Unusual trinuclear complex of copper(II) containing a 4′-(3-methyl-2-thienyl)-4,2′:6′,4″-terpyridine ligand. Structural, spectroscopic, electrochemical and magnetic properties

We report the synthesis, characterization, crystal and molecular structure as well as the spectroscopic, electrochemical and magnetic properties of an unexpected trinuclear copper(II) complex (1), made of three Cu(2-TTA)₂ units (2-TTA = 2-thenoyltrifluoroacetone) bridged by two 4'-(3-methyl-2-thienyl)-4,2′:6′,4″-terpyridine (4-stpy) ligands. The central Cu(II) atom shows an octahedral geometry, while the lateral metal centers present a slightly distorted square pyramidal coordination sphere. It is suggested that the introduction of the relatively bulky substituent groups (2-thienyl and [sbnd]CF₃) in the 2-TTA ligand are responsible of this uncommon coordination mode. The magnetic behavior of 1 is reported in terms of a combination of monomer and dimer units, leading to weak antiferromagnetic interaction (J = −1.93 cm⁻¹). The cyclovoltammogram of 1 exhibits, in the cathodic potential region, three redox events due to Cu²⁺/Cu⁺ and Cu⁺/Cu⁰ redox couples and to the mono-electronic reduction of the 4-stpy ligand.