Electrochemical synthesis of metal(II) complexes of schiff bases: the crystal structure of acetonitrile-bis{2-[(2-pyrrole)methylimino]-4,6-dimethylphenolato}zinc(II)

Self-Assemblies of Zinc Complexes for Aggregation-Induced Emission Luminogen Precursors

Positional isomers of zinc-nitrobenzoate complexes possessing pyridine -3-(or-4-) carboxamide are used for a comparative theoretical and experimental study to understand their utility as model complexes to understand the role of metal-to-ligand charge transfer in aggregation-induced emission (AIE). Among the five different model zinc complexes, four of them are non-ionic, and one is an ionic complex. The frontier molecular energy levels of different combinations of the positional isomeric complexes and the absorption maximum were ascertained by density functional theory calculations. The PolyQ value obtained from solid samples of each complex is different. Shifts in the emissions to higher wavelengths than the expected emission for the S₁ to S₀ transition were observed due to aggregations. The highest value of PolyQ among the complexes was 13.56% observed for emission at 439 nm (λ_ex = 350) of the non-ionic complex, namely, (di-aqua)bis(pyridine-3-carboxamide)di(2-nitrobenzoato)zinc(II) monohydrate. Close resemblance in emission lifetime decay profiles of the solid samples of those complexes and the respective solutions of those complexes in dimethyl sulfoxide with or without water showed a common trend, suggesting aggregation-induced emission in each case. Aggregation-induced emission caused by adding water in dimethyl sulfoxide solution of each complex showed an initial increase without a shift in the emission wavelength followed by a quenching with a shift of the respective emission peak to a short wavelength. Dynamic light scattering studies showed an increase in the average particle sizes upon an increase in the concentration of water. This indicated initial participation of water molecules to form aggregates with the complexes, favoring an increase in the AIE intensity. Aggregation of each complex changes with the concentration of water, and an increase in the concentration of water beyond a characteristic limit causes lowering of the emission intensity to the short wavelength.

Zinc(II)/ketoxime system as a simple and efficient catalyst for hydrolysis of organonitriles

The hydrolysis of sterically hindered and unhindered alkyl nitriles, and also of benzyl and phenyl nitriles RCN (R = Me, CH(2)Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC(6)H(4)CH(2), Ph), to carboxamides is catalyzed by a novel system of superior simplicity consisting of cheap, widely commercially available, and rather environmentally friendly compounds, that is, a ZnX(2)/ketoxime combination, but it does not proceed at all with either the zinc salt or the ketoxime taken alone. The nature of the anion X(-) in the zinc salt (X = NO(3), Cl, CF(3)SO(3)) or of the ketoxime (Me(2)C=NOH, C(4)H(8)C=NOH, C(5)H(10)C=NOH) does not affect strongly the catalytic properties of the system, but the best results were obtained so far with a Zn(NO(3))(2).6H(2)O/2-propanone oxime molar ratio of 1:4; turnover numbers are typically above ca. 100 but reach as high as 1000 for p-MeOC(6)H(4)CH(2)C(=O)NH(2). The previously unknown structures of the two carboxamide products n-BuC(=O)NH(2) and p-MeOC(6)H(4)CH(2)C(=O)NH(2) were determined by X-ray diffraction studies. The complexes [ZnX(2)(R(2)C=NOH)(2)] (X = Cl, R(2) = 2Me, C(4)H(8), C(5)H(10); X = NO(3), R = C(4)H(8)), prepared by heating the appropriate zinc salts with 2 equiv of the ketoxime in acetone and characterized by C, H, N analyses, FAB-MS, (1)H and (13)C[(1)H] NMR spectroscopies, and also X-ray crystallography (for X = Cl, R(2) = 2Me; X = NO(3), R = C(4)H(8)), proved to be catalyst precursors in the conversions because the activity of these species is high only in the presence of 2 equiv of the ketoxime.