Solvent-Driven\nSelf-Assembly of Discrete Ni(II)-Azide\nComplexes: Unraveling Unusual Behavior in Mimicking Jack Bean Urease

The\nwell-known inhibitory strength of 3d metal Schiff base complexes\nagainst urease enzymes has long been acknowledged, but their untapped\npotential to act as ureolytic mimics of active metallobiosites remained\nunexplored. To break the new ground, we present pyrrolidine-based\nmononuclear Ni(II)-azide complex <b>1</b> {[NiL(HL)(N<sub>3</sub>)]·1.5(H<sub>2</sub>O)} using the N,N,O donor ligand, namely\n(<i>E</i>)-4-bromo-2-(((2-(pyrrolidin-1-yl)ethyl)imino)methyl)phenol.\nThe initial spectrophotometric analysis showed catalytic inefficiency\nin methanol since it undergoes unexpected ligand dissociation to generate\na new octahedral nickel complex (<b>INC</b>), catalyzing condensation\nto form <b>BrTz</b>. Notably, complex <b>1</b> was subjected\nto self-assembly in DMF into UV-responsive tetranuclear complex <b>2</b> {[NiL(H<sub>2</sub>O)(N<sub>3</sub>)]<sub>4</sub>} and structurally\ncharacterized using single-crystal XRD. Furthermore, complex <b>2</b> was utilized as a functional urease model, demonstrating\ncatalytic efficiency in urea hydrolysis with the estimation of the\nliberated ammonia and CO<sub>2</sub> in MeOH. The mechanistic pathway\nwas speculated to proceed via the hydrogen bonding of urea with bridging\nazides, facilitating coordination with the nickel center. Moreover,\nit significantly inhibited hydrolysis in the presence of external\nNBPTO [<i>N</i>-(<i>n</i>-butyl)thiophosphoric\ntriamide], guanidine, etc., revealing its potential for precise catalytic\ncontrol. To the best of our knowledge, this is the first report of\nthe urease-mimicking activity of the tetranuclear Ni(II) complex and\nelucidating the mechanism through detailed chemical analysis.