Carbon–nitrogen bond cleavage by copper(II) complexes

Inorganic Molecular Complexes: Potential for Growth of a New Subject Area in Self-Assembly

The non-covalent assemblies among multiple non-identical metal complexes have scopes to develop a new subject area. There are infinite numbers of ways for different combinations among inorganic neutral or ionic complexes. Each partnering species of those molecular complexes would also have diversities by changing metal ions, ligands, oxidation states of metal ions, and coordination numbers. Keeping a view of the emergence of framework materials and self-assembled nano-structures of metal complexes, the non-covalently linked assemblies of inorganic molecular complexes would have scopes for new nano-dimensional materials. This account provides a systematic description of the different inorganic molecular complexes for a concerted effort to develop a new area that would have importance in applied materials.

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

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.

Tetra-μ-acetato-κO:O'-bis-[(3,5-di-methyl-1H-pyrazole-κN)-copper(II)]

The dinuclear centrosymmetric title compound, [Cu₂(CH₃CO₂)₄(C₅H₈N₂)₂], has a distorted square-pyramidal coordination geometry around each Cu^II atom in which four O atoms from the bridging acetate ligands form the basal plane while two N atoms from the pyrazole ligands occupy the apical positions. The crystal has two half mol­ecules in the asymmetric unit with a Cu⋯Cu distance of 2.6762 (4) Å. Disorder was found for two O atoms and two C atoms of one acetate ligand and refined with occupancies of 0.265 (7) and 0.735 (7). The crystal also features mol­ecules linked through two N—H⋯O hydrogen bonds resulting in one-dimensional chains extending along the crystallographic b axis.

Bis(acetato-κO,O')bis-(3,5-dimethyl-1H-pyrazole-κN)copper(II)

In the title compound, [Cu(C(2)H(3)O(2))(2)(C(5)H(8)N(2))(2)], the Cu(II) atom has a distorted tetra-gonal-bipyramidal geometry, with the equatorial plane formed by two N atoms belonging to two 3,5-dimethyl-1H-pyrazole ligands and two O atoms from two acetate anions. The second O atoms of the acetate groups provide elongated Cu-O axial contacts, so that the acetates appear to be coordinated in a pseudo-chelate fashion. The pyrazole ligands are situated in cis positions with respect to each other. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming a one-dimensional chain.