Field-induced slow magnetic relaxation, molecular docking and antibacterial studies of quasi-isotropic copper(ii) (S = ½) systems stabilised by tetradentate (ONNO) and tridentate (NNO)-donor ligands

Abstract

A series of penta-coordinate Cu(II) complexes were synthesised and structurally characterised to explore the relationship between coordinating environment, molecular magnetism, and antibacterial activities. A dinuclear complex, [Cu₂(L₁)₂] (1), derived from an ONNO-coordinated tetradentate ligand (H₂L₁ = N,N′-bis[(3-methoxy-2-hydroxybenzylidene)]ethane-1,2-diamine), and three paramagnetic Cu(II) complexes, [Cu₂(N₃)₂(L₂)₂] (2), [Cu(SCN)(L₂)]_n (3), and [Cu(CH₃COO)(L₂)]_n (4), stabilised by a tridentate NNO-donor ligand (HL₂ = (E)-1-(pyridin-2-yldiazenyl)naphthalen-2-ol), were isolated. Dinuclear complex 2 features an asymmetric end-on μ₁,₁-azido bridge, whereas 3 and 4 exhibit end-to-end μ₁,₃-thiocyanate/acetate bridges, forming one-dimensional polymeric architectures. Single-crystal X-ray diffraction confirmed their square-pyramidal molecular geometries. Complexes 1 and 4 exhibit field-induced single-molecule magnet (SMM) behaviour, consistent with quasi-isotropic S = ½ Cu(II) centres. All complexes show χ_MT ≈ 0.4 cm³ mol⁻¹ K⁻¹ with a slight decrease below 10 K. EPR parameters support the existence of mixed orbital character d_z2/d_x2−y2 (g_x = 2.23, g_y = 2.06, g_z = 1.90) (1) and d_x2−y2 (g_∥ = 2.21, g_⊥ = 2.06) (4) in the ground states. Molecular docking analyses demonstrated complex 3 has strong binding affinities against four biologically relevant targets: B-DNA (PDB ID: 1BNA), human DNA topoisomerase I (hTOPI, PDB ID: 1SC7), Escherichia coli MenB enzyme (EC-MenB, PDB ID: 3T88), and human serum albumin (HSA, PDB ID: 4LA0), indicating its potential for target-specific activity.