From molecules to aggregates: crystal structures of molybdenum binuclear complexes

The new complexes [MoCl(η3-C3H5)(CO)2(H2biim)], [NnBu4][{Mo(η3-C3H5)(CO)2}2(μ-Cl)2(μ-OMe)], and [PPN][{Mo(η3-C3H5)(CO)2}2(μ-Cl)3] (PPN is Ph3PN+PPh3) were synthesized and the two binuclear compounds were characterized by single-crystal X-ray diffraction. Although an anion [{Mo(η3-C3H5)(CO)2}2(μ-Cl)3]− has been described in the literature, being formed both in solution and in the solid, another conformer was present in the crystal of [PPN][{Mo(η3-C3H5)(CO)2}2(μ-Cl)3], exhibiting an eclipsed arrangement of the allyl groups. The same arrangement was found for the [{Mo(η3-C3H5)(CO)2}2(μ-Cl)2(μ-OMe)]− anion. Cyclic voltammetry data show that the eclipsed conformer of [{Mo(η3-C3H5)(CO)2}2(μ-Cl)3]− remains in solution, as the other one, with staggered allyl groups, is formed when dissolving the parent compound [MoCl(η3-C3H5)(CO)2(NCMe)2] and exhibits a distinctive pattern. Density functional theory (DFT) calculations showed the two conformers to have very similar energies, both for this and for the related anion [{Mo(η3-C3H5)(CO)2}2(μ-Cl)2(μ-OMe)]−. The crystal structure of [PPN][{Mo(η3-C3H5)(CO)2}2(μ-Cl)3] exhibits double channels formed by the PPN cation which are occupied by chains of the binuclear anions.