Synthesis, structure and spectral properties of O,N,N coordinating ligands and their neutral Zn(ii) complexes: a combined experimental and theoretical study

Abstract

Mononuclear Zn(ii) complexes with the general formula [Zn(L)2] have been synthesized in good yields by reacting Zn(OAc)2 with HL in a ratio of 1 : 2 in methanol solvent. Here L is the deprotonated form of 6-[(quinolin-8-ylamino)methylene]cyclohexa-2,4-dienone (HL(1)), 4-chloro-6-[(quinolin-8-ylamino)methylene]cyclohexa-2,4-dienone (HL(2)), 4-methyl-6-[(quinolin-8-ylamino)methylene]cyclohexa-2,4-dienone (HL(3)), 2,4-dimethyl-6-[(quinolin-8-ylamino) methylene]cyclohexa-2,4-dienone (HL(4)), 2-methoxy-6-[(quinolin-8-ylamino) methylene]cyclohexa-2,4-dienone (HL(5)). The electronic structures and photophysical properties of the ligands were calculated by DFT and TDDFT methods. The X-ray structure of one complex is reported. The ligands have a strong binding ability [(0.75-15.37) × 10(4)] and ratiometric response to Zn(2+) ions. With the addition of Zn(2+) ions to the ligands in THF solution a sharp color change is observed visually, and as well a significant enhancement of the fluorescence intensity and the quantum yield for this series occurs. The introduction of other metal ions having biological and environmental effects results in either unaltered or quenched emission intensity. However we observed the sensing property of the ligands strongly depends on the substituent at the ortho position of the phenol group. DFT calculation reveals that the ICT process take place from the salicylaldehyde (donor moiety) to quinoline (acceptor moiety) which is responsible for the enhancement of the fluorescence intensity of ligands after complexation.

A colorimetric and fluorescent probe for multiple transition metal ions (Cu2+, Zn2+ and Ni2+): Fast response and high selectivity

“…This newly designed sensor L was an "O-N-N" type ligand containing three coordination sites which would increase the binding efficiency with metal ions. 35 On the other hand, the typical electron pushing substituent tertiary butyl was introduced to improve the selectivity to Job's plot by using fluorescence data was carried out, the analytical result confirmed a 2 : 1 stoichiometry for the L-Zn 2+ complex (Fig. S5, ESI †), which was highly consistent with the fluorescence and UV titration experiment results.…”

Synthesis of Ni-Based Metallo-Supramolecular Polymer with Bis-NNO-Tridentate Ligand for Electrochromic Devices

“…The color of polyNiL1 was located in the red region of the CIE chromaticity diagram (x = 0.5779, y = 0.3543). L1 was coordinated to various metal ions such as Zn(II), Fe(III), and Al(III) [47][48][49]. However, as for the EC properties, the Ni(II)-based polymer is better than the other metal-based polymers because of the stable redox activity.…”

Photophysical property vs. medium: mononuclear, dinuclear and trinuclear Zn(ii) complexes

“…Recently, we reported the synthesis and the structure of a Zn(II)-mononuclear complex [ZnL 2 ]. 6 This bischelate Zn(II) complex displayed a moderately strong uorescence in THF solution. We synthesized HL in different ways besides the two unique coordination modes of dinuclear and trinuclear Zn(II) complexes, synthesized to achieve our goal.…”

“…Schiff bases play a vital role in modern coordination chemistry, [1][2][3] where tridentate salen-type ligands are one of the most popular classes [4][5][6] of Schiff-base ligands amongst the coordination chemists. These systems possess an extra dimension to their optical properties as metal coordination signicantly alters the photophysical processes they are capable of.…”