Synthesis, Spectroscopic, Thermal and Catalytic Properties of Four New Metal (II) Complexes with Selected N- and O-Donor Ligands

Four solid compounds with formulae: Co(OAc)₂(Im)·H₂O (I), Ni(OAc)₂(Im)_1.5·2H₂O (II), Cu₂(OAc)₄(Im) (III) and Zn(OAc)₂(Im)·H₂O (IV) (where: Im = 1H-Imidazole) were prepared and characterized by chemical and elemental analysis, powder X-ray diffraction patterns and FTIR spectroscopy. Catalytic properties of each complex for styrene oxidation reaction were investigated. Furthermore, thermal properties of compounds were studied using the TG-DTG and DSC techniques under dry air atmosphere. Additionally, volatile thermal decomposition and fragmentation products were also investigated using the TG-FTIR spectra in air.

A model complex for carbonic anhydrases: Crystal structure of tris-imidazole maleato zinc(II) dihydrate

A novel zinc complex containing three simple imidazole rings as a model compound for carbonic anhydrase and as a rare model for the carboxylate–imidazole–zinc triad interactions frequently observed in zinc enzymes has been made and its structure determined by X-ray diffraction in which the zinc atom has a distorted tetrahedral geometry.

Ionothermal synthesis, properties and vibrational spectra of zinc (II) complex with nicotinamide

The zinc (II) complex with nicotinamide, (C₆H₁₁N₂)[ZnBr₃(C₆H₆N₂O)], was prepared under ionothermal condition by using the ionic liquid 1-ethyl-3-methylimidazolium bromide ([EMIM]Br) as a solvent. At the same time, [EMIM]Br also functions as a structure-directing agent, leading to a framework structure different from those obtained by the conventional methods. Single-crystal X-ray analysis revealed that the coordinated compound crystallizes in monoclinic space group P2(1)/c, and the Zn (II) ion is four-coordinated by one pyridine ring N atom and three bromide anions in a slightly distorted tetrahedron arrangement. The [EMIM](+) cations acting as the extra framework charge balancing species occupy the channels of this asymmetric unit. In the crystal structure, intermolecular NH⋯Br and NH⋯O hydrogen bonds link the molecules to form a supramolecular structure. In addition, this compound was further characterized by FT-IR and Raman spectroscopic techniques, and the observed important bands were assigned. Thermogravimetric analysis (TG), Differential Scanning Calorimetry (DSC) and fluorescent properties of solid samples were also studied at room temperature.

Tris(2-ethyl-1H-imidazole-κN)(terephthalato-κO)zinc(II)

The title compound, [Zn(C₈H₄O₄)(C₅H₈N₂)₃], has a neutral monomeric structure in which one terephthalate dianion and three 2-ethyl-1H-imidazole ligands coordinate to the Zn^II ion in a distorted tetra­hedral geometry. The methyl group of one of the ethyl groups is disordered over two positions with occupancies of 0.66 (2) and 0.34 (2). In the crystal structure, mol­ecules are linked into a three-dimensional hydrogen-bonded network by inter­molecular N—H⋯O interactions involving the uncoordinated carboxyl­ate O atoms.

The competition between acetate and pyrazolate in the formation of polynuclear Zn(ii) coordination complexes

Hydrated zinc(II) acetate reacts with pyrazole (Hpz) and, depending on the reaction conditions, forms different pyrazole-containing species, i.e. [[Zn(CH3COO)(mu-pz)(Hpz)]2] (1), [[Zn(CH3COO)2(Hpz)2.CH3COOH]] (2), [[Zn(mu-pz)2]n] (3), and [[Zn(mu-CH3COO)(mu-pz)]n] (4). Their structural models have been derived from single-crystal X-ray diffractometry as well as from less conventional ab-initio X-ray powder methods. All species contain tetrahedrally coordinated Zn(II) ions, with Zn-N and Zn-O bond distances close to 2.0 angstroms. The existence of the [Zn(mu-pz)]2 core in the species 1, 3 and 4 indicates the propensity for the formation, in the presence of pyrazolate ligands, of well-defined dinuclear entities (with Zn...Zn contacts in the range 3.6-3.8 angstroms). The latter can mutually interact, in the crystals, through either hydrogen-bonding of ancillary ligands (as in 1) or coordinative bonds (via acetates, as in 4, or by self-complementarity, as in 3). The interconversion paths among these species have been studied, employing chemical and thermal methods. In particular, the topotactic and quantitative transformation of 1 into 3 by moderate heating is likely based on a solid-state cooperative condensation mechanism of the dangling pyrazolates toward neighbouring zinc(II) ions, with concomitant acetic acid extrusion.