The Preparation and Magnetic and Structural Examination of Monomeric, Dimeric,and Polymeric Adenine Complexes of Copper (II).

摘要

Under acidic aqueous conditions,reaction of adenine with copper(II) yields monomeric (AdH2(2+)) CuCl6,dimeric (Ad)CuCl2,and linear chain polymeric (AdH+2)2CuCl4,as well as the previously reported trimeric (AdH+)2Cu3Cl8.4H2O. The crystal structure of (AdH+)2CuCl4is analogous to that of (AdH+)2CuBr4. The chloro analogue crystallizes in the space group C2/c of the monoclinic system with the cell dimensions being a = 18.117(4), b = 8.576(1), c = 11.814(4) A and beta = 114.29(1) degrees with Z = 4. The copper atom is roughly tetrahedrally coordinated and lies on a crystallographic two-fold axis with the four coordination sites being occupied by two chloride ligands with a Cu-Cl distance of 2.228(1) A and by the N(9) atoms of two adeninium cations with a Cu-N(9) distance of 2.012(2) A. The cationic purine is protonated at N(1) and N(7). There are weak Cl... Cl interactions of length 3.755(2) A which link the monomeric units into zig-zag polymeric chains with a Cu-Cl... Cl angle of 169.23(7). The corresponding Br... Br contacts are calculated to be 3.791 A. These ligand-ligand contacts support Heisenberg linear chain antiferromagnetism with J(Cl) = -7.6/cm and J(Br) = -36.5/cm. The exchange coupling constant observed for dimeric (Ad)CuCl2is -32/cm. (Author)