X-RAY STRUCTURES AND REDOX PROPERTIES OF COPPER(II) BIS(PYRAZOLE) COMPLEXES
MARTENS CF, SCHENNING APHJ, FEITERS MC, BERENS HW, VANDERLINDEN JGM, ADMIRAAL G, BEURSKENS PT, KOOIJMAN H, SPEK AL, NOLTE RJM
INORGANIC CHEMISTRY 34 (19): 4735-4744 SEP 13 1995

Abstract:
The copper complexes of bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl] amine (1) and its benzylated derivative (2) have been studied as single crystals by X-ray crystallography and as powders and solutions by a variety of techniques. [Cu(1). 2NO(3)] (C14H25CuN7O7 including 1 H2O, 3) crystallized in the monoclinic space group Pc (No. 7) with a = 8.1596(9) Angstrom, b = 31.164(2) Angstrom, c = 7.7966(9) Angstrom, beta = 94.75(2)degrees, V = 1975.7(3) Angstrom(3), and Z = 4 (structure refinement converged to R(F) = 0.066 and R(wF)(2) = 0.227); [Cu(1)ClO4 . C2H5OH]ClO4 (C16H29Cl2CuN5O9, 4) crystallized in the orthorhombic space group Pna2(1) (No. 33) with a = 13.3463(7) Angstrom, b = 10.3925(9) Angstrom, c = 17.511(1) Angstrom, V = 2432.1(3) Angstrom(3), and Z = 4 (refined to R(F) = 0.063 and R(wF) = 0.052); [Cu(2). 2NO(3)] (C21H29CuN7O6, 5) crystallized in the monoclinic space group C2/c (No. 15) with a = 28.719(2) Angstrom, b = 8.6043(6) Angstrom, c = 23.034(2) Angstrom, beta = 124.767(7)degrees, V = 4675.7(7) Angstrom(3), and Z = 8 (refined to R(F) = 0.042 and R(wF) = 0.034); [Cu .(2). C2H5OH . Y](ClO4)(n) (C48H78Cl4Cu2N10O20, 6) (Y = H2O, n = 2, or ClO4-, n = 1) crystallized in the monoclinic space group P2(1)/c (No. 14) with a = 10.9488(9) Angstrom, b = 17.030(2) Angstrom, c = 32.893(3) Angstrom, beta = 92.185(7)degrees, V = 6129(1) Angstrom(3) and Z = 4 (refined to R(F) = 0.104 and R(wF) = 0.119). In complexes 3, 4, and 6, the ligand coordinated Cu(II) with a T-shaped arrangement of the nitrogen donor atoms. Ethanol coordinated in one of the apical positions in complexes 4 and 6. The amine nitrogen moved from the basal plane in 3 to the apical position in 5, where the copper had square pyramidal coordination geometry. The largest difference between 4 and 6 was a lengthening of 0.1 Angstrom in the bond between the Cu(II) and the amine nitrogen. Conductivity measurements revealed that the nitrate complexes behave as 1:1 electrolytes in acetonitrile solution, whereas the perchlorate complexes behaved as 2:1 electrolytes. The half-wave potentials, measured in acetonitrile by cyclic voltammetry, were -0.01, +0.15, +0.10, and +0.28 V for 3-6, respectively. The high redox potentials of the copper(II) bis(pyrazole) complexes, in particular for complex 6, are explained by the fact that the Cu(II) complexes have the correct ligand geometry for the stabilization of Cu(I).