Copper(ii) tetrafluoroborate complexes with the N3,N4-bridging coordination of 1-(tert-butyl)-1H-tetrazole: synthesis, crystal structure and magnetic properties

Abstract

1-(tert-Butyl)-1H-tetrazole (L) reacts with copper(II) tetrafluoroborate hexahydrate to give the complexes [Cu₂L₈(H₂O)₂](BF₄)₄ (1) or [Cu₃L₆(H₂O)₆](BF₄)₆ (2) depending on the reaction conditions. These complexes, as well as compound L, were characterized using single crystal X-ray analysis. Complex 1 was found to comprise a dinuclear complex cation [Cu₂L₈(H₂O)₂]⁴⁺ (the C_i symmetry point group), with six tetrazole ligands L showing monodentate N⁴-coordination, and two ligands L providing two tetrazole ring N³,N⁴ bridges between the copper(II) cations; water molecules complete the distorted octahedral coordination of the metal ions. Complex 2 includes a linear trinuclear complex cation [Cu₃L₆(H₂O)₆]⁶⁺ (the S₆ symmetry point group), in which neighbouring copper(II) cations are linked by three ligands L via tetrazole ring N³,N⁴ bridges; central and terminal metal ions show octahedral CuN₆ and CuN₃O₃ coordination cores, respectively. The temperature-dependent magnetic susceptibility measurements of complex 2 revealed that the copper(II) ions were weakly ferromagnetically coupled showing a coupling constant J of 2.2 cm⁻¹ {H = −2J(S₁S₂ + S₂S₃)}. The quantum-chemical investigation of the electronic structure and basicity of ligand L was carried out.