Nickel(II) Complexes of Benzoylpyridine Diaminoguanidinedihydrazone via In Situ One-Pot Method: Structural, Spectral, and Catalytic Studies

Abstract

Seven Ni(II) complexes (1–7) designed from a new nitrogen-rich ligand 1,3-bis(phenyl(pyridin-2-yl)methylideneamino)guanidine hydrochloride (H₃L‧ HCl) are reported. The complexes were synthesized using in situ one-pot method and characterized by elemental analyses, FT-IR, Far-IR, electronic solution-phase spectra, solid-state electronic diffuse reflectance spectra (UV-DRS), conductivity measurements, and room temperature magnetic moment calculations. The structures of H₃L‧ HCl and complex 7 were confirmed via SCXRD analysis. Additionally, complex 4 on crystallization yielded a new mononuclear complex, [Ni(H₂L)]Cl‧ 2H₂O (4a), which was confirmed by SCXRD analysis. The molecular packing of the compounds is affected by the counter anions and stabilized by various noncovalent interactions within the crystal lattice, which were analyzed quantitatively by Hirshfeld surface analysis. The band gaps of the compounds indicate semiconductor characteristics, which were evaluated experimentally and subsequently analyzed by DFT calculations. The catalytic investigation reveals that the Ni(II) complex 7 facilitates a cinnamyl alcohol conversion of 90% with a selectivity of 92% for cinnamaldehyde under the optimal reaction conditions of 80°C for 24 h, employing TBHP in decane as the oxidizing agent. Similarly, all other complexes are also found to exhibit comparable conversions in the range of 81%–91% under optimal conditions. Furthermore, in silico molecular docking studies demonstrated the binding affinity of the ligand and complex 4 with SARS-CoV-2 main protease active site (M^pro), which makes them suitable candidates for further biological exploration.