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Complex [Cu(II)(Br)(PhCO2)(Sp)] 1 is obtained starting from copper(0), (-)-sparteine (sp) and benzoyl bromide. 1 Crystallizes in the monoclinic space group P2(1) with a = 14.8857(11), b = 8.9257(9), c = 17.4456(14) angstrom, beta = 111.689(5)degrees, and Z = 4. The UV-vis spectrum is characteristic of Cu(II) complexes with tetragonally distorted square pyramidal geometry. The far IR spectrum of 1 shows characteristic vibrations of Cu-Br (239 cm(-1)), Cu-N (437 cm(-1)) and Cu-O (466 cm(-1)) bonds. The H-1 NMR broad chemical shifts of 1 integrated for a total of 31 protons and are typical of Cu(II) complexes. ESR spectra of polycrystalline 1 at 77 and 300 K show axial spectra with areas in the ratio A(77)/A(300) = 4.02, suggesting a very weak Cu-Cu ferromagnetic interaction. Complex 1-doped with Zn(II) gives hfs with hyperfine interaction constant value A(parallel to) = 112.45 X 10(-4) cm(-1). The magnetization vs temperature data in the 2-299 K range, show that cupric ion pairs interact through a small antiferromagnetic Heisenberg exchange energy-JS(1)(.)S(2) with a ground singlet state S = 0, separated by J = -1.3 cm(-1) from the excited triplet state S = 1. The sign of the very weak interchange interaction constant, J, does not agree with the ESR spectra areas ratio of 1 at 77 and 300 K, which is a more accurate quantification of the weak ferromagnetic interaction Cu-Cu through the space. (c) 2005 Elsevier B.V. All rights reserved. |
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