A novel fluorescent turn on probe derived from Schiff base for highly selective and sensitive detection of Cu2+ ion

A fluorescent probe (L) of bis Schiff base secondary amine ligand was designed and synthesized from 2,6-pyridinedicarboxylic acid, ethylenediamine and salicylaldehyde by condensation and reduction reaction. Its structure was characterized by IR, UV-Vis, LIF, 1HNMR, 13C NMR, MS and elementary analysis. Investigation of binding test indicated that probe L could sensitively and selectively detect Cu2+ ion with striking fluorescent signaling responses in anhydrous ethanol solvent. Results from Job's plot, fluorescent titration, and MS experiments indicated a 1:1 binding ratio between probe L and Cu2+, with a complexation constant of 1.28 × 108 M-1. According to MS, IR and molar conductivity analysis, the mechanism of the probes' detection of Cu2+ may due to CHEF mechanism by the lone electron pairs in the N atom, and the enhancement of the molecular rigidity caused by disruption of intermolecular hydrogen bonding force, which leading to the occurrence of chelation fluorescence enhancement. The detection limit of complexation constant was 2.69 × 10-8 M in the linear range of 0-40 μM, which provided an effective and convenient testing for trace copper in surface water and drinking water.

Building-up host-guest helicate motifs and chains: a magneto-structural study of new field-induced cobalt-based single-ion magnets

In this work, we present the synthetic pathway, a refined structural description, complete solid-state characterization and the magnetic properties of four new cobalt(ii) compounds of formulas [Co(H₂O)₆][Co₂(H₂mpba)₃]·2H₂O·0.5dmso (1), [Co(H₂O)₆][Co₂(H₂mpba)₃]·3H₂O·0.5dpss (2), [Co₂(H₂mpba)₂(H₂O)₄]_n·4nH₂O (3), and [Co₂(H₂mpba)₂(CH₃OH)₂(H₂O)₂]_n·0.5nH₂O·2ndpss (4) [dpss = 2,2'-dipyridyldisulfide and H₄mpba = 1,3-phenylenebis(oxamic) acid], where 2 and 4 were obtained from [Co(dpss)Cl₂] (Pre-I) as the source of cobalt(ii). All four compounds are air-stable and were prepared under ambient conditions. 1 and 2 were obtained from a slow diffusion method [cobalt(ii) : H₂mpba^2- molar ratio used 1 : 1] and their structures are made up of [Co₂(H₂mpba)₃]^2- anionic helicate units and [Co(H₂O)₆]²⁺ cations, exhibiting supramolecular three-dimensional structures. Interestingly, a supramolecular honeycomb network between the helicate units interacting with each other through R₂²(10) type hydrogen bonds occurs in 2 hosting one co-crystallized dpss molecule. On the other hand, for the first time, linear (3) and zigzag (4) cobalt(ii) chains were isolated by slow evaporation of stirred solutions of mixed solvents with cobalt(ii) : H₂mpba^2- in 1 : 2 molar ratio at room temperature. Magnetic measurements of Pre-I revealed a quasi magnetically isolated S = 3/2 spin state with a significant second-order spin-orbit contribution as expected for tetrahedrally coordinated cobalt(ii) ions. The analysis of the variable temperature static (dc) magnetic susceptibility data through first- (1 and 3) and second-order spin-orbit coupling models (2 and 4) reveals the presence of magnetically non-interacting high-spin cobalt(ii) ions with easy-axis (1 and 4)/easy-plane magnetic anisotropies (2 and 4) with low rhombic distortions. Dynamic (ac) magnetic measurements for Pre-I and 1-4 below 8.0 K show that they are examples of field-induced Single-Ion Magnets (SIMs).

Hydrazone-based cobalt complexes toward multielectron redox and spin crossover

Hydrazone-based derivatives modified by substitution at different positions were utilized to prepare a series of bis-homoleptic cobalt complexes. One species, [Co^III(L1)₂]⁺ (1), which incorporated deprotonated ligands, adopted a Co(iii) diamagnetic ground state. However, the substituent of a hydrogen atom with a methyl group precluded the possibility of deprotonation upon metal coordination, which led to two species, [Co^II(L2^Me)₂]²⁺ (2) and [Co^II(L3^NO2)₂]²⁺, (3) which underwent a gradual spin crossover with an adjustable substituent effect and a mixed character of low-spin (doublet) and high-spin (quartet) populations in wide temperature ranges. Depending on the electronic effects of the substituents on the ligand, the multielectron redox behavior of the cobalt center was systematically modulated as well. This result demonstrates redox-switchable spin crossover in a new hydrazone-based Co(ii) system, in which the deprotonation of the coordination pocket and substituent groups in aromatic ligands can have a profound effect on the redox potential and spin state of the metal center.

Hydrazone-based derivatives modified by substitution at different positions were utilized to prepare a series of bis-homoleptic cobalt complexes toward multielectron redox and spin crossover.

σ-Hole halogen bonding interactions in a mixed valence cobalt(iii/ii) complex and anti-electrostatic hydrogen bonding interaction in a cobalt(iii) complex: a theoretical insight

Supramolecular interactions in the solid state structures of a mixed valence cobalt(ii/iii) complex and a cobalt(iii) complex have been studied using DFT calculations.