STRUCTURAL AND MAGNETIC STUDIES ON MACROCYCLIC DICOPPER(II) COMPLEXES - INFLUENCE OF ELECTRON-WITHDRAWING AXIAL LIGANDS ON SPIN EXCHANGE

The antiferromagnetically coupled macrocyclic binuclear copper(II) complexes [Cu2(UPM)X2]->'H20 (X = Cl, Br, I, N3) (UPM derived by template condensation of 4-methyI-2,6-diformylphenol with 1,3-diaminopropane) are structurally similar with a trans-axial arrangement of ligands X. Exchange integrals fall in the range-2J = 720-855 cm-1with Cl < Br < N3 < I. The complex [Cu2(UPM)Br2]-4H20 (II) crystallizes in the monoclinic system, space group C2/m, with a = 7.9196 (13) A, b = 17.1380 (4) A, c = 11.2232 (14) A, β= 92.Ill (13)°, and Z = 2. The complex [Cu2(UPM)12]-H20 (III) crystallizes in the monoclinic system, space group P21a, with a = 8.2826 (8) A, b = 16.7383 (8) A, c = 9.6470 (12) A, 0 = 99.107 (14)°, and Z = 4. Both complexes have an essentially flat, macrocyclic, binuclear structure involving square-pyramidal copper(II) centers. The halogens are bound in a trans-axial arrangement (Cu-Br = 2.737 (2) A; Cu-I = 3.026 (2) A, and the copper centers are displaced toward the halogen from the basal N202donor set (Br, 0.205 (4) A; I, 0.176 (5) A). © 1990, American Chemical Society. All rights reserved.