Thiocyanato-bridged new copper(II) 1D polymeric chains: structures, electrical properties, catecholase activity and DFT studies

Abstract

Thiocyanato-bridged two new copper(II) complexes of 1D polymeric chains of molecular formula [Cu(L1)(μ1,3-NCS)]n (1) and [Cu(L2)(μ1,3-NCS)]n (2) [HL1 = N-propyl-N-(5-bromosalcylidine)ethane-1,2-diamine; HL2 = N-propyl-N-(5-chlorosalcylidine)ethane-1,2-diamine] have been synthesized and characterized. Characterizations of 1 and 2 have been accomplished by several physicochemical techniques, including single crystal X-ray diffraction studies. X-ray diffraction analyses of 1 and 2 reveal that the monomeric units of 1D polymers are bridged and interconnected via the μ1,3-thiocyato group. The coordination geometry around the Cu centers in 1 and 2 can be best described as distorted square pyramidal environments. The current-voltage characteristics of the Al/1/ITO and Al/2/ITO structures have been analysed by considering the thermionic emission theory of the Schottky barrier diode. Employing a conventional method, the barrier height and ideality factor have been calculated to be 0.89 eV and 3.84 for 1, and 0.84 eV and 3.75 for 2, respectively. The series resistances have been obtained graphically as 4.24×103 Ω for Al/1/ITO and 2.65×103 Ω for Al/2/ITO structures using modified Norde’s technique. Both complexes 1 and 2 show moderate catecholase activity as observed by examining the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ). Density functional theory (DFT) calculations, including HOMOs and LUMOs were carried out to acquire the Fukui function values at the Cu centers in 1 and 2 to understand that the substrate 3,5-DTBC most likely binds with the Cu(II) for its activation during the catalytic process. However, a comparative assessment of their catecholase activities indicates that 2 (kcat = 29.76 h-1) has superior catalytic efficacy in comparison to 1 (kcat = 11.15 h-1).