Crystal Structure and Properties of a New Copper(II) Complex of Dioxocyclam Appended with 8-Methylquinoline (Dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-5,7-dione)

A new macrocyclic dioxotetraamine ligand 1-(quinolin-8-ylmethyl)-1,4,8,11-tetraazacyclotetradecane-5,7-dione (H2L) has been synthesized. The resulting dioxocyclam readily forms a 1 : 1 Cu(II) complex (CuL) with concomitant double deprotonation of the ligand. CuL has been isolated as single crystals and the structure was determined by X-ray diffraction analysis. CuL·5H2O (1·5H2O) crystallizes in monoclinic crystal system, P21/n space group with a = 12.979(2), b = 13.638(6), c = 13.634(4) A, β = 103.02(2)°, V = 2351(2) A3, Mr = 521.07, Z = 4, Dcalc = 1.472 g/cm3, μ = 9.78 cm-1, F(000) = 1100, room temperature, and R = 0.039, Rw = 0.042 for 2137 observed reflections with I > 3σ(I). In complex 1, the Cu atom is five coordinate to form a distorted square pyramid in which N(5) of the quinoline pendant is at the apical site. The Cu—N(5) bond distance (2.262(4) A) is longer than the basal average Cu—N bond lengths (1.994(4) ring;). The behavior of CuL in solution has been studied further with ESR, UV-Vis and cyclic voltammetry.