HYBRIDIZATION EFFECTS ON THE SPECTRA AND STRUCTURE OF SOLVATOCHROMIC COPPER(II) CHELATES CONTAINING BETA-DIONES AND NITROGENOUS BASES

A series of copper(II) chelates containing a bidentate nitrogenous bas e (1,2-diamine or heteroaromatic alpha-diimine, enR), the anion of a b eta-dione, beta(-), and the ClO4- group, [Cu(enR)beta]ClO4, was prepar ed and characterized and the influence of hybridization of the nitroge n donor atoms on the spectra and structure of these compounds was asse ssed. The spectra (IR, ESR, electronic excitation) indicate that in th e absence of steric interference, the CuN2O2 chromophore attains squar e planar geometry. The ESR observables suggest appreciable covalency. Changes in the structure occur because of the susceptibility of the co ordinatively unsaturated [Cu(enR)beta](+) entity to covalent interacti ons, which are enhanced as the hybridization of the nitrogen donor ato ms changes from sp(3) to sp(2). The solvatochromism of the compounds i mplicates tetragonal distortions in strongly polar solvents and deform ed square pyramidal structures in the presence of weakly coordinating anions or molecules. Details of the structure of the [Cu(enR)beta](+) entity and the conformation and configuration of the 1,2-diamines were gathered from the X-ray study of (1-(2-aminoethyl)pyrrolidine)(pentan e-2,4-dionato) copper(II) perchlorate, [Cu(aep)acac]ClO4. The orthorho mbic compound crystallises in the Pna2(1) space group. The crystal dat a and the R value are: a = 24.5370(7), b = 8.4785(4), c = 7.6720(3) An gstrom, V-c = 1596(1) Angstrom(3), Z = 4, R = 0.0428 for 1099 observed unique reflections.