Cobalt-containing polyoxometalates exhibit catalytic performance for toxic chromium(vi) reduction using formic acid under mild conditions.

Theoretical calculations have been performed in order to study the stability of the low-spin hydridomethyl complexes HMCH 3 + for the first-row transition metals (M + ) Sc + -Cu + ). Originally experimental results have been rationalized by assuming a low-spin hydridomethyl complex as a stable intermediate in the reactions of methane with singly charged metal cations. Recently, theoretical studies showed that for some late transition metals of the first row (Fe + and Co + ) no stable low-spin insertion product could be located on the potential energy surface. For the early elements of this row (Sc + -V + ) the experimental cross section ratios σ(MH + )/ σ(MCH 3 + ) indicate that the elimination reactions for these cations proceed via a statistically behaved intermediate. Our CASPT2 calculations indeed confirm a stable hydridomethyl complex for these cations. The reason for the stability of the insertion complexes could be traced back to the relative position of the lowest lying low-spin s 0 d n state and the lowest lying low-spin s 1 d n-1 state in the electronic spectrum of the corresponding free transition metal cations. Further, an analysis of the wave function clearly reveals a correlation between the extent of the participation of the 4s orbital in the metal-ligand bonds and the experimentally observed dominance of the H 2 elimination over the other elimination reactions for the cations Sc + to Cr + . An explanation in terms of the frontier orbital approach is given.

Mechanistic aspects of the reaction of Co + with ammonia are investigated by ab initio calculations. The potential energy surface is explored at the CASSCF level. Relative stabilities of the various stationary points on the reaction path are obtained by applying the CASPT2 technique. Binding energies for the reaction products CoNH 3 + , CoNH 2 + , and CoH + are calculated to be 52.1, 66.7, and 51.5 kcal/mol, respectively. They correspond reasonably well with the relevant experimental values of 58.8 ( 5, 61.3 ( 2, and 46.6 ( 2 kcal/mol, respectively, falling just a few kcal/mol outside the error bars of the measurements. The HCoNH 2 + isomer of the CoNH 3 + adduct is confirmed to represent a local minimum on the potential energy surface. It is separated from the adduct by an energy barrier of 15 kcal/mol, and its formation from the reactants is just slightly exothermic by a few kcal/mol. The H 2 elimination is experimentally not observed as a consequence of a complex tight four center transition state at about 58 kcal/mol above the ground state asymptote. The CoNH 2 + and CoH + exit channels are energetically situated below this barrier. Due to the high threshold energy, both reaction products are formed directly by simple N-H bond fission without HCoNH 2 + acting as an intermediate.

Polyanionic cluster [β-As8V14O42(H2O)](4-) is well embedded in a large porous eight-membered cationic ring of the copper ligand, giving a stable host-guest supramolecular system. The assembly exhibits an efficient heterogeneous catalytic performance for the reduction of Cr(VI) using formic acid at ambient temperature.

¼ 1,3-bi(4pyridyl)-propane) have been constructed and characterized. The inorganic moieties of the three hybrids consist of 'hourglass-shaped' anionic clusters, composed of two reduced polymolybdenum phosphate units [P 4 V Mo 6 V O 28 (OH) 3 ] 9 {P 4 Mo 6 } bridged by one manganese ion. Preliminary experiments show that these hybrids, as a unique class of molecular catalyst, are highly active for promoting the inorganic electron transfer (redox) reaction of ferricyanide to ferrocyanide by thiosulphate with high rate constants under mild conditions. These catalysts maintain their structural identity both in solution and solid state and can be easily separated from the reaction solution for the next catalytic cycle.