Three 2,2′-biimidazole transition metal complex-supported octamolybdates derived from hexamolybdochromate

Abstract

Three octamolybdate compounds, namely [Cu(H2biim)2]2[β-Mo8O26{Cu(H2biim)2}2][β-Mo8O26] (1), [{Fe(H2biim)2(Hbiim)}2(γ-Mo8O26)]·5H2O (2), and [{Co(H2biim)2(Hbiim)}2(γ-H2Mo8O26)]·5 H2O (3) (H2biim = 2,2′-biimidazole) have been hydrothermally synthesized from the reaction of mixtures of hexamolybdochromate ({CrMo6}), transition metal, and H2biim in acetate buffer solution, and characterized by physico-chemical and spectroscopic methods. They represent the first examples of the conversion of hexamolybdochromate to octamolybdate. Single-crystal X-ray diffraction analysis reveals that compound 1 is composed of a β-[Mo8O26]4− polyoxoanion bi-supported by two [Cu(H2biim)2]2+ complex cations, an isolated β-[Mo8O26]4− anion, and two [Cu(H2biim)2]2+ complex cations. The copper complex cations are situated at two different sites and associate with β-[Mo8O26]4− anions to give 2D layers, which are further packed into a 3D framework via strong hydrogen bonding interactions. Compounds 2 and 3 are isostructural, and contain a γ-[Mo8O26N2] unit and two symmetrical {M(H2biim)2(Hbiim)} (M=Fe or Co) fragments grafted onto the polyoxoanion through Mo–N bonds. The two compounds also exhibit 3D supramolecular frameworks involving hydrogen bonding interactions.