Discrete bimetallic Co(II) phosphinate complexes supported by 2,6-dimesitylphenylphosphinate ligand

Reactions of Co(II) sources with 2,6-dimesitylphenylphosphinate were conducted in two phase (toluene/water) solvent systems. The presence of small coordinating anions (X) and neutral ligands (L) was found to be a determining factor for the outcome of these reactions. When both were present, discrete bimetallic complexes of the type [X-Co-μ-(DmpP(H)O2)3-Co-L] were produced (X = Cl−, L = p-fluorobenzylnitrile (1a), p-cyanoaniline (1b), acetonitrile (1c), or pyridine (1d); X = Br−, L = DMF (2); X = thiocyanate, L = H2O (3)). In these complexes both Co(II) centers are in distorted tetrahedral ligand geometries that are formed by the three oxygens of the bridging phosphinate ligands and either X or L ligands. In the absence of a coordinating anion and with p-cyanoaniline as a small neutral ligand bimetallic cation [p-NH2-C6H4-CN-Co-μ-(DmpP(H)O2)3-Co(H2O)3]+ (4) was obtained. Cation 4 contains a tetrahedral and an octahedral Co(II) center; an additional phosphinate serves as a counterion and is attached to the cation via hydrogen bonding to water molecules coordinated to the octahedral cobalt center. Complexes 1a–d, 2, 3, and 4 [DmpP(H)O2] were characterized by elemental analyses, spectroscopic (UV–Vis and IR) and magnetic measurements, and by single crystal X-ray diffraction experiments. When Co(BF4)2 was reacted with two equivalents of DmpP(H)O2− with no other neutral ligands present, slow evaporation of the reaction mixtures produced blue powdery solids. In one of such reactions several large blue crystals were produced and analyzed by single crystal X-ray diffraction. The compound was characterized as trimetallic complex [((H2O)DmpP(H)O2-Co-(μ-DmpP(H)O2)2)2Co] (5). The formation of compound 5 suggests that under selected conditions formation of oligomeric/polymeric compounds with the general formula “Co(DmpP(H)O2)2” may be possible.