Construction of organic-inorganic hybrid molybdophosphonate clusters with copper-bipyridine

An organic-inorganic hybrid polyoxomolybdate with formula as [Cu(2,2'-bpy)(H2O)]2[Cu(2,2'-bpy)(H2O)3][(O3PCCH3(OH)PO3)2Mo(VI)4O11(H2O)2]·7H2O (1) (2,2'-bpy=2,2'-bipyridine) has been successfully synthesized constructing by diphosphonate H2O3PC(CH3)(OH)PO3H2 (1-hydroxyethylidene-1,1-bisphosphonic acid, noted as HEDP or etidronate) under conventional aqueous solution. 1 was characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric (TG) analysis, and X-ray photoelectron spectroscopy (XPS). Each anion cluster of 1 can be regarded as the fusion of two [{Cu(2,2'-bpy)(H2O)}(O3PCCH3(OH)PO3)Mo(VI)2O6](2-) subunits with an additional six-coordinated [Cu(2,2'-bpy)](2+) coordination cation linking on one side and there exist weak π-π interactions among the bipyridine groups. The XPS spectra indicate that the oxidation states of Mo and Cu in 1 are +6 and +2, respectively. Photoluminescence properties of 1 and the free 2,2'-bipyridine ligand have been both analyzed, showing that the presence of ligand-to-metal-charge-transfer (LMCT) transitions and metal-ligand coordination have an important effecting on the photoluminescence.