Gabriel A. Kolawole

Cadmium ethylxanthate: A novel single-source precursor for the preparation of CdS nanoparticles

CdS nanoparticles capped with tri-n-octylphosphine oxide (TOPO) have been synthesised by a single-source route using cadmium ethylxanthate as a precursor. The nanoparticles obtained show quantum size effects in the optical absorption spectra and the photoluminescence shows an emission maximum that is characteristically red shifted in relation to the band edge. The X-ray diffraction (XRD) pattern shows the material to be hexagonal with a calculated particle size (from the Scherrer equation) of 3.9 nm. The size of the particles is confirmed by the transmission electron microscope (TEM) image, which shows well-defined, spherical particles with an average size of 4.2 nm ± 10%.

Synthesis, characterization, antibacterial, and thermal studies of unsymmetrical Schiff-base complexes of cobalt(II)

Cobalt(II) complexes of a new series of unsymmetrical Schiff bases have been synthesized and characterized by their elemental analyses, melting points, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry, infrared (IR), and electronic spectral measurements. The purity of the ligands and the metal complexes are confirmed by microanalysis, while the unsymmetrical nature of the ligands was further corroborated by 1H-NMR. Comparison of the IR spectra of the Schiff bases and their metal complexes confirm that the Schiff bases are tetradentate and coordinated via N2O2 chromophore. The magnetic moments and electronic spectral data support square-planar geometry for the cobalt(II) complexes. The complexes were thermally stable to 372.3°C and their thermal decomposition was generally via the partial loss of the organic moiety. The Schiff bases and their complexes were screened for in vitro antibacterial activities against 10 human pathogenic bacteria and their minimum inhibitory concentrations were determined. Both the free ligands and cobalt(II) complexes exhibit antibacterial activities against some strains of the microorganisms, which in a number of cases were comparable with, or higher than, that of chloramphenicol.

Synthesis and characterisation of some N-alkyl/aryl and N,N′-dialkyl/aryl thiourea cadmium(II) complexes: the single crystal X-ray structures of [CdCl2(CS(NH2)NHCH3)2]n and [CdCl2(CS(NH2)NHCH2CH3)2]

A series of cadmium(II) complexes with N -alkyl or aryl and N ,N ?-dialkyl or diaryl thioureas (RNHCSNHR?; where R � /R?� / CH3 ,C H 2CH3 ,C 6H5 and or R ?� /H) have been synthesised and characterised. The structures of the polymer [CdCl2(CS(NH2)NHCH3)2]n (I) and monomer [CdCl2(CS(NH2)NHCH2CH)2 ]( II) were determined by single crystal X-ray methods. The structure (I) is a polymer chain built from [CdCl3S3] distorted octahedra. Complex II is monomeric with a distorted tetrahedral geometry at the cadmium centre. 1 H NMR spectroscopy in deuterated dimethyl sulfoxide at room temperature had broadened NH peaks in the lower field (region 6.0 � /10.0 ppm) which indicates the presence of both cis and trans -isomers for the N alkylthioureas. All the spectroscopic data obtained are consistent with the coordination of ligands by sulphur atom to the metal ion. Thermogravimetric studies show that several of these complexes decompose cleanly to CdS and may be useful in materials preparation.

Preparation of CdS nanoparticles using the cadmium(II) complex of N,N′-bis(thiocarbamoyl)hydrazine as a simple single-source precursor

CdS nanoparticles have been synthesised by thermolysing Cd(SCNHNH2)2Cl2 in tri-n-octylphosphine oxide (TOPO) at 230°C. The optical properties and structural characteristics of the particles are reported.

Synthesis, Physicochemical, and Biological Properties of Nickel(II), Copper(II), and Zinc(II) Complexes of an Unsymmetrical Tetradentate Schiff Base and Their Adducts

Nickel(II), copper(II) and zinc(II) complexes of unsymmetrical Schiff base derived from 2-hydroxy-1-naphthaldehyde, 2,4-pentanedione and p-phenylenediamine of the general formula [M(C10H6OCH:N(C6H4)N:C(CH3)CH:C(CH3)O)], [ML], and their adducts with 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) have been synthesized and characterized by elemental analyses, conductance, room temperature magnetic susceptibility, and infrared and electronic spectral measurements. The ligand is tetradentate, coordinating via the imine N and enolic O atoms. The magnetic moments and electronic spectra corroborate octahedral geometry for Ni(II) and Cu(II) complexes whereas the Zn(II) Schiff base complex analyzed 4-coordinate and the adduct 6-coordinate. The Ni(II) and Cu(II) complexes incorporated two water molecules each. The antimicrobial properties of the ligand and compounds against Staphylococcus aureus, Streptococcus faecalis, Bacillus sp, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Klebsiella pneumoniae, Acinetobacter sp, Flavobacterium sp, Enterococcus faecalis and Candida albicans are reported. The compounds generally exhibited good activity against the selected organisms. The compound [CuLphen] has comparable activity to gentamycin. The minimum inhibitory concentrations (MICs) of the sensitive compounds are between 1.0–12.0 mg/mL.

Synthesis, characterization, and insulin-enhancing studies of unsymmetrical tetradentate Schiff-base complexes of oxovanadium(IV)

A series of unsymmetrical tetradentate Schiff bases were synthesized by interaction of 2-hydroxy-1-naphthaldehyde, phenylenediamine and salicylaldehyde, or substituted salicylaldehyde in an ethanolic medium. The oxovanadium(IV) complexes and the ligands were synthesized and characterized by elemental analyses, 1H NMR, infrared, electron paramagnetic resonance, electronic spectra, cyclic voltammetry, and room temperature magnetic susceptibility measurements. The elemental analyses for both the ligands and the metal complexes confirmed purity of the compounds as formulated. Electron paramagnetic resonance spectra of the complexes were measured as powder and in toluene/dichloromethane (9 : 1, v/v) solution at room and liquid N2 temperatures. The g values, g o = 1.971, g ⊥ = 1.978, and g = 1.950, are the same for all the complexes examined. The vanadium nuclear hyperfine splitting, A o = 101–99, A ⊥ = 65–64, A ∥ = 179–177, vary slightly with substituents on the salicylaldehyde. Infrared spectra reveal strong V=O stretching bands in the range 970–988 cm−1, typical of monomeric five-coordinate complexes. The room temperature magnetic moments of 1.6–1.8 BM for the complexes confirmed that the complexes are V(IV) complexes, with d1 configuration. Only one quasi-reversible wave is observed for each compound and they all showed redox couples with peak-to-peak separation values (ΔE p) ranging from 78 to 83 mV, indicating a single step one electron transfer process. Insulin-mimetic tests on C2C12 muscle cells using Biovision glucose assay showed that all the complexes significantly stimulated cell glucose utilization with negligible cytotoxicity at 0.05 µg µL−1.

Synthesis, characterization and biological studies on unsymmetrical Schiff-base complexes of nickel(II), copper(II) and zinc(II) and adducts with 2,2′-dipyridine and 1,10-phenanthroline

A series of metal(II) unsymmetrical Schiff-base complexes, {M(C10H6OCH:N(CH2)2N : C(CH3)CH : C(CH3)O), where M=Ni(II), Cu(II) and Zn(II)}, and their 2,2′-dipyridine (bipy) and 1,10-phenanthroline (phen) adducts are synthesized and characterized by microanalysis, magnetic susceptibility, conductance, IR and UV-Vis spectra. The ligand coordinates using the N2O2 chromophore to give a two-metal-center four-coordinate square-planar geometry. IR and UV-Vis spectra are consistent with octahedral adducts. The compounds are non-electrolytes in nitromethane and magnetic moments indicate that the complexes are magnetically dilute. The antimicrobial activity of the compounds against ten bacteria and one fungus are reported. The Cu(II) and Zn(II) complexes showed good activity against many of the organisms while their adducts are generally not sensitive. The minimum inhibitory concentrations (MICs) of the sensitive compounds are between 3.0–13.0 mg mL−1.

Cd(NH2CSNHNHCSNH2)Cl2: a new single-source precursor for the preparation of CdS nanoparticles

Abstract The complex of cadmium with dithiobiurea, [Cd(NH 2 CSNHNHCSNH 2 )Cl 2 ], has been used as a precursor for the synthesis of CdS nanoparticles. The precursor was decomposed in tri- n -octylphosphine oxide to give CdS nanoparticles that show quantum confinement effects with characteristic close to band edge luminescence. The broad diffraction in the XRD pattern and diffused diffraction rings of the SAED pattern are typical of nanometer-sized particles. The particle morphology was found to depend on the temperature of injection of the precursor. Transmission electron microscopy shows irregular non-spherical particles prepared by injection at 150 °C, whilst with injection at 240 °C the particles are formed as spherical aggregates of relatively uniform size (50 nm).

MAGNETIC AND SPECTRAL PROPERTIES OF OXOVANADIUM(IV) COMPLEXES OF QUADRIDENTATE NAPHTHALDIMINE LIGANDS

Abstract Oxovanadium(IV) complexes of 2-hydroxy-1-naphthaldehyde and the Schiff-base complexes [VO{OC10H8CH=N—CR1R2—(CH2) n–1—N=CHC10H8O}] where n = 2 (R1 = R2 = H or CH3) and n = 3–8 (R1 = R2 = H) along with the corresponding ligands have been synthesised and characterised by elemental analysis, i.r. and electronic spectral and magnetic susceptibility measurements. There is evidence that the conversion of the bis-napthaldehyde complex to the Schiff-base complexes is accompanied by an inversion of the eπ∗ and b 1∗ energy levels. Moreover, the introduction of a second phenyl ring results in a reduction of the in-plane ligand field. The v(V=O) frequencies suggest that the complexes are five-coordinate, except VO(naph2-tn) which is likely to be six-coordinate and polymeric. Although the magnetic moments at room temperature for the complexes vary between 1.59 and 1.77 B.M. the variation of the moments with temperature is not appreciable.

Spectroscopic and magnetic properties of Schiff base complexes of oxovanadium(IV) derived from 3-methoxysalicylaldehyde and aliphatic diamines

Abstract Oxovanadium(IV) complexes of 3-methoxysalicylaldehyde and the Schiff base complexes VO[OC6H3(OCH3)CHNCR1R2(CH2)n−1NCH(OCH3)C6H3O] were n = 2(R1  R2  H or CH3) and n = 3 to 10(R1  R2  H) have been prepared and characterised by elemental analysis, IR and electronic spectra and magnetic susceptibility measurements. Evidence is adduced that the conversion of the bis-aldehyde complex to the Schiff base complexes is accompanied by an inversion of the e π ∗ and b 1 ∗ energy levels. The ν (V = 0) frequency of 979–988 cm−1 observed for most of the complexes, except when R1  R2  H and n = 3 where ν (V = 0) is 864 cm−1, are normal for five-coordinate oxovanadium(IV) complexes. The magnetic moments at room temperature of the chelates fall in the range 1.72–1.83 B.M. and vary very slightly over the temperature range 320-80 K.