Oxidation of coordinated ethylenediamine in platinum(IV) complexes with bromine. Crystal structures of [Pt(en)Py₂Br₂]Br₂ · H₂O, [Pt(HN-C(O)-C(O)-NH)Py₂Br₂] · H₂O, and [Pt(en)PyBr₃]NO₃

Abstract

Heating of an aqueous solution of [Pt(en)Py₂Cl₂]Cl₂ · 2H₂O (I) with KBr excess leads to the formation of [Pt(en)Py₂Br₂]Br₂ · H₂O (II). The interaction of a solution of II with bromine water results in the precipitation of polybromide ([Pt(en)Py₂Br₂]Br₂ · Br₂), which within a few days in the reaction solution partly transforms into oximide platinum(IV) complex, [Pt(HN-C(O)-C(O)-NH)Py₂Br₂] · H₂O (III). Complex [Pt(en)PyBr₃]Br · H₂O (IV) with an impurity of II was prepared by reacting KBr excess and the product of [Pt(en)Py₂]Cl₂ oxidation with chlorine in 0.05 N HCl. The action of HNO₃ on the solution of IV produced a nitrate derivative ([Pt(en)PyBr₃]NO₃, V). Complex IV, unlike II, does not react with bromine. The IR spectra of all the obtained compounds were recorded. Complexes II, III, and V were studied by X-ray crystallography. The crystals of II are monoclinic, space group P2₁/c, a = 15.640(2) Å, b = 9.345(1) Å, c = 14.167(2) Å, β = 102.63(1)°, V = 2020.5(5) ų, Z = 4, R _hkl = 0.033. The crystals of III are triclinic, space group P $\bar 1$, a = 7.108(1) Å, b = 10.946(1) Å, c = 11.020(2) Å, α = 83.63(1)°, β = 80.31(1)°, γ = 75.02(1)°, V = 814.4(2) ų, Z = 2, R _hkl = 0.033. In the near-planar five-membered chelate ring (torsion angle NCCN is 7°), the C-O distances (1.23(1) Å) correspond to double bonds; the C-C (1.53(1) Å) and C-N (1.31(1) Å), distances correspond to ordinary bonds. The crystals of V are monoclinic, space group P2₁/c, a = 8.306(2) Å, b = 8.995(2) Å, c = 20.231(4) Å, β = 97.48(2)°, V = 1498.6(6) ų, Z = 4, R _hkl = 0.037.