A Fluxional Cu I N 2 O 2 Core: Binding of a Keto Oxygen Atom to Cu I and Ag I

[Cu(2‐acetylpyridine) 2 ]ClO 4 ( 1 ), characterised here, has a novel Cu I N 2 O 2 core in the solid state. Variable‐temperature 1 H NMR studies show that the two chelate rings open up in solution at room temperature and the keto oxygen atoms dangle freely. As the temperature is lowered, the O atoms tend to bind to the metal atom. The corresponding silver( I ) complex, [Ag(2‐acetylpyridine) 2 ]ClO 4 ( 4 ), characterised by single‐crystal X‐ray crystallography, has an Ag I N 2 core in the solid state as well as in solution. Thus, while 1 is fluxional, 4 is not. In cyclic voltammetry, complex 1 displays a quasireversible Cu II/I couple with a half‐wave potential of 0.40 V vs. SCE. Complex 1 is easily oxidised by air and H 2 O 2 in methanol to give rise to a dinuclear copper( II ) complex where the ligand framework is not simple acetylpyridine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)