Synthesis, properties and crystal structure of a Zn,Nb compound with homo- and heterodinuclear oxalate-bridged units – [{Zn(bpy)2}2(μ-C2O4)][Zn(bpy)2(μ-C2O4)NbO(C2O4)2]2·0.5bpy·7H2O: The impact of weak interactions on the crystal packing

A heterometallic Zn,Nb compound of the formula [{Zn(bpy)2}2(μ-C2O4)][Zn(bpy)2(μ-C2O4)NbO(C2O4)2]2·0.5bpy·7H2O (1) (bpy = 2,2′-bipyridine) has been synthesized by the reaction of the tris(oxalato)oxoniobate(V) anion, [NbO(C2O4)3]3− and [Zn(bpy)3]2+ in an aqueous solution, and characterized by IR and UV/vis spectroscopy, elemental and thermogravimetric analyses and X-ray single crystal diffraction method. The compound crystallizes in the triclinic P1¯ space group with a = 15.9060(9), b = 16.0804(9), c = 21.5892(12) Å, α = 69.504(4), β = 82.598(5), γ = 86.012(5)°, V = 5127.5(5) Å3, and Z = 2. The molecular structure consists of three dinuclear oxalate-bridged units, one homodinuclear ZnIIZnII and two heterodinuclear ZnIINbV units, seven water molecules and half of a bipyridine molecule. Zinc atoms are in all units octahedrally surrounded by four nitrogen atoms from the bipyridine ligands and by two oxygen atoms from the bridging oxalate groups. Niobium atoms in the two mixed ZnIINbV units adopt a pentagonal bipyramidal coordination formed by six oxygen atoms from the oxalate groups and one oxo-oxygen atom. Weak interactions, primarily hydrogen bondings and π–π stacking interactions, influence greatly the supramolecular motifs recognized in the crystal packing. Thermal decomposition of the title compound resulted in the formation of the mixed-metal Zn3Nb2O8 oxide phase.