrivos,^[a]

Agnieszka Czapik,^[c]Barbara Wicher,^[c]Maria Gdaniec,*^[c]and

Nikolai Tkachenko*^[b]

Keywords: Copper / N ligands / Electronic structure / Structure elucidation

A group of bis(aryl)acenaphthenequinonediimine (Ar-BIAN)

ligands were synthesized through a modified procedure,

which bypasses the need for absolutely dry conditions during

the initial template synthesis. The molecular and electronic

structure of the corresponding homoleptic [Cu(Ar-BIAN)₂]-

BF₄complexes were probed by means of a variety of spectro-

scopic methods. In accord with solution ¹³C NMR spectra, X-

ray crystallography reveals D₂or approximate D₂symmetry

for the [Cu(p-Cl-BIAN)₂]⁺and [Cu(p-Me-BIAN)₂]⁺cations

and noncrystallographic C₂symmetry for the [Cu(o-Ph-

BIAN)₂]⁺cation. The structures of the p-Cl-, p-Me, and o-Ph-

BIAN complexes agree with the presence of ligands in their

neutral form according to the lengths of the relevant C–C and

C=N bonds of the organic skeleton. The concerted stereo–

electronic effects of the substituents on the aryl rings affect

the electron donor/acceptor capacities of the ligands and the

structures of the complexes, as the study of the visible ab-

sorption spectra of the complexes indicates. The spectra of

the complexes are dominated by intense and broad metal-

to-ligand charge transfer (MLCT) bands that enter the near-

infrared (NIR) region. Additionally, electrochemical studies

undertaken reveal several successive electron capture and

release processes, which further manifest the redox versatil-

ity of the ligands.

These copper(I) compounds do not have the high cost and

environmentally hazardous nature of the former com-

pounds.

Introduction

The emerging need for renewable energy sources, in par-

ticular solar radiation, has turned scientific interest towards

the discovery and manipulation of the behavior of new

photoactive materials^[1]that can capture, store, and redirect

or re-release energy more efficiently. Although the main

concern has been devoted to second and third row transi-

tion-metal complexes with bi- or tridentate polypyridyl li-

gands,^[2]copper(I) compounds bearing mainly 2,9-disubsti-

tuted phenanthrolines emerged recently as an alternative

with many potential applications in lighting technologies.^[3]

Despite the advantages of Cu^Icomplexes, one of the

main goals still to achieve is the synthesis of materials that

absorb in the red and near-infrared (NIR) part of the spec-

trum. In 1999, Miller and Karpishin reported the synthesis

of a Cu^Iblack absorber that bears two phenylethynyl-disub-

stituted phenanthroline ligands.^[4]The aim of this work was

to investigate the possibility of redshifting the energy of the

metal-to-ligand charge transfer (MLCT) absorption by low-

ering the energy of the π*-acceptor orbitals of the diimine

through enhancement of the electronic delocalization and

to study its impact on the photophysics and photochemistry

of the system. The authors concluded that to expand the

absorption of the Cu^I–bisdiimine systems a substantial dis-

tortion of the molecule from the ideal D_2dsymmetry is re-

quired. This results in poor photophysical behavior further

underpinned according to the energy gap law by an ex-

tended delocalization that reduces the energy gap between

the ground state and the excited MLCT state.

[a] Dept. of Chemistry, Aristotle University of Thessaloniki

P.O.B. 135, 54124 Thessaloniki, Greece

Fax: +30-2310-997738

E-mail: panpapan@chem.auth.gr

[b] Tampere University of Technology, Faculty of Science and

Environmental Engineering, Department of Chemistry and

Bioengineering,

33101 Tampere, Finland

E-mail: nikolai.tkachenko@tut.fi

Homepage: http://kemia.me.tut.fi/nick

[c] Faculty of Chemistry, Adam Mickiewicz University,

ul. Grunwaldzka 6, 60-780 Poznan, Poland

E-mail: magdan@amu.edu.pl

In this paper, we report the synthesis, characterization,

structure, and optical and redox properties of a group of

Cu^INIR absorbers with a series of exocyclic diimines as

ligands (Figure 1). The bis(aryl)acenaphthenequinonedi-

Homepage: http://ww w .chemia.amu.edu.pl/main/staff/

Gdaniec.htm

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.201201507.

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imine (Ar-BIAN) series was selected for this purpose as the lated as air stable almost black powders with quite interest-

enhanced delocalization of the acenaphthenequinone cen- ing optical and electrochemical behavior as will be dis-

tral skeleton can reduce the energy of the MLCT absorp- cussed below. The color of the free ligands in dichlorometh-

tion compared to those of the ordinary diimines reported ane varies from yellow to deep red. The dichloromethane

to date. Although these ligands have been used in many solutions of the complexes bearing the p-Cl, o-Ph, m-Cl,

studies for catalytic purposes,^[5]some publications with and m-CF₃substituents are deep purple, whereas those with

heavier metals^[6]raised our interest in the photophysics of p-MeO and p-Me substitution are dark green and dark

compounds bearing these redox active molecules. Addition- blue, respectively.

ally, these latter systems have been proposed as potent com-

A point to be discussed is the nature of the isolated com-

ponents in bulk heterojunction photovoltaic devices.^[7]The plexes. The ligands used in this study are known for their

electronic behavior of the Ar-BIAN molecules appears to tendency to stabilize radical species after their reactions

be rich as they can act as efficient “electron sponges” and with the main group metals^{[10i,10j,10k]}and first row transi-

[8]

store up to four electrons, which results in the respective tion elements,^[10l]which results in noninnocent behav-

anionic forms,^[9]and recently they have been shown to form ior.^[14,10l]Therefore, the question arises about the oxidation

stable radicals following coordination to several metal cen- state of both the metal center and the ligands. Together with

ters.^[10]Our studies indicate that although the Cu^Icenter EPR spectroscopy, the safest way to assign the electronic

adopts an almost tetrahedral coordination in the solid state, structure of redox-active molecules is crystallographic

its geometry in solution is flattened as is revealed by the analysis, as significant differences are expected in bond

rise of a low-energy shoulder accompanying the MLCT ab- lengths with different numbers of accommodated elec-

sorption maximum. The bathochromic shift imposed by the trons.^[10l,15]The X-ray results verify that the stoichiometry

electronic system of the ligands results in an enhanced ab- of the complexes agrees with the existence of a Cu^Icenter

sorption of the complexes that extends into the NIR region and that the coordinated BIAN ligands are structurally

of the spectrum.

identical to the neutral Ar-BIAN molecules within experi-

mental error.^{[12,13,16–18]}Additionally, the lineshape of the

NMR spectra for the complexes is another strong sign of

the lack of any paramagnetic behavior, which would result

from the formation of radical metal or ligand species.

Therefore, we think it is safe to assign the metal center as

Cu^Iand the ligands in their neutral closed-shell structure.

Vibrational Spectroscopy

The IR spectra of the free ligands are characterized by

the presence of a weak band in the region 3045–3060 cm^–1,

which is assigned to the stretching vibration of the =C–H

bonds present in all of them, whereas the C–H bond vi-

brations for the p-MeO-BIAN and the p-Me-BIAN ligands

are observed as weak peaks at 2948 and 2914 cm^–1, respec-

tively. All of the spectra demonstrate a set of two strong

absorptions in the region 1669–1617 cm^–1, which are as-

signed to the stretching vibration of the imine bonds al-

though such an assignment cannot be unambiguous as the

stretching frequencies of the naphthalene C=C bonds also

appear in the same region.^[19]The absence of any absorp-

tion above 1700 cm^–1confirms the purity of the compounds

and excludes the presence of the 1:1 condensation byprod-

uct of the diketone and the substituted anilines.^[20,21]The

imine bond absorption of the complexes appears as one

peak in the region 1644–1634 cm^–1. The shift to lower wave-

numbers on coordination is due to the weakening of the

C=N bond, and the appearance of a single peak is indica-

Figure 1. Schematic representation of the Ar-BIAN ligands and the

corresponding homoleptic Cu^Itetrafluoroborate complexes

studied. The position of the substituent on the phenyl rings is rela-

tive to the imine nitrogen atoms.

Results and Discussion

Synthesis

Except for m-Cl-BIAN, the ligands have been reported tive of the coordination of the diimines in a chelating man-

previously and their characterization was confirmed by ner.^[17]The magnitude of the observed shifts further sup-

comparison with the published data.^[7b,11–13]The m-Cl- ports the hypothesis that the ligands are present in the com-

BIAN ligand was characterized in an analogous manner as plexes in their neutral oxidation state,^[22,23]as in their corre-

the other members of this group, in particular the 3,5- sponding radical or anionic forms the C–N bonds would

dichloro-substituted one.^[11]The Cu^Icomplexes were iso- be expected to reveal considerably larger shifts.^[10k]Ad-

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ditionally, the characteristic bands of the methyl group signals as will be discussed further below, the spectrum of

stretches are present in the typical positions of the methyl- [Cu(6)₂]BF₄reveals the expected number of signals, which

and methoxy-substituted BIAN ligands, and their positions indicates that the extra signals in 6 belong to the syn–anti

shift slightly upon coordination. In the spectra of the cop- isomer and that it transforms to the anti–anti one after

per complexes, there is generally a strong band with a broad complexation with the metal center.

maximum at 1050–1060 cm^–1, which is indicative of the

In the NMR spectra recorded in CDCl₃, the typical reso-

presence of tetrafluoroborate counteranions, however in

some cases this band appears to be split. This is probably

due to intra- or intermolecular interactions of the anion,

which result in breakdown of the local T_dsymmetry.^[24]

nances expected for the proton and carbon atoms of the

Ar-BIAN ligands are observed. In particular, and as ex-

pected, the methyl proton and carbon resonances of the 4-

Me and 4-MeO ligands do not shift upon coordination.

Very small shifts are observed for the resonances of the

characteristic imino carbon atoms and the aryl group di-

rectly attached to the nitrogen atom. In the ¹³C spectra, a

single line is observed for each chemically equivalent set of

atoms, which indicates that equilibration occurs in solution

and, therefore, steric crowding or π–π intra- or intermo-

lecular interactions are not important in the determination

of the overall structure of the compounds in solution. For

4 and 6, the spectroscopic data listed in the experimental

Solution NMR Spectroscopy

Ragaini et al. reported the solution behavior of Ar-BIAN

ligands.^[25]These molecules can exist in two different iso-

mers denoted as anti–anti and syn–anti, which refer to the

imine bonds (Scheme 1). Although asymmetric Ar-BIAN

molecules do appear in both forms in solution, symmetric

ones seem to occur only as the anti–anti isomer. From the

number of peaks in the ¹³C NMR spectra of the ligands

under study, this is also confirmed for ligands 1, 2, 3 and

5, whereas 4 and 6 are characterized by the existence of

additional signals. For these two latter cases, the peaks

could be assigned either to the existence of the syn–anti

molecule in solution as a minor isomer or to the inequiva-

lence of the ligand carbon atoms owing to sterically hin-

dered rotation of the phenyl pendant rings. The presence of

two isomers in solution does not alter the reactivity of the

Ar-BIAN ligands.^[25,26]Although the ¹³C-NMR spectrum

of [Cu(4)₂]BF₄is characterized by an excessive number of

1

section, especially the H NMR data, refer mainly to the

major isomer although a clear separation was not possible.

From the integration of proton signals, the ratio of the two

isomers appears to be 5:1 for 4 and 20:1 for 6.

In the solution (CDCl₃) NMR spectra of the complexes,

1

the H and ¹³C resonances are observed in the typical re-

gions, which suggests that they comprise neutral Ar-BIAN

ligands coordinated to Cu^Icenters. The spectra are domi-

nated by the resonances of the aromatic rings, and their

assignment was carried out in accordance with previously

published results.

The ¹³C NMR spectra are more informative of the coor-

dination of the ligands. The relevant resonances of the

imino carbon atom, the 5a and 8b carbon atoms of the

acenaphthene backbone, and the carbon atom at the 1Ј-

position of the aryl substituents along with the one bearing

the substituent are reported in Table 1. The carbon atoms

of the acenaphthene skeleton reveal a slight shift upon co-

ordination, which is not uniform and is, therefore, ascribed

to the aryl ring substituent rather than to the coordination

itself. The value of the imino carbon resonance is very con-

sistent throughout the ligand series and undergoes a lower

Scheme 1.

Table 1. ¹³C NMR spectroscopic data for the most relevant carbon atoms of the ligands and the copper complexes studied (for numbering

scheme see Figure 1). Chemical shifts are reported in ppm downfield from internal TMS standard. Primed numbers refer to the pendant

aryl rings and Y to the carbon of the aryl ring substituent.

Compound

Imino

1Ј

5a

8b

3Ј, 4Ј

Y

1

161.8

163.0

161.5

163.8

161.9

163.4

160.9

164.2–165.6

161.9

157.1

159.4

149.4

145.1

150.2

145.7

149.7

144.3–145.1

152.9

145.1

142.5

141.9

142.9

142.1

141.8

141.5

141.8–142.4

142.2

141.9

140.2

131.4

131.5

130.1

130.9

139.4

137.4–138.2

131.5

129.1

131.5

134.1

138.0

131.5

131.2

55.7

56.0

21.3

21.5

–

[Cu(1)₂]BF₄

2

[Cu(2)₂]BF₄

3

[Cu(3)₂]BF₄

4

131.3

[a]

[Cu(4)₂]BF₄

5

135.3

136.0

–

[Cu(5)₂]BF₄

6

165.0

162.0

165.2

148.5

152.0

147.6

143.5

142.3

143.5

132.2

132.4

132.8

115.6

116.8

[Cu(6)₂]BF₄

–

[a] Several signals observed.

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field shift upon coordination. The same is also true for the molecules as is well documented for the series of Ar-BIAN

carbon atoms of the aryl rings that bear the substituent, ligands. Under the same experimental conditions the ferro-

whereas an opposite trend is observed for the carbon atom cene/ferrocenyl oxidation potential was observed at

attached to the imine site. In all cases, a single signal is +0.68 V.

observed for each carbon atom with the exception of the o-

phenyl-substituted Ar-BIAN, for which quartets are ob-

Visible Spectroscopy

served within small margins in typical region of 120–

130 ppm for the more downfield resonances. This is attrib-

uted to the severely crowded nature of the ligand around

the diimine coordination site, which prevents the typical

equilibration through fast rotation about the single bonds

that connect the aryl rings to each other and to the central

backbone of the ligand. However, the average shift of each

group of lines relative to the one observed for the free li-

gand follows the observations made for the other com-

pounds.

The spectra of the ligands in dichloromethane show in-

tense absorptions in the UV region and a broad chromo-

phoric band that extends to ca. 500 nm (Figure 2). The UV

absorptions are π–π* in nature and display variations at-

tributed to the substituents on the pendant phenyl rings.

The broad band in the visible part of the spectra could be

assigned to n–π* transitions potentially involving a partial

charge transfer from the imine region or the phenyl rings

(intraligand π–π* charge transfer) to the naphthyl backbone

of the molecules. The intensity differences of this band in

various solvents do not reveal any apparent regularity and

are ascribed to conformational changes induced by solvent–

solute interactions. Such interactions should affect the elec-

tronic communication between the pendant phenyl rings

and the acenaphthenequinone main skeleton, which sup-

ports further the proposed partial CT character. However,

the solvatochromic shifts observed are very small.

Electrochemical Studies

The redox behavior of the Ar-BIAN ligands and their

Cu^Ihomoleptic complexes in dichloromethane containing

0.1 m tetrabutylammonium tetrafluoroborate as supporting

electrolyte was investigated by differential pulse voltamme-

try (DPV). The obtained redox potentials (V vs. Ag wire)

have some common characteristics presented below. For the

ligands, there are two reduction processes in the regions

–1.10 to –1.25 V (–1.78 to –1.93 V vs. Fc⁺/Fc) and –1.69 to

–1.87 V (–2.37 to –2.55 V vs. Fc⁺/Fc). There are also two

distinct oxidation peaks in the regions +1.45 to +1.65 (0.77

to 0.97 V vs. Fc⁺/Fc) and +1.75 to +1.98 V (1.07 to 1.30 V

vs. Fc⁺/Fc) with the notable exception of 1, for which the

two oxidation peaks are observed at +1.20 and +1.64 V

(0.52 and 0.96 V vs. Fc⁺/Fc respectively).

The voltamogramms of the complexes reveal a more

complicated pattern with up to four reduction and oxi-

dation processes. Generally, the reduction peaks are revers-

ible and the oxidation ones are not. The first peak observed

close to +0.6 V (–0.08 V vs. Fc⁺/Fc) may be attributed to

metal-centered processes, however in view of the noninno-

cent character of the ligands, strong participation of the

diiminic region or even formation of species with delocal-

ized electron density cannot be overlooked. Oxidation at

potentials of over + 1.0 V (0.32 V vs. Fc⁺/Fc) are most

Figure 2. UV/Vis spectra of representative Ar-BIAN ligands in

dichloromethane solution. The curves correspond to 1- (bold), 3-

(thin), and 4-substituted (dashed) Ar-BIAN ligands.

Methoxy and chloro substituents at the para position of

probably related to ligand-based processes affected to a the phenyl rings give rise to enhanced visible absorption,

small extent by the presence of the metal core. Such phe- which indicates that their action through conjugation

nomena could take place in a region of the ligand away causes incremental changes in the electronic density of the

from the Cu^Icenter such as the naphthyl part. In some lone pair of the iminic nitrogen atoms and a decrease in

cases, there are close lying and even overlapping peaks, the energy of the n–π* transitions. para-Methyl substitution

which suggests successive one- and two-electron transfer appears to operate through its negative hyperconjugation

processes or even the existence of chemical processes such effect, which depletes electron density from the π system of

as fragmentation of radical species coupled to the electron the main skeleton. The ligands with meta substituents re-

transfers.^[27]Finally, reductive signals at ca. –0.6 V (–1.28 V veal spectra with intensity features intermediate to the

vs. Fc⁺/Fc) could correspond to the formation of Cu⁰spe- aforementioned ones and severe changes in the shape of the

cies or reduction of the diiminic region of the ligands stabi- spectra are not observed, which indicates that their influ-

lized by the presence of the metal center, and those at more ence on the electronic wavefunction of the main chromo-

negative potentials could be related to anionic species with phore is not significant. Finally, the ortho-phenyl substitu-

the negative charge located on the organic skeleton of the ent leads to an absorption pattern similar to that of the p-

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MeO one in the ultraviolet region. The maximum of the

chromophoric band matches better that of the p-MeO and

p-Cl substituents and its intensity follows that of the Me

substituent.

The absorption of the homoleptic Cu^Icomplexes (Fig-

ure 3) covers the whole monitoring window in the form of

two broad bands. The first has a maximum at ca. 350 nm

with molar extinction coefficients greater than

20000 m^–1cm^–1and is assigned to ligand-centered transi-

tions, although partial MLCT character cannot be ex-

cluded. This band appears redshifted relative to those of

the respective free ligands owing to the presence of the posi-

tively charged metal center. The second band is relatively

intense with maxima in the visible region between 580 and

610 nm and extends to the NIR part of the spectrum. The

results of theoretical calculations and the apparent similar-

ity of this part of the spectrum to the MLCT absorption

pattern of Cu^I–bis(phenanthroline) and related bisdiimine

systems allows us to assign it as a MLCT transition.^[4,28–33]

Such transitions are generally characterized by high molar

extinction coefficients and when they are the low lying as is

the case for Cu^Isystems, they result in long lifetimes of the

excited state and potential luminescence.^[34]In analogy to

the MLCT band in [Cu(phen)₂]⁺systems, this absorption is

considered as an envelope of at least three distinct exci-

tations referred to as Bands I, II, and III.^[34,35]Band I,

which is totally forbidden for an ideal D_2dsymmetry, corre-

sponds to the excitation to the lowest singlet MLCT state

(S1) and appears as a shoulder at the low energy side of the

main visible absorption. The main part of the envelope,

Band II, is assigned to the excitation to the third singlet

MLCT state (S3),^[36]and an additional MLCT absorption

(Band III) is located at ca. 520 nm, overlapped by Band

II. The low-lying π* orbitals of the acenaphthene moiety

promote a considerable redshift relative to the typical corre-

sponding Cu^I–diimine MLCT bands. The enhanced inten-

sity of these bands can be related to the transition dipole

length of the given excitations. Owing to the extended delo-

calization of the diimine π system, the π* accepting orbitals

are spread away from the Cu^Icenter, which leads to an in-

creased charge displacement during the excitation. This in

turn results in an increased transition dipole length and en-

hanced absorptivity.^[29]

Figure 3. UV/Vis spectra of representative [Cu(Ar-BIAN)₂]BF₄

complexes in dichloromethane. Curves correspond to [Cu(1)₂]BF₄

(bold), [Cu(3)₂]BF₄(thin), and [Cu(4)₂]BF₄(dashed). Bands I, II

and III, which result in the overall visible absorption, are indicated

for [Cu(1)₂]BF₄by arrows.

are reported in Table 2. The above ratio varies between 0.57

and 1.11. Consequently, the least planar geometry in solu-

tion is ascribed to [Cu(2)₂]BF₄and the most distorted to

[Cu(1)₂]BF₄. The following series for the ground state dis-

tortion emerges [Cu(2)₂]BF₄Ͻ [Cu(5)₂]BF₄≈ [Cu(3)₂]BF₄

Ͻ [Cu(6)₂]BF₄Ͻ [Cu(4)₂]BF₄Ͻ [Cu(1)₂]BF₄and correlates

well with the experimentally observed geometries as can be

seen further below. For [Cu(2)₂]BF₄, [Cu(3)₂]BF₄, and

[Cu(4)₂]BF₄, the dihedral angles between the two chelate

rings are 85.6, 80.09, and 75.80°, respectively.

Table 2. Band maxima related to the excitations for the compounds

studied in dichloromethane. ε⁷⁸⁰refers to the absorption of the

complexes at the specific wavelength as an indication of their NIR

absorptivity.

Compound

λ^vis

[nm]

ε^vis

ε⁷⁸⁰

Intensity

ratio

max

λmax

[m^–1cm^–1]

[(m^–1cm^–1]

1

429

409

400

9400

3000

6650

2800

4500

–

2

3

4

402

5

386 (sh)

383 (sh)

609

596

587

561

579

580

6

4150

–

[Cu(1)₂]BF₄

[Cu(2)₂]BF₄

[Cu(3)₂]BF₄

[Cu(4)₂]BF₄

[Cu(5)₂]BF₄

[Cu(6)₂]BF₄

15800

13800

12500

11750

10850

19750

5030

2680

2730

1840

2270

1770

1.11

0.57

0.66

0.85

0.64

0.78

As is generally accepted, the intensities of the above three

bands are related to the symmetry of the complexes in solu-

tion. The low energy shoulder (Band I) serves as a finger-

print for the flattening distortion of the ground state geom-

etry away from the ideal D_2done,^[34,35,27c]which renders the

corresponding transition more allowed. In an effort to

In the investigation of the solvatochromic shift of the

quantify this and in view of the crystallographic data avail- MLCT absorption, it was observed that dissociation of the

able for three of the complexes, we proceeded with the com- complexes takes place in coordinative solvents.^[37]This

putation of the intensity ratio of Band I to Band II. The means that there is a concentration-dependent substitution

digitized spectra were treated with the Peakfit algorithm by equilibrium between the diimines coordinated to the metal

using the second-derivative technique for locating maxima. center and solvent molecules, which can be described by the

When the simulation reached an R²value of 0.9999, the reaction in Scheme 2, in which S corresponds to coordina-

sum of the individual Gaussian bands located within the tive solvent molecules. Despite the exocyclic imine bonds of

low energy shoulder and the main part of the MLCT enve- the Ar-BIAN ligands leading to an increased σ-donating

lope and their intensity ratio were calculated. The results ability compared to phenanthroline or bipyridine^[20]and the

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enhanced π acidity of the main skeleton,^[6,38]these com-

plexes are not stable enough to prevent the formation of

new species in a coordinative environment. Therefore, all

the electronic spectroscopic studies were confined to dichlo-

romethane solutions, in which two important observations

were made. More precisely, the absorption spectra do not

reveal the characteristic absorptions of the monoanionic

Ar-BIAN radicals in the region 480–550 nm, which further

supports that the diimines in these coordination com-

pounds are in the typical neutral form.^[10k]Additionally, lu-

minescence studies carried out in optically diluted and care-

fully deaerated solutions produced no emission in the vis-

ible part of the spectrum after excitation of the MLCT

band as has been previously observed for analogous sys-

tems.^[39]This observation may be assigned to the energy gap

law and to the lack of steric hindrance close to the metal

center, which could prevent structural deformations in the

excited state of the complexes.

Figure 4. X-ray structures of [Cu(2)₂]BF₄·CH₂Cl₂(top) and

[Cu(3)₂]BF₄(bottom). H atoms omitted for clarity. Only the asym-

metric unit is labeled in each case. Solvent CH₂Cl₂molecules exhi-

bit disorder. Displacement ellipsoids are shown at the 30% prob-

ability level.

Scheme 2.

X-ray Crystal Structures

As already mentioned, the safest way to assign the elec-

tronic structure of a redox-active organic molecule is to per-

form crystallographic studies. Our X-ray crystallography re-

sults reveal that the stoichiometry of the complexes agrees

with the existence of a Cu^Icenter and that both of the coor-

dinated Ar-BIAN molecules are structurally identical

within experimental error and have bond lengths that match

those of the neutral Ar-BIAN molecules.^{[12,13,17,18]}The C–

N and C–C bond lengths within the chelate rings fall within

small margins around 1.28 and 1.50 Å, respectively, which

are representative of the corresponding double and single

bonds. For anionic ligands, the above values are ca. 1.35

and 1.45 Å, and for dianionic ligands, mainly observed for

s- and p-block metal complexes, values of ca. 1.40 Å for

both bonds have been recorded.^[40]

Figure 5. Crystal packing of [Cu(3)₂]BF₄. (a) Intermolecular inter-

actions lead to the formation of a porous 3D framework and (b)

twofold-interpenetrated 3D frameworks leave isolated empty voids

of 83 Å³(H atoms are omitted for clarity).

acenaphthene plane, and the relevant dihedral angle is

The complex [Cu(3)₂]BF₄(Figure 4, bottom) crystallizes 88.6(1)°; the two chelate-ring planes are also almost perpen-

in the orthorhombic system, space group Ccca, and both dicular [dihedral angle 80.9(1)°]. This latter dihedral angle

the coordination cation and the anion occupy special posi- is similar to those found in the four symmetry-independent

[41]

tions with 222 site symmetry. Its crystal structure is similar cations in [Cu(p-iPr-BIAN)₂]BF₄

(Ͼ80°) and is ca. 20°

to that of the mesityl analogue [Cu(o,oЈ,p-CH₃-BIAN)]- larger than those found in other D₂symmetric complexes

BF₄·pentane.^[39]However, the crystal structure of [Cu(3)₂- [Cu(o,oЈ,p-Me-BIAN)₂]BF₄·pentane (62.2°) and [Cu(o-iPr-

[41]

]BF₄was determined for the solvent-free form, which con- BIAN)₂]BF₄(55.3°).

tained isolated voids of 83 Å³that form ca. 11% of the unit

cell volume (Figure 5b).

The crystal packing of [Cu(3)₂]BF₄is best described as

consisting of (010) layers of the coordination cations as-

The coordination environment of the Cu^Iatom is sembled through π–π stacking interactions of p-chloro-

strongly distorted tetrahedral, and because of the D₂crys- phenyl groups (centroid–centroid distance 3.93 Å) and C–

tallographic symmetry of the coordination cation, all Cu–N Cl···π interactions with the π system of the α-diimine group

bond lengths of 2.059(2) Å are equivalent. The imine C=N (Cl1···Cg 3.227 Å, ϽC11–Cl1···Cg 163.2°; Cg is the center

bonds are also equivalent and their length of 1.274(4) Å of the C1–C1 bond). The neighboring (010) layers are

–

confirms the sp²character of the atoms involved. The bridged by the BF₄anions involved in C–H···F interac-

BIAN bite angle is 81.90(12)°. The pendant aromatic rings tions to the acenaphthene H4 atoms (H4···F12 40 Å, ϽC4–

adopt an almost perpendicular orientation relative to the H4···F1 168°), which results in a 3D porous framework

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(Figure 5, a). The crystal consists of two such 3D frame-

works, which are related by the translation vector 1/2, 1/2,

0 and mutually interpenetrate (Figure 5, b).

The related 4-methyl compound [Cu(2)₂]BF₄·1.5CH₂Cl₂

crystallizes in the monoclinic system, space group C2/c, and

the asymmetric unit consists of the coordination cation

–

[Cu(2)₂]⁺, the BF₄anion, one CH₂Cl₂molecule in a gene-

ral position, and one half of a CH₂Cl₂molecule disordered

around an inversion center (Figure 4, top). The coordina-

tion to the metal center is not exactly symmetrical, and the

Cu–N distances are in the range 1.992(2)–2.038(4) Å

(Table 3). All these distances are shorter than the Cu–N dis-

tance in [Cu(3)₂]BF₄. The sp²character of the C and N

atoms in the chelate ring is confirmed by the imine C=N

Figure 6. Crystal packing of [Cu(2)₂]BF₄·1.5CH₂Cl₂. π–π stacking

interactions between the acenaphthene groups and C–H···π interac-

tions between the acenaphthene and tolyl groups lead to chains of

coordination cations.

bond lengths of 1.281(6)–1.296(5) Å. The two bite angles of [Cu(4)₂]⁺has an approximate C₂symmetry (Figure 7, bot-

the Ar-BIAN ligands are similar and are larger than those tom). This reduction in symmetry results from the confor-

in the p-chlorophenyl analogue (Table 3). Three of the four mation adopted by the o-Ph-BIAN ligand, in which both

pendant tolyl groups are strongly twisted relative to the cen- ortho-phenyl substituents point to the same site of the ace-

tral diimine plane with dihedral angles in the range 59.5(2)– naphthene group. This structural change is probably caused

69.6(2)°. The acenaphthene ring systems are not coplanar by intramolecular C–H···π interactions between the bi-

with the fused chelate rings and, thus, the dihedral angle phenyl groups and not solely the bulkiness of the ortho sub-

between the two chelate rings of 86.5(2)° is significantly dif- stituent because in the recently reported o-iPr-BIAN Cu^I

ferent from the dihedral angle between the acenaphthene complex the coordination cation had an approximate D₂

best planes of 81.7(2)°. The crystal packing of this com- symmetry.^[59]The attached benzene rings are twisted rela-

pound (Figure 6) is dominated by π–π stacking interactions tive to the chelate rings and have twist angles in the range

between acenaphthene groups, which results in chains of 67.6(3)–74.7(4)°. Moreover, all biphenyl groups in the cat-

the coordination cations extending along [112] and [–11–2]. ion show identical helicity as they are twisted around the

In turn, the BF₄^–anions form a few short C–H···F contacts central C–C bond by 42.2(4)–52.8(4)°. As in the crystals of

with CH₂Cl₂solvent molecules and with the benzene ring [Cu(2)₂]BF₄·1.5CH₂Cl₂, the crystal packing of this com-

(H44···F3 2.26 Å, ϽC44–H44···F3 143°).

pound is dominated by π–π stacking interactions between

The o-phenyl derivative [Cu(4)₂]BF₄·3CHCl₃crystallizes acenaphthene groups (centroid–centroid distance 3.63–

¯

in the triclinic P1 space group, and the asymmetric unit 4.07 Å), which result in chains of coordination cations that

–

consists of the coordination cation [Cu(4)₂]⁺, the BF₄

extend along [011]. The BF₄anions and chloroform mole-

anion, and three CHCl₃solvent molecules (Figure 7, top). cules are accommodated in voids formed between the

As is evident from Table 3, the coordination geometry chains.

around the Cu^Icenter is distorted tetrahedral and does not

There are some marked differences between the struc-

show any unusual features. The dihedral angle between the tures reported here and those reported for similar com-

two chelate rings is 75.8(2)°. However, in contrast with the pounds. Firstly, in the crystal structures reported here,

previously described complexes, the coordination cation which exhibit quite different patterns of intermolecular in-

Table 3. Selected bond lengths [Å] and angles [°] for the studied compounds.^[a]

[Cu(2)₂]BF₄·1.5CH₂Cl₂

[Cu(3)₂]BF₄

[Cu(4)₂]BF₄·3CHCl₃

Cu1–N1

Cu1–N2

Cu1–N3

Cu1–N4

N1–C1

N2–C2

C1–C2

N3–C27

N4–C28

C27–C28

N3–Cu1–N1

N3–Cu1–N2

2.012(3)

2.033(4)

1.992(2)

2.038(4)

1.286(5)

1.294(5)

1.504(6)

1.281(6)

1.286(5)

1.502(6)

124.10(14)

130.50(15)

Cu1–N1

2.059(2)

Cu1–N1

Cu1–N2

Cu1–N3

Cu1–N4

N1–C11

N1–C21

C11–C21

N3–C12

2.0607(19)

2.0216(18)

2.0531(19)

2.0353(18)

1.285(3)

1.288(3)

1.497(3)

1.286(3)

1.283(3)

1.503(3)

113.63(8)

133.04(8)

N1–C1

C1–C1ⁱ

1.274(4)

1.495(6)

N4–C22

C12–C22

N3–Cu1–N1

N3–Cu1–N2

N1–Cu1–N1ⁱⁱ120.11(12)

N1–Cu1–

129.74(12)

N1ⁱⁱⁱ

N1–Cu1–N2

N3–Cu1–N4

N1–Cu1–N4

N2–Cu1–N4

83.12(15)

82.80(15)

121.24(15)

120.28(14)

N1–Cu1–N1ⁱ81.90(12)

N1–Cu1–N2

N3–Cu1–N4

N1–Cu1–N4

N2–Cu1–N4

82.39(8)

82.56(7)

129.82(8)

121.95(7)

[a] Symmetry codes: (i) –x, y, –z + 1/2; (ii) –x, –y + 1/2, z; (iii) x, –y + 1/2, –z + 1/2.

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mation, and the relevant geometrical parameters are given

in Table 4.

Figure 8. Different views and atom numbering of the optimized

structure of [Cu(3)₂]⁺. The twist of the pendant phenyl rings rela-

tive to the acenaphthene skeleton and the distortion from the ideal

tetrahedral structure are in accordance with the experimental evi-

dence.

Table 4. Relevant optimized bond lengths and angles for [Cu(3)₂]⁺.

A complete list of atomic parameters and numbering are provided

in the Supporting Information.

Bond

Length [Å]

Bond

Angle [°]

Cu–N19

Cu–N20

Cu–N42

Cu–N43

C44–C45

C17–C18

C17–N19

C18–N20

2.112

2.108

2.112

1.516

1.292

N19–Cu–N20

N42–Cu–N43

N19–Cu–N43

N20–Cu–N42

–

80.25

135.21

136.61

–

Figure 7. X-ray structure of [Cu(4)₂]BF₄·3CHCl₃. ORTEP repre-

sentation with atom labeling (top) and the noncrystallographic C₂

symmetry of the coordination cation with the twofold symmetry

axis perpendicular to the figure plane and passing through Cu1

(bottom). H atoms and solvent CHCl₃molecules omitted for clar-

ity. Displacement ellipsoids are shown at the 30% probability level.

A distortion towards a flattened geometry is revealed

and, in view of the crystal structure of the compound, its

geometry alteration upon dissolution is opposite to the one

expressed by typical Cu^I–bisdiimine complexes as it is more

tetragonally distorted than in the solid state. Furthermore,

the phenyl rings of the ligand are almost perpendicular to

the diimine central skeleton in the solid state, whereas in

solution this angle is predicted to be 59.0°. The two Cu–N

bonds between the nitrogen atoms of a chelating ligand and

the Cu^Icenter are almost equal, and the dihedral angle be-

tween the two diimines is 65.5°.

As can be seen in Figure 9, the highest occupied molecu-

lar orbital (HOMO) of this molecule is of a d–σ* nature

and comprises an almost equal contribution from the metal

and the diimine regions. The lowest unoccupied molecular

orbital (LUMO) is mainly located in the diazabutadiene re-

gion of the ligand with small participation of the naphthyl

moiety and the metal core and accommodates a bonding

character between the carbon atoms of the diazabutadiene

and an antibonding character for the two imine bonds. The

teractions, the dihedral angle between the two chelate rings

(close to 90°) is ca. 20° larger than that for the earlier re-

ported mesityl derivative.^[39]Furthermore, for the mesityl

and o,o-diisopropyl-substituted Ar-BIAN ligands, the Cu–

N distances in the related [Cu(Ar-BIAN)₂]⁺and [Cu(Ar-

BIAN)(NCMe)₂]⁺units are longer than the ones in our

compounds, and the ligand bite angles are smaller and

range in a small margin around 80°. Analogous differences

are observed also relative to [{Cu(Ar-BIAN)}₂(μ-X)₂] di-

mers, for which there is asymmetry in the bonding of the

Ar-BIAN ligand; the Cu–N bonds are longer, and the bite-

angles are close to 80°.^[18]The same observations hold also

for a series of heteroleptic copper(I) complexes with BIAN-

type ligands and phosphanes.^[38]

Molecular Geometry Calculations

The geometry of the [Cu(3)₂]⁺cation was optimized in a picture for the HOMO–1 and LUMO+1 is analogous and

dichloromethane medium by utilizing the polarizable con- the HOMO–1 has contributions from the phenyl pendant

tinuum model (PCM).^[42]A relevant view of the final struc- rings. Further frontier molecular orbitals (FMOs) are given

ture is given in Figure 8, the atomic coordinates of the opti- in the Supporting Information. Taking into account that

mized structure are available in the Supporting Infor- the orbitals that are mainly expected to be involved in the

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low-energy excitations of the system are localized in the di-

Another point that has to be emphasized is the influence

iminic region, a mixing between them and not a clear spa- of the phenyl ring substituents on the energy of the MLCT

tial separation would be expected to characterize the charge bands of the complexes. As is obvious from the shape of

transfer (CT) bands of the system. This feature explains in the FMOs in Figure 9, the π system of these rings is

part the enhanced intensity of the absorption of the com- strongly involved in the HOMO–1 and so the substituent

plexes assigned as MLCT with a potent admixture of intra- will have an energetic impact on it. The participation of the

ligand (IL) character. The CT character of this transition phenyl rings on the excitations should be expected owing to

can be revealed by considering mainly the higher virtual their free rotation in solution. Alternatively, the differences

MOs located in the naphthyl part (see Supporting Infor- in the form and energy of the visible absorption of the com-

mation), which will also be involved in these transitions and plexes further support this hypothesis as the lack of elec-

result in a charge displacement from the region of the Cu^Itronic communication between the substituted rings and the

center. Additionally, the mixing that seems to exist between main acenapthene skeleton would result in absorption spec-

the highest occupied and the lowest virtual MOs of the sys- tra with minor variations between the complexes. Therefore,

tem in conjunction with the impure atomic orbital origin of the energy changes of the MLCT absorption when the sub-

mainly the HOMO and HOMO–1, as they comprise a par- stitution pattern is altered will mainly be expressed through

tial metallic and a partial diimine character, can result in a a change in the energy of the HOMO–1 and this can offer a

potent noninnocent character for the complexes and this further explanation for the substantially redshifted MLCT

compromises with their complicated electrochemical behav- absorption of [Cu(1)₂]BF₄, for which the strong donor abil-

ior. Finally, considering that the lowest lying MLCT state of ity of the p-MeO group will raise the energy of its HOMO–

these molecules will mainly arise from electronic transitions 1 and reduce the respective energy gap with the associated

between the highest occupied and the lowest unoccupied virtual orbitals.

MOs (Figure 9), a highly delocalized nature and an in-

creased stabilization^[43–48]for this state is expected, which

supports the lack of emission according to the energy gap

law and also renders this state with an impure charge-trans-

Conclusions

fer character. Time resolved studies of the excited state dy-

A new family of Cu^I–bisdiimine complexes bearing redox

namics of these molecules are underway to unravel the im- active Ar-BIAN ligands has been synthesized and charac-

pact of the above delocalized character of the CT states on terized. Ligand 5 is new and its synthesis, as well as that of

the electron relaxation pathways of the compounds.

the other studied ligands, is achieved by a modified pro-

cedure in which extremely dry conditions are not required.

The complexes appear to possess a tetrahedral copper envi-

ronment, and the complex with the p-chloro-substituted Ar-

BIAN ligand is a rare example of an almost symmetrical

complex with two identical chelating ligands. The o-phenyl

derivative offers an example of an extremely crowded coor-

dination environment in which the carbon atoms are all

nonequivalent even in solution.

Despite the well-known noninnocent character of the do-

nors when combined with certain metal centers, Cu^Iseems

to preserve its oxidation state in these complexes and the

Ar-BIAN molecules remain in their closed-shell neutral oxi-

dation state. The extended π system of the acenaphthene-

quinone skeleton induces an enhanced absorption in the

visible part of the spectrum and into the NIR region and

thus improves the light-gathering characteristics of the com-

plexes. Although no emission was observed in the visible

region, it could not be excluded for wavelengths greater

than 900 nm as the lack of appropriate equipment did not

allow us to investigate such a hypothesis. Additionally, in a

series of time-resolved absorption studies performed for

these complexes, which be published in a subsequent paper,

the lifetime of their lowest excited state is still sufficient for

bimolecular processes to occur. In conjunction with the

strong absorption features of the complexes in the 500–

600 nm region, the compounds can be regarded as attract-

ive candidates for a number of energy-conversion applica-

tions such as dopant chromophores in organic solar cells.

The absorption characteristics of the complexes follow

Figure 9. FMOs of the optimized structure of [Cu(3)₂]⁺in dichloro-

methane solution.

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formed in a one-compartment cell with a silver wire as a pseudo-

reference electrode and a glassy carbon auxiliary electrode. A plati-

num working electrode was used for the measurements. Recordings

were carried out in the potential region –2000 to +2000 mV at am-

bient temperature at a scan rate of 50 mVs^–1. Recrystallized tetra-

butylammonium tetrafluoroborate (0.1 m) was used as the electro-

lyte. All scans were recorded with degassed solvent and with a flow

of moisture-free dinitrogen over the solution surface.

those of the related bis-phenanthroline systems and in com-

bination with the well-known ability of the ligands to stabi-

lize radical and anionic species they could result in a family

of potent photo-oxidizers through a possible reductive

quenching^[49,50]of their MLCT excited states. As has al-

ready been reported by Miller and Karpishin, the expansion

of the absorption of Cu^I–bisdiimine systems in the NIR re-

gion necessitates a severe flattening distortion in their

ground state. In the same context, the use of highly conju-

gated organic skeletons coordinated to the metal center

leads to an extended delocalization, which brings the energy

of the excited MLCT state rather close to that of the ground

state. Both the above characteristics result in poor photo-

Synthesis of the Ligands: The preparation of the investigated Ar-

BIAN ligands was the one proposed by Ragaini et al.^[11]with some

modifications described below. The synthesis was performed in air

and in glassware dried overnight at 100 °C. A major difficulty in

the process relates to the extremely dry conditions required for the

use of ZnCl₂and this was bypassed by forming the ethyl ether

physical behavior of the systems. In the present case, the complex of ZnCl₂, which has been utilized in various organozinc

syntheses as intermediate.^[51]The procedure applied is efficient re-

gardless of exposure to moist air and the results are comparable to

capacity of the complexes to absorb up to the NIR region,

even though with low ε values, seems mainly to stem from

those obtained with fresh anhydrous ZnCl₂samples. In a typical

the enhanced mixing of their FMOs, which results in a

preparation, ZnCl₂(4.4 g, 32.3 mmol) was sonicated in Et₂O

highly delocalized nature of their MLCT excited state and

(40 mL) in a sealed flask until an almost biphasic emulsion re-

a lack of emission at least in the visible part of the spec-

sulted. After the addition of Na₂SO₄, this emulsion was stirred for

trum, in accordance with Miller and Karpishin’s remarks.^[4]

20 min and filtered over a flask containing acenaphthenequinone

To the best of our knowledge, these complexes are rare ex-

(2.30 g, 12 mmol) stirred in glacial acetic acid (28 mL) at 60 °C. A

amples of Cu^Isystems that absorb light up to 900 nm.

reflux condenser was attached to the flask, and the suspension was

The absorption spectra of the complexes in dichloro-

methane solutions reveal the capacity of the substituents to respective aniline (27.6 mmol) was added, and the flask was left

further stirred and heated. When the solvent started to boil, the

open for about 5 min to allow evaporation of the ether. The mix-

ture was then heated to reflux for an additional 40 min. Filtration

of the hot suspension through a Gooch filter produced the

ZnCl₂(Ar-BIAN) complex. The solid was washed with a portion

(5 mL) of glacial acetic acid and two portions of cold Et₂O and

dried in air overnight. The purity of this intermediate product was

verified by the absence of any absorption in the IR spectrum above

1700 cm^–1. If needed, further purification was achieved by suspen-

sion of the product for 10 min in a small amount of dichlorometh-

ane, filtration, and air drying. For the decomplexation, the Zn com-

tune both the intensity and the energy of the MLCT band

by affecting mainly the energy level of the HOMO–1 of

these molecules. The enhanced absorption intensity ob-

served for these systems stems from orbital mixing between

the FMOs and the displacement of charge away from the

metal center following the MLCT excitation. Additionally,

the mixing of the FMOs as revealed by DFT calculations

indicates a potent noninnocent character for these com-

plexes, although without changes in the oxidation states of

the metal core and the ligands as is revealed by crystallo- plex was dissolved in dichloromethane (200 mL) in a sealed conical

flask, into which a solution of potassium oxalate (36 mmol) in

water (20 mL) was added. The solution was vigorously stirred for

15 min, and the two phases were separated with a separating fun-

nel. The organic layer was washed with water and dried with

Na₂SO₄. Filtration of the organic layer and evaporation to dryness

produced the analytically pure ligand in good yield. Alternatively,

this decomplexation was carried out by stirring the intermediate

complex in aqueous potassium oxalate (36 mmol, 300 mL), into

which a few drops of acetone were added, for 20 min. The suspen-

sion gradually changed color, which indicated the progress of the

decomplexation. The solid was collected by filtration and washed

with cold water and methanol to afford the free ligand, which was

left to dry in air. This alternative decomplexation does not seem to

work for p-MeO-BIAN, for which a product with a different IR

spectrum compared to that isolated by the conventional route was

obtained. This was not investigated further. The addition of the

small amount of acetone is essential as several experiments re-

vealed. The analytical data for all of the ligands including the new

compound 5 are given below. The isolation yields were comparable

to the reported ones.^[11]

graphic and spectroscopic data. Despite the increased basic-

ity and the π acidity of the ligands, the respective complexes

are not stable in strongly coordinating solvents.

Experimental Section

Materials and Measurements: Acenaphthenequinone and the sub-

stituted anilines were purchased from ACROS (p.a. grade) and

were used without any prior purification. The solvents used were

of reagent grade and were not subjected to any further drying pro-

cess prior to use. Elemental analyses for C, H, and N were per-

formed with a Perkin–Elmer 240B elemental analyzer. Infrared

spectra of KBr pellets were recorded with a Perkin–Elmer Spec-

trum One FTIR spectrometer with a resolution of 2 cm^–1following

the collection of 16 scans over the range 4000–360 cm^–1. Electronic

excitation spectra were recorded for samples in dichloromethane in

1 cm cuvettes with a Shimadzu UV-3600 UV/Vis/NIR spectropho-

tometer with a resolution of 0.1 nm. Emission studies were per-

formed with optically diluted solutions with a Jobin–Yvon Fluo-

rolog-3 Fluorometer. Solution ¹H and ¹³C NMR spectra of CDCl₃

solutions were recorded at 300 and 75 MHz, respectively, with a

Varian 300 spectrometer and tetramethylsilane (TMS) as internal

standard. Differential pulse voltammetry was used for the electro-

chemical measurements with an Ivium CompactStat potentiostat/

p-MeO-BIAN (1): Red solid, overall yield 70% (8.40 mmol, 3.30 g).

C₂₆H₂₀N₂O₂(392.46): calcd. C 79.57, H 5.14, N 7.14; found C

79.40, H 5.12, N 7.00. IR (KBr): ν = 3045 (w, =C–H), 2948 (w,

˜

–C–H), 1642 (m, C=C), 1617 (m, C=N–), 1600 (w), 1502 (s), 1238

1

(s), 1030 (s), 835 (s) cm^–1. H NMR (CDCl₃, 300 MHz, 25 °C): δ

galvanostat with an impedance analyzer. Measurements were per- = 7.88 (d, J = 8 Hz, 2 H), 7.38 (t, J = 7 Hz, 2 H), 7.12–7.07 (m, 4

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H), 7.04–6.99 (m, 6 H), 3.89 (s, 6 H) ppm. ¹³C{¹H} NMR (CDCl₃, left to evaporate in air after the addition of Et₂O (3 mL) to afford

75 MHz, 25 °C): δ = 161.8, 157.1, 145.1, 141.9, 131.4, 129.1, 128.9,

127.8, 123.9, 120.0, 114.8, 55.7 ppm.

the final products. Crystals of [Cu(2)₂]BF₄and [Cu(3)₂]BF₄suitable

for X-ray analysis were obtained by layering diethyl ether over

CH₂Cl₂solutions of the complexes and slow evaporation at room

temperature. For [Cu(4)₂]BF₄, CHCl₃was used instead of CH₂Cl₂.

For [Cu(1)₂]BF₄and [Cu(3)₂]BF₄, broad ¹H NMR signals in

CDCl₃were recorded, which indicates that the compounds undergo

conformational changes in solution.

p-Me-BIAN (2): Orange solid, overall yield 72% (8.64 mmol,

3.11 g). C₂₆H₂₀N₂(360.46): calcd. C 86.64, H 5.59, N 7.77; found

C 85.96, H 5.62, N 7.67. IR (KBr): ν = 3051 (w, =C–H), 2914 (w,

˜

–C–H), 1655 (m, C=C), 1628 (s, C=N–), 1602 (m), 1500 (s), 1237

(m), 826 (s) cm^–1. ¹H NMR (CDCl₃, 300 MHz, 25 °C): δ = 7.87 (d,

J = 8 Hz, 2 H), 7.37 (t, J = 7 Hz, 2 H), 7.26 (d, J = 7 Hz, 4 H),

[Cu(1)₂]BF₄: Dark solid, overall yield 89% (0.45 mmol, 0.46 g).

7.05–7.01 (tt, 4 H), 6.92 (d, J = 7 Hz, 2 H), 2.4 (s, 6 H) ppm. C₅₂H₄₀BCuF₄N₄O₄·CH₂Cl₂: calcd. C 62.40, H 4.15, N 5.49; found

¹³C{¹H} NMR (CDCl₃, 75 MHz, 25 °C): δ = 161.5, 149.4, 141.9, C 62.50, H 4.19, N 5.51. IR (KBr): ν = 3047 (w, =C–H), 2927 (w,

˜

134.1, 131.4, 130.2, 129.0, 128.9, 127.8, 124.1, 118.4, 21.3 ppm.

–C–H), 1634 (m, C=N–), 1599 (m), 1504 (m), 1298 (m), 1246 (s),

1053 (s), 1028 (s), 830 (s) cm^–1. ¹H NMR (CDCl₃, 300 MHz,

25 °C): δ = 8.07 (br d, J = 8 Hz, 2 H), 7.48 (br t, J = 8 Hz, 4 H),

7.26–7.03 (br m, 8 H), 3.90 (s, 3 H) ppm. ¹³C{¹H} NMR (CDCl₃,

75 MHz, 25 °C): δ = 163.0, 159.4, 142.5, 140.2, 131.5, 131.2, 128.7,

127.0, 124.4, 122.8, 115.3, 56.0 ppm.

p-Cl-BIAN (3): Orange solid, overall yield 76% (9.12 mmol,

3.66 g). C₂₄H₁₄Cl₂N₂(401.29): calcd. C 71.83, H 3.52, N 6.98;

found C 71.24, H 3.63, N 6.86. IR (KBr): ν = 3052 (w, =C–H),

˜

1652 (m, C=C), 1629 (m, C=N–), 1619 (m), 1478 (s), 1240 (s), 1089

1

(s), 839 (s) cm^–1. H NMR (CDCl₃, 300 MHz, 25 °C): δ = 7.93 (d,

J = 8 Hz, 2 H), 7.47–7.40 (m, 6 H), 7.09–7.05 (m, 4 H), 6.96 (d, J [Cu(2)₂]BF₄: Dark solid, overall yield 93% (0.47 mmol, 0.45 g).

= 7 Hz, 2 H) ppm. ¹³C{¹H} NMR (CDCl₃, 75 MHz, 25 °C): δ = C₅₂H₄₀BCuF₄N₄·CH₂Cl₂: calcd. C 66.57, H 4.43, N 5.86; found C

161.9, 150.2, 142.1, 131.5, 130.1, 129.9, 129.6, 128.4, 128.0, 124.3,

119 ppm.

66.62, H 4.48, N 5.83. IR (KBr): ν = 3050 (w, =C–H), 2919 (w,

˜

–C–H), 1636 (m, C=N–), 1597 (m), 1488 (s), 1288 (m), 1057 (s),

830 (s) cm^–1. ¹H NMR (CDCl₃, 300 MHz, 25 °C): δ = 8.09 (d, J =

8 Hz, 2 H), 7.51 (t, J = 7 Hz, 2 H), 7.33–7.29 (m, 6 H), 7.05 (d, J

= 8 Hz, 4 H), 2.46 (s, 6 H) ppm. ¹³C{¹H} NMR (CDCl₃, 75 MHz,

25 °C): δ = 163.8, 145.1, 142.9, 138.0, 131.5, 131.4, 130.9, 128.7,

126.7, 124.8, 120.7, 21.5 ppm.

o-Ph-BIAN (4): Red solid, overall yield 71% (8.52 mmol, 4.13 g).

C₃₆H₂₄N₂(484.60): calcd. C 89.23, H 4.99, N 5.78; found C 88.97,

H 5.17, N 5.64. IR (KBr): ν = 3053 (w, =C–H), 1664 (m, C=C),

˜

1633 (m, C=N), 1589 (m), 1473 (s), 1427 (s), 1232 (m), 830 (s), 734

1

(s), 699 (s) cm^–1. H NMR (CDCl₃, 300 MHz, 25 °C): δ = 7.8 (d,

J = 8 Hz, 2 H), 7.5 (d, J = 7 Hz, 2 H), 7.44–7.40 (m, 5 H), 7.38–

[Cu(3)₂]BF₄: Dark solid, overall yield 91% (0.46 mmol, 0.48 g).

7.34 (dd, J = 7 Hz, 2 H), 7.32–7.29 (m, 2 H), 7.26 (q, J = 7 Hz, 2 C₄₈H₂₈BCl₄CuF₄N₄·CH₂Cl₂: calcd. C 56.71, H 2.91, N 5.40; found

H), 7.15 (m, 5 H), 7.3 (d, J = 7 Hz, 2 H), 6.8 (d, J = 7 Hz, 2 H)

ppm. ¹³C{¹H} NMR (CDCl₃, 75 MHz, 25 °C): δ = 160.9, 149.7,

141.5, 139.4, 131.3, 131.1, 130.9, 129.7, 129.3, 129.2, 128.9, 128.6,

128.2, 128.1, 127.9, 126.9, 125.0, 123.6, 118.8 ppm.

C 56.63, H 2.91, N 5.44. IR (KBr): ν = 3089 (w, =C–H), 1644 (s,

˜

C=N–), 1604 (m), 1482 (s), 1290 (s), 1250 (s), 1085 (s), 1053 (s),

1010 (s), 829 (s), 775 (s) cm^–1. ¹H NMR (CDCl₃, 300 MHz, 25 °C):

δ = 8.07 (br pd), 7.45 (br), 7.21 (br), 7.05 (br) ppm. ¹³C{¹H} NMR

(CDCl₃, 75 MHz, 25 °C): δ = 163.4, 145.7, 141.8, 131.2, 130.9,

129.8, 128.6, 126.2, 126.0, 123.9, 122.5 ppm.

m-Cl-BIAN (5): Yellow solid, overall yield 73% (8.76 mmol,

3.52 g). C₂₄H₁₄Cl₂N₂(401.29): calcd. C 71.83, H 3.52, N 6.98;

found C 71.22, H 3.63, N 6.89. IR (KBr): ν = 3047 (m, =C–H),

[Cu(4)₂]BF₄: Dark solid, overall yield 88% (0.44 mmol, 0.49 g).

˜

1668 (s, C=C), 1630 (s, C=N–), 1589 (s), 1466 (s), 1416 (m), 1234 C₇₂H₄₈BCuF₄N₄(1119.55): calcd. C 77.24, H 4.32, N 5.00; found

(m), 938 (s), 827 (s), 774 (s) cm^–1. ¹H NMR (CDCl₃, 300 MHz, C 76.83, H 4.19, N 4.88. IR (KBr): ν = 3055 (w, =C–H), 1637 (m,

˜

25 °C): δ = 7.96 (d, J = 8 Hz, 2 H), 7.46–7.38 (q, J = 7 Hz, 4 H),

7.27–7.23 (m, J = 7 Hz, 2 H), 7.14 (t, J = 8 Hz, 2 H), 7.04–6.99

C=N–), 1593 (m), 1472 (s), 1429 (s), 1284 (m), 1050 (s), 830 (s)

1

776(s), 764 (s), 740 (s), 700 (s) cm^–1. H NMR (CDCl₃, 300 MHz,

(m, 2 H), 6.92 (d, J = 7 Hz, 2 H) ppm. ¹³C{¹H} NMR (CDCl₃, 25 °C): δ = 8.08–7.93 (m), 7.54–6.86 (m), 6.86–6.65 (m) ppm.

75 MHz, 25 °C): δ = 161.9, 152.9, 142.2, 135.3, 131.5, 130.9, 129.7,

128.3, 128.1, 124.8, 124.4, 118.6, 116.7 ppm.

¹³C{¹H} NMR (CDCl₃, 75 MHz, 25 °C): δ = 165.6, 164.6, 164.2,

145.1, 144.3, 142.4, 141.8, 137.9, 133.8, 133.2, 133.0, 132.2, 131.6,

131.0, 129.5, 128.8, 128.7, 128.1, 127.8, 127.4, 126.5, 125.1, 123.0,

121.9 ppm.

m-CF₃-BIAN (6): Yellow solid, overall yield 72% (8.64 mmol,

4.05 g). C₂₆H₁₄F₆N₂(468.40): calcd. C 66.67, H 3.01, N 5.98; found

C 66.44, H 3.15, N 5.87. IR (KBr): ν = 3060 (w, =C–H), 1669 (m,

[Cu(5)₂]BF₄: Brown solid, overall yield 92% (0.46 mmol, 0.44 g).

˜

C=C), 1644 (m, C=N–), 1604 (m), 1592 (m), 1434 (m), 1324 (s),

1176 (s), 1123 (s), 1123 (s), 940 (s), 776 (s) cm^–1. ¹H NMR (CDCl₃,

300 MHz, 25 °C): δ = 7.95 (d, J = 8 Hz, 2 H), 7.64–7.53 (q, J =

7 Hz, 4 H), 7.45–7.40 (q, J = 7 Hz, 4 H), 7.33 (d, J = 7 Hz, 2 H),

6.84 (d, J = 7 Hz, 2 H) ppm. ¹³C{¹H} NMR (CDCl₃, 75 MHz,

25 °C): δ = 162.04, 151.98, 142.29, 132.42, 131.99, 131.58, 130.35,

129.88, 128.19, 128.11, 125.98, 124.18, 122.37, 121.94, 121.56,

121.45, 121.41, 115.64, 115.53 ppm.

C₄₈H₂₈BCl₄CuF₄N₄(952.94): calcd. C 60.50, H 2.96, N 5.88; found

C 59.95, H 3.10, N 5.64. IR (KBr): ν = 3066 (w, =C–H), 1637 (m,

˜

C=N–), 1584 (s), 1469 (s), 1420 (s), 1280 (s), 1059 (s), 829 (s), 776

1

(s), 688 (s) cm^–1. H NMR (CDCl₃, 300 MHz, 25 °C): δ = 8.14 (d,

J = 8 Hz, 2 H), 7.62–7.53 (m, 4 H), 7.43 (d, J = 8 Hz, 2 H), 7.24

(d, J = 8 Hz, 2 H), 7.15 (d, J = 8 Hz, 2 H) 7.07 (s, 2 H) ppm.

¹³C{¹H} NMR (CDCl₃, 75 MHz, 25 °C): δ = 165.0, 148.5, 143.5,

136.0, 132.2, 132.1, 131.6, 129.0, 128.1, 126.0, 125.4, 120.6, 119.2

ppm.

Synthesis of the Cu^IComplexes: The synthesis of the Cu^Icomplexes

was carried out according to the following general procedure: An

appropriate amount of [Cu(MeCN)₄]BF₄(0.5 mmol) was added to

a solution of the Ar-BIAN ligand (1.0 mmol) in CH₂Cl₂(25 mL).

The mixture was stirred for 2 h under an Ar atmosphere. The com-

plex forms instantly as indicated by the sudden color change of the

solution to dark purple, blue, or green depending on the substitu-

tion of the ligand. The solution was filtered, and the filtrate was

[Cu(6)₂]BF₄: Dark solid, overall yield 91% (0.46 mmol, 0.54 g).

C₅₂H₂₈BCuF₁₆N₄·CH₂Cl₂: calcd. C 54.31, H 2.58, N 4.78; found

C 54.52, H 2.65, N 5.04. IR (KBr): ν = 3074 (w, =C–H), 1644 (m,

˜

C=N–), 1587 (m), 1487 (m), 1438 (m), 1327 (m), 1182 (s) 1166 (s),

1

1126 (s), 1066 (s), 1049 (s), 778 (s), 697 (s), 662 (s) cm^–1. H NMR

(CDCl₃, 300 MHz, 25 °C): δ = 8.13 (d, J = 8 Hz, 2 H), 7.85 (t, J

= 8 Hz, 2 H), 7.72 (d, J = 8 Hz, 2 H), 7.53 (t, J = 8 Hz, 4 H), 7.36

Eur. J. Inorg. Chem. 2013, 2418–2431

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Table 5. Crystallographic data and refinement details for [Cu(2)₂]BF₄·1.5CH₂Cl₂, [Cu(3)₂]BF₄, and [Cu(4)₂]BF₄·3CHCl₃.

[Cu(2)₂]BF₄·1.5CH₂Cl₂

[Cu(3)₂]BF₄

[Cu(4)₂]BF₄·3CHCl₃

Crystal system

Temperature [K]

Radiation

monoclinic

120

Mo-K_α

C2/c

orthorhombic

293

Cu-K_α

Ccca

triclinic

130

Cu-K_α

¯

Space group

P1

a [Å]

b [Å]

c [Å]

α [°]

38.145(5)

14.461(1)

19.864(2)

90

121.76(2)

90

9316.5(17)

14.1998(11)

21.9723(14)

14.9553(11)

90

4666.1(6)

a = 11.8970(5)

b = 15.5900(7)

c = 18.5407(7)

α = 99.743(3)

β = 91.870(3)

γ = 94.147(3)

3376.8(2)

β [°]

γ [°]

Volume [Å³]

Z, ZЈ

8, 1

0.700

52588

8200

99.6%

8200/0/614

1.040

4, 0.25

3.214

7603

2071

99.9%

2071/0/143

1.105

R₁= 0.0537, wR₁= 0.1465

R₂= 0.0656, wR₂= 0.1570

0.55, –0.38

2, 1

4.213

49932

13800

Absorption coefficient

Reflections collected

Independent reflections

Completeness to θ (max.)

Data/restraints/parameters

Goodness- of-fit on F²

Final R indices [IϾ2σ(I)]

R indices (all data)

99.8%

13800/6/885

1.044

R₁= 0.0545, wR₁= 0.1453

R₁= 0.0582, wR₁= 0.1485

0.76, –1.04

R₁= 0.0706, wR₁= 0.1329

R₂= 0.1217, wR₂= 0.1556

Largest diff. peak and hole 0.68, –0.90

(s, 2 H), 7.10 (d, J = 8 Hz, 2 H) ppm. ¹³C{¹H} NMR (CDCl₃, (Figures S25–S30), absorption spectra of ligands and complexes

75 MHz, 25 °C): δ = 165.2, 147.6, 143.5, 132.8, 132.4, 132.0, 131.4,

128.8, 125.8, 125.2, 125.0, 124.4, 121.6, 116.8 ppm.

(Figures S31 and S32), additional FMOs of the cationic unit opti-

mized (Figure S33).

X-ray Crystal Structure: The diffraction data were collected with

Oxford Diffraction Xcalibur E ([Cu(2)₂]BF₄·1.5CH₂Cl₂) or Super-

Nova A ([Cu(3)₂]BF₄and [Cu(4)₂]BF₄·3CHCl₃) CCD diffractomet-

ers. Data collection and reduction were performed with the Crys-

Alis software.^[52]The structures were solved by direct methods with

the SHELXS-97 program^[53]and refined by full-matrix least-

squares method on F²with SHELXL-97. The hydrogen atoms from

C–H groups were placed in idealized positions and refined by using

a riding model. [Cu(2)₂]BF₄·1.5CH₂Cl₂and [Cu(4)₂]BF₄·3CHCl₃

contain disordered solvent molecules. Additional details concern-

ing crystal data and structure refinement are given in Table 5. Se-

lected bond lengths and angles are listed in Table 3. Molecular

graphics were generated with ORTEP-3 for Windows^[54]and Mer-

cury 2.2 software.^[55]

Acknowledgments

P. P. acknowledges support by the Centre for International Mo-

bility of Finland (CIMO) under grant TM-11-7670. The authors

would like to thank Alexander Efimov and Vladimir Chukharev at

Tampere for their support throughout the project and Dr. Anasta-

sios Papadopoulos at AUTH for his graphical work.

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Received: December 15, 2012

Published Online: March 6, 2013

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2431

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Homoleptic bis(aryl)acenaphthenequinonediimine-CuI complexes-Synthesis and characterization of a family of compounds with improved light-gathering characteristics

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