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

Herein, quasi-square planar Cu-II(Hmbm)Cl-2 (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 pi center dot center dot center dot pi interactions resulted in distorted hexagonal layers. DFT calculations reveal a bond strength order of Cu-Cl > Cu-O/N >> Cu center dot center dot center dot Cl. ESI-MS data reveal several small fragments from CBC, but oligomeric [Cu-2(II)], [Cu-3(II)], and [Cu-4(II)] 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-Cl2a center dot center dot center dot Cu) = +0.99(30) cm(-1) and J'(pi center dot center dot center dot pi) = +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-Cl2a center dot center dot center dot Cu) of +3.6 at 296 K and +4.1 cm(-1) at 90 K that dominates the magnetic properties, whereas J'(pi center dot center dot center dot pi) = 0.04 cm(-1) is negligibly small.