FERROMAGNETIC EXCHANGE COUPLING AND MAGNETOSTRUCTURAL CORRELATIONS IN MIXED-BRIDGED TRINUCLEAR COPPER(II) COMPLEXES - MAGNETIC DATA AND THEORETICAL INVESTIGATIONS AND CRYSTAL-STRUCTURES OF 2 ANGLED CU(II)(3) COMPLEXES

The structural and magnetic data of two angled trinuclear compounds, [CuII3(2-CH3C6H4CO2)4{(C2H5)2-NC2H4O}2H2O], 3, and [CuII3(C6H5CO2)4{(C2H5)2NC2H4O}2H2O], 6, are reported. Crystal data: for 3, space group C2/c, a = 27.726 (5) angstrom, b = 20.190 (4) angstrom, c = 8.314(2) angstrom, beta = 101.08 (1)-degrees, Z = 4; for 6, space group C2/c, a = 14.549 (5) angstrom, b = 12.456 (4) angstrom, c = 24.368 (8) angstrom, beta = 90.14 (1)-degrees, Z = 4. Both complexes show similar molecular structures with an isosceles triangular Cu3 unit and the central Cu(2) on the C2 axis. The Cu(1) and Cu(2) coordination spheres are square pyramidal with H2O as a common apical ligand. The mixed bridging by an aminoethanolato oxygen atom and a bidentate carboxylato group leads to a noncoplanarity of adjacent basal copper coordination planes with dihedral angles phi(AB) = 66.8-degrees (3) and 66.6-degrees (6). The isosceles structures are compared to the linear analogues of the series [CuII3(RC6H4CO2)4(R'2NC2H4O)2(R''OH)n] (R', R'' = alkyl; n = 2). Structural correlations are presented, and the role of hydrogen-bond bridging is discussed. Susceptibility measurements (4.2-290 K) reveal ferromagnetic exchange coupling in the mixed-bridged moiety Cu(II)-RO/RCO2-CU(II) leading to a quartet ground state for 3 and 6. Fit parameters are as follows: for 3, J12 = 26.8 (10-0), J13 = 0 CM-1, g = 2.18 (0.06), THETA = -0.1 (0.5) K; for 6, J12 = 26.6 (5.0), J13 = 0 cm, g = 2.11 (0.03), THETA = -1.5 (0.5) K (H = -2SIGMA(j<i=1)J(ij)S(i)S(j)). The ferromagnetic exchange coupling is discussed using SCF-Cl calculations on model compounds. A summary of the theoretical results for the mixed-bridged unit Cu(II)-RO/RCO2-CU(II) is given including calculated magneto-structural correlations as functions 2J(calcd) VS phi(AB). The singly occupied molecular orbitals used for the construction of magnetic orbitals are analyzed. The experimental magneto-structural data for the series [CUII3(RC6H4CO2)4(R'2NC2H4O)2(R''OH)n] agree with the theoretical results.