Deaggregation properties and transmetalation studies of a zinc(II) salen-type Schiff-base complex

This paper reports the synthesis and the deaggregation properties of a Lewis acidic Zn(II) salen-type Schiff-base complex derivative from diaminomaleonitrile and a systematic detailed study of its transmetalation with other metal ions in solution. In a solution of non-coordinating solvents, the complex is in a dimeric form, while in coordinating solvents or upon addition of a Lewis base it is stabilized as monomeric adducts. Experiments done in two solvents with different Lewis basicities indicate a major role of the stability of the starting adduct in transmetalation. Thus, using nitrate or perchlorate salts, acetonitrile solutions of the complex give an immediate and complete transmetalation with Cu²⁺, while with Co²⁺ and Ni²⁺ a much slower transmetalation rate is observed. Instead, using chloride salts a fast and complete transmetalation is observed for divalent ions of the first transition series (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺), indicating the role of the chloride in stabilizing the transition state of the transmetalation. On the other hand, DMF solutions of the complex are less prone to transmetalation, according with the greater basicity of the solvent and, hence, the greater stability of the related adducts with the complex. Therefore, the nature of the solvent and the counteranion allow controlling the transmetalation process of this Zn(II) Schiff-base complex.

A β-ketoiminato palladium(II) complex for palladium deposition

The ¦-ketoiminato complex [Pd(OAc)L] (3) can be synthesized by the reaction of bis(benzoylacetone)diethylenetriamine (1, = LH) with [Pd(OAc)2] (2). The structure of 3 in the solid state has been determined by single X-ray diffraction analysis. Complex 3 crystallizes as a dimer (3 2), which is formed by hydrogen bonds between NH and OOAc functionalities of two adjacent ligands. Each of the Pd atoms is complexed by one ON2 donor unit of the polydentate ligand L − and an acetate group. Pd–Pd interactions and hydrogen bond formation between a NH and the C=O acetate moiety lead to a [4 + 2] coordination at Pd. The non-coordinated part of L exists in its ¦-keto-enamine form. The thermal decomposition behavior of 3 2 was studied by TG (thermogravimetry) and TG-MS showing that 3 2 decomposes between 200 and 500°C independent of the applied atmosphere. Under oxygen PdO is produced, while under argon Pd is formed as confirmed by PXRD measurements. Complex 3 2 was applied as a spin-coating precursor (conc. 0.1 mol L−1, volume 1.5 mL, 3000 rpm, deposition time 6 min, heating rate 50 K min−1, holding time 60 min (Ar) and 120 min (air) at T = 800°C). The as-obtained samples are characterized by granulated particles of Pd/PdO on the substrate surface. EDX (energy-dispersive X-ray spectroscopy) and XPS (X-ray photoelectron spectroscopy) measurements confirmed the formation of Pd (Ar) or PdO (O2) with up to 12 mol% C impurity.

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.