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 Au2(MTP)2X2 (MTP=CH2P(S)Ph2−; X=Cl, Br, I) with bands at 157, 125, and 105 cm−1 for Cl, Br, and I, respectively, being assigned to ν(Au–Au). The corresponding Au–X vibrations have also been identified. The trend observed in the shift of ν(Au–Au) with changes in halogen is comparable to the situation with the analogous [Au(CH2)2PPh2]2X2 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 ν(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.