Synthesis, Characterization, and Magnetic Properties of a Series of Copper(II) Chloride Complexes of Pyridyliminebenzoic Acids

A series of Cu-II halide complexes, Cu(HL1)Cl-2 center dot CH3OH (1), [Cu(L1)Cl](2)center dot H2O(2), [Cu(HL2)Cl-2](2)center dot 2DMF(3), [Cu(HL2)(2)Cl](n)Cl-n center dot 2nH(2)O (4), and [Cu(L-3)Cl](n) (5), containing pyridyliminebenzoic acids HL1, HL2, and HL3 derived from o-, m-, and p-aminobenzoic acids, respectively, have been obtained as single crystals and characterized by elemental analysis, IR, EPR spectroscopy, magnetic measurements, and single-crystal X-ray diffraction techniques. The results obtained show the formation of molecular (1), dimeric (2, 3), and polymeric structures (4, 5) based on chloride (1-4) and carboxylate bridges (5) with copper( II) ions in the square pyramidal geometry of varying degrees of distortion. In the case of 2 and 5 the ligand deprotonation was completely achieved even in the absence of a base. The closest Cu center dot center dot center dot Cu separations are found in the crystal lattices of the polymer 5 (3.33 angstrom) and dimers 2 (3.35 angstrom) and 3 (3.38 angstrom). The X-band polycrystalline EPR spectra of 1-3 with typical axial patterns show no indication of exchange interactions between copper ions in the range 295-77 K. The observed rhombic features of the EPR spectra of 4 arise from the coupling of g-tensors from differently oriented Cu-II coordination polyhedra in the solid state. A characteristic spin-triplet EPR spectrum of 5 at 77 K was simulated by using the spin-Hamiltonian parameters for S = 1, g(x) = 2.08, g(y) = 2.11, g(z) = 2.37 and the value of the zero-field splitting parameter D of 0.137 cm(-1). Magnetic susceptibility measurements revealed antiferromagnetic (1-3, 5) and ferromagnetic coupling (4) between the metal atoms at low temperatures. Theoretical methods were employed to provide additional insight into magnetic interactions in the studied compounds.