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The iar-infrared spectra (170-460 cm.-l) of 43 complexes of the types cis-and trans-[PtX,L,] (X = C1 or Br; L = neutral ligand), and trans- [PtXR(PEt,),] (X = C1 or Br; R = H, Me, or Ph) have been recorded, and the metal-halogen stretching frequencies v(Pt-C1) and v(Pt-Br) assigned. v(PK1) falls in the range 340-269 cm.-l and v(Pt-Br) 251-184 cm.-l. The wide ranges of v(Pt-C1) and v(Pt-Br) indicate considerable dependence of the platinum-halogen bond strength on L, but this is found only in the ciscomplexes, i.e., when L is in transposition to the halogen. In the transcomplexes v(Pt-X) is almost insensitive to L. The most important factor determining the platinum-halogen bond strength is the electronegativity of L but there are anomalies which might be attributed to x-bonding in the Pt-L bond. There is a rough inverse correlation between the trans-directing influence of L and v(Pt-X), with the notable exception of [PtX,. cyclooctadiene] in which v(Pt-X) is relatively high although the olefin has a high trans-effect. This accords with the view that there are inductive and mesomeric mechanisms whereby a ligand can exert its trans-effect. trans-Bond weakening is to be associated only with the inductive mechanism, whereas olefins exert their trans-effect mainly by the mesomeric mechanism.

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The equilibrium (Ph3P)AuX + (n -I)Ph3P % (Ph3P),Au+ + X' was studied in nitrobenzene solution and evidence for the occurrence of tricoordinate (Ph3P)2AuX was obtained. The results indicate that %.bonding of phosphine to gold(1) is much stronger than that of phosphine to silver(1). Attempts to prepare tricoordinate complexes from di(tertiary)phosphine or arsine failed. Chloro-and bromo(triphenylstibine)gold(I) have been prepared. The dipole moments of Ph3-MAuX, where M = or As, and X = C1, Br, and I, or M = Sb and X = Br have been determined. Metal-ligand stretchibg frequencies are compared.