The ligating versatility of pseudohalides like thiocyanate and cyanate in copper(II) complexes of 2-benzoylpyridine semicarbazone: Monomer, dimer and polymer

Solvent Effect on the Regulation of Urea Hydrolysis Reactions by Copper Complexes

Abiotic allosterism is most commonly observed in hetero-bimetallic supramolecular complexes and less frequently in homo-bimetallic complexes. The use of hemilabile ligands with high synthetic complexity enables the catalytic center by the addition or removal of allosteric effectors and simplicity is unusually seen in these systems. Here we describe a simpler approach to achieve kinetic regulation by the use of dimeric Schiff base copper complexes connected by a chlorido ligand bridge. The chlorido ligand acts as a weak link between monomers, generating homo-bimetallic self-aggregating supramolecular complexes that generate monomeric species in different reaction rates depending on the solvent and on the radical moiety of the ligand. The ligand exchange was observed by electron paramagnetic resonance (EPR) and conductivity measurements, indicating that complexes with ligands bearing methoxyl (CuIIL2) and ethoxyl (CuIIL5) radicals were more prone to form dimeric complexes in comparison to ligands bearing hydrogen (CuIIL1), methyl (CuIIL3), or t-butyl (CuIIL4) radicals. The equilibrium between dimer and monomer afforded different reactivities of the complexes in acetonitrile/water and methanol/water mixtures toward urea hydrolysis as a model reaction. It was evident that the dimeric species were inactive and that by increasing the water concentration in the reaction medium, the dimeric structures dissociated to form the active monomeric structures. This behavior was more pronounced when methanol/water mixtures were employed due to a slower displacement of the chlorido bridge in this medium than in the acetonitrile/water mixtures, enabling the reaction kinetics to be evaluated. This effect was attributed to the preferential solvation shell by the organic solvents and in essence, an upregulation behavior was observed due to the intrinsic nature of the complexes to form dimeric structures in solution that could be dismantled in the presence of water, indicating their possible use as water-sensors in organic solvents.

Crystal structure of 2-[(2E)-2-methyl-3-phenyl-prop-2-en-1-yl-idene]-N-phenyl-hydrazinecarboxamide

The title compound, C17H17N3O, crystallizes with two independent mol-ecules in the asymmetric unit. The semicarbazone moieties of these independent mol-ecules (I and II) are essentially planar [maximum deviation of 0.042 (1) Å in mol-ecule I and 0.041 (1) Å in mol-ecule II], with the terminal phenyl rings twisted away from the mean plane of the semicarbazone moiety, making dihedral angles of 60.26 (8) and 28.76 (9)° in mol-ecule I and 31.07 (9) and 35.45 (8)° in mol-ecule II. The mol-ecules both exhibit an E configuration with respect to the C=C and azomethine C=N bonds. In the crystal, two classical N-H⋯O hydrogen-bonding inter-actions are present between the two mol-ecules, forming a centrosymmetric dimer, while a weak C-H⋯O non-classical hydrogen-bonding inter-action, with a donor-acceptor distance of 3.476 (2) Å, inter-connects two neighbouring centrosymmetric dimers to form a cage-like structure. These cage structures are inter-connected by weak C-H⋯π inter-actions with an H⋯π distance of 2.790 Å, forming supra-molecular chains along the c-axis direction.