Raman spectroscopic investigations of dinuclear gold ylide complexes; further relationships of Au-Au bond lengths versus Au-Au stretching frequencies

Raman spectroscopic data have been collected for the singly bonded Au(II) halogen complexes Au-2(MTP)(2)X-2 (MTP = CH2P(S)Ph-2(-); X = Cl, Br, I) with bands at 157, 125, and 105 cm(-1) for Cl, Br, and I, respectively, being assigned to nu(Au-Au). The corresponding Au-X vibrations have also been identified. The trend observed in the shift of nu(Au-Au) with changes in halogen is comparable to the situation with the analogous [Au(CH2)(2)PPh2](2)X-2 series reported by Clark et al., for which the corresponding values are 162, 132, and 103 cm(-1). In both cases, these data show a trend toward decreasing Au-Au and Au-X stretching frequencies with increasing halide size. Interestingly, a plot of r(Au-Au) versus nu(Au-Au) for the six oxidized complexes does not yield a single line, but instead two nearly parallel lines. The general relationship between metal-metal bond lengths and stretching vibrations for the six complexes are compared with other single-bonded dinuclear complexes in the light of various proposed empirical relationships. (C) 2000 Elsevier Science S.A. All rights reserved.