Tungstorhenate heteropolyanions. 2. Synthesis and characterization of enneatungstorhenates(V), -(VI), and -(VII)

The tungstorhenate(V) heteropolyanion [W₉ReO₃₂]^5- has been isolated as guanidinium and cesium salts from reaction of [ReO₂(PPh₃)(py)₃]⁺ with sodium tungstate. Crystallographic analysis of black Cs₅[W₉ReO₃₂]·3H₂O [triclinic, P1 or P1̄; a = 10.194(1), b = 11.503(2), c = 9.682(1) Å; α = 100.55(1), β = 115.81(1), γ = 99.13(1)°; Z = 1], based on 3743 reflections, shows the anion to be isostructural with decatungstate, [W₁₀O₃₂]^4-. Refinement in P1̄ led to reliability indices R = 0.084, R_w = 0.046. Electrochemical investigation revealed the existence of Re^VI and Re^VII analogues, which were hydrolytically unstable in aqueous solution but which were isolated as crystalline tetra-n-butylammonium and tetra-n-heptylammonium salts, respectively, from nonaqueous solvents. The tetra-n-butylammonium salts of [W₉Re^VIO₃₂]^4- and [W₁₀O₃₂]^4- were shown to be isomorphous by X-ray powder diffraction. Simulation of the Q-band ESR spectrum of [W₉Re^VIO₃₂]^4- (polycrystalline solid solution in [W₁₀O₃₂]^4-) gave g_x = 1.69(1), g_y = 1.66(1), g_z = 1.730(2) and 10⁴A_x(^185,187Re, I = ⁵/₂) = (−)252(10), 10⁴A_y = (−)398(10), 10⁴A_z = (−)653(5) cm^-1. The orthorhombic ESR spectrum proves that the Re atom occupies one of the eight equivalent “equatorial” sites in the decatungstate structure.