Copper(II), Zinc(II), and Cadmium(II) Formylbenzoate Complexes: Reactivity and Emission Properties

Abstract

Synthesis, characterization, reactivity, and sensing properties of 4-formylbenzoate complexes of copper(II), zinc(II), and cadmium(II) possessing the 1,10-phenanthroline ancillary ligand are studied. The crystal structures of the (1,10-phenanthroline)bis(4-formylbenzoate)(aqua)copper(II) and (1,10-phenanthroline)bis(4-formylbenzo-ate)zinc(II) and a novel molecular complex comprising an assembly of mononuclear and dinuclear species of (1,10-phenanthroline)bis(4-formylbenzoate)cadmium(II) are reported. These zinc and cadmium complexes are fluorescent; they show differentiable sensitivity to detect three positional isomers of nitroaniline. The mechanism of sensing of nitroanilines by 1,10-phenanthroline and the complexes are studied by fluorescence titrations, photoluminescence decay, and dynamic light scattering. A plausible mechanism showing that 1,10-phenanthroline ligand-based emission quenched by electron transfer from the excited state of 1,10-phenanthroline to nitroaniline is supported by density functional theory calculations. In an anticipation to generate a fluorescent d10-copper(I) formylbenzoate complex by a mild reducing agent such as hydroxylamine hydrochloride for similar sensing of nitroaromatics as that of the d10-zinc and cadmium 4-formylbenzoate complexes, reactivity of d9-copper(II) with hydroxylamine hydrochloride in the presence of 4-formylbenzoic acid and 1,10-phenanthroline is studied. It did not provide the expected copper(I) complex but resulted in stoichiometry-dependent reactions of 4-formylbenzoic acid with hydroxylamine hydrochloride in the presence of copper(II) acetate and 1,10-phenanthroline. Depending on the stoichiometry of reactants, an inclusion complex of bis(1,10-phenanthroline)(chloro)copper(II) chloride with in situ-formed 4-((hydroxyimino)methyl)benzoic acid or copper(II) 4-(hydroxycarbamoyl)benzoate complex was formed. The self-assembly of the inclusion complex has the bis(1,10-phenanthroline)(chloro)copper(II) cation encapsulated in hydrogen-bonded chloride-hydrate assembly with 4-((hydroxyimino)methyl)benzoic acid.

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

“…Furthermore, the increase in the concentration of water initially competes with the solvent to make an organized structure by taking possible coordination sites and making an assembly suitable for showing AIE. As the amount of water increases, water reorganizes the assembly to segregate the self-assembled zinc complexes yet provides scope to remain as newly formed assemblies through fast exchange that are not detected in the NMR time scale in solution . Such equilibriums are possible as the change of solvents makes different zinc complexes and dimensionality of carboxylate polymers changes with solvent coordination .…”

“…As the amount of water increases, water reorganizes the assembly to segregate the self-assembled zinc complexes yet provides scope to remain as newly formed assemblies through fast exchange that are not detected in the NMR time scale in solution. 37 Such equilibriums are possible as the change of solvents makes different zinc complexes 27 and dimensionality of carboxylate polymers changes with solvent coordination. 56 The changes in dimensionality also affect the photoluminescence properties.…”

“…The self-assembly of various zinc complexes shows novel emission properties. − Many zinc complexes have prospects as applied optoelectronic materials. − Besides enhanced chemical reactivity for catalytic reactions, − optoelectronic properties of zinc oxide necessitate the study of polynuclear zinc clusters possessing a ZnO 4 environment. − Solvent plays an important role in the synthesis of such zinc clusters or coordination polymers. , Design of ligands − and improvisation of noncovalent interactions of ligands are common ways to synthesize complexes with less conventional coordination numbers such as five-coordinated , zinc complexes. A careful look at the number of zinc complexes suggests that, irrespective of ligands, they show emissions near 400–430 nm with some exceptions. − Some d 10 zinc complexes show sample- and size-dependent fluorescence emissions, whereas in certain cases, aggregation-induced emissions (AIE) of zinc complexes are comparable to similar emissions by corresponding d 10 cadmium complexes . Those observations together with the emergence of AIEgens of zinc complexes − and the development of newer aspects of AIEgens , make one curious to explore the emission behavior of simple zinc complexes.…”

“…1−8 Some d 10 zinc complexes show sample-and size-dependent fluorescence emissions, 36 whereas in certain cases, aggregation-induced emissions (AIE) of zinc complexes are comparable to similar emissions by corresponding d 10 cadmium complexes. 37 Those observations together with the emergence of AIEgens of zinc complexes 38−41 and the development of newer aspects of AIEgens 42,43 make one curious to explore the emission behavior of simple zinc complexes. Furthermore, the AIEgens are generally developed from fluorescent compounds, whereas a metal complex helps to bring together nonfluorescent components to modulate emission based on metal-to-ligand charge-transfer transitions.…”

Influence of a series of pyridine ligands on the structure and photophysical properties of Cd(ii) complexes

“…The bond lengths and bond angles range between 2.2939(17)-2.3637( 14) Å and 56.26(5)-154.07( 6)°( ESI: † Table S4), presenting similar values to that of other hexacoordinated Cd(II) compounds based on μ 1 -η 2 coordinated carboxylate moieties and 1,10-phen ligands. 50,51 Their intermolecular interactions expand the structure along the bc plane, forming a 2D supramolecular structure (Fig. 4b).…”