X-RAY STRUCTURES AND REDOX PROPERTIES OF COPPER(II) BIS(PYRAZOLE) COMPLEXES

The copper complexes of bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl] amine ( 1) and its benzylated derivative (2) have been studied as single cryst als by X-ray crystallography and as powders and solutions by a variety of techniques. [Cu(1). 2NO(3)] (C14H25CuN7O7 including 1 H2O, 3) crys tallized in the monoclinic space group Pc (No. 7) with a = 8.1596(9) A ngstrom, 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]C lO4 (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 (refine d 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) (C48H 78Cl4Cu2N10O20, 6) (Y = H2O, n = 2, or ClO4-, n = 1) crystallized in t he monoclinic space group P2(1)/c (No. 14) with a = 10.9488(9) Angstro m, b = 17.030(2) Angstrom, c = 32.893(3) Angstrom, beta = 92.185(7)deg rees, 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 coor dinated 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 larg est difference between 4 and 6 was a lengthening of 0.1 Angstrom in th e bond between the Cu(II) and the amine nitrogen. Conductivity measure ments revealed that the nitrate complexes behave as 1:1 electrolytes i n acetonitrile solution, whereas the perchlorate complexes behaved as 2:1 electrolytes. The half-wave potentials, measured in acetonitrile b y cyclic voltammetry, were -0.01, +0.15, +0.10, and +0.28 V for 3-6, r espectively. The high redox potentials of the copper(II) bis(pyrazole) complexes, in particular for complex 6, are explained by the fact tha t the Cu(II) complexes have the correct ligand geometry for the stabil ization of Cu(I).