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

Abstract

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 π⋯π interactions resulted in distorted hexagonal layers. DFT calculations reveal a bond strength order of Cu–Cl > Cu–O/N ≫ Cu⋯Cl. ESI-MS data reveal several small fragments from CBC, but oligomeric [Cu^II₂], [Cu^II₃], and [Cu^II₄] 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⋯Cu) = +0.99(30) cm⁻¹ and J′(π⋯π) = +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⋯Cu) of +3.6 at 296 K and +4.1 cm⁻¹ at 90 K that dominates the magnetic properties, whereas J′(π⋯π) = 0.04 cm⁻¹ is negligibly small.