Solvent-Driven Self-Assembly of Discrete Ni(II)-Azide Complexes: Unraveling Unusual Behavior in Mimicking Jack Bean...

The well-known inhibitory strength of 3d metal Schiff base complexes against urease enzymes has long been acknowledged, but their untapped potential to act as ureolytic mimics of active metallobiosites remained unexplored. To break the new ground, we present pyrrolidine-based mononuclear Ni(II)-azide complex 1 {[NiL(HL)(N₃)]·1.5(H₂O)} using the N,N,O donor ligand, namely (E)-4-bromo-2-(((2-(pyrrolidin-1-yl)ethyl)imino)methyl)phenol. The initial spectrophotometric analysis showed catalytic inefficiency in methanol since it undergoes unexpected ligand dissociation to generate a new octahedral nickel complex (INC), catalyzing condensation to form BrTz. Notably, complex 1 was subjected to self-assembly in DMF into UV-responsive tetranuclear complex 2 {[NiL(H₂O)(N₃)]₄} and structurally characterized using single-crystal XRD. Furthermore, complex 2 was utilized as a functional urease model, demonstrating catalytic efficiency in urea hydrolysis with the estimation of the liberated ammonia and CO₂ in MeOH. The mechanistic pathway was speculated to proceed via the hydrogen bonding of urea with bridging azides, facilitating coordination with the nickel center. Moreover, it significantly inhibited hydrolysis in the presence of external NBPTO [N-(n-butyl)thiophosphoric triamide], guanidine, etc., revealing its potential for precise catalytic control. To the best of our knowledge, this is the first report of the urease-mimicking activity of the tetranuclear Ni(II) complex and elucidating the mechanism through detailed chemical analysis.