STRUCTURAL AND SPECTROSCOPIC STUDIES OF COBALT(II) COMPLEXES INCORPORATING THE BIDENTATE PHOSPHINE LIGAND PH2PCH2SI (CH3)(2)CH2PPH2

A series of cobalt(II) complexes of general formula [CoX2L2] (X = Cl, Br, I, NO3, ClO4, NCS; L-2 = Ph2PCH2Si(CH3)(2)CH2PPh2) have been synth esised and characterised by electronic and infrared spectroscopy and b y magnetic moment studies. The bidentate phosphine ligand is an analog ue 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)degrees. A range of evidence supports the existence of tetrahedral geometry abo ut 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 nu(2) and nu(3) transitions clearly visibl e. Calculations of D-q and B', the RACAH parameter, have been performe d for each complex; the relative magnitudes of B' indicate that the me tal-phosphorus bonds are of increased covalency in comparison with Co( dppp) analogues. Magnetic moment studies show values of mu(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 complexe s are bound in monodentate fashion, while the [Co(NCS)(2)(L-2)] comple x exhibits N-bonded thiocyanate groups. (C) 1997 Elsevier Science Ltd.