Hydrothermal synthesis and structure of a mixed valent heteropoly-oxometallate keggin salt:[PMo_4.27W_7.73O^6-₄₀][H₃N(CH ₂)₆NH²⁺₃]₃

Abstract

The polyoxometallate Keggin (atype) [PMo_4.27W_7.73O^6-₄₀] [H₃N(CH₂)₆NH²⁺₃]₃, involving molybdenum and tungsten present in both V and VI oxidation states, has been synthesized under hydrothermal conditions and its structure determined by single crystal X-ray analysis. Black platelet crystals are formed in the monoclinic system, space group C2/m(No. 12), a=10.336(9), b=20.097(5), c=13.276(6) Å, β=106.41(7)°, V_cell=2645(3) ų, Z=8, d_calc=3.555 Mg m^-3(CuKaradiation, 2θ_max=144°, R(F)=6.56 for 1729 reflections). Due to its location at the origin (2/msite), the anion is found to be disordered, its four independent metal sites occupied with molybdenum and tungsten atoms; a significant preferred localization of the molybdenum on two sites is also reported. The structure has a lamellar organization formed from alternating organic-inorganic planes with their normal parallel toc. A study by ESR has proven the presence of paramagnetic Mo/W(V) in the compound with the observation of a strong signal (g=1.983).