Complexes containing CuOaCu Bridges

In the mcthoxy-complex (77) the metal has a distorted square-pyramidal co-ordination the basal sites are occupied by two bridging oxygen atoms, a nitrogen, and a chlorine atom, the Cu-N and Cu-Cl distances being 2.01(1) and 2.265(4) A. The apical position contains the chlorine atom of an adjacent dimeric unit the Cu-Cl(apical) distance of 2.944(4) A is rather long. The Cu-Cu distance between metal atoms in different dimers is 2.80 A, rather shorter than the corresponding value of 3.02 A between metal atoms in the same dimer. 

The metal co-ordination in the pyridine oxide complexes (78) and (79) shows interesting differences. In (78) the metal adopts a distorted square-pyramidal configuration. The apical Cu-CI distance of 2.354(3) A is longer than the corresponding basal distance of 2.258(3) A, and the terminal Cu-O bond of 1.925(5) A is shorter than those involved in the bridging unit. The basal O3CI unit is planar to 0.2 A, with the metal displaced from it by 0.44 A. The crystal structure of (79) contains two independent 

400(1) and 2.454(1) A in the other, are rather irregular, as are the corresponding Br-Cu-Br angles of 118.6(1) and 134.7(1) . The complex (79) is unusual in that it does not belong to one of the twelve recognized structural types of pyridine oxide-copper(n) complexes. 

Interest in the constraints imposed by chelate ring formation on the coordination at the metal, and the correlation of structural and magnetic properties, has led to the determination of the structures of the salicylidene-imine complexes (80)—(83). In (80), (81), and (82) the CuO Nj units 

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