Soluble heterometallic coordination polymers based on a bis-terpyridine-functionalized dioxocyclam ligand

Article abstract of DOI:10.1021/ic901832q

Soluble homo- and heterometallic coordination polymers containing transition metal cations (Cu²⁺, Fe²⁺, Co²⁺, and Ni²⁺ ions) were prepared in a two-step procedure using a polytopic bis(terpyridine)dioxocyclam ligand 1H₂ (dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-5,7-dione). These supramolecular systems incorporate two different metal complexes, the metal cations being located both between two terpyridine units and in the macrocyclic framework. The characterization of these soluble architectures was investigated by cyclic voltammetry, mass spectrometry, viscosimetry, and UV-vis absorption and electron paramagnetic resonance (EPR) spectroscopies. Our results clearly indicate the formation of well-organized heterometallic polymers in which two different metal ions alternate in the self-assembled structure. These investigations furthermore brought to light an original acid-controlled disassembling process of the homometallic copper(II) polymer into dinuclear complexes.

Full text of DOI:10.1021/ic901832q

2592 Inorg. Chem. 2010, 49, 2592–2599
DOI: 10.1021/ic901832q
Soluble Heterometallic Coordination Polymers Based on a
Bis-terpyridine-Functionalized Dioxocyclam Ligand
†
‡
†
†
†
ꢀ
Aurelien Gasnier, Jean-Michel Barbe, Christophe Bucher, Carole Duboc, Jean-Claude Moutet,
Eric Saint-Aman,† Pierre Terech,§ and Guy Royal*,†
†
ꢀ
ꢀ
ꢀ
Universite Joseph Fourier Grenoble I, Departement de Chimie Moleculaire, UMR CNRS-5250, Institut de
‡
ꢀ
Chimie Moleculaire de Grenoble, FR CNRS-2607, BP 53, 38041, Grenoble Cedex 9, France, Institut de Chimie
ꢀ
ꢀ
Moleculaire de l’Universite de Bourgogne, UMR CNRS 5260, 9 avenue Alain Savary, BP 47870, 21078 Dijon
§
ꢀ
cedex, France, and CEA Grenoble, INAC-SPrAM-LASSO, UMR CEA-CNRS-Universite Joseph Fourier
Grenoble1, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France
Received September 16, 2009
Soluble homo- and heterometallic coordination polymers containing transition metal cations (Cu2þ, Fe2þ, Co2þ, and
Ni2þ ions) were prepared in a two-step procedure using a polytopic bis(terpyridine)dioxocyclam ligand 1H2
(dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-5,7-dione). These supramolecular systems incorporate two
different metal complexes, the metal cations being located both between two terpyridine units and in the macrocyclic
framework. The characterization of these soluble architectures was investigated by cyclic voltammetry, mass
spectrometry, viscosimetry, and UV-vis absorption and electron paramagnetic resonance (EPR) spectroscopies.
Our results clearly indicate the formation of well-organized heterometallic polymers in which two different metal ions
alternate in the self-assembled structure. These investigations furthermore brought to light an original acid-controlled
disassembling process of the homometallic copper(II) polymer into dinuclear complexes.
Introduction
built-up in solution through the formation of coordination
bonds between metal ions and polytopic bridging ligands
(Scheme 1).2
Supramolecular polymers fabricated by self-assembly pro-
cesses represent an interesting class of materials because of
their potential applications in material science and functional
devices.1 In particular, metal coordination has been used to
prepare a wide range of supramolecular polymers. However,
if there is an extensive literature about coordination polymers
in the solid state,1d the number of metallopolymers that has
been characterized in solution is much less extensive. Recent
research is now devoted to the conception of soluble one-
dimensional (1D) to three-dimensional (3D) metallo-poly-
mers in which supramolecular chains are spontaneously
In these macromolecular metal-containing systems, the
relation between concentrations, binding constants, and
chain trajectory can be exploited to elaborate materials with
specific behaviors. Importantly, these materials may exhibit
the properties of standard organic polymers (viscosity, pro-
cessability, etc.), but the incorporation of metallic species
in the polymer chain opens new perspectives giving access
to magnetic, redox, optical, electrochromic, or specific me-
chanical properties. In addition, the use of kinetically labile
metal complexes may provide to the coordination polymers
dynamic features relevant to the construction of environ-
ment-adaptable materials.2,3 These dynamic coordina-
tion polymers are thus promising systems for the develop-
ment of smart stimuli-responsive molecular materials, and
a major challenge in this emerging domain is to design and
elaborate functional self-organized architectures with tun-
able properties.
*To whom correspondence should be addressed. E-mail: guy.royal@
ujf-grenoble.fr. Fax: (33) 04 76 51 42 67.
(1) (a) Lehn, J.-M. Prog. Polym. Sci. 2005, 30, 814–831. (b) Hofmeier, H.;
Schubert, U. S. Chem. Commun. 2005, 2423–2432. (c) Supramolecular Poly-
mers; Ciferri, A., Ed.; Marcel Dekker: New York, 2000.(d) Brunsveld, L.; Folmer,
B. J. B.; Meijer, E. W.; Sijbesma, R. P. Chem. Rev. 2001, 101, 4071–4097.
(2) (a) Friese, V. A.; Kurth, D. G. Coord. Chem. Rev. 2008, 252, 199–211.
(b) Kurth, D. G.; Higuchi, M. Soft Matter 2006, 2, 915–927. (c) Dobrawa, R.;
W€urthner, F. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 4981–4995. (d)
Lin, X.; Jia, J.; Zhao, X.; Thomas, K. M.; Blake, A. J.; Walker, G. S.; Champness,
€
N. R.; Hubberstey, P.; Schroder, M. Angew. Chem., Int. Ed. 2007, 45, 7358–
(3) (a) Fages, F. Angew. Chem., Int. Ed. 2006, 45, 1680–1682. (b) Beck
J. B.; Rowan, S. J. J. Am. Chem. Soc. 2003, 125, 13922–13923. (c) Zhao, Y.;
Beck, J. B.; Rowan, S. J.; Jamieson, A. M. Macromolecules 2004, 37, 3529–
3531. (d) Rowan, S. T.; Beck, J. B. Faraday Discuss. 2005, 128, 43–53. (e) Weng,
W.; Beck, J. B.; Jamieson, A. M.; Rowan, S. T. J. Am. Chem. Soc. 2006, 128,
11663–11672.
7364. (e) Hoogenboom, R.; Schubert, U. S. Chem. Soc. Rev. 2006, 35, 622–629.
(f ) Janiak, C. Dalton Trans. 2003, 2781–2804. (g) Oh, M.; Mirkin, C. A. Nature
2005, 438, 651–654. (h) Vermonden, T.; Van Der Gucht, J.; De Waard, P.;
Marcelis, A. T. M.; Besseling, N. A. M.; Sudholter, E. J. R.; Fleer, G. J.; Stuart,
M. A. C. Macromolecules 2003, 36, 7035–7044.
€
r
pubs.acs.org/IC
Published on Web 12/04/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2593
Scheme 1. Schematic Formation of a 1D Coordination Polymer
Because of its ability to form strong and well-defined 2:1
(L:Mnþ) octahedral complexes with a range of transition
metal cations,4,5 the tridentate 2,20:60,200 terpyridine is cer-
tainly one of the most popular building block for the
preparation of coordination polymers.2,4 On the other hand,
the design of the spacer itself (i.e., the bridge between the
coordinating units, see Scheme 1) is also essential since it
might introduce a great variety of structural arrangements
and/or physicochemical properties (e.g., viscosity, optical,
mechanical properties, etc.) to the targeted metallo-polymer.
Numerous organic spacers exhibiting various shapes, rigid-
ities, and conjugations have already been reported2 but a
promising and almost unexplored route to build-up multi-
responsive coordination polymers relies on the use of com-
plexing spacers. This strategy may especially allow the
introduction of additional metal ions in the polymer chain
to produce homo- or heterometallic coordination polymers
with a wider range of properties and potential applications.
Recently we have demonstrated that cyclam derivatives
(cyclam = 1,4,8,11-tetraazacyclotetradecane) are particu-
larly suited as spacers because of their exceptional coordina-
tion properties and the abundant available literature
describing efficient and straightforward N- or C- substitution
strategies.6 Metal complexes of cyclam have furthermore
been shown to exhibit switching properties7 that can be
advantageously exploited to produce redox responsive co-
ordination polymers. For example, we have reported a novel
class of such responsive polymers.8,9 In these systems, the
nature and redox state of the metal ions located in the
macrocyclic spacer units drastically influences the properties
(length, shape, solubility, color, etc.) of the polymeric mate-
rials as exemplified by a rare reversible redox controlled gel to
liquid transition.8 An original acid-base driven interconver-
sion between a mononuclear copper(II) complex and co-
ordination polymers was also presented.9
Another particular interesting property of polytopic li-
gands having two chemically different coordination sites is
their ability to form heterometallic coordination polymers,
that is, polymers that incorporate two kinds of ions or metal
complexes in the same chain. Advanced molecular materials
could be obtained by the integration in the same polymer
architecture of different metal complexes presenting comple-
mentary functions, for example, a photosensitive metal
complex could activate a close catalytic metal center.
Here we describe the preparation and the characterization
of organized homo- and heterometallic coordination poly-
mers based on the dioxocyclam ligand 1H2 (dioxocyclam =
1,4,8,11-tetraazacyclo-tetradecane-5,7-dione10), following
the synthetic strategy depicted in Scheme 2. The 1H2 “mono-
mer” was formed by selective trans-disubstitution of the 1,8-
dioxocyclam by two tolyl-terpyridine units. This derivative
was shown to selectively bind copper(II) inside the macro-
cyclic framework when the metalation was conducted in the
presence of a mild base (K2CO3), and the red stable mono-
nuclear 1Cu complex was readily isolated.9 This complex
features two metal free terpyridine fragments which can be
advantageously used to prepare homo- and heteronuclear
polymers 1CuM by reaction with one molar equivalent of a
divalent transition metal cation (M = Fe, Co, Ni, or Cu,
Scheme 2).
(4) (a) Schubert, U. S.; Hofmeier, H.; Newkome G. R. In Modern
Terpyridine Chemistry; Wiley-VCH: New York, 2006.(b) Schubert, U. S.;
Eschbaumer, C. Angew. Chem., Int. Ed. 2002, 41, 2892–2926. (c) Andres,
P. R.; Schubert, U. S. Adv. Mater. 2004, 16, 1043–1068.
(5) (a) Constable, E. C. Chem. Soc. Rev. 2007, 36, 246–253. (b) Constable,
E. C.; Lewis, J.; Liptrot, M. C.; Raithby, P. R. Inorg. Chim. Acta 1990, 178, 47–
54.
Results and Discussion
Preparation of 1H2 and Its Metal Complexes 1CuM.
The 1CuM complexes were prepared following the two-
step strategy represented in Scheme 2. 1H2 was prepared
in good yield following a previously described procedure 9
based on the reaction of 40-(4-bromomethylphenyl)-
2,20:60200-terpyridine11 with trans-dioxocyclam10 in re-
fluxing CH3CN in the presence of base. When one molar
equivalent of Cu2þ cations was added to a solution of 1H2
in MeOH in the presence of K2CO3 in excess, a pink-red
species (λmax = 503 nm) was formed and was isolated
after precipitation by addition of diethyl ether and finally
(6) (a) Lindoy, L. F. The Chemistry of Macrocycle Ligand Complexes;
Cambridge University Press: Melbourne, Australia, 1989.(b) Denat, F.; Brandes,
S.; Guilard, R. Synlett 2000, 561–574. (c) Royal, G.; Dahaoui-Gindrey, V.;
Dahaoui, S.; Tabard, A.; Guilard, R.; Pullumbi, P.; Lecomte, C. Eur. J. Org.
Chem. 1998, 1971–1975. (d) Develay, S.; Tripier, R.; Chuburu, F.; Baccon, M. L.;
Handel, H. Eur. J. Org. Chem. 2003, 3047–3050.
ꢀ
(7) (a) Bucher, C.; Moutet, J.-C.; Pecaut, J.; Royal, G.; Saint-Aman, E.;
Thomas, F. Inorg. Chem. 2004, 43, 3777–3778. (b) Bucher, C.; Moutet, J.-C.;
ꢀ
Pecaut, J.; Royal, G.; Saint-Aman, E.; Thomas, F.; Torelli, S.; Ungureanu, M.
Inorg. Chem. 2003, 42, 2242-2252 and references therein.(c) Callegari, V.;
Bucher, C.; Moutet, J.-C.; Royal, G.; Saint-Aman, E. J. Solid State Electrochem.
2005, 758–763. (d) Amatore, C.; Barbe, J.-M.; Bucher, C.; Duval, E.; Guilard, R.;
Verpeaux, J.-N. Inorg. Chim. Acta 2003, 356, 267–278. (e) Bucher, C.; Duval, E.;
Barbe, J.-M.; Verpeaux, J.-N.; Amatore, C.; Guilard, R. C. R. Acad. Sci. II C.
2000, 3, 211–222.
(8) Gasnier, A.; Royal, G.; Terech, P. Langmuir 2009, 25, 8751–8762.
(9) Gasnier, A.; Barbe, J.-M.; Bucher, C.; Denat, F.; Moutet, J.-C.; Saint-
Aman, E.; Terech, P.; Royal, G. Inorg. Chem. 2008, 47, 1862–1864.
(10) Tomalia, D. A.; Wilson, L. R. U.S. Patent 4 517122, 1985.
(11) Johansson, O.; Borgstrom, M.; Lomoth, R.; Palmblad, M.; Bergquist
€
˚
€
J.; Hammarstrom, L.; Sun, L.; Akermark, B. Inorg. Chem. 2003, 42, 2908–
2918.

2594 Inorganic Chemistry, Vol. 49, No. 6, 2010
Gasnier et al.
Scheme 2. Schematic Preparation of the Polynuclear Species 1CuM
(M = Fe, Co, Ni, or Cu)
spectrometry, electrochemical and spectroscopic meth-
ods (see Table 1 and the Experimental Section). Bis-
(terpyridine)metal complexes synthesized with the 40-
phenyl-2,20:60600-terpyridine were used as reference com-
pounds (2M, with M = Fe, Co, Ni, Cu, Scheme 3).
(i). UV-visible and FTIR Analysis. The UV-vis ab-
sorption spectrum of the isolated 1CuCu complex dis-
solved in MeOH indicated the presence of bis(ter-
pyridine)Cu2þ units in the structure, featuring an absorp-
tion band at λmax = 687 nm similar to that observed in the
same condition with 2Cu (Table 1). The dfd transition
still seen at λmax = 501 nm confirmed that copper ions
remained also present in the dioxocyclam framework.9,12
The UV-vis spectra corresponding to the heterometallic
complexes also unambiguously showed the formation of
bis(terpyridine)M2þ units (see Table 1). As an example,
the band at λmax = 572 nm and its molar absorptivity co-
efficient (ε ∼25000) recorded for the purple 1CuFe com-
plex were a clear signature for the quantitative formation
of bis(terpyridine)Fe2þ complexes.
The presence of Cu2þ in the cyclam-based spacer of the
1CuM self-assembled complexes was furthermore con-
firmed by FTIR spectra, which show a νCO stretching
band around 1545 cm-1 against 1645 cm-1 in the free
ligand.9 All these results fully corroborate the presence of
metal ions between the terpyridine units and in the
dioxocyclam spacer.
(ii). Mass Spectrometry Analysis. Molecular weight
determinations of dynamic coordination polymers still
represent a real challenge.2,13 Usually, most available
methods such as gel permeation chromatography or mass
spectrometry indeed turned out to generate inconclusive
results because of the polyelectrolytic nature of the sys-
tems and the inherent lability of the metal-ligand inter-
actions.13 Actually, coordination polymers are thermally
equilibrated polymers, and the molecular weight of such
self-assembled species is dependent upon the concentra-
tion of the complexes, the temperature, and various
thermodynamic constants of the aggregation reactions.
However, in the present study, ESI-MS spectrometry
(Electropray Ionization, positive mode) appeared parti-
cularly helpful to characterize the heterometallic 1CuM
species: even if only short oligomers could be identified
because of fragmentation processes during the experi-
ments, the relative position of each metal ion in the
structures could be determined using isotopic patterns.
A dicationic {12Cu2M}2þ fragment containing two
deprotonated dioxocyclam, two Cu2þ, and one M2þ ion
(M = Fe, Co, Ni, or Cu) was systematically observed on
the ESI-MS spectra recorded with all the 1CuM com-
plexes. As an illustration, the experimental and calculated
spectra corresponding to the trinuclear {12Cu2Ni}2þ frag-
ment centered at m/z = 961 are shown in Figures 1A and
1B, respectively. In addition, the calculated spectra of
some hypothetical {12(Cu)n(M)m}2þ species (m þ n = 3)
featuring three Cu2þ cations or one Cu2þ and two Ni2þ
purified by chromatography on alumina. This red com-
pound was characterized by mass spectrometry, elemen-
tal analysis, FTIR and UV-visible spectroscopies and
electrochemistry (data are given in Table 1) and was
identified as the neutral square planar trans-dioxo-
cyclam-Cu(II) 1Cu complex formed by metal-assisted
deprotonation of the two macrocyclic amide fragments,
both terpyridine units remaining free (Scheme 2).9 In a
second step the formation of polynuclear complexes
1CuM (Scheme 2) was achieved by addition of one molar
equivalent of a transition metal ion M2þ (M2þ= Fe2þ
,
Ni2þ, Co2þ, or Cu2þ) to a solution of 1Cu in methanol. In
the case of Fe2þ and Co2þ, the initially light-red solution
of 1Cu turned out instantaneously purple and deep
red, respectively, in agreement with the formation of
the corresponding bis(terpyridine)-metal complexes. All
these materials were isolated by precipitation with diethyl
ether in 80-90% yields.
ꢀ
(12) (a) Meyer, M.; Fremond, L.; Espinosa, E.; Guilard, R.; Ou, Z.;
Kadish, K. M. Inorg. Chem. 2004, 43, 5572–5587. (b) Hegedus, L. S.;
Sundermann, M. J.; Dorhout, P. K. Inorg. Chem. 2003, 42, 4346–4354. (c)
Fabbrizzi, L.; Foti, F.; Patroni, S.; Pallavicini, P.; Taglietti, A. Angew. Chem., Int.
Ed. 2004, 43, 5073–5077.
(13) Meier, M. A. R.; Hofmeier, H.; Abeln, C. H.; Tziatzios, C.; Rasa, M.;
Schubert, D.; Schubert, U. S. e-Polym. 2006, 16, 1–7.
Characterization of the Metal Complexes. The isola-
ted metal complexes 1CuM were characterized by mass

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2595
Table 1. Characteristic Visible Absorption Bands and Electrochemical Data Recorded with the Reference Complexes and 1CuM Polymers
electrochemical data E1/2 (ΔEp)b,c,V
λ
max, nma
ligand centered
reduction
compounds
(ε, L mol-1 cm-1
)
(Tpy)MII/I
(Cy)CuII/I
(Cy)CuIII/II
(Tpy)MIII/II
2Cu
2Fe
687 (73)
572 (25800)
e
-0.733 (0.080)
d
0.600 (0.080)
-1.640 (0.080);
-1.730 (0.080)
-1.830 (0.110)
-1.990 (0.070)
-2.465 (0.080)
e
d
2Ni
2Co
1Cu
1CuCu
1CuFe
793 (56)
519 (2800)
503 (156)
500 (170); 687 (100)
575 (24700)
-1.625 (0.090)
-1.185 (0.080)
d
-0.225 (0.070)
-1.475 (0.085)
d
-1.420 (0.080)
þ0.435 (0.085)
þ0.480 (0.130)
Epa = 0.510
Epc = -0.855
d
d
-1.600 (0.070);
-1.730 (0.095)
-1.875 (0.110)
þ0.650(0.080)
1CuNi
1CuCo
787 (45)
522 (1900)
-1.595 (0.080)
-1.140 (0.090)
-1.425 (0.120)
-1.520 (0.180)
þ0.495 (0.060)
þ0.510 (0.180)
d
E
pc = -2.090
-0.225 (0.090)
a In MeOH. b Because of the low solubility of some compounds in MeOH in the presence of supporting electrolyte, experiments were conducted in
DMF þ 0.1 M TBAP; E (V) vs E1/2(ferrocenium/ferrocene); (TPy)M: electron transfer centered on the metal ion located between two terpyridine units,
(Cy)Cu: electron transfer centered on the copper(II) ion located in the dioxocyclam unit. c E1/2 = (Ep þ Epc)/2 at 0.1 V s-1; ΔEp = Epa - Ep
d Not
a
c
.
observed under these experimental conditions. e Not observed because of the prior electrodeposition of Cu0.
Scheme 3. Bis(terpyridine) Complexes (2M) Used As Reference Com-
pounds
ions are shown on Figure 1C and 1D, respectively. These
signals that correspond to disordered fragments contain-
ing two or three successive units based on the same metal
cation would be experimentally observed if metal ex-
change occurred during the self-assembling process. Such
fragments being not observed in the experimental spectra,
these results thus corroborate the expected alternation of
the metal ions in the heterometallic structures.
In the case of the 1CuFe system, a longer fragment
was observed on the ESI-MS spectrum with an isotopic
pattern centered at m/z = 727. This signal was attributed
to the tetracationic pentanuclear species {13Cu3Fe2}4þ
containing three monomer units, three Cu2þ and two
Fe2þ ions (Figure 1E). Here again, the comparison
with spectra calculated for different stoichiometries
(Figure 1F-H) unambiguously shows that the polymer
Figure 1. ESI-MS spectra of trinuclear fragments of 1CuNi (left) and
pentanuclear species of 1CuFe (right). A and E correspond to experi-
mental data and B, C, D, F, G, and H are calculated spectra.
is formed from alternating dioxocyclam-Cu and bis(ter-
pyridine)Fe moieties.
(iii). Electrochemical Investigations. The electrochemi-
cal characterization of the 1CuM complexes (M = Fe,
Co, Ni, or Cu) was performed by cyclic voltammetry (CV)
in N,N-dimethylformamide (DMF) containing tetra-n-
butylammonium perchlorate (TBAP, 0.1 M) as the sup-
porting electrolyte (DMF was used because of the low
solubility of some complexes in MeOH in the presence
of TBAP). Representative curves are shown in Figure 2,
and the electrochemical data are summarized in Table 1.
To assign the observed electron transfers, the reference
compounds 1Cu and 2M14 were studied under the same
experimental conditions. For all the complexes, the oxi-
dation processes were centered on the metal cations
whereas metal and ligand-centered reductions were ob-
served (see Table 1 for assignment). As previously re-
ported,9 the Cu2þ ion in the mononuclear 1Cu complex
was reversibly reduced at E1/2 = -1.47 V and oxidized at
E
1/2 = þ0.43 V to form the corresponding mononuclear
copper(I) and copper(III) complexes, respectively.
Logically, the electrochemical signatures of the poly-
nuclear 1CuM complexes roughly correspond to the
superposition of those of the reference derivatives 1Cu
~
(14) Arana, C.; Yan, S.; Keshavarz, M.; Potts, K. T.; Abruna, H. D.;
Chen, S.-H. J. Electroanal. Chem. 1998, 457, 23–30.

2596 Inorganic Chemistry, Vol. 49, No. 6, 2010
Gasnier et al.
Figure 3. Viscosimetry experiments. Stepwise addition of metallic salt
(II) solutions to a solution of 1Cu (C0 = 13 mM). Full lines are guidelines.
(b), Fe(BF4)2; (O), Co(BF4)2; (2), NiCl2; (9), Cu(OTf)2.
second metal ion being pinched between two terpyridine
chelates).
(iv). Viscosimetry Experiments. When a bridging
“monomer” such as 1Cu reacts with a stoichiometric
amount of metal ion, 1D polymer/oligomer chains or
rings can potentially be formed.2h,16,17 The self-assem-
bling of 1Cu with transition metal ions was thus investi-
gated by viscosimetry experiments: this technique can
give good qualitative information on the polymerization
degree in metallorganic aggregates8,9,17 and can be used
to establish the polymeric character of the soluble 1CuM
materials.
Figure 2. Cyclic voltammograms of 1Cu, 2M, and 1CuM (M = Cu, Co,
Ni, and Fe) species in DMF þ TBAP (0.1 M). Scan rate 0.1 V s-1
(normalized currents).
and the corresponding 2M. Such behavior is well-illus-
trated in Figure 2 that shows the cyclic voltammogram of
the 1CuCo system: copper(II) and cobalt(II) centered
oxidation and reduction potentials are close to those
measured with 1Cu and bis(terpyridine)Co derivatives.15
These data indicate that the redox active units in the
polymer behave almost independently in the polymer
chain, and it can be concluded that there are none or only
very weak electrochemical interactions between two vic-
inal metallic ions. This result was expected considering
the non-conjugated nature of the 1H2 ligand. It is also
interesting to note that these macromolecules can be
regarded as real electron-reservoirs since, except for
1CuCu, at least four reversible or quasi-reversible elec-
tron-transfer processes have been observed under our
experimental conditions. Depending on the nature of
M2þ in the 1CuM self-assembly, the first oxidation or
reduction process can be centered either on the linker
(macrocyclic complex) or on the terminal terpyridine
connectors. For instance, Cu2þ cations are oxidized at a
lower potential than Fe2þ cations in 1CuFe but at a higher
potential than Co2þ in 1CuCo.
Figure 3 displays the variation of the reduced viscosity
ηr = η/ηs (ηs being the viscosity of the solvent) as a
function of the molar ratio M2þ/1Cu in EtOH/DMF. In
these experiments, the initial concentration of 1Cu was 13
mM and the M2þ/1Cu ratio was varied from 0 to 2.
All experiments led to the same profile with an increas-
ing reduced viscosity up to an apex for a M2þ/1Cu molar
ratio of 1, followed by a decrease of the reduced viscosity
for higher ratios. The presence of a maximal ηr value at a
1:1 metal on ligand ratio can be unambiguously related to
an increase of the average chain contour length and is in
agreement with the formation of linear coordination
polymers. It is important to note that the maximal
reduced viscosity value depends on the metal ion type:
the apex extended in the range 1.54 < 1.60 < 1.85 < 2.2
for the series Cu2þ < Ni2þ < Co2þ < Fe2þ. These values
depend on the degrees of polymerization of the supra-
molecular coordination polymers (i.e., longer chains are
obtained with Fe2þ) and are essentially related to the
stability constants of the mono or bis(terpyridine) com-
plexes. At this stage, only qualitative trends of the effect
of added metallic cations on the viscosity can be discussed
since parameters such as the polydispersity of the aggre-
gated species, the attractive and repulsive interactions
between them, and the balance between hydrodynamic
In addition, the absence of electrochemical signal cor-
responding to the presence of bis(terpyridine)Cu units in
the 1CuM structures is a strong indication that no metal
exchange occurred during the synthesis of these com-
plexes and that metal ions of different natures regularly
follow one another in the macromolecular chain (the
dioxocyclam units containing copper(II) ion and the
(16) (a) Constable, E. C.; Housecroft, C. E.; Smith, C. B. Inorg. Chem.
Commun. 2003, 6, 1011–1013. (b) Li, S.; Moorefield, C. N.; Wang, P.; Shreiner,
C. D.; Newkome, G. R. Eur. J. Org. Chem. 2008, 19, 3328–3334.
(17) Schmatloch, S.; Van Den Berg, A. M. J.; Alexeev, A. S.; Hofmeier,
H.; Schubert, U. S. Macromolecules 2003, 36, 9943–9949.
(15) (a) Padilla-Tosta, M. E.; Lloris, J. M.; Martinez-Manez, R.; Pardo,
T.; Sancenon, F.; Soto, J.; Marcos, M. D. Eur. J. Inorg. Chem. 2001, 5, 1227–
1234. (b) Yoshimura, A.; Nozaki, K.; Ikeda, N.; Ohno, T. J. Phys. Chem. 1996,
100, 1630–1637.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2597
and Brownian forces should also be considered. These
values of ηr at the apex are in full agreement with those
measured by Schubert and coworkers for high molecular
weight coordination polymers based on poly(ethylene
oxide) spacers.17 In addition, it is interesting to note that
a maximal reduced viscosity of 1.54 was obtained for the
1CuCu polymer, whereas a ηr of only 1.26 was mea-
max
sured9 when 1 equiv of Cu2þ was added directly to a
solution of 1H2 without base, leading to the polymer in
which the dioxocyclam unit remains metal free. This
difference suggests that the metal-containing spacer is
rigidified in the 1CuCu species compared to the metal-free
macrocycle and certainly adopts a square planar geome-
try which promotes the formation of longer 1D polymer
chains.
Beyond M2þ/1Cu = 1, the reduced viscosity decreased
for all metal ions. This effect was indicative of the
presence of reversible complexation processes and can
be explained by the fragmentation of the 1D polymer
chains into shorter species, increasing the proportion of
lower molecular weight complexes with two metallic ends.
It is important to note that the change in the reduced
viscosity upon addition of an excess of metal ions ap-
peared also metal-dependent. Consistently, when the
M2þ/1Cu ratio approaches 2, the sequence Cu < Ni <
Co < Fe was still observed, and the value of the viscosity
indicated that non-negligible volume fractions of self-
assembled polymeric species with significant molecular
weights remained in the solutions. This behavior was
related to the sequence of stability constants of two types
of complexes, a first one where a metal ion is coordinated
by a single terpyridine unit (stability constant K1) and a
second type, in which a metal ion is coordinated by two
terpyridine units (stability constant K2). Ideally, if K2 .
K1 the bis-terpyridine complex (hence a polymer chain
in this case) is present in solution, even at a large
excess of metal ion and a stable viscosity should be
observed above the ratio of 1. In the case of K1 g K2,
beyond a M2þ/monomer ratio of 1, the mono-
(terpyridine) complex is favored relative to the bis-
(terpyridine) one, and the profile of the reduced
viscosity versus stoichiometry should be roughly sym-
metric with weak ηr final values at stoichiometry 2.
Experimentally, this last case was observed only with
Cu2þ. This result was expected since K1 and K2 present
similar values for this ion, and stable mono(terpyridine)-
copper(II) complexes can be easily obtained when a 1:1
(metal/ligand) molar ratio is used.9,17,18 For the other
metal ions, the sequence of ηr observed at stoichiometry 2
indicates also the sequence of K1 with respect to K2, and
Figure 4. X-Band EPR spectra of 1Cu, 2Co, and 1CuCo in DMF at
100 K (concentration = 15 mM).
Figure 5. X-Band EPR spectra of 1CuFe, 1CuCo, and 1CuCu in DMF
at 100 K (concentration as monomer: 15 mM).
originating from the nuclear spin 55I = 3/2 and 59I =
7/2 of the Cu2þ and Co2þ ions, respectively (Figure 4).
The EPR spectrum of 1Cu displayed an axial signature
comparable to analogous tetra-coordinated Cu2þ com-
plexes in square planar geometries with an electronic
ground state 3dx2-y2
12a
.
Concerning 2Co, under our ex-
perimental conditions of temperature and concentration,
only the ground spin state S = 1/2 was observed,
although it has been shown that an S = 3/2 contribu-
tion can be expected at 100 K.19 The orthorhombic
symmetry indicated by the g values is consistent with a
D2d symmetry.
The EPR spectra of the 1CuM polymers appeared to be
strongly influenced by the nature and spin state, that is,
the paramagnetism of the M2þ ion (Figures 4 and 5). The
broad EPR signature recorded with 1CuCo was clearly
not a simple addition of signals attributed to the 1Cu
and 2Co units (Figure 4). The significant line broadening
especially prevented the observation of Cu and/or
Co-based hyperfine interactions. In agreement with
logically, the higher viscosity was observed with Fe2þ
.
(v). Electron Paramagnetic Resonance (EPR) Spectros-
copy. X-band EPR spectra have been recorded for all
samples including references complexes in DMF at 100 K.
Since 2Fe is diamagnetic, no signal was observed in the
EPR spectrum. 2Ni (S = 1) was also X-band EPR silent
because of the large magnetic anisotropy of the complex.
By contrast, 1Cu and 2Co presented characteristic S =
1/2 EPR spectra with observable hyperfine coupling
(18) (a) Jiang, Q.; Wu, Z.; Zhang, Y.; Hotze, A. C. G.; Hannon, M. J.;
Guo, Z. Dalton Trans. 2008, 3054–3060. (b) Dobrawa, R.; Lysetska, M.;
Ballester, P.; Gr€une, M.; W€urthner, F. Macromolecules 2005, 38, 1315–1325.
(19) Kremer, S.; Henke, W.; Reinen, D. Inorg. Chem. 1982, 21, 3013–
3022.

2598 Inorganic Chemistry, Vol. 49, No. 6, 2010
Gasnier et al.
electrochemical results that did not present significant
interactions between metal centers, this EPR spectrum
was not characteristic of a strong magnetically coupled
system. Two types of interactions can be taken into
account, the exchange magnetic interaction, which is
generally dominant, and the dipolar interaction. A strong
antiferromagnetic exchange coupling would lead to a
diamagnetic system, whereas a strong ferromagnetic cou-
pling would afford additional EPR lines at least arising
from the resulting S = 1 ground spin state. The EPR
spectrum of 1CuCo could be thus explained by the
existence of weak magnetic interactions between vicinal
metallic ions and/or of interchains dipolar interactions
between metal ions, the latter hypothesis being less plau-
sible since the shape of the EPR spectrum appeared to be
concentration-independent.
While results similar to those obtained with the 1CuCo
polymer were observed with the 1CuCu system, our
investigations on 1CuNi were greatly limited by the
unusual line width of the EPR signal, covering few
hundred gauss at a concentration of 15 mM. Because of
the low solubilities of these compounds, it was thus not
possible to record a spectrum at high concentration.
Finally, a remarkable similarity was obtained between
the signature of 1CuFe and 1Cu. This result unambigu-
ously excludes magnetic interactions between chains. The
signal broadening, which significantly increased with the
spin state of M2þ (Fe2þ < Cu2þ = Co2þ < Ni2þ), was
thus mainly attributed to weak (exchange and/or dipolar)
magnetic interactions between vicinal metallic ions along
the polymeric chain.
Figure 6. Evolution of the visible absorption spectrum of 1CuCu in
MeOH upon addition of 2.5 equiv of triflic acid by monomer unit, as a
function of time. T = 25 °C, l = 1 cm. (a) without addition of acid, (b)
immediately upon addition of acid, and (c) final spectrum. b to c: one
spectrum every 90 s.
Scheme 4. Disassembling Process of 1CuCu in Presence of Acid
Acid-Controlled Disassembling of 1CuCu. As shown
above with viscosimetry experiments, when two molar
equivalents of Cu2þ cation are added to a solution of 1Cu,
mono(terpyridine)Cu2þ adducts are formed with solvent
molecules or counteranions completing the coordination
sphere of the metal ion. In addition, we have previously
demonstrated that the Cu2þ ion can be readily removed
from the dioxocyclam unit in the presence of acid because
of the protonation of both amide groups.9
Taking advantage of this promising acid-responsive
feature, we were keen to investigate the effect of acid on
the self-assembled architectures 1CuCu. Addition of tri-
fluoromethanesulfonic acid (2.5 mol equiv by dioxo-
cyclam unit) to a solution of 1CuCu in methanol led
to drastic color changes from red-brown to green. The
evolution of the solution was followed by UV-visible
spectroscopy (Figure 6).
formation of end-capping mono(terpyridine)Cu com-
plexes to afford, in conclusion, the tetracationic dinuclear
complex 1H2Cu2 (Scheme 4). The formation of this di-
nuclear monomer was confirmed by the CV study of the
resulting solution, which displayed one single and poorly
reversible reduction wave at Ep = -0.65 V in agreement
with the formation of a simple mono(terpyridine)Cu2þ
adduct.9 The absence of redox process around þ0.4 V
also corroborated the absence of dioxocyclam- Cu2þ
fragment.
In addition, a mass spectrometry analysis of the green
solid obtained by precipitation with diethyl ether further
supports the formation of 1H2Cu2 species through the
presence of an intense signal at m/z = 647 corresponding
to the dicationic species {1H2Cu2, 2CF3SO3}2þ. Unfor-
tunatly, because of precipitation phenomena, the reverse
process, that is, the regeneration of the 1CuCu polymer by
The main absorption band instantaneously experi-
enced a bathochromic shift from λmax = 503 nm to
λ
max = 530 nm (spectrum a to b, Figure 6). In agreement
with previous studies,9,12 this 530 nm absorption band
was attributed to a dfd transition in the monoproto-
nated 1HCuCu intermediate, wherein copper is bound to
only three nitrogen atoms of the dioxocyclam unit, one
amide function being protonated. This band at 503 nm
then progressively disappeared, and the initial band at
λmax = 687 nm corresponding to the signature of the
bis(terpyridine)Cu was slightly red-shifted and more in-
tense (Figure 6, curves b to c). These changes can be
attributed to a disassembling process originated by the
dissociation of the dioxocyclam-Cu(II) complexes and to
the progressive release of free Cu2þ ions promoting the

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2599
addition of base to a solution of 1H2Cu2, was unsuccess-
ful.
298 K. 1H chemical shifts (ppm) were referenced to residual
solvent peaks. UV-vis spectra were recorded on a Varian Cary
100 spectrophotometer using quartz cells (l = 1 cm). Infrared
spectroscopy was carried out on a Perkin-Elmer GS 2000.
Preparation of Ligand 1H2 and Metal Complexes. Preparation
of Bis-(40-phenyl-2,20:60,600-terpyridine)Metal(II) Complexes. The
2M complexes with M = Fe, Co, Ni, or Cu were prepared as
Conclusions
Supramolecular coordination polymers were self-as-
sembled from a polytopic bis(terpyridine)-dioxocyclam re-
ceptor. The formation of polymers was demonstrated by
viscosimetry experiments. The use of a macrocyclic complex-
ing spacer in this bridging ligand allowed the introduction of
additional metal ions in the polymer chain, and thus the
synthesis of both homo- and heterometallic architectures.
The regular alternation of different metal ions in the structure
was demonstrated by CV, mass spectrometry, and UV-vis
spectroscopy. EPR experiments also revealed the existence of
weak intramolecular magnetic interactions between vicinal
metal ions. In addition, the homometallic Cu2þ polymer
could be converted into dinuclear complexes in the presence
of acid. This work shows that the use of polytopic bridging
ligands containing complexing spacers opens perspectives
for further developments of functional supramolecular
materials.
-
-
BF4 salts (CF3SO3 salt was used in the case of Cu) following
previously reported experimental procedures.5b,9
Synthesis of 1,8-Bis-(4-[2,20;60,200]terpyridin-40yl-benzyl)-1,4,8,11-
tetraazacyclotetradecan-5,12-dione (1H2). This ligand was prepared
as previously reported: to a stirred solution of 0.876 mmol (200 mg)
of 1,4,8,11-tetraazacyclotetradecane-5,12-dione,10 in a mixture of
methanol (30 mL) and acetonitrile (100 mL) containing 7.2 mmol
(1.0 g) of potassium carbonate were added dropwise 2 mmol (0.805
g) of 40-(4-bromomethylphenyl)-2,20:60,200-terpyridine11 dissolved
in dichloromethane (10 mL). This solution was refluxed for 4 days,
and the resulting mixture was filtered. Upon removal of the solvent
under reduced pressure, the crude product was dissolved in aqueous
NaOH (pH ∼ 12) and extracted three times by dichloromethane.
The combined organic layers were dried (Na2SO4), filtered, and
concentrated under vacuum. The residue was purified by column
chromatography on alumina (dichloromethane-methanol, 98:2;
v:v) to afford 1H2 as a light-yellow solid. Yield: 0.374 g (49%).
1H NMR (250 MHz, CDCl3, δ): 8.74-8.66 (m, 8 H, tpy 3-300 and
tpy 30-,50) ; 8.61-8.57 (m, 6 H, tpy, 6-,600 and -CONH); 7.86-7.79
(m, 8 H, tpy 4-,40 and -Ph); 7.40-7.38 (m, 4 H, Ph); 7.34-7.29 (m,
4 H, tpy 5-,500); 3.78 (s, 4 H, PhCH2); 3.51 (br, 4 H, CONHCH2);
2.73 (t, br, J = 5.1 Hz, 8 H, NCOCH2CH2 and CONCH2CH2);
2.49 (t, br, J = 5.1 Hz, 4 H, NHCOCH2). 13C NMR (75 MHz,
CDCl3): δ 171.9 ; 155.9; 155.7; 149.2; 149.0; 137.9; 137.2; 136.7;
130.1; 127.4; 123.8; 121.2; 118.5; 57.4; 52.2; 49.3; 35.8; 32.2. FABþ-
MS, m/z: 871 {1H2 þ H}þ. IR (KBr, cm-1): 1645 (νCdO) ; 1584
Experimental Section
Reagents, Instrumentation, and Procedures. All reagents were
commercial grade and used without further purification. TBAP
was purchased from Fluka. Electrochemical experiments were
conducted under an argon atmosphere in a conventional three-
electrode cell under an argon atmosphere at 298 K using a CH
Instrument potentiostat (CHI 660B). The reference electrode
was Ag/AgNO3 (10 mM in CH3CN containing 0.1 M TBAP).
The working electrode was a vitreous carbon disk (3 mm in
diameter) polished with 1 μm diamond paste before each record.
The regular ferrocene/ferrocenium (E1/2 = þ0.054 V vs Ag/10
mM AgNO3 under our experimental conditions) redox couple
was used as internal reference. CV curves were recorded at a scan
rate of 0.1 V s-1. Electrochemical experiments were done on
millimolar solutions of the compound in the case of the mono-
nuclear 2M complexes. In the case of the 1CuM polymers, since
their exact molar concentration can not be accurately deter-
mined, a mass concentration of ∼1 mg of complex per milliliter
of solvent was used.
Viscosimetry measurements have been performed using a
Cannon-Fenske viscometer (Comecta) appropriate for New-
tonian liquids undergoing a Poiseuille type flow. The tempera-
ture was regulated at T = 18.6 ( 0.3 °C. The apparatus was
calibrated using water and a standard oil (ThermoFisher Scien-
tific) having a 5.3 mPas dynamic viscosity. The density of the
specimens was measured with a DMA 35N densimeter. The
mononuclear 1Cu complex was dissolved in DMF (60%)-
EtOH(40%) and increasing volumes of metal ions ([ ] = 260
mM in DMF) were added. All measurements were repeated 5
times. The initial concentration of the 1Cu complex is 13 mM
while at the end of the sequence of metal ion additions, the
concentration at the stoichiometry 2, becomes 11.8 mM. ESI
experiments were performed in the positive mode on a Bruker
(δN-H). Anal. Calcd for C54H50N10O2 0.5CH3OH (%): C, 73.79,
3
H, 5.90, N, 15.79; found C, 73.64, H, 5.89, N, 15.50.
Preparation of 1Cu Complex.9 To a solution of 0.172 mmol of
1H2 (150 mg) in methanol (6 mL) containing 0.342 mmol of
potassium carbonate (24.0 mg) was added dropwise 0.172 mmol
of Cu(CF3SO3)2 (62.4 mg) dissolved in methanol (6 mL). Upon
addition, the reaction medium turned dark-green. The mixture
was refluxed for 12 h to afford a deep-purple solution. Potas-
sium carbonate was removed by filtration, and the filtrate was
evaporated under reduced pressure. Purification was carried out
by column chromatography (alumina), with dichloromethane-
methanol (96:4 ; v:v) as eluent to afford the expected complex as
a purple solid; yield: 51.1 mg (32%). ESI-MS: m/z 932.34
[1H2þH]þ. UV-vis (MeOH) λmax, nm (ε, M-1 cm-1): 503
(156). IR (KBr, cm-1): 1544 (νCdO). Anal. Calcd for C54H48-
N10O2Cu. Three CH3OH (%): C, 66.55, H, 5.88, N, 13.61; found
C, 66.62, H, 6.00, N, 13.28.
Preparation of 1CuM polymers with M = Fe, Co, Ni, or Cu.
1CuM complexes were prepared by mixing 15 mg of 1Cu in 4 mL
MeOH and 1 mol equiv of metal salt (as BF4- salts for M2þ
=
Fe2þ, Co2þ, and Ni2þ and as CF3SO3- salt for Cu2þ) dissolved
in 1 mL MeOH under an inert atmosphere. After 1 h, the
complex was precipitated by addition of diethyl ether, collected
by suction filtration, washed with diethyl ether, and dried under
reduced pressure. Yields: 80-90%. 1CuCu: ESI-MS: m/z 963.81
{1Cu3}2þ; IR (KBr, cm-1): 1545 (νCdO). 1CuFe: ESI-MS: m/z
960.29 {1Cu2Fe}2þ, 727.47 {1Cu3Fe2}4þ; IR (KBr, cm-1): 1542
(νCdO). 1CuCo: ESI-MS: m/z 961.80 {1Cu2Co}2þ; IR (KBr,
ꢀ
MicrOTOF-Q instrument of the “Centre de Spectrometrie
ꢀ
ꢀ
Moleculaire de l’Universite de Bourgogne” in Dijon. Methano-
lic solutions of 10-6 M concentration were introduced into the
mass spectrometer at a flow rate of 4 μL/min. Nitrogen was used
as nebulizer gas, and the needle voltage was set at 4500 V with a
end plate offset of -500 V. FAB (positive mode) mass spectra
were recorded with an AEI Kratos MS 50 spectrometer fitted
with an Ion Tech Ltd. gun and using m-nitrobenzyl alcohol
as matrix. NMR spectra were recorded on a Bruker AC 250 at
cm-1): 1544 (νCdO). 1CuNi: ESI-MS: m/z 961.31 {1Cu2Ni}2þ
IR (KBr, cm-1): 1543 (νCdO).
;
Acknowledgment. The authors thank the Fondation Nano-
ꢀ
sciences Grenoble (RTRA program) and the Region Rhone-
Alpes (Cluster Nano project) for their financial support.
^