Vibrational spectra of halogen-bridged systems. Part III. The infrared spectra (450—80 cm.–1) of binuclear palladium, platinum (M2X4L2), and rhodium (Rh2X2L4) complexes
Infrared absorption frequencies (450–80 cm.–1) are given for 46 palladium and platinum compounds of the type M2X4L2(X = Cl, Br, l; L = neutral donor ligand), and for some halogen-bridged rhodium compounds, Rh2X2L4. The predicted number of absorptions due to terminal and bridge bond stretching vibrations has been found, and their ranges are suggested for use as correlations. The lower of the two bridge modes for the platinum and palladium complexes is markedly sensitive to change of L, varying in a similar order (that of the trans-effect of L) to that previously found for mononuclear complexes cis-[PtX2L2]. A clear distinction can be made, on the basis of halogen-sensitive bands, between halogen-bridged and sulphide-bridged complexes M2X4(SR2)2. Assignments for ν(M—L)(L = S, P, As, Te) are discussed. For the rhodium complexes, the number of bands found in the ν(Rh—X)b region allows distinction to be made between planar and bent bridges.