Synthesis and characterization of acetonitrile-ligated transition-metal complexes with tetrakis(pentafluorophenyl)borate as counteranions

Complexes with the general formula [M^II(NCCH₃) ₆][TPFB]₂ [M = Cr, Fe, Co, Ni, Cu, Zn, (TPFB)^- = tetrakis-(pentafluorophenyl)borate] were synthesized and characterized both in the solid state and in solution. According to the spectroscopic data, [TPFB] can be considered as a truly noncoordinating anion. The NCCH₃ ligands are lost if the samples are kept at room temperature for extended periods of time. Thermolysis leads to the loss of the NCCH₃ ligands and decomposition of the anion above 100°C with the formation of MF₂. It has to be noted that distortion of the geometries of the Cu^II, Zn^II and Cr^II complexes occurs, as evidenced by infrared spectroscopy. The complexes can be easily prepared and obtained in high yields and are moderately sensitive to air.