SYNTHESES OF CHROMIUM AND COPPER-COMPLEXES OF HEXAAZAMACROCYCLES - CRYSTAL-STRUCTURES OF CHROMIUM(III) COMPLEXES OF 1,4,7,10,13,16-HEXAAZACYCLOOCTADECANE AND 1,4,7,11,14,17-HEXAAZACYCLOEICOSANE

Chromium(III) complexes of two hexaazamacrocycles, 1,4,7,10,13,16-hexaazacyclooctadecane (2) and 1,4,7,11,14,17-hexaazacyloeicosane (3), have been prepared and the structures of the complex ions determined by single-crystal X-ray diffraction. For the 18-aneN6 ring (2), a rare facial isomer has been identified. The complex crystallizes in the space group I(1)2/m1 (No. 12). Refinement of the species [Cr(2)]Br3 (a = 12.486(4) angstrom, b = 9.550(2) angstrom, c = 8.038(3) angstrom; beta = 105.27(4)-degrees) converged at R = 0.0639 (R(w) = 0.0713) for 57 parameters using 751 reflections with I > 2sigma(I). The mean Cr-N bond length is 2.091(9) angstrom. However, the bite angle of the five-membered chelate ring subtended at the central chromium, 81.9(10)-degrees, indicates significant distortion from octahedral symmetry. The complex [Cr(3)]Br3-H2O crystallizes in the monoclinic space group P2(1)/c (No.14). Refinement of the complex (a = 19.509(12) angstrom, b = 15.608(8) angstrom, c = 14.692(7) angstrom, beta = 99.30(8)-degrees) using a blocked-matrix approach converged at R = 0.0630 (R(w) = 0.0617) for a total of 446 parameters using 2862 reflections with I > 2sigma(I). The average Cr-N bond distance is 2.095(15) angstrom, and the five-membered chelate angle is 83.5(6)-degrees. Thus there is reduced strain within the ring compared to the smaller 18-membered macrocycle. This feature is also reflected in UV-visible spectroscopic and electrochemical measurements. The preparation, characterization, and electrochemistry of the analogous copper(II) complexes are also reported.