Ferromagnetic coupling in copper benzimidazole chloride: structural, mass spectrometry, magnetism, and DFT studies

Herein, quasi-square planar Cu^II(Hmbm)Cl₂ (CBC, Hmbm = (1-methyl-1H-benzo[d]imidazol-2-yl)methanol) was arranged in a pseudo orthogonal way to form Cl-bridged chains, and further ππ interactions resulted in distorted hexagonal layers. DFT calculations reveal a bond strength order of Cu-Cl > Cu-O/N ≫ CuCl. ESI-MS data reveal several small fragments from CBC, but oligomeric [Cu], [Cu], and [Cu] for non-zero in-source energies; MS data indicates the occurrence of several chemical processes, viz. splitting of the ligand, oligomerization, and redox reaction of alcohol to aldehyde and Cu^II to Cu^I. Gibbs free energies for the fragments were estimated using DFT. The magnetic susceptibility was modeled with the ferromagnetic coupling J(Cu-Cl2aCu) = +0.99(30) cm^-1 and J'(ππ) = +0.35(16) cm^-1 and g = 2.38(2). HF-EPR determined the anisotropic g-values, g_x = 2.24, g_y = 2.16, and g_z = 2.09, and a hyperfine constant of A_z = 450 G. DFT calculations from crystal structure data reveal a J(Cu-Cl2aCu) of +3.6 at 296 K and +4.1 cm^-1 at 90 K that dominates the magnetic properties, whereas J'(ππ) = 0.04 cm^-1 is negligibly small.