Gareth M. Watkins

Thermal and structural studies of amide complexes of transition metal(II) chlorides. I: Stoichiometry

Abstract A series of aliphatic amide complexes of nickel(II), cobalt(II) and copper(II) chlorides has been prepared. These complexes have the general formulae: NiL 2 Cl 2 ·2H 2 O, NiL 2 Cl 2 , Ni 3 L 2 Cl 6 , Ni 3 LCl 6 , CoL 2 Cl 2 and CuL 2 Cl 2 , where L is the amide ligand. Ligands ranging from formamide to butyramide, both with and without N -methyl and N -ethyl substituents, were used. The complexes were found, from the absorption spectra, to be octahedral or distorted-octahedral, except for some of the cobalt complexes with dimethyl substituted ligands which are tetrahedral. Infrared spectra confirm that coordination to the metal ion is through the carbonyl oxygen. The effects of the structure and the nature of the different amide ligands on the thermal stabilities of the complexes have been investigated by thermal analysis. As indicators of the stability of the metal–amide binding, thermal decomposition onset temperatures ( T e ), peak temperatures ( T max ) and enthalpies (Δ H L ) were compared for complexes with similar composition, geometrical structure and decomposition stoichiometry. Results do not support the enhancement of thermal quantities with increasing basicity of the amides. Instead, steric factors appear to play a more important role in determining the magnitudes of Δ H L , T e and T max

Crystal structures, spectroscopic and theoretical study of novel Schiff bases of 2-(methylthiomethyl)anilines

New Schiff bases derived from p-methoxysalicylaldehyde and 2-(methylthiomethyl)anilines (substituted with methyl, methoxy, nitro) were synthesized and characterized by elemental analyses, FT-IR, NMR, electronic spectra and quantum chemical calculations. X-ray crystallography of two compounds showed the solid structures are stabilized by intramolecular and intermolecular H-bonds. The effect of OH⋯N interaction between the phenolic hydrogen and imine nitrogen on the proton and carbon NMR shifts, and the role of CH⋯O and CH⋯S contacts are discussed. The bond lengths and angles, (1)H and (13)C NMR data, E(LUMO-HOMO), dipole moments and polarizability of the compounds were predicted by density functional theory, DFT (B3LYP/6-31G∗∗) method. The experimental geometric parameters and the NMR shifts were compared with the calculated values, which gave good correlations. The electronic effects of aryl ring substituents (methyl, methoxy and nitro) on the properties of the resulting compounds, such as the color, NMR shifts, electronic spectra and the calculated energy band gaps, dipole moments and polarizability are discussed. Increase in electron density shifted the phenolic proton resonance to lower fields. The methoxy-substituted compound has a small dipole moment and subsequent large polarizability value. Highest polarity was indicated by the nitro compound which also showed high polarizability due to its larger size. The energy gaps obtained from E(LUMO-HOMO) calculations suggest these compounds may have applications as organic semiconducting materials.

Copper(II) Complexes of 2-(Methylthiomethyl)anilines: Spectral and Structural Properties and In Vitro Antimicrobial Activity

Copper(II) complexes of 2-(methylthiomethyl)anilines (1a–1f) have been obtained and characterized by elemental analyses, IR, electronic spectra, conductivity, and X-ray crystallography. The complexes (2a–2f) have the structural formula [CuCl2L] with the bidentate ligand coordinating through sulfur and nitrogen. The single crystal X-ray diffraction data reveal that the copper complex (2f) has a tetragonally distorted octahedral structure with long Cu–Cl equatorial bonds. Magnetic susceptibility measurements indicate the availability of one unpaired electron in the complexes and the conductivity measurements in DMF show their behaviour as nonelectrolytes. The solid reflectance spectra and the electronic spectra of the complexes in DMSO were determined. The ligands and their copper complexes were screened for in vitro antimicrobial activity against S. aureus, B. subtilis, E. coli, and C. albicans. The methoxysubstituted complex (2c) showed more promising antibacterial activity against S. aureus and B. subtilis than other compounds at the concentration tested.

Biomimetics of mononuclear and dinuclear Cu(II) and Fe(III) complexes of a newly synthesized piperazyl Mannich base with or without thiocyanate towards catechol

This paper presents the synthesis and characterization of Cu(II) and Fe(III) complexes of a newly synthesized Mannich base N-[4-hydroxy-3-[[4-(pyridin-2-yl)piperazin-1-yl]methyl]phenyl]acetamide. The spectro-analytical techniques employed include 1H, 13C NMR, IR, UV spectroscopy, conductivity measurements, and elemental analysis. Both mononuclear and dinuclear metal complexes were encountered in the study. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, catecholase activity of all four complexes was evaluated with the detailed kinetic studies reported. The nature of the bonding of the thiocyanate is discussed based on the observation of νCN (2150–2050xa0cm−1). All the metal complexes are catalytically active with turn over numbers ranging from 9.47 to 31.86xa0h−1 in DMF.Graphical abstract

Impact of Thiocyanate on the Catecholase Activity of Cu(II) and Fe(III) Complexes of 2-((4-(2-Hydroxy-4-Methylbenzyl)Piperazin-1-YL)Methyl)-5-Methylphenol (A Mannich Base)

Abstract Four metal complexes viz Cu(II) and Fe(III) with or without thiocyanate have been synthesized from a Mannich base prepared by a simple synthetic route. These complexes were characterized by elemental and spectroscopic techniques. Bonding modes of the thiocyanate group with the metal complexes as studied by infrared spectroscopy revealed the presence of bridging N- and S- bonding modes. Detailed kinetic studies of these complexes were carried in the evaluation of their catecholase activity. The Fe(III) complex demonstrated the highest catalytic activity using 3,5-di-tert-butyl catechol (3,5-DTBC) as substrate with a turnover rate (kcat) of 112.32 h−1.

Synthesis, structure, and theoretical studies of bis(five-coordinate) μ–O–[CuL2]2: predicting distortion toward trigonality

Abstract An oxo-bridged binuclear Cu(II) complex, [CuL2]2, has been synthesized and characterized by microanalysis, spectra (infrared and electronic), and X-ray diffraction crystallography. The theoretical properties of the complex were studied using the semi-empirical PM3 method. The optimized geometries, dipole moment, thermodynamic parameters, and vibrational frequencies were investigated. The crystal structure revealed that each Cu(II) was five-coordinate with a distorted square pyramidal geometry (τu2009=u20090.324 and 0.307). The two units of the complex were bridged by phenolic oxygens to give a binuclear Cu(II) complex with the average bridging angle and Cu⋯Cu distance being 98.49° and 3.413 Å, respectively. Theoretical studies revealed that the geometric parameters are in agreement with the experimental data. The compound was stable and has good non-linear optical properties.