Structural and spectroscopic studies of cobalt(II) complexes incorporating the bidentate phosphine ligand Ph 2PCH 2Si(CH 3) 2CH 2PPh 2

Abstract

A series of cobalt(II) complexes of general formula [CoX 2L 2] (X = Cl, Br, I, NO 3, ClO 4, NCS; L 2 = Ph 2PCH 2Si(CH 3) 2CH 2PPh 2) 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 [CoBr 2L 2] 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 d 7 metal ion in each case, with the v 2 and v 3 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(L 2)] complex exhibits N-bonded thiocyanate groups.