EFFECTS ON MOLECULAR ASSOCIATION, CHELATE CONFORMATION, AND REACTIVITY TOWARD SUBSTITUTION IN CU(5-X-SALEN) COMPLEXES, SALEN(2-)=N,N-ETHYLENEBIS(SALICYLIDENAMINATO), X=H, CH3O, AND CL - SYNTHESIS, X-RAY STRUCTURES, AND EPR INVESTIGATIONS

Three copper(II) complexes, Cu(5-X-salen), where salen(2-) = N,N'-ethylenebis(salicylidenaminato) and X = H (1), CH3O (2), or Cl (3), have been synthesized and characterized by various physicochemical techniques. Single crystal X-ray data of the complexes are as follows: 1, C16H14N2O2CU, monoclinic C2/c, a = 26.658(7) Angstrom, b = 6.983(1) Angstrom, c = 14.719(2) Angstrom, beta = 97.42(2)degrees, V = 2717(6) Angstrom(3), Z = 8, R = 0.038 (R(W) = 0.058); 2, C18H18N2O4CU.CH3OH, monoclinic P2(1/n), a = 11.061(3) Angstrom, b = 7.537(6) Angstrom, c = 21.765(5) Angstrom, beta = 92.86(2)degrees, V = 1812(2) Angstrom(3), Z = 4, R = 0.066(R(W) = 0.067); 3, C16H12N2O2Cl2CU, triclinic P (1) over bar, a = 8.318(1) Angstrom, b = 9.502(4) Angstrom, c = 11.016(4) Angstrom, alpha = 63.78(4)degrees, beta = 75.62(3)degrees, gamma = 78.83(4)degrees, V = 753(15) Angstrom(3), Z = 2, R = 0.039 (R(W) = 0.059). In solid state, 1 exists as strong dimers (Cu...O1' = 2.414(2) Angstrom) whereas 2 forms weak dimers (Cu...O1' = 2.801(7) Angstrom) intermolecularly bridged through phenolate oxygen and 3 is essentially a monomer. Copper is tetragonally distorted square pyramidal in 1 and 2 and tetrahedrally distorted square planar in 3. Complexes exhibit color isomerism and solvatochromism in both solid and solution. EPR spectra are characterized by axial g and A(Cu), tensors with g parallel to > g perpendicular to indicating that the unpaired electron occupies a ''formal'' d(xy) orbital. A good correlation is obtained between the sigma-basicity of the solvent and the spin Hamiltonian parameters. The mechanism for solvatochromism is discussed in terms of conformational changes and solvent coordination. EPR studies and extended Huckel molecular orbital calculations suggest that 3 forms more stable pyridine complexes than 1 and 2. The effect of substitution on molecular electronic structure and reactivity toward solvent coordination is discussed.