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Chloride- and oxalate-bridged heterometallic [CuIICrIII] compounds with 2, 2′:6′, 2′′- terpyridine – the influence of the starting copper(II)salt

Enormous efforts are made in synthesizing of new homo- and heterometallic coordination polymers of 1D, 2D, and 3D structures. Incorporation of both organic and inorganic components in these compounds has created a new dimension in searching for functional materials that have desired structures and properties. In the design of heteropolynuclear complexes an important role belongs to the oxalate ion, C2O42−, because of its various possibilities of coordination to metal centers as well as its ability to mediate magnetic interactions between paramagnetic metal centres. Stable mononuclear anionic oxalate complexes such as tris(oxalato)metalate anions, [MIII(C2O4)3]3− (MIII = Mn, Cr, Fe, V), are often used as ligands toward another metal ion for the preparation of extended multifunctional systems. In addition, the introduction of organic ligands containing N- donors, into the metal–oxalate systems prevents the formation of highly insoluble oxalate species and, moreover, influences the nuclearity and topology of the metal centres and stabilizes their solid-state structures. Applying the layering technique, the deep green prismatic crystals of compound [Cu4(µ-Cl)3Cl2(terpy)4][Cr(C2O4)3]·9H2O (1) grew from the reaction of an aqueous solution of K3[Cr(C2O4)3]·3H2O and methanol solution containing CuCl2·2H2O and tridentate ligand 2, 2′:6′, 2′′-terpyridine (terpy). Interestingly, the crystal structure of 1 (space group P¯1) consists of the chloride-bridged tetranuclear cation of copper(II), [Cu4(µ-Cl)3Cl2(terpy)4]3+, the mononuclear [Cr(C2O4)3]3– anion and nine molecules of water of crystallization. Using the same technique, solvents and reactants, but using Cu(NO3)2·3H2O instead of chloride salt, green prismatic crystals of complex salt [Cu(H2O)3(terpy)][Cu(H2O)(terpy)(µ- C2O4)Cr(C2O4)2]2·7H2O (2), crystallizing in P21/c space group, are formed. The structure 2 contains one symmetrical mononuclear [Cu(H2O)3(terpy)]2+ cation, two symmetry-equivalent oxalate-bridged heterodinuclear [Cu(H2O)(terpy)(µ-C2O4)Cr(C2O4)2]– anions and seven water molecules of crystallization. In addition to the single crystal X-ray diffraction study, characterization of the new complexes has been accomplished by means of the IR spectroscopy and thermal analysis.

coordination polymers ; building blocks ; X - ray diffraction

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