ORGANIC-INORGANIC CHARGE-TRANSFER SALTS BASED ON THE BETA-[MO8O26]4- ISOPOLYANION - SYNTHESIS, PROPERTIES AND X-RAY STRUCTURE

The complex reaction between the organic electron donor N,N,N',N'-tetramethyl-p-phenylenediamine (tmpd) and the inorganic acceptor [Mo6O19]2- in air has been investigated. Conversion of the inorganic polyanion to beta-[Mo8O26]4-, as well as protonation and/or oxidation of the organic base are possible. Different charge-transfer salts of the type beta-[Htmpd]x[tmpd]4-x[Mo8O26] and beta-[Htmpd]x[tmpd]3-x[HMo8O26] have been isolated and characterized. They contain positively charged tetramethyl-p-phenylenediamine molecules which may be present, simultaneously or not, as monoprotonated units (Htmpd+) or radical cations (tmpd+). According to optical and magnetic properties, isolated radicals or tightly bound dimers have been found. The X-ray crystal and molecular structure of beta-[Htmpd]2[tmpd]2[Mo8O26] has been solved by the heavy-atom method and refined to a final R = 0.057 for 3129 reflections with l greater-than-or-equal-to 3-sigma(l); monoclinic, space group P2(1)/c with a = 11.607(5), b = 24.830(9), c = 11.047(4) angstrom, beta = 106.82(3)-degrees and Z = 2. The beta-octamolybdate polyanion has the well known Lindqvist structure. The radical cations form eclipsed dimeric units with an intradimeric distance 3.35 angstrom and do not interact with the polyanion. The protonated molecules are isolated from one another, but linked to the polyanion through bifurcated hydrogen bonds of 2.87 and 3.11 angstrom.