THE STRUCTURAL EFFECTS OF STERIC OVERCROWDING IN BIS(TRICYCLOHEXYLPHOSPHINE)PLATINUM(II) COMPLEXES - THE CRYSTAL AND MOLECULAR-STRUCTURE OF TRANS-PTBR2(PCY3)2

The crystal and molecular structure of trans-PtBr2(PCy3)2 has been determined. Crystals are triclinic, space group P1, a = 10.038(1), b = 10.212(1), c = 10.775(1) Å, α = 113.18(1), β = 109.81(1), γ = 91.51(1)°, V = 938.8 Å3, Z = 1 and Dc = 1.620 g cm-3. Refinement, based on 4021 reflections with I > 3σ(I) converged at R = 0.032. The structure consists of discrete trans-PtBr2(PCy3)2 molecules in which steric overcrowding is indicated by a long PtP bond length of 2.345(1) Å and Br...C and Br...H non-bonded contact distances significantly smaller than the sum of the van der Waals' radii of the respective atoms. A comparison of structural parameters for trans-PtXY(PR3)2 (X, Y = H, Cl, Br or I; R = Me, Et or Cy) permits identification of the modes of the steric distortion in these complexes. For the symmetrical complexes (X = Y), PtP bond extension is found to be the principal type of distortion in response to unfavourably short intramolecular X...H and X...C non-bonded interactions that arise in these molecules on account of overcrowding. © 1990.