Synthesis and magnetostructural properties of two crystalline phases of [CuBr2(sp)] (sp = (-)-sparteine)

Abstract

Two crystalline phases, 1a, 1b, of [CuBr2(SP)] complex (sp = (-)-sparteine) were obtained by direct synthesis. Crystal data: complex 1a, triclinic, P1, a = 7.4715(6) Angstrom, b = 7.7082(7) Angstrom, c = 9.1435(6) Angstrom, alpha = 97.429(6)degrees, beta = 112.808(5)degrees, gamma = 110.666(6)degrees

complex 1b, orthorhombic, P212121, a = 11.0563(7)(6),Angstrom, b = 11.9877(9) Angstrom, c = 12.8002(9) Angstrom. The molecular locality of Cu(II) ion is tetra-coordinated in each case and show close values of angle and bonds length for 1a, 1b. The UV-Vis and IR spectra of 1a and 1b are very similar. H-1 NMR spectra of 1a, 1b, are typical of Cu(II) paramagnetic complexes with broad lines in a range between 34 to -21 ppm. ESR spectra at 300 and 77 K of a polycrystalline sample for complex 1a show a broad signal with g = 2.036. Two species Cu(II) are developed by power saturation study. For 1b the ESR spectrum at 300 K is a singlet with composition Lorentzian 20%/Gaussian 80%. At 77 K the ESR singlet is still narrower with Lorentzian 90%/Gaussian 10%. The ratio areas is A(77)/A(300) = 5.22. All this features indicate clearly a weak ferromagnetic Cu...Cu exchange interaction. Standard magnetization measurements at low temperatures show that cupric ion pairs exchange interact weakly, obtaining J(1a) = \2.56\ cm(-1) and J(1b) = \1.93\ cm(-1). The crystallographic data correlate quite well with 1H NMR results such as: the line shapes, the relative areas and position of the signals, with the hydrogen atoms-spheres that interact with the central copper ion. (C) 2004 Elsevier B.V. All rights reserved.