New bis[cis-{MoO2}] complexes with dihydrazone ligands: synthesis, characterization, theoretical investigation and their peroxidase mimicking activity

Abstract

Three binuclear dioxidomolybdenum complexes designated as [{Mo^VIO₂}₂(L¹)(H₂O)₂] 1, [{Mo^VIO₂}₂(L²)(H₂O)₂] 2, and [{Mo^VIO₂}₂(L³)(H₂O)₂] 3 with dihydrazone ligands, H₄L¹I, H₄L²II, and H₄L³III, have been prepared by the process with ligands and MoO₂(acac)₂ in a ratio of 1 : 2. Many analytical techniques have been used to describe these complexes, including elemental (CHN) analysis, spectroscopy (FT-IR, UV-vis, ¹H, and ¹³CNMR), and TGA analysis. SC-XRD analysis has been employed to study the structures of these complexes 1a, 2a, and 3a revealing the octahedral geometry and the binding of one molybdenum atom to each side of azomethine nitrogen, enolate oxygen, and a phenolic oxygen atom. The second molybdenum is bound to donor atoms similarly to the first. Powder X-ray investigations of the complexes are also performed to ensure the purity of the bulk material, and it was discovered that the single crystal reflects the bulk material. DFT was used to calculate the theoretical properties of ligands at the B3LYP/6-31G(d,p) level of the model. In contrast, the LANL2DZ level of the model was used to compute the theoretical properties of the synthesised complexes. Frequency, ¹H NMR, and ¹³C NMR calculations were also attempted, and the calculated results were found to correspond well with the experimental data. Furthermore, the peroxidase-mimicking activity of these complexes was investigated, followed by the oxidation of pyrogallol and dopamine. The K_cat values observed in the pyrogallol oxidation were 0.44 h⁻¹, 0.52 h⁻¹, and 0.54 h⁻¹ for catalysts 1, 2, and 3, respectively. However, high K_cat values of 5.2 h⁻¹, 4.8 h⁻¹, and 3.7 h⁻¹ were achieved in dopamine oxidation employing catalysts 1, 2, and 3, respectively.