Inorganica Chimica Acta 362 (2009) 284–290

Contents lists available at ScienceDirect

Inorganica Chimica Acta

journal homepage: www.elsevier .com/locate / ica

Note

Binuclear copper and zinc complexes based on polypyridyl ligand2,3,5,6-tetra(2-pyridyl)pyrazine (tppz): Synthesis, spectral and structuralcharacterization

Manoj Trivedi a,*, Daya Shankar Pandey a, Nigam P. Rath b,*

a Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, U.P., Indiab Department of Chemistry and Biochemistry and Centre for Nanoscience, University of Missouri – St. Louis, One University, Boulevard, St. Louis, MO 63121-4499, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 November 2007Received in revised form 28 February 2008Accepted 28 February 2008Available online 7 March 2008

Keywords:Metal complexes2,3,5,6-Tetra(2-pyridyl)pyrazine (tppz)ligandX-rayWeak interactions

0020-1693/$ - see front matter � 2008 Elsevier B.V. Adoi:10.1016/j.ica.2008.02.064

* Corresponding authors. Tel.: +91 0 9984549276 (5333 (N.P. Rath).

E-mail addresses: manojtri@gmail.com (M. Trivedi)

The reaction of MCl2 � 2H2O (M = Cu, Zn) with 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) (referred hereafteras L) in 2:1 molar ratio in acetonitrile at room temperature afforded binuclear complexes [M2(j3-L)Cl4][Cu (1), Zn (2)] where the ligand is bis-tridentate manner. The complexes have been characterized by ele-mental analyses, FAB-MS, IR, EPR, NMR and electronic spectral studies. Solid state structures of both the[Cu2(j3-L)Cl4] � 5H2O (1), [Zn2(j3-L)Cl4] � H2O (2) have been determined by single crystal X-ray analyses. Awell-resolved uudd cyclic water tetramer and water monomer were reported in the crystal host of[Cu2(j3-L)Cl4] � 5H2O (1) and [Zn2(j3-L)Cl4] � H2O (2) showing the contribution of the water cluster tothe stability of the crystal host 1 and 2.

� 2008 Elsevier B.V. All rights reserved.

1. Introduction

The design of binuclear metal complexes incorporating suitablebridging ligands which lead to the formation of stable mixed va-lence states has attracted considerable research interest in recentyears [1]. This has been primarily due to their relevance for biolog-ical processes, molecular electronics and for theoretical studies ofelectron transfer kinetics [2]. Since the discovery of the pyrazine-mediated strong intermetallic coupling in the Creutz–Taube com-plex [3,4], polyazine-based heterocyclic bridging ligands capableof mediating intermetallic electronic communication through thep-symmetry orbitals have been investigated [5–9]. 2,3,5,6-Tetra-kis(2-pyridyl)pyrazine (tppz) was first reported in 1959 by Good-win and Lions [10], has been found to be a suitable mediator forintermetallic coupling almost of the order of the Creutz–Taubeion [9]. The coordination modes of tppz ligand toward metal ionshas shown its great versatility as bidentate [11], terdentate [12],bis-bidentate [11a,13], tris-bidentate [11a] and bis-terdentate[9f,9g,12a,12f,14].

In 1989 Escuer et al. first reported a hexafluoroacetylacetonatebinuclear copper complex of tppz [Cu2(tppz)(hfacac)4] (hfa-

ll rights reserved.

M. Trivedi); tel.: +1 314 516

, rathn@umsl.edu (N.P. Rath).

cac = hexafluoroacetylacetonate) [15]. Ruminski et al. have synthe-sized and characterized mono and bimetallic Ru(II) [9a], Rh(II) [16]and Fe(II) [17] complexes of tppz. However, structurally character-ized complexes of binuclear copper and mononuclear zinc contain-ing tppz in bis-tridentate were reported by Stoeckli-Evans and co-workers [12a]. The ability of tppz ligand to mediate magnetic inter-actions between paramagnetic centers separated by more than6.4 Å in the tppz-bridged metal complexes has renewed the inter-est in this ligand [12f,12g]. More recently, structural and magneticstudies on tppz-bridged metal complexes have been reported[12f,12h,12i,12j].

Because of our interests in polypyridyl ligands [18] we haveexamined reactivity of 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) withCu(II), and Zn(II) salts. We describe herein the synthesis, spectraland structural characterization of five-coordinate binuclear copper[Cu2(j3-L)Cl4] � 5H2O (1), and zinc [Zn2(j3-L)Cl4] � H2O (2) com-plexes containing 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) ligand.

2. Results and discussion

2.1. Syntheses

Reactions of MCl2 � 2H2O (M = Cu, Zn) with L in acetonitrile in2:1 molar ratio with stirring at room temperature gave the neutral

N

N

N

NN

NN

N

N

NN

N

Cu

CuCl2.2H2O

CH3CN

ZnCl2CH3CN

[1] [2]ClCl

Cu

ClCl

N

N

N

NN

N

Zn

ClCl

Zn

ClCl

Scheme 1.

Fig. 1. (a) EPR spectra of [1] in CH3CN at rt; (b) at LNT.

M. Trivedi et al. / Inorganica Chimica Acta 362 (2009) 284–290 285

complexes [Cu2(j3-L)Cl4] � 5H2O (1), [Zn2(j3-L)Cl4] � H2O (2) inexcellent yield. Synthesis of 1 has been previously described byStoeckli-Evans et al. following a quite different procedure [12g].A reaction Scheme 1 showing the synthesis of the complexes is gi-ven below .

2.2. Characterization

The complexes 1 and 2 are air stable, non-hygroscopic shinycrystalline solids, soluble in common organic solvents, and insolu-ble in diethyl ether and petroleum ether. The complexes were fully

Table 1Crystal data for1 and 2

1 2

Empirical formula C24H22Cl4Cu2N6O5 C24H18Cl4N6OZn2

Formula weight 743.36 678.98Colour and habit green block yellow blockCrystal size (mm) 0.30 � 0.25 � 0.20 0.19 � 0.17 � 0.11Crystal system, space group monoclinic, P21/c triclinic, P�1a (Å) 15.0329(18) 10.2724(9)b (Å) 13.2118(7) 14.7001(13)c (Å) 15.3192(17) 18.2065(16)b (�) 105.394(10) 77.678(4)V (Å3) 2933.4(5) 2544.2(4)Z, Dc (g cm�3) 4, 1.683 2, 0.791l (mm�1) 1.860 1.062T (K) 293(2) 100(2)k(MoKa) (Å) 0.71073 0.71073No. of reflections 23696 45582No. of refined parameter 5133 11013R factor [I > 2r(I)] 0.0228 0.0618wR2 [I > 2r(I)] 0.0625 0.1647R factor (all data) 0.0266 0.0935wR2 (all data) 0.0642 0.1823Goodness-of-fit 1.083 1.063

Fig. 2. Projection views of 1 (top) and 2 (bottom) shown with 50%

286 M. Trivedi et al. / Inorganica Chimica Acta 362 (2009) 284–290

characterized by IR, UV–Vis, FAB-MS, NMR and EPR spectroscopy.Analytical data of the complexes (presented in Section 4) corrobo-rated well to their respective formulae. The positions of variouspeaks and overall fragmentation patterns (see Section 4) are con-sistent with the formulae of the complexes. Infrared spectra in Nu-jol displayed bands corresponding to m(C@N) at �1593 cm�1 andbands around 289–330 cm�1 assignable to m(M–Cl). The 1H NMRspectrum of 2 shows resonance at 8.68 (s, 4H), 8.06 (t, 4H,J = 7.2 Hz), 7.87 (d, 4H, J = 6.0 Hz), 7.67 (d, 4H, J = 6.4 Hz) ppmassignable to protons of tppz ligand. Absorption spectra of 1, and2 in acetonitrile displayed bands at 370 nm and an intense high-er-energy band at 310–312 nm. The lowest-energy bands in therange of 370 nm can be assigned to metal to ligand charge transfertransition MLCT ½MðIIÞ ! p�L�. The intense band in the region 310–312 nm has been assigned to L-centered intra-ligand (p–p*)transitions.

Information regarding the immediate environment about themetal centre in complex 1 was obtained from ESR spectral studies.The X-band ESR spectra of 1 in CH3CN were recorded at liquid-nitrogen and room temperatures (Fig. 1). The spectrum at roomtemperature shows four intense bands in the high field while inthe frozen state it shows six resolved peaks. Presences of more

probability ellipsoids; hydrogen atoms are omitted for clarity.

Table 2Selected bond lengths (Å) bond angles (�) for 1 and 2

1 2

Cu(1)–N(1) 1.9763(16) Zn(1)–N(3) 2.133(5)Cu(1)–N(3) 2.0259(17) Zn(1)–N(2) 2.145(5)Cu(1)–N(2) 2.0183(16) Zn(1)–N(1) 2.168(5)Cu(l)–Cl(1) 2.5382(6) Zn(1)–Cl(1) 2.2567(17)Cu(1)–Cl(2) 2.2130(6) Zn(1)–Cl(2) 2.2662(16)

N(1)–Cu(1)–N(2) 78.91(6) N(2)–Zn(1)–N(1) 73.8(2)N(l)–Cu(1)–N(3) 80.08(6) N(3)–Zn(1)–N(1) 74.08(19)N(2)–Cu(1)–N(3) 155.80(7) N(3)–Zn(1)–N(2) 147.5(2)N(1)–Cu(1)–Cl(1) 87.20(5) N(1)–Zn(1)–Cl(1) 117.90(15)N(2)–Cu(1)–Cl(l) 92.58(5) N(1)–Zn(1)–Cl(2) 125.40(15)N(3)–Cu(1)–Cl(1) 98.26(5) N(2)–Zn(1)–Cl(1) 96.78(15)N(2)–Cu(1)–Cl(2) 99.78(5) N(2)–Zn(1)–Cl(2) 100.52(14)N(1)–Cu(1)–Cl(2) 167.53(5) N(3)–Zn(1)–Cl(1) 102.19(15)N(3)–Cu(1)–Cl(2) 98.14(5) N(3)–Zn(1)–Cl(2) 94.20(14)Cl(1)–Cu(1)–Cl(2) 105.27(2) Cl(1)–Zn(1)–Cl(2) 116.70(7)C(1)–N(1)–Cu(1) 126.33(14) C(14)–N(3)–Zn(1) 121.9(4)C(5)–N(1)–Cu(1) 114.04(12) C(10)–N(3)–Zn(1) 118.1(4)

M. Trivedi et al. / Inorganica Chimica Acta 362 (2009) 284–290 287

than four hyperfine lines in the spectrum of 1 indicate the exis-tence of Cu2+–Cu2+ interactions. Four bands are at a higher field rel-ative to that of DPPH. The copper complex exhibits the gk value of2.201 and g\ 2.124. These values indicate that the ground state ofCu(II) is predominantly dx2�y2 [19].

2.3. Molecular structures

Molecular structures of 1 and 2 were determined crystallo-graphically. The details of data collection, structure solution andrefinement are listed in Table 1. The molecular structures of thecomplexes 1 and 2 with atom numbering scheme are shown inFig. 2 and the important geometrical parameters are presented inTable 2. Complex 1 crystallizes in the monoclinic space groupP21/c. Complex 2 crystallizes in the triclinic space group P�1 andthe crystallographic asymmetric unit contains two independent

O1w'

O5w'

O4w'

O H

H

O

O

H

OH

H

H

H

H

Tetramer C2

Fig. 3. Mercury plot showing the cyclic water tetramer an

molecules, which are essentially identical. The molecular structureof 1 shows distorted square pyramidal coordination around eachcopper centre and is a binuclear complex with the ligand coordi-nated in bis-tridentate manner. The intramolecular Cu(l)� � �Cu(2)distance is 6.570 Å, a value which compares well with those ob-served in the tppz-bridged binuclear copper(II) complexes[Cu2(tppz)Cl4] � 5H2O [6.565(1) Å] [12g] and [Cu2(tppz)(H2O)4](-ClO4)4 � 2H2O [6.497(2) Å] [12a]. The pyrazine ring is twisted by27.45� (dihedral angle between the planes N(1)–C(1)–C(2) andN(4)–C(3)–C(4)). Pyridine rings, coordinated to Cu(1), are inclinedto one another by 5.21(13)�, while other pyridine rings coordinatedto atom Cu(2), arc inclined by 6.15(14)�. The ligand is highlytwisted as seen by the large dihedral angles, varying from 19.1�to 60.3�, between adjacent and opposite pyridine rings. The Cu–N(pz, pyrazine) distances Cu(1)–N(2) and Cu(2)–N(5) are1.9763(16) and 1.9835(16) Å, respectively. The average Cu–N(py,pyridine) distance is 2.0246 Å.

Molecular structure of 2 shows trigonal bipyramidal geometryaround each zinc centre and is a binuclear complex with the ligandcoordinated in bis-tridentate manner. The pyrazine ring is twistedby 27.99� (dihedral angle between the planes N(1)–C(1)–C(2) andN(4)–C(3)–C(4)). Pyridine rings, coordinated to Zn(1), are inclinedto one another by 4.0(4)�, while other pyridine rings coordinatedto atom Cu(2), arc inclined by 4.2(5)�. In this case, the ligand is alsohighly twisted as seen by the large dihedral angles, varying from20.9� to 59.8�, between adjacent and opposite pyridine rings. TheZn–N (pz, pyrazine) distances Zn(1)–N(1) and Zn(2)–N(4) are2.168(5) and 2.200(5) Å, respectively. The average Zn–N (py, pyri-dine) distance is 2.147 Å.

Bond distances and angles of the tppz group in 1 and 2 agreewith those previously observed for this ligand exhibiting the bis-terdentate coordination mode in a few structurally characterizedexamples with Cu(II), Ni(II) [12a,12g,12f], Ru(II) [9f,9g], and Rh(I)[14g].

Interestingly, a cyclic water tetramer is perpendicularly locatedin each cavity of the 2D box and hydrogen-bonded to the symme-

O2w

O3wO2w'

O3w'

O5w

O4w

O1w

d its immediate environment as found in complex 1.

Fig. 4. 2D box connected into 3D structure by the water tetramer through hydrogen bonding of symmetry-related O3W and symmetry-related Cl4 atoms of host from left andright 2D box viewed along the a axis in complex 1.

288 M. Trivedi et al. / Inorganica Chimica Acta 362 (2009) 284–290

try-related O5 atoms with symmetry-related O3W (O3W� � �O5)2.739(7) Å in 1 (Fig. 3). The most remarkable feature in 1 is thatthe 2D box is connected into a 3D structure (Fig. 4) only by thewater tetramer through hydrogen bonding between symmetry-re-lated O1W and symmetry-related Cl4 atoms of 1 from the left andright 2D box (O1� � �Cl4) 3.223 Å, respectively, indicating that thewater tetramer plays a crucial role in contributing to the stabilityof the 1. The coordination environment of the water tetramer isshown in Fig. 3. Each water monomer in the cluster is involvedin the formation of three hydrogen bonds, from water–water inter-action and one from water–chlorine interaction. Within the cluster,the three water molecules are fully coplanar and each water mono-mer acts as both single hydrogen bond donor and acceptor. Thehydrogen bond distances and angles within the water tetramerare as follows: O2w� � �O3w 2.772(4) Å, O2w� � �03w0 2.908(17) Å,O4w� � �O5w 2.740(7) Å, O1w� � �O2w 2.905(4) Å, O3w� � �O5w 2.739(7) Å, O2w–H2wA� � �O3w 178(3)�, O2w–H2wB� � �O3w0 170(2)�,O1w–H1wA� � �O2w 168(3)�, O3w–H3wA� � �O5w 169(4)�. Such anarrangement results in the formation of an irregular uudd watertetramer in 1 [20]. The average hydrogen bond distance withinthe water tetramer is 2.812 Å, significantly longer than 2.78 Å esti-mated in the udud water tetramer of (D2O)4 in the gas phase [21],and 2.743 Å calculated in the discrete udud water tetramer [22]while in 2, C–H� � �O interactions lead to linear chains. Contact dis-tances and angles between C–H� � �O are 2.47 Å and 161–163�,respectively (see F-1, Supplementary material). Crystal packing in2 is also stabilized by C–H� � �Cl type inter-molecular hydrogenbonds which lead to butterfly motif (see F-2, Supplementary mate-rial). Contact distances between C–H� � �Cl are in the range of 2.85–2.86 Å and associated angles are in the range of 152–159�. It alsoexhibits C–H� � �p interactions (C–H� � �p distance = 2.78–2.83 Å)and p–p stacking interactions (p–p distances = 3.22–3.39 Å) (seeF-3, Supplementary material). These distances are comparable tothe literature values [23].

3. Conclusions

In this work we have presented synthesis, spectral and struc-tural properties of the Cu(II), and Zn(II) complexes derived fromtppz ligand with a well-resolved uudd cyclic water tetramer andmonomer in their crystal lattice, respectively. The result showsthat the water molecules play vital roles in the stability of these

complexes in the solid state. Detailed study about the reactivityof substituted complexes, and structural characterization is in pro-gress in our laboratory.

4. Experimental

4.1. Materials and physical measurements

All the synthetic manipulations were performed under oxygenfree nitrogen atmosphere. The solvents were dried and distilledbefore use following the standard procedures. Copper chloridedihydrate, zinc chloride, was used as received. 2,3,5,6-Tetra(2-pyridyl)pyrazine (tppz) was procured from Aldrich and used as is.

Elemental analyses were performed at Sophisticated AnalyticalInstrumental Facility, Central Drug Research Institute, Lucknow.Infrared spectra and Electronic spectra were obtained on a Per-kin–Elmer 577 and Shimadzu UV-1601 spectrometer, respectively.Electron paramagnetic resonance (epr) spectra were recorded witha Varian 109 C (fitted with a quartz dewar for measurements at300 K and at 120 K) and Bruker EMX 1444 spectrometer. The EPRspectra were calibrated with diphenylpicrylhydrazyl, DPPH(g = 2.0037). 1H NMR spectrum was recorded on a JEOL AL-300FTNMR instrument. The FAB mass spectra were recorded on a JEOLSX 102/DA 6000 mass spectrometer using Xenon (6 kV, 10 mA) asthe FAB gas. Accelerating voltage was 10 kV and the spectra wererecorded at room temperature with m-nitrobenzyl alcohol as thematrix.

4.2. Synthesis

4.2.1. [Cu2(j3-L)Cl4] � 5H2O (1)To a suspension of CuCl2 � 2H20 (0.340 g, 2.0 mmol) in 20 mL of

acetonitrile, L (0.388 g, 1.0 mmol) was added and the resultingsolution was stirred at room temperature for 2 h. Slowly, color ofthe solution changes from green to yellow and green yellow col-ored precipitate separated out. The resulting precipitate was fil-tered and washed with diethyl ether. It was dissolved inacetonitrile and water mixture in 1:1 molar ratio and left in roomtemperature for slow crystallization. In a couple of days dark greenblocked shaped diffraction quality crystals obtained. The crystalswere separated from the mother liquor and air dried. Yield:0.527 g (71%). Anal. Calc. for C24H22Cl4N6O5Cu2: C, 38.76; H, 2.96;

M. Trivedi et al. / Inorganica Chimica Acta 362 (2009) 284–290 289

N, 11.30. Found: C, 39.20; H, 2.10; N, 11.89%. FAB-MS m/z: 656(655), 30 [Cu2(j3-L)Cl4]; 585 (585), 20 [Cu2(j3-L)Cl2]+; 549 (549),10 [Cu2(j3-L)Cl]+; 514(514), 10 [Cu2(j3-L)]+. IR (KBr, cm�1): 1630,1590, 1545, 1474, 1420, 1390. UV–Vis {CH3CN, kmax nm (e/M�1 cm�1)}: 310 (22430), 370 (20480).

4.2.2. [Zn2(j3-L)Cl4] � H2O (2)Complex 2 was prepared by the reaction of ZnCl2 (0.272 g,

2.0 mmol) in acetonitrile (20 mL) with L (0.388 g, 1.0 mmol) underrefluxing condition for 4 h. The color of the solution changes fromwhite to yellow. The resulting solution was filtered to remove anysolid residue and left for slow crystallization in the room temper-ature by adding few drop of distilled water. Slowly, yellow blockedshaped diffraction quality crystals appeared. These were separatedand air dried. Yield: 0.549 g (81%). Anal. Calc. for C24H18Cl4N6OZn2:C, 42.47; H, 2.65; N, 12.39. Found: C, 42.13; H, 2.45; N, 11.91%. FAB-MS m/z: 660 (660), 40 [Zn2(j3-L)Cl4]; 589 (588), 30 [Zn2(j3-L)Cl2]+;553 (552), 10 [Zn2(j3-L)Cl]+; 517 (516), 10 [Zn2(j3-L)]+. IR (KBr,cm�1): 1593, 1541, 1545, 1473, 1406, 1302. 1H NMR (d ppm,300 MHz, DMSO-d6, 298 K): 8.68 (s, 4H), 8.06 (t, 4H, J = 7.2 Hz),7.87 (d, 4H, J = 6.0 Hz), 7.67 (d, 4H, J = 6.4 Hz). UV–Vis {CH3CN, kmax

nm (e/M�1 cm�1)}: 312 (22240), 370 (21550).

4.3. X-ray crystallographic study

Crystals suitable for single-crystal X-ray analyses for the com-plexes [Cu2(j3-L)Cl4] � 5H2O (1), and [Zn2(j3-L)Cl4] � H2O (2) weregrown at room temperature. Preliminary examination and inten-sity data were collected using Enraf-Nonius CAD-4 four-Circle andBruker APEX II area detector diffractometers using graphitemonochromatized MoKa radiation at 293(2) and 100 K for 1and 2, respectively. SMART and SAINT software packages [24] wereused for data collection and data integration for 2. Structure solu-tion and refinement were carried out using the SHELXTL-PLUS soft-ware package [23]. The non-hydrogen atoms were refined withanisotropy thermal parameters. All the hydrogen atoms weretreated using appropriate riding models. The computer programPLATON was used for analyzing the interaction and stacking dis-tances [25].

Acknowledgements

We gratefully acknowledge financial support from council ofScientific and Industrial Research, New Delhi (Senior Research Fel-lowship to M.T.). We also thank the Head, SAIF, Central Drug Re-search Institute, Lucknow for analytical and spectral facilities,and the Head, Department of Chemistry, Faculty of Science, Banar-as Hindu University, Varanasi for extending laboratory facilities.We acknowledge funding from the National Science Foundation(CHE0420497) for the purchase of the APEX II diffractometer.

Appendix A. Supplementary material

CCDC 666130 and 665188 contain the supplementary crystallo-graphic data for 1 and 2. These data can be obtained free of chargefrom The Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif.

References

[1] (a) W. Kaim, A. Klein, M. Glöckle, Acc. Chem. Res. 33 (2000) 755;(b) K.D. Demandis, C.M. Hartshorn, T.J. Meyer, Chem. Rev. 101 (2001) 2655;(c) W.R. Browne, R. Hage, J.G. Vos, Coordin. Chem. Rev. 250 (2006) 1653;(d) W. Kaim, B. Sarkar, Coordin. Chem. Rev. 251 (2007) 584.

[2] (a) E.I. Solomon, T.C. Brunold, M.I. Davis, J.N. Kemsley, S.K. Lee, N. Lehnert, F.Neese, A.J. Skulan, Y.S. Yang, J. Zhou, Chem. Rev. 100 (2000) 235;(b) F. Paul, C. Lapinte, Coordin. Chem. Rev. 178–180 (1998) 431;

(c) M.D. Ward, Chem. Ind. (1997) 640;(d) B.S. Brunschwig, N. Sutin, Coordin. Chem. Rev. 187 (1999) 33;(e) A. Bencini, I. Ciofini, C.A. Daul, A. Ferretti, J. Am. Chem. Soc. 121 (1999)11418.

[3] (a) C. Creutz, H. Taube, J. Am. Chem. Soc. 91 (1969) 3988;(b) C. Creutz, H. Taube, J. Am. Chem. Soc. 95 (1973) 1086.

[4] U. Furholz, S. Joss, H.B. Burgi, A. Ludi, Inorg. Chem. 24 (1985) 943.[5] D.P. Rillema, D.G. Taghdiri, D.S. Jones, C.D. Keller, L.A. Wori, T.J. Meyer, H.A.

Levy, Inorg. Chem. 26 (1987) 578.[6] (a) J.D. Petersen, W.R. Murphy Jr., R. Sahai, K. Brewer, R.R. Ruminski, Coordin.

Chem. Rev. 64 (1985) 261;(b) E.V. Dose, L.J. Wilson, Inorg. Chem. 17 (1978) 2660;(c) M. Hunziker, A. Ludi, J. Am. Chem. Soc. 99 (1977) 7370;(d) R.R. Ruminski, J.D. Petersen, Inorg. Chem. 21 (1982) 3706.

[7] (a) C.H. Braunstein, A.D. Baker, T.C. Strekas, H.D. Gafney, Inorg. Chem. 23(1984) 857;(b) R.R. Ruminski, T. Cockroft, M. Shoup, Inorg. Chem. 27 (1988) 4026;(c) V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem. Rev. 96(1996) 759;(d) S. Serroni, S. Campagna, G. Denti, T.E. Keyes, J.G. Vos, Inorg. Chem. 35 (1996)4513.

[8] (a) A. Gourdon, J.P. Launay, Inorg. Chem. 37 (1998) 5336;(b) P. Bonhote, A. Lecas, E. Amouyal, Chem. Commun. (1998) 885.

[9] (a) R. Ruminski, J. Kiplinger, T. Cockroft, C. Chase, Inorg. Chem. 28 (1989)370;(b) J.P. Collin, P. Lainé, J.P. Launay, J.P. Sauvage, A. Sour, J. Chem. Soc., Chem.Commun. (1993) 434;(c) C.R. Arana, H.D. Abruna, Inorg. Chem. 32 (1993) 194;(d) L.M. Vogler, B. Scott, K.J. Brewer, Inorg. Chem. 32 (1993) 898;(e) L.M. Vogler, K.J. Brewer, Inorg. Chem. 35 (1996) 818;(f) C.M. Hartshorn, N. Daire, V. Tondreau, B. Loeb, T.J. Meyer, P.S. White, Inorg.Chem. 38 (1999) 3200;(g) N. Chanda, R.H. Laye, S. Chakraborty, R.L. Paul, J.C. Jeffery, M.D. Ward, G.K.Lahiri, J. Chem. Soc., Dalton Trans. (2002) 3496;(h) N. Chanda, B. Sarkar, J. Fiedler, W. Kaim, G.K. Lahiri, Dalton Trans. (2003)3550;(i) D.M. Dattelbaum, C.M. Hartshorn, T.J. Meyer, J. Am. Chem. Soc. 124 (2002)4938.

[10] H.A. Goodwin, F. Lions, J. Am. Chem. Soc. 81 (1959) 6415.[11] (a) X. Chen, F.J. Femia, J.W. Babich, J. Zubieta, Inorg. Chim. Acta 315 (2001) 66;

(b) C. Metcalfe, S. Spey, H. Adams, J.A. Thomas, J. Chem. Soc., Dalton Trans.(2002) 4732.

[12] (a) M. Graf, B. Greaves, H. Stoeckli-Evans, Inorg. Chim. Acta 204 (1993) 239;(b) L.M. Vogler, B. Scott, K.J. Brewer, Inorg. Chem. 32 (1993) 898;(c) P. Lainé, A. Gourdon, J.P. Launay, Inorg. Chem. 34 (1995) 5156;(d) V. Tondreau, A.M. Leiva, B. Loeb, Polyhedron 15 (1996) 2035;(e) J. Kozisek, J. Marek, Z. Baloghova, D. Valigura, Acta Crystallogr., Sect. C 53(1997) 1813;(f) J. Carranza, C. Brennan, J. Sletten, J.M. Clemente-Juan, F. Lloret, M. Julve,Inorg. Chem. 42 (2003) 8716;(g) M. Graf, Helen Stoeckli-Evans, A. Escuer, R. Vicente, Inorg. Chim. Acta 257(1997) 89;(h) J. Carranza, J. Sletten, C. Brennan, F. Lloret, J. Cano, M. Julve, J. Chem. Soc.,Dalton Trans. (2004) 3997;(i) H. Hadadzadeh, A.R. Rezvani, G.P.A. Yap, R.J. Crutchley, Inorg. Chim. Acta358 (2005) 1289;(j) L.M. Toma, D. Armentano, G.D. Munno, J. Sletten, F. Lloret, M. Julve,Polyhedron 26 (2007) 5263.

[13] W.M. Teles, N.L. Speziali, C.A.L. Filgueiras, Polyhedron 19 (2000) 739.[14] (a) M. Graf, H. Stoeckli-Evans, Acta Crystallogr., Sect. C 50 (1994) 1461;

(b) E.C. Constable, A.J. Edwards, D. Phillips, P.R. Raithby, Supramol. Chem. 5(1995) 93;(c) M. Koman, Z. Baloghov’a, D. Valigura, Acta Crystallogr., Sect. C 54 (1998)1277;(d) Y. Yamada, Y. Miyashita, K. Fujisawa, K.I. Okamoto, Bull. Chem. Soc. Jpn. 73(2000) 1843;(e) D. Hagrman, P. Hagrman, J. Zubieta, Inorg. Chim. Acta 212 (2000) 300;(f) E. Burkholder, J. Zubieta, Chem. Commun. (2001) 2056;(g) J.K. Bera, C.S. Campos-Fernandez, R. Clerac, K.R. Dunbar, Chem. Commun.(2002) 2536;(h) C.J. Kuehl, R.E. Da Re, B.L. Scott, D.E. Morris, K.D. John, Chem. Commun.(2003) 2336;(i) E. Burkholder, V. Golub, C.J. O’Connor, J. Zubieta, Inorg. Chem. 42 (2003) 6729.

[15] A. Escuer, T. Comas, J. Ribas, R. Vicente, X. Solans, C. Zanchini, D. Gatteschi,Inorg. Chim. Acta 162 (1989) 97.

[16] R.R. Ruminski, C. Letner, Inorg Chim. Acta 162 (1989) 175.[17] R.R. Ruminski, J.L. Kipling, Inorg. Chem. 29 (1990) 4581.[18] (a) M. Trivedi, D.S. Pandey, Q. Xu, Inorg. Chim. Acta 360 (2007) 2492;

(b) S.K. Singh, M. Chandra, S.K. Dubey, D.S. Pandey, Eur. J. Inorg. Chem. (2006)3954.

[19] B.J. Hathaway, in: G. Wilkinson, R.D. Gillard, J.A. McCleverty (Eds.),Comprehensive Coordination Chemistry, vol. 5, Pergamon Press, Oxford,1987, p. 533.

[20] L.S. Long, Y.R. Wu, R.B. Huang, L.S. Zheng, Inorg. Chem. 43 (2004) 3798.[21] J.D. Cruzan, L.B. Braly, K. Liu, M.G. Brown, J.G. Loeser, R.J. Saykally, Science 271

(1996) 59.

290 M. Trivedi et al. / Inorganica Chimica Acta 362 (2009) 284–290

[22] (a) S.S. Xantheas, J. Chem. Phys. 100 (1994) 7523;(b) S.S. Xantheas, J. Chem. Phys. 102 (1995) 4505.

[23] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond in Structural Chemistry andBiology, Oxford University Press, Oxford, 1999.

[24] G.M. Sheldrick, Bruker Analytical X-ray Division, Madison, WI, 1998.[25] (a) G.M. Sheldrick, SHELX-97; Programme for Refinement of Crystal Structures,

University of Gottingen, Gottingen, Germany, 1997;(b) PLATON, A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) C34.