Iwona Kuźniarska-Biernacka

UV–Vis–NIR spectroscopy and colour of bis(N-phenylsalicylaldiminato)cobalt(II) in a variety of solvents

Abstract Cobalt(II) complex with Schiff base obtained by condensation aniline with salicylaldehyde cobalt(II) complex, was studied in variety of solvents. The product i.e. salicylidene-anilinecobalt(II) ([Co(salan)2]) complex is a red crystalline compound easily soluble in common solvents like chloroform (CHCl3), benzene (Bz), toluene (MBz), dioxane (DX), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetonitrile (ACN) that is a necessary condition to observe solvatochromism. It has been characterised by elemental analyses, molar conductivities, ultraviolet (UV) and visible (Vis) spectroscopy. The molar conductivities indicate their non-electrolytic properties in all the solvents. Electronic spectra have been used to postulate the tetrahedral geometry for the species in solutions and to determine the coordination properties of ligators and their bonding abilities (ligand-field parameters), as well as their solvatochromism. The results obtained show fine colour changes. For discrimination of colour changes we applied CIE and CIELAB colour spaces.

Epoxidation of styrene by a manganese(III) salen complex encapsulated in an aluminium pillared clay

The manganese(III) complex—carboxylate-[N,N′-bis(salicylaldehyde)cyclohexanediaminate]manganese(III), [Mn(salhd)CH3COO]—was encapsulated into an aluminium pillared clay (denoted as Al-WYO) using a two-step liquid phase methodology: (i) adsorption of manganese(II) acetate in ethanolic solution within Al-WYO, followed by (ii) diffusion of N,N′-bis(salicylaldehyde)cyclohexanediamine in ethanolic solution. The new material was characterised by several techniques (ICP-AES, XPS, FTIR, UV–Vis and low temperature nitrogen adsorption) which showed that in situ synthesis of the manganese(III) complex took place within the aluminium pillared clay porous structure. n The catalytic activity of the heterogenised [Mn(salhd)CH3COO] in the epoxidation of styrene was studied in acetonitrile, at room temperature, using iodosylbenzene or sodium hypochlorite as oxygen source. With PhIO the new heterogeneous catalyst showed high styrene epoxide chemoselectivity and could be reused at least 3 times without significant loss in styrene epoxide yield, suggesting that no complex leaching took place under the reaction conditions used. When sodium hypochlorite was used as oxidant, high selectivity in by-products was observed, as well as extensive leaching of the catalyst into solution. XPS spectra of the catalyst after the catalytic reaction confirm manganese complex leaching and also show a significant decrease in aluminium content, thus suggesting that partial damage of aluminium pillars took place in this reaction media, inducing complex leaching.

Spectrochemical properties of cobalt(II) complex with bidentate Schiff base in various solvents

As a continuation of our previous studies on copper(II) complexes with a bidentate Schiff base derived from 5-bromosalicylaldehyde and α-aminopyridine, we have investigated the electronic spectra of the cobalt(II) complex with this ligand. The complex is a red crystalline compound soluble in common solvents, such as chloroform, dioxane, dimethyl formamide, dimethyl sulfoxide, and methanol. The time-elapsed spectral measurements of the complex and ligand, as well as conductivities of the complex in chloroform and dioxane solutions, are presented and discussed. Molar conductivities indicate that the complex exists as a nonelectrolyte in nonpolar solvents and as a 1:1 or 1:2 electrolyte in polar solvents. The ligand-field parameters (CFM/AOM) for the complex in chloroform solution are estimated and discussed.

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solutions. XV. Solution Properties of bis(Salicylideneaniline)Copper(II)

The complex obtained by condensation of salicylideneaniline with copper(II) acetate was studied in a variety of solvents. This deep-brown crystalline compound is soluble in common solvents, such as, chloroform, toluene, dioxane, methanol, ethanol, dimethyl formamide, dimethyl sulfoxide, and acetonitrile—a necessary condition for observing solvatochromism. The complex has been characterized by elemental analysis, molar conductivity, EPR, and ultraviolet (UV) and visible (VIS) spectroscopy. The available X-ray data shows planar coordination geometry for the copper center. Combined multi-technique experiments have been applied to confirm the structure of the complex in solution. The molar conductivities indicate nonelectrolytic properties. EPR measurements preclude the possibility of solvent coordination at the axial positions of the complex. Spectroscopic measurements were used to study the coordination properties of donor atoms and their bonding ability, as well as trichromaticity coordinate calculations. The results obtained show that the interactions of metal with donors depend on donor strength and polarity of solvent.

Spectrochemical properties of noncubical transition metal complexes in solution. XII. Angular overlap studies of salicylideneethylenediamine Cu(II) complex in various solvents

As a part of our general interest in the UV-Vis spectroscopy of multidentate mixed-donor ligands, the (salicylideneethylenediamine)Cu(II) complex has been prepared and characterized by elemental analyses, solubility in common solvents, molar conductivities, and ultraviolet (UV), and visible (Vis) spectroscopy. The combined results of spectrophotometric measurements and EPR spectra, as well as known the X-ray structure for solids, were used to determine the structure of the investigated complex in solutions. The spectra of [Cu(salen)] (H2salen = salicylideneethylenediamine), were measured in various solvents at room temperature, resolved by Gaussian analysis, and angular overlap model (AOM) treated in C2v symmetry. Because of overparametrization problems, the bis(salicylaldehyde)Cu(II) complex has been characterized and AOM treated. The results of this have been used for AOM studies of [Cu(salen)]. The effect of the solvents upon the σ- and π-bonding ligand abilities is discussed.

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solutions. VIII. Angular Overlap Treatment of a Schiff Base Copper(II) Complex in Various Solvents

The electronic absorption spectra of trans-[Cu(Brsap)2], where [HBrsap = 5-bromosalicylidine-o-aminopyridine (Schiff base)], were measured in various solvents at room temperature. The d-d transition energies were used to derive the angular overlap model (AOM) parameters in the C2h symmetry. The experimental curves were resolved by Gaussian analysis. A comparison of the spectra and ligand field parameters in various solutions was made. The effect of the solvents upon the σ-, π-bonding, and bite angle of the bidentate asymmetric ligand is discussed.

K10-montmorillonite as support for a cationic manganese(III)-salen complex

A commercial K10-montmorillonite was used as support for the immobilization of a cationic manganese(III)-salen complex. The catalytic behavior of the resulting material was tested in the enantioselective epoxidation of three different alkenes, viz.: styrene, α-methylstyrene and 6-cyano-2,2-dimethylchromene, at 0 oC, using three different oxidant systems: m-chloroperoxybenzoic acid (m-CPBA) and N-methylmorpholine (NMO) as co-oxidant, iodosylbenzene (PhIO) and sodium hypochlorite. All samples, before and after the catalytic studies, were characterised by nitrogen adsorption at -196 oC, DRX, FTIR and chemical analysis, in order to evaluate the influence of the substrate/oxidant system on catalyst integrity. The catalytic results demonstrated a strong influence of the substrate and oxidant system on the enantiomeric excess (%ee) values. In some cases, these values were comparable to those in the corresponding homogeneous phase reactions. The results also highlighted the importance of optimizing the oxidant systems, since they may lead to the disruption of the complex from the support, and the consequent catalyst deactivation.

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solutions. XIV. Angular Overlap Studies of bis(Salicylidene-2-aminothiazole)Copper(II) in Various Solvents

The copper(II) complex [Cu(sat)], where Hsat is salicylidene-2-aminothiazole (bidentate Schiff - base), was studied in variety of solvents. In the solid state, the complex is black. It has been characterized by elemental analysis, solubility in common solvents, molar conductivity, and ultraviolet (UV) and visible (Vis) spectroscopy. The complex is easily soluble in common solvents such as chloroform, dimethylformamide, dimethyl sulfoxide, and 1,4-dioxane. The known crystal structure of similar compounds shows planar coordination geometry for the copper center. Combined multitechnique experiments have been applied to confirm the structure of the complex in solutions. The molar conductivities indicate their nonelectrolyte properties in all these solvents. The spectroscopic measurements were used to study the coordination properties of donoratoms and their bonding abilities.