Mono- and Binuclear Copper Complexes with N₂O₂ Schiff-Base Ligands. Agnete la Cour, Oren P. Anderson, Susie M. Miller, Department of Chemistry, Colorado State University, Fort Collins, Colorado, USA, Rita Hazell, Department of Chemistry, Aarhus University, (rhus, Denmark, and Jens Z. Pedersen, Department of Chemistry, Odense University, Odense, Denmark.

We have prepared a series of copper complexes with symmetric tetradentate N₂O₂ Schiff-base ligands incorporating pyrazole and bridged by polymethylene chains. The influence of the number, n, of methylene units of the bridge has been investigated in the solid state by X-ray crystallography and in solution by spectroscopic methods (epr, uv/vis/nir). Cu(II) complexes with n = 2 (complex A) or 3 (complexes B, C and D) are mononuclear, and a complex (E) with n = 4 is a mixed-valence Cu(1.5)--Cu(1.5) complex. The structure of E reveals a Cu--Cu distance of 5.342 (, and the seven-line epr spectrum yields parameters typical of mixed-valence copper complexes: a g₍ value of 2.385 and a very small value of the coupling constant, A₍, of 8.1 x 10^-3 cm^-1. The corresponding values of the epr parameters for the typical mononuclear Cu(II) complexes are: g₍/A₍ 2.208/20.6 x 10^-3 cm^-1 (A), and 2.252/18.6 x 10^-3 cm^-1 (B). In ethanol the four-coordinate n = 3 complex C is in equilibrium with the five-coordinate complex D, the fifth ligand being an ethanol molecule; we have obtained the structures of both C and D using crystals grown from such a solution.