Synthesis and crystal structures of two tri- and tetra-heterometallic Ni(ii)–Mn(ii)/Ni(ii)–Co(iii) complexes from two different Ni(ii)-containing metalloligands: effective catalytic oxidase activity and Schottky device approach

Abstract

Using two different metalloligands [NiLA] and [NiLB], developed using two different N₂O₂ donor Schiff bases, H₂LA 6,6′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azaneylylidene))bis(2-methoxyphenol) and H₂LB 6,6′-((1E,1′E)-((2,2 (2-ethoxyphenol), two new tetra- and trinuclear heterometallic complexes, [(NiLA)₂(CH₃COO)₂(SCN)₂(Co)₂] (complex 1) and [(NiLB)₂(SCN)₂Mn] (complex 2), have been synthesized. The two newly formed complexes have primarily been characterized using several spectroscopic techniques. According to the single-crystal structural study, the metalloligand portion is shared by both crystals. Complex 1 is a tetranuclear complex where Ni(II) is connected to Co(II) via acetate and phenoxide bridging, whereas complex 2 is a trinuclear complex where each Ni(II) center is coordinated to Mn(II) via phenoxide bridging only. It is interesting to note that the thiocyanate moiety in complex 1 is linked to Co(II), whereas in complex 2, it is linked to Ni(II) as a secondary anionic residue. Following structural analysis, both complexes were exposed to catecholase-like activity to test their ability to aerially oxidize 3,5-di-tert-butylcatechol. The calculated turnover numbers (K_cat) 355 h⁻¹ and 286 h⁻¹ for complexes 1 and 2, respectively, unveiled that complex 1 is more susceptible to this catalytic process. The generation of Ni(I) in complex 1 is more favorable than the formation of Mn(I) in complex 2 during catalysis and this is the factor responsible for the higher susceptibility of complex 1 towards the catalytic process. To determine whether both the studied complexes can function as effective Schottky devices, the band gap values for complexes 1 and 2 were used to calculate the diode parameters. The results show that complex 1 will function as a better Schottky device than the complex 2.