Ehsan Rezaee

Dinuclear copper(II) complexes with tetraacetylpropane bridge; synthesis and solvatochromism study

Two new mixed-chelate dinuclear copper(II) complexes, [Cu2(tmen)2(TAP)]X2 where tmen = N,N,N′,N′-tetramethylethylenediamine, TAP = tetraacetylpropane, and X =  or , were prepared and characterized by physicochemical and spectral (IR, UV–vis) data. The X-ray diffraction study of [{Cu(tmen)(CH3CN)}{Cu(tmen)(ClO4)}(TAP)](ClO4) demonstrated that coordination geometry around the copper centers is square pyramidal where axial position of one copper is occupied by a ClO4 − and the second copper with acetonitrile. However, in solution, the resulting complexes display affinity for axial ligation so that the apical ligands are driven out by solvent molecules. The solvatochromism of the complexes was investigated in various organic solvents and was compared with that of the corresponding mononuclear complex [Cu(tmen)(CH3-acac)]ClO4. A multi-parametric equation has been utilized to explain the solvent effect on the d–d transition of the complexes using SPSS/PC software. To explore the mechanism of the interaction between the solvent molecules and the complexes, different solvent parameters such as DN, AN, α, E T(30), π ∗, and β using stepwise multiple linear regression method were employed. In pyridine, the original color of the solution changed over time due to removal of tmen chelates and substitution by pyridine in two successive steps.

Investigation of keto–enol tautomerism in tetraketonate ligands

Molecular structure, vibration analysis, and natural bond orbital study of four derivatives of tetraketonate ligand were investigated in three different solvents using density functional theory B3LYP/6-31++G** method. The solution phase studies were carried out using an Onsager model. According to the obtained results the enol form of the ligands is more stable than keto form, even in solvents with high dielectric constant such as DMSO. This result is also confirmed experimentally using NMR studies for tetraacetylethane. Their stabilities are due to the presence of hydrogen bonding in the enol tautomers. A comparison among different possible enol forms of the substituted tetraketonate ligands demonstrated that three factors control the stability of the compounds as hydrogen bonding, steric hindrance, and charge distribution. The effectiveness of each of these factors on the stability of ligands depends on the nature of the substituent attached to the ligand.

Experimental and theoretical characterization of 3-amino-1-phenyl-2-buten-1-onato ligand and its copper(II) and nickel(II) complexes: synthesis, characterization, X-ray structures, DFT and TDDFT studies

This article presents a combined experimental and computational investigation of 3-amino-1-phenyl-2-buten-1-onato, APBO ligand and its copper(II) and nickel(II) complexes. APBO is an unsymmetrical, bidentate and monoanionic ligand with different coordinating atoms (N,O). A comparison among different possible conformers of the ligand has been carried out using density functional theory (DFT) method at the B3LYP/6-31+G(d,p) level. It was demonstrated that two factors control stability of the compounds as hydrogen bonding (conventional and nonconventional) and resonance effect. The effectiveness of each of these parameters on the stability of ligands is discussed. The prepared homoleptic complexes of [Ni(APBO)2] and [Cu(APBO)2] were characterized with IR, NMR, UV–Vis spectroscopic techniques. The X-ray crystallography of [Ni(APBO)2] demonstrated that the bidentate APBO binds to the metal center in trans fashion and the geometry around the nickel atom is square planar. The experimental studies on the complexes were accompanied computationally by the DFT and time-dependent DFT calculations.