A mixed valence Cu(I)/Cu(II) chain compound: crystal structure of 1,4,8,11-tetraazacyclotetradecanecopper(II) tribromocuprate(I)

The essentially anaerobic reaction of CuBr₂ and 14ane-N₄ in water/acetone solvent (14ane-N₄ = 1,4,8,11-tetraazacyclotetradecane) yields a mixed valence Cu(I)/Cu(II) compound. The compound is orthorhombic, space group Pcnn, with a = 23.6310(1) Å, b = 23.6429(2) Å, c = 12.4537(1) Å and V = 6957.95(9) ų with Z = 16, for _calc = 2.349 g/cc. Refinement of a twinned crystal with 8,504 unique reflections yielded final values of R₁ = 0.0725 (|F| > 2) and w R₂ = 0.114 and a goodness of fit of 1.448. The compound contains chains of Cu(14ane-N₄)²⁺ cations and CuBr₃ ^2– anions, which are linked together by long semicoordinate Cu(II)···Br bonds. The chains run perpendicular to the c axis and are arranged in layers in which the chains alternately run parallel to the (1 1 0) and to the (1 –1 0) crystal directions. The Cu(II) ion is coordinated by the tetradentate macrocycle to yield an approximate square planar coordination. The CuBr₃ ^2– anions have a nearly trigonal planar with Cu–;Br(ave) = 2.38(1) Å.