Role of Labile Methanol on the Bio-inspired Catalytic Activity of a Zn(II)-based Compound: An Experimental and...

Two Zn(II)-based compounds, [Zn₂ L¹ (OAc)₃ (MeOH)] (1) and [Zn₂ L² (OAc)₃ ]_n (2), have been reported where HL¹ is (E)-4-bromo-2-methoxy-6-(((2-morpholino ethyl)imino) methyl)phenol and HL² is (E)-4-bromo-2-methoxy-6-(((2-(piperazine-1-yle)ethyl)imino)methyl) phenol. Single-crystal X-ray diffraction (SCXRD) analysis unveils vivid change in structural arrangements and dimensionality from 1 to 2 due to change in coordinated atom from oxygen to nitrogen of the ligands. SCXRD study shows that compound 1 is dinuclear but compound 2 has a 1-dimensional polymeric structure having helical chain. Structural diversity greatly influences the catalytic activity. Compound 1 acts as excellent catalyst for conversion of 3, 5-di-tert-butyl catechol (3, 5-DTBC) to 3, 5-di-tert-butylbenzoquinone (3, 5-DTBQ) with the turnover number (k_cat ) value of 34.94 sec^-1 . Further, compound 1 reveals phosphatase like activity for conversion of disodium salt of (4-nitrophenyl)-phosphate hexahydrate to p-nitrophenolate with the k_cat value of 24.64 sec^-1 . Interestingly, compound 2 does not show any catalytic activity. To correlate this distinctly different catalytic behavior of two compounds, DFT calculation was carried out. The calculation reveals that detachment of coordinated methanol from coordination sphere of zinc in compound 1 is energetically favourable which creates room for substrate binding, resulting in high catalytic activity. By contrast, in compound 2, detachment of piperazine or Zn-O of -COOH group is energetically unfavourable, resulting in no catalytic activity.