EXCHANGE INTERACTION IN MULTINUCLEAR TRANSITION-METAL COMPLEXES .14. EXCHANGE INTERACTIONS IN A NOVEL COPPER(II) LINEAR-CHAIN COMPOUND WITH LADDERLIKE STRUCTURE - CU2(1,4-DIAZACYCLOHEPTANE)2CL4

The synthesis, crystal structure, and magnetic properties are reported for the novel compound Cu2(1,4-diazacycloheptane)2Cl4. The blue compound, Cu2C10H24N4Cl4, crystallizes in the monoclinic space group P21/c. Cell dimensions are as follows: a = 13.406 (3), b = 11.454 (2), c = 12.605 (3) Å; β = 115.01 (2)°; Z = 4. The structure was solved at room temperature by Patterson and direct methods and refined to an R value of 0.037 (Rw = 0.040), for 2089 observed reflections and 183 parameters. The binuclear unit of the complex is roughly centrosymmetric, and the coordination environments around the two copper atoms are very similar. Each metal center shows distorted (4+1) square-pyramidal geometry. The four short bonds involve the two nitrogens of 1,4-diazacycloheptane, a terminal chlorine atom, and a bridging chlorine atom. The long, apical bond involves a basal chlorine atom of the other copper atom. The binuclear units are packed along the [101] direction. Each dimer is related to its two nearest neighbors along this axis by cristallographic inversion symmetry and is connected to each of them by two Cu-Cl⋯H-N-Cu hydrogen bonding interactions. As a result of this 1-D network of hydrogen bonds, the binuclear units are connected into infinite ladderlike chains. The X-ray analysis of the compound does not reveal any close contacts between chains that may be regarded as bonding interactions. The magnetic susceptibility vs temperature curve for the compound exhibits a maximum at about 8 K, strongly indicative of antiferromagnetic exchange. Comparisons between theory and experiment with use of approximate Heisenberg models have been made. The results indicate that, in order to account for the magnetic properties of the compound, both interactions between nearest neighbors and interactions between next nearest neighbors must be considered explicitly in the spin Hamiltonian, since they are of the same order of magnitude. © 1990, American Chemical Society. All rights reserved.