Synthesis, crystal structures and properties of five-coordinate Schiff-base Zn(II) complexes

Abstract

Five-coordinate Schiff-base Zn complexes (1,2-cyclohexanediamino-N,N 0 -bis(salicylidene)) zinc-pyridine 1 and (1,2-cyclohexanediamino-N,N 0 -bis(3,5-di-tert-butylsalicylidene)) zincpyridine 2 were synthesized and the structures of 1 and 2 have been determined by single-crystal X-ray analysis. All Zn atoms are five-coordinate in both structures. Both complexes exhibit interesting structures based on intermolecular -stacking and hydrogen bond interactions. Complex 1 has a one-dimensional molecular chain structure via -stacking interaction, while complex 2 has an interesting lattice structure (with cavities with dimensions 10.9 Â 6.9 Å ) formed through intermolecular -stacking and hydrogen bond interactions. 1 and 2 are compared and characterized by MS, elemental analysis, IR, UV-Vis and Photoluminescence (PL). Fluorescence spectra show that the maximal emission wavelength of 1 and 2 are 454 nm, and 480 nm, respectively, upon radiation by UV light. Cyclic voltammetry performed on 1 and 2 indicate a dependence of the cathodic potentials upon conformational and electronic effects. Electronic spectral properties of 1 and 2 were studied by TD-DFT methods. The fluorescent emission of these complexes originates from ligand-centred -* transitions. The Zn (II) centres play a key role in enhancing the fluorescent emission of the ligands.

Crystal structure of dibromo(N-ethyl-N'-pyridinylmethyleneethane-1,2- diamino)zinc(II), ZnBr2(C10H15N3)

“…In the title complex, the Zn(II) atom is coordinated by the pyridine N, imine N and amine N atoms of the Schiff base ligand and by two bromide anions, forming a distorted trigonal bipyramidal environment. The ZnN and ZnBr bond lengths are comparable to the values in other similar complexes [10][11][12]. The bond angles subtended at the Zn atom at the basal plane range from 112.35(9)°t o 131.66(9)°, and the bond angle of N1Zn1N3 at the axial positions deviates from the ideal value of 180°by 29.5(1)°, indicating a distorted trigonal bipyramid coordination.…”

Five Coordinate M(II)-Diphenolate [M = Zn(II), Ni(II), and Cu(II)] Schiff Base Complexes Exhibiting Metal- and Ligand-Based Redox Chemistry

“…1.98 Å) and Zn(1)-N(imine) (ca. 2.08 Å) bond distances (Table ) are comparable to those of (1,2-cyclohexanediamino- N , N ′-bis(3,5-di- tert -butylsalicylidene))pyridine zinc(II) and 2,2′-(methyl-4-azaheptane-1,7-diylbis(nitrilomethylidyne))-diphenolato zinc(II) which also contains a Zn II metal center in an N 3 O 2 coordination sphere (ca. 1.96 Å and 2.07 Å, respectively) .…”

Synthesis, Spectral and Thermal Behavior of Some New Four Coordinated Complexes

“…IR spectra of the complexes showed obviously change in the location of absorbance band especially for ν(C=N) indicated that the Schiff base was coordinated to the metals atom. The band appearing at 1651 cm -1 due to the azomethine group (C=N) [22][23][24] was shifted to lower frequency by 4-14 cm -1 indicating participation of the azomethine nitrogen in the complexation. Schiff base ligand spectrum showed the stretching frequencies at 3035, (2927 and 2907) and 2848 cm -1 assigned to C-H of aromatic, aliphatic and iminic groups respectively.…”