Hydrothermal Synthesis and Structure of a Mixed Valent Heteropoly-oxometallate Keggin Salt: [PMo4.27W7.73O6−40] [H3N(CH2)6NH2+3]3

The polyoxometallate Keggin (αtype) [PMo4.27W7.73O6− 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 groupC2/m(No. 12),a=10.336(9),b=20.097(5),c=13.276(6) Å,β=106.41(7)°,V cell=2645(3) Å3,Z=8,d calc=3.555 Mg m−3(CuKαradiation, 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).