Nitrogen-14 magnetic resonance study of pyridine exchange in bis(pentane-2,4-dionato)dipyridine-cobalt(II) and -nickel(II) complexes

Abstract

A ¹⁴N n.m.r. study of the exchange of pyridine in trans-[M(acac)₂(py)₂] complexes (M = Co^II or Ni^II acac = 2,4-pentanedionato) is reported. When M = Co^IIk_ex(298 K)=(15 ± 2)× 10⁵ s^–1, ΔH^‡= 28 ± 2·5 kJ mol^–1 and ΔS^‡=–33 ± 17 J K^–1 mol^–1 and when, M = Ni^II, k_ex(298 K)=(9·8 ± 1·2)× 10⁴ s^–1ΔH^‡= 42 ± 3 kJ mol^–1, ΔS^‡=–9 ± 10 J K^–1 mol^–1. Kinetic parameters are discussed in terms of a solvent-exchange model involving solvent interactions outside the first co-ordination sphere in the activation process.