Structural and spectroscopic studies of cobalt(II) complexes incorporating the bidentate phosphine ligand Ph2PCH2Si(CH3)2CH 2PPh2

Article abstract of DOI:10.1016/S0277-5387(97)00273-8

A series of cobalt(II) complexes of general formula [CoX₂L²] (X = Cl, Br, I, NO₃, ClO₄, NCS ; L² = Ph₂PCH₂Si(CH₃)₂CH ₂PPh₂) have been synthesised and characterised by electronic and infrared spectroscopy and by magnetic moment studies. The bidentate phosphine ligand is an analogue of 1,3-bis(diphenylphosphino)propane (dppp). X-ray analysis of the [CoBr₂L²] complex proves tetrahedral geometry at the metal centre with the bidentate phosphine exhibiting a bite angle of 101.54(6)°. A range of evidence supports the existence of tetrahedral geometry about the metal in all the complexes in both the solid state and solution. Electronic spectroscopy is diagnostic for the tetrahedral d⁷ metal ion in each case, with the v₂ and v₃ transitions clearly visible. Calculations of D_q and B′, the RACAH parameter, have been performed for each complex ; the relative magnitudes of B'′ indicate that the metal-phosphorus bonds are of increased covalency in comparison with Co(dppp) analogues. Magnetic moment studies show values of μ_B in the range 4.4-4.9 B.M., as expected for tetrahedral cobalt(II). IR studies show that the nitrate and perchlorate ions in the respective complexes are bound in monodentate fashion, while the [Co(NCS)₂(L²)] complex exhibits N-bonded thiocyanate groups.