CRYSTAL-STRUCTURE AND MAGNETIC-BEHAVIOR OF CU(C14H24N4)CUCL4 - AN ALTERNATING-METAL-SITE, ALTERNATING-EXCHANGE, SPIN 1/2 LINEAR-CHAIN SYSTEM

The crystal structure of the macrocyclic Cu(II) complex Cu(TIM)CuCl4 (TIM = 2,3,9,10-tetramethyl-1,3,8,10-tetraenecyclo-1,4,8,11-tetraazatetradecane) has been determined. The crystals, which are orthorhombic, space group P2(1)2(1)2(1) with a = 8.086 (2) angstrom, b = 14.266 (5) angstrom, c = 17.544 (2) angstrom, V = 2024 (1) angstrom 3, and rho-calcd = 1.70 g cm-3 (Z = 4), contain infinite chains running parallel to the c axis. The four-coordinate macrocyclic Cu(TIM)2+ cations are bridged by distorted tetrahedral CuCl4(2-) anions to form alternating -(Cu(TIM)-Cu(Cl4)n chains. The cations thus achieve a distorted-square-bipyramidal geometry. The bridging of the CuCl4(2-) anion to adjacent to Cu(TIM)2+ cations is asymmetric, leading also to alternating magnetic exchange pathways along the chain. Magnetic susceptibility measurements confirm the existence of two different exchange parameters: one ferromagnetic and one antiferromagnetic. Analysis of the data yields approximate values of J1/k = 13.3 (4) K and J2/k = -2.6 (1) K.