STRUCTURES AND PROPERTIES OF COPPER(II) AND COPPER(I) COMPLEXES CONTAINING AN ETHANE-BRIDGED DIMERIC PHENANTHROLINE LIGAND

The structures of [Cu(Diphen)(H2O)](ClO4)2(1) and [Cu(Diphen)]2(ClO4)2(2),where Diphen is 1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane, have been determined by single-crystal X-ray diffraction. Complex 1 crystallizes in the monoclinic space group P2(1)/c with cell dimensions a = 12.075 (2) angstrom, b = 14.340 (2) angstrom, c = 16.201 (2) angstrom beta = 103.27 (1)-degrees, Z = 4, and D(cald) = 1.692 g cm-3. Of the 3514 unique reflections (Mo K-alpha, 3.5-degrees less-than-or-equal-to 2-theta less-than-or-equal-to 45-degrees), 2431 reflections with F(o) > 4-sigma(F(o)) were used in full-matrix least-squares refinement. Final residuals were R(F) = 0.0434 and R(w)(F) = 0.0428. The copper cation is in a trigonal bipyramidal environment with four sites occupied by nitrogen donor atoms from the L2 ligand and the fifth site occupied by a water molecule. The cation exhibited dd transitions in the 600-900-nm range and a Cu(II/I) half-wave potential near 0.25 V vs SSCE. Both the energy of the dd transitions and the E1/2-value depend on solvent donor number. ESR parameters were g(perpendicular-to) = 2.18, A(perpendicular-to) = 89.5 x 10(-4) cm-1 and g(parallel-to) = 2.01, A(parallel-to) = 80.7 x 10(-4) cm-1. The dinuclear complex 2 crystallized in the monoclinic space group C2/c with cell dimensions of a = 24.445 (11) angstrom, b = 16.119 (9) angstrom, c = 17.270 (9) angstrom, beta = 118.75 (4)-degrees, Z = 8, and D(cald) = 1.560 g cm-3. Of the 3921 unique reflections (Mo K-alpha, 3.5-degrees less-than-or-equal-to 2-theta less-than-or-equal-to 45-degrees), 2685 reflections with F(o) > 4-sigma(F(o)) were used in full-matrix least-squares refinement. Final residuals were R(F) = 0.0557 and R(w)(F) = 0.0677. Complex 2 forms a double-helicate structure with the two copper ions in distorted tetrahedral environments. The Cu... Cu separation is 5.729 angstrom. The bimetallic complex displayed an optical transition in the 450-nm region of the visible spectrum. Broad, featureless emission (lambda(ex) = 450 nm) located over the 600-800-nm region was observed at 77 K. A Cu(II/I) redox couple is found near 0.70 V vs SSCE. The unusual difference between redox couples of complex 1 and complex 2 is rationalized on the basis of slow structure changes which occur between the Cu(II) and Cu(I) complexes.