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)Cl₂·CH₃OH (1), [Cu(L1)Cl]₂·H₂O (2), [Cu(HL2)Cl₂]₂·2DMF (3), [Cu(HL2)₂Cl]_nCl_n·2nH₂O (4), and [Cu(L3)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···Cu separations are found in the crystal lattices of the polymer 5 (3.33 Å) and dimers 2 (3.35 Å) and 3 (3.38 Å). 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.