The Hydrolysis Kinetics of ds-diamminedichloroplatinum(II). 10. Activation Volumes for Halide Anation of Some czs-[Pt(N)2(OH2)2]2+ Systems

Abstract For the following equations relating to the aquation and anation processes of cisplatin and similar squareplanar platinum(II) diamine complexes: rate constant (k-2, Μ-1 s-1,25°C), activation enthalpy (ΔΗ#, kJ mol-1) , activation entropy (ΔS#, JΚ-1 mol-1) and activation volume (ΔV#, cm3 mol-1) data have been found for the bromide anation of cis- [Pt(N)2(OH2)2]2+ where (N)2 = tn, en, cis-(NH3)2, trans-(NH3)2, Me2tn, chxn; CJS-(NH3)2: k-2 = 0.45, ΔH# = 68, ΔS# = -25, trans-(NH3)2: 4.23,56, -44, chxn: 1.13, 70, -9, Me2tn: 1.53, 65, -24, en: 1.29, 71, -5, ΔV# = -5.3, tn: 1.86,68, -12, ΔV# = -7.4. Further activation volumes (ΔV#, cm3 mol-1) have been determined for selected k-1 and k-2 bromide or chloride anation data. k-1(cm3 mol-1, CI-): en -7.4. k-1(cm3 mol-1, Br-): cis-(NH3)2-11, en -9.4, tn -7.66. k-2(cm3 mol-1, CI-): cis-(NH3)2-5.1, en -5.7, tn -5.8. For all kx above where ΔV# has been measured, values lie in the range -4 to -11 cm3 mol-1 and apart from two exceptions ΔS# is negative in 36 cases implying an associative mechanism for the substitution process at square-planar platinum(II) centres.