Mohamed R. Mahmoud

Bio: Mohamed R. Mahmoud is an academic researcher from Assiut University. The author has contributed to research in topics: Stability constants of complexes & Denticity. The author has an hindex of 11, co-authored 79 publications receiving 497 citations. Previous affiliations of Mohamed R. Mahmoud include Al Jouf University.

Synthesis, X-ray powder structure, and magnetic properties of layered NiII methylphosphonate, [Ni(CH3PO3)(H2O)], and NiII octadecylphosphonate, [Ni(CH3-(CH2)17-PO3)(H2O)].

Abstract: [Ni(CH 3 PO 3 )(H 2 O)] (1) and [Ni{CH 3 -(CH 2 ) 1 7 -PO 3 )(H 2 O)] (2) were synthesised by reaction of NiCl 2 .6H 2 O and the relevant phosphonic acid in water in presence of urea. The compounds were characterised by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy, and their magnetic properties were studied by using a SQUID magnetometer. The crystal structure of 1 was determined "ab initio" from X-ray powder diffraction data and refined by the Rietveld method. The crystals of 1 are orthorhombic, space group Pmn2 1 , with a= 5.587(1), b=8.698(1), c = 4.731(1) A. The compound has a hybrid, layered structure made up of alternating inorganic and organic layers along the b direction of the unit-cell. The inorganic layers consist of Ni" ions octahedrally coordinated by five phosphonate oxygen atoms and one oxygen atom from the water molecule. These layers are separated by bilayers of methyl groups and van derWaals contacts are established between them. A preliminary structure characterisation of compound 2 suggests the crystallisation in the orthorhombic system with the following unit-cell parameters: a = 5.478(7), b =42.31(4), c= 4.725(3) A. The oxidation state of the Ni ion in both compounds is +2, and the electronic configuration is d 8 (S = 1), as determined from static magnetic susceptibility measurements above 50 K. Compound 1 obeys the Curie-Weiss law at temperatures above 50 K; the Curie (C) and Weiss (θ) constants were found to be 1.15 cm 3 K mol - 1 and - 32 K, respectively. The negative value of θ indicates an antiferromagnetic exchange coupling between near-neighbouring Ni I I ions. No sign of 3D antiferromagnetic long-range order is observed down to T= 5 K, the lowest measured temperature. Compound 2 is paramagnetic above T= 50 K, and the values of C and 0 were found to be 1.25 cm 3 K mol - 1 and - 24 K, respectively. Below 50 K the magnetic behavior of 2 is different from that of 1. Zero-field cooled (zfc) and field-cooled (fc) magnetisation plots do not overlap below T= 21 K. The irreversible magnetisation, ΔM f c - c f c , obtained as a difference from fc and zfc plots starts to increase at T= 20 K, on lowering the temperature, and it becomes steady at T= 5 K. The presence of spontaneous magnetisation below T= 20 K indicates a transition to a weak-ferromagnetic state for compound 2.

Molecular Complexes of some N-Aryldithiocarbamates with π-Electron Acceptors

Abstract: Solid 1:1 CT complexes formed between some S-alkyl-N-aryldithiocarbamates and π-electron acceptors (2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoethylene (TCNE), chloranil (CHL)) are synthesized and characterized. Spectral characteristics and stability of the complexes are investigated and discussed in terms of donor molecular structure, π-acceptor electron affinity, and solvent polarity. It is deduced that the complexes are mainly of the n-π type where the ground state wave function can be described primarily by the non-bonding structure. Ionization potentials of the donors are estimated from the CT transition energies of their complexes.

Open-framework structures of transition-metal compounds.

Abstract: Inorganic framework solids are no longer limited to just the silicates and phosphates. Recent research has revealed that carboxylates, arsenates, sulfates, selenates, selenites, germanates, phosphites can also form such structures. One of the emerging areas combines the rich coordination chemistry of the central metal ions of many of these structures with the flexibility and functionality of the organic linkers to give rise to organic-inorganic hybrid compounds. The compounds of the transition-metals appear to provide many variations arising from their coordination preferences, ligand geometry, and the valence state. In addition, the combination of the magnetic nature of the transition metal center with the channel structure of open frameworks suggests interesting potential applications. In this Review the synthesis, structures and properties of the various transition-metal open-framework compounds are discussed.

Antimicrobial activity studies of the binuclear metal complexes derived from tridentate Schiff base ligands

Abstract: Three novel tridentate Schiff base ligands derived from␣the 3-hydroxysalicylaldehyde (H2L1), 4-hydroxysalicylaldehyde (H2L2) and 5-bromosalicylaldehyde (H2L3) with a new amine N-(pyridyl)-2-hydroxy-3-methoxy-5-aminobenzylamine (2) have been prepared. The ligands and their metal complexes have been characterized by elemental analyses, conductivity and magnetic susceptibility measurements, i.r., electronic absorption and 1H and 13C n.m.r. spectroscopy. All complexes are binuclear and, in some, the H2O molecules are coordinated to the metal ion. Antimicrobial activities of the ligands and their complexes have been tested against to the Bacillus subtilis IMG 22 (bacteria), Micrococcus luteus LA 2971 (bacteria) Saccharamyces cerevisiae WET 136 (yeast), and Candida albicans CCM 314 (yeast). Thermal properties of all complexes have been studied by t.g. and d.t.a techniques.

Chemistry of Azoimidazoles: Synthesis, Spectral Characterization, Electrochemical Studies, and X-ray Crystal Structures of Isomeric Dichloro Bis[1-alkyl-2-(arylazo)imidazole] Complexes of Ruthenium(II)

Abstract: Several new ligands, azoimidazoles belonging to the class 1-methyl-2-(arylazo)imidazoles (L1 (3)) and 1-benzyl-2-(arylazo)imidazoles (L2 (4)) (R = H (a), Me (b), OMe (c), Cl (d), NO2 (e)) have been synthesized and reacted with RuCl3 in ethanol under refluxing conditions. Two isomers of the composition RuL2Cl2, green (i) and blue (iii), are chromatographically separated. The green isomer is quantitatively transformed to the blue isomer on refluxing in a high boiling solvent. The isomeric structures have been confirmed by X-ray crystallography. Crystal data are as follows. Green complex C38H34Cl2N8Ru (6a): crystal system monoclinic; space group C2/c; a = 15.680(8) A; b = 22.766(14) A; c = 11.473(5) A; β = 119.27(4)°; V = 3573(3) A3 Z = 4; R = 3.59%; Rw = 4.38%. Blue complex C22H24Cl2N8Ru (7b): crystal system monoclinic; space group P21/n, a = 9.547(6) A; b = 22.554(14) A; c = 11.748(8) A; β = 99.07(5)°; V = 2498(3) A3; Z = 4; R = 3.15%; Rw = 4.51%. With reference to the pairs of Cl, N(imidazole), and N(az...