A NOVEL TYPE OF TWISTED ANTIPARALLEL DOUBLE-CHAIN STRUCTURE WITH STACKING BETWEEN THE 2 STRANDS - STRUCTURE, SYNTHESIS AND MAGNETIC-PROPERTIES OF [([CU3L2(DIEN)(H2O)2].3H2O)INFINITY] [L = 1H-1,2,4-TRIAZOLE-3,5-DICARBOXYLATE(3-), DIEN = 3-AZAPENTANE-1,5-DIAMINE]

The synthesis and structure of a completely new type of copper(II) pol ymer [{[Cu3L2(dien)-(H2O)2].3H2O}infinity], where L = 1H-1,2,4-triazol e-3,5-dicarboxylate(3-) and dien = diethylenetriamine (1,4,7-triazahep tane), is reported. The compound crystallizes in the tetragonal space group P42(1)cBAR, with a = b = 15.845(3), c = 22.743(1) angstrom and Z = 8. Least-squares refinement of 818 reflections with I > 2sigma(I) a nd 174 parameters gave R = 0.0694, R' = 0.0969. The polymer is essenti ally a double chain, the building blocks of which are trinuclear coppe r(II) entities arranged zigzag clockwise and anticlockwise parallel to each other. The copper-copper distances within the trinuclear unit ar e Cu(1) ... Cu(2) 5.937(4), Cu(1) ... Cu(3) 4.014(6) and Cu(2) ... Cu( 3) 5.937(4) angstrom. The two strands of the chain are linked to each other by apical Cu-O bonds with Cu(2) ... Cu(2') 3.498(6) A. The magne tic susceptibility data (5.8-284 K) are interpreted on the basis of an exchange Hamiltonian function giving J1[Cu(1)-Cu(3)] = -30.0 cm-1, J2 [Cu(2)-Cu(2')] = -1.5 cm-1 and g = 2.0. The nature and the strength of the antiferromagnetic exchange are discussed on the basis of the stru ctural features, and compared with previously reported magneto-structu ral data for related copper(II) compounds with N1,N2- and N1,N4-linked 1,2,4-triazole ligands.