Crystal structures of dichlorobis(triphenylphosphine oxide)zinc(II) and dibromobis(triphenylphosphine oxide)zinc(II) and an EPR study of manganese(II) in dibromobis(triphenylphosphine oxide)zinc(II)

Article abstract of DOI:10.1021/ic00138a051

The structures of ZnX₂(OPPh₃)₂ (X = Cl, Br) have been determined. Crystals of the chloride are orthorhombic, with a = 32.95 (1) ?, b = 20.702 (6) ?, c = 9.792 (3) ?, space group Fdd2, and Z = 8; those of the bromide are triclinic, with a = 10.188 (1) ?, b = 9.987 (1) ?, c = 11.189 (1) ?, α = 114.58 (1)°, β = 121.29 (1)°, γ = 89.82 (1)°, space group P1, and Z = 1. The environment of the metal atom in each case approximates to a tetrahedral arrangement of two oxygens and two halide ions. A single crystal of the bromide doped with manganese in the zinc site was studied by electron paramagnetic resonance at room temperature, and its spin Hamiltonian parameters are reported, notably D = 0.523 cm^-1 and E = 0.133 cm^-1. The high value of D for the bromide relative to that of the chloride is in keeping with the general observation that D increases in the order of Cl < Br < I for a given class of compound, which is also the order of increasing electron release from the ligand. The orientations of the principal values of D found for the bromide are used as a basis for assigning their most probable orientations in the chloride, where there are two magnetically independent molecules. We observe that the principal axes of D avoid the bond directions, D_x lying along or close to the bisector of the XMnX direction (X = Cl, Br) and D_y and D_z lying close to the OMnX planes (X = Cl, Br). Chlorine, being the more electronegative, more strongly influences the direction of D_y in the chloride than does bromine in the bromide. But in the latter the π-electron density of a phenyl group may be a contributory factor.