Crystal and electronic structure of a protonated imidazole diphosphopentamolybdenum(VI) polyoxometalate:: (C4H7N2)4[HP2No5O23]•H3O-4.5H2O

The protonated imidazole diphosphopentamolybdenum polyoxometalate (C4H7N2)(4)[HP2Mo5O23].H3O.4.5H(2)O has been synthesized and its structure has been determined by single-crystal X-ray diffraction. This compound crystallizes in the triclinic crystal system, space group P(-1), a = 10.171(2), b = 11.839(2), c = 20.170(4) Angstrom, alpha = 75.69(3), beta = 84.56(3), gamma = 64.90(3)degrees, V = 2130.8(7) Angstrom(3), Z = 2 and R = 0.0329. The compound is composed of [HP2MO5O23](5-) clusters and C4H7N2+ and H3O+ cations as well as water of crystallization, and forms a supramolecular network structure through hydrogen bonds. The monoprotonated polyanions are held together by two strong hydrogen bonds [d(O...O) = 2.582(7) and 2.581(8) Angstrom]. Density functional theory (DFT) calculation has been carried out to investigate the electronic properties of the [HnP2Mo5O23]((6-n)-) (n = 0, 1,2) polyanions. Mulliken charges for all atoms have been analyzed. The results show that the negative charges delocalize over all types of oxygen atoms, and molybdenum and phosphorus atoms accept electrons from the oxygen atoms. The protonation affects the charge distribution, redox properties and relative stability of the polyanion; the non-protonated polyanion [P2Mo5O23](6-) can be more easily reduced.