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The hydrolysis products of cis-diamminedichloroplatinum(II) 9. Chloride and bromide anation kinetics for some [PtII(N)2(OH2)2]2+ complexes and the structures of [PtIVBr4(N)2] ((N)2 = en, tn)1

1997; Elsevier BV; Volume: 257; Issue: 1 Linguagem: Inglês

10.1016/s0020-1693(96)05403-5

1873-3255

Kathryn Hindmarsch, Donald A. House, Mark M. Turnbull,

Radioactive element chemistry and processing

The rate of the first step in the chloride ion anation of [Pt(N)2(OH2)2]2+ (k−2, M−1s−1) has been measured spectrophotometrically (I = 1.0 M) for (N)2 = cis-(NH3)2, cis-(py)2, en, chxn, tn, Me2tn and trans-(NH3)2. Kinetic parameters at 25°C are: cis-(NH3)2, 102k−2 = 9.27 M−1s−1, ΔH≠ = 66.3 kJ mol−1, ΔS≠ = −42 J K−1mol−1; cis-(py)2, 20.0, 72.0, −17; en, 24.5, 58.8, −59; chxn, 21.4, 66.0, −36; tn, 34.4, 67.2, −28; Me2tn, 33.2, 57.4, −61; trans-(NH3)2, 151, 50.6, −72. Similar data for the bromide ion anation of cis-[Pt(py)2(OH2)2]2+ are: 97, 58.8, −48. Bromide ion anation rates for [PtBr(N)2(OH2)]+ (k−1, M−1s−1) have also been measured giving kinetic parameters (25°C, I = 1.0 M): cis-(NH3)2, 102 k−1 = 1.99 M−1s−1, ΔH≠ = 57.8 kJ mol−1, ΔS≠ = −84 J K−1mol−1; cis-(py)2, 2.10, 57.2, −85; en, 6.40, 63.5, −55; chxn, 9.72, 56.6, −17; tn, 9.25, 52.9, −87; Me2tn, 8.70, 54.8, −62; trans-(NH3)2; 12.6, 69.0, −31. These data also allow an estimation of the rate of bromide release from [PtBr2(N)2] (k1, s−1) with kinetic parameters (25°C, I = 1.0 M): cis-(NH3)2, 104 k1 = 4.25 s−1, ΔH≠ = 87.0 kJ mol−1, ΔS≠ = −17 J K−1mol−1; cis-(py)2, 15.8, 38.5, −93; en, 5.12, 70.0, −73; chxn, 17.4, 53.3, −42; tn, 6.05, 112, +70; Me2tn, 9.88, 109, +141; trans-(NH3)2, 15.2, 45.7, −69. Dilute solutions of [Pt(N)2(OH2)2]2+, in the presence of excess bromide ion and on long (weeks) exposure to air, slowly deposit orange crystals of [Pt(IV)Br4(N)2] on spontaneous evaporation. The structures of (N)2 = en (monoclinic, C2/c, a = 10.414(3), b = 8.356(2), c = 11.651(9) Å, β = 112.77(3)°, V = 934.8(8) Å3, Z = 4) and (N)2 = tn (orthorhombic, Pnma, a = 12.666(4), b = 9.789(5), c = 8.352(3) Å, V = 1035.5(7) Å3, Z = 4) have been determined by single crystal X-ray diffraction. The average Pt(IV)-Br and Pt(IV)-N distances are 2.455(5) and 2.04(2) Å, respectively.