Ahmed T. Mubarak

Supramolecular structural and spectral perspectives of novel ruthenium(III) azodye complexes

Five bis-[5-(4′-R-phenylazo)-8-hydroxyquinoline] ruthenium complexes [RuLn · Cl2 · OH2]; where Ln = 5-(4′-R-phenylazo)-8-hydroxyquinolinol, R = OCH3 (n = 1), CH3(2), H(3), Cl(4), NO2(5), have been prepared and characterized on the basis of elemental analyses, IR, 1H NMR, ESR, thermal analysis and magnetic susceptibility measurements. The data show that these complexes exist in trans-isomeric solid form. Two inversion-related ligands and two Ru3+ atoms form a cage-like dimer. Both ligands of the dimer are bridged by a pair of inversion-related Ru–N (azodye) bonds. The octahedral coordination geometry of Ru3+ is made up of an N of pyridine, the deprotonated quinoline O atom, one of the azodye N atoms, two chlorides and one water. The ligands in the dimer are stacked over one another. In the solid state of azo-8-hydroxyquinoline, the dimers have inter-and intramolecular hydrogen bonds. Interactions between the ligands and the metal are discussed. The azo group was involved in chelation for all the prepared complexes. The effect of Hammets constant on the ligand field parameters are also discussed and drawn.

Highly sensitive and selective catalytic determination of formaldehyde and acetaldehyde

A highly sensitive, simple and selective kinetic method was developed for the determination of ultra-trace levels of formaldehyde and acetaldehyde based on their catalytic effect on the oxidation of N,N-diethyl-p-phenylenediamine (DPD) with hydrogen peroxide. The reaction was monitored spectrophotometrically by tracing the formation of the red-colored oxidized product of DPD at 510nm, within 30s of mixing the reagents. The optimum reaction conditions were: 20mmolL(-1) DPD, 250mmolL(-1) H(2)O(2), 150mmolL(-1) phosphate, 150mmolL(-1) citrate and pH 6.60+/-0.05 at 25 degrees C. Following the recommended procedure, formaldehyde and acetaldehyde could be determined with linear calibration graphs up to 0.50 and 1.4microg mL(-1) and detection limits, based on the 3S(b)-criterion, of 0.015 and 0.035microg mL(-1), respectively. In addition, analytical data for other 10 aldehydes were also presented. The high sensitivity and selectivity of the proposed method allowed its successful application to rain water, mainstream smoke (MSS) and disposed tips of smoked cigarettes (DTSC). A sample aliquot was directly analyzed for its total water-soluble aldehyde content. A second sample aliquot was heated at 80 degrees C for 10min to expel acetaldehyde and the aliquot was analyzed for its content of other water-soluble aldehydes (expressed as formaldehyde equivalent), and acetaldehyde was determined by difference. The analytical results were in excellent agreements with those obtained following the standard HPLC method based on pre-column derivatization with 2,4-dinitrophenylhydrazine. Moreover, published catalytic-spectrophotometric methods for the determination of aldehydes were reviewed.

A novel kinetic determination of dissolved chromium species in natural and industrial waste water.

A highly sensitive, selective and simple kinetic method was developed for the determination of dissolved chromium species based on the catalytic effect of Cr(III) and/or Cr(VI) on the oxidation of 2-amino-5-methylphenol (AMP) with H(2)O(2). The fixed time and initial rate variants were used for kinetic spectrophotometric measurements by tracing the oxidized product at 400nm for 10min after starting the reaction. Boric acid and Tween-40 exerted pronounced activating and micellar sensitizing effects on the studied redox reaction, respectively. The optimum reaction conditions were: 3.0mmoll(-1) AMP, 0.45moll(-1) H(2)O(2), 0.50moll(-1) boric acid, 4v/v% Tween-40, 10mmoll(-1) phosphate buffer and pH 6.45+/-0.02 at 35 degrees C. Both Cr(III) and Cr(VI) ions exerted the same catalytic effect on the studied reaction. Linear calibration graphs were obtained for the determination of up to 6.0ngml(-1) Cr with detection limits of 0.054 and 0.10ngml(-1) Cr; following the fixed time and initial rate methods, respectively. The proposed method was successfully applied to the speciation and determination of trace levels of dissolved Cr(III) and Cr(VI) in natural and effluents of industrial waste water. The total dissolved Cr(III) and Cr(VI) species was determined first. In a second run, Cr(VI) was determined alone after precipitation of Cr(III) ions in presence of Al(OH)(3) collector, where Cr(III) is then determined by difference. Moreover, published catalytic-spectrophotometric methods for chromium determination were reviewed.

Highly sensitive catalytic determination of molybdenum.

A novel, highly sensitive, selective, and simple kinetic method was developed for the determination of Mo(VI) based on its catalytic effect on the oxidation of 1-amino-2-naphthol-4-sulfonic acid (ANSA) with H(2)O(2). The reaction was followed spectrophotometrically by tracing the oxidized product at 465nm after 30min of mixing the reagents. The optimum reaction conditions were: 10mmol l(-1) ANSA, 50mmol l(-1) H(2)O(2), 100mmol l(-1) acetate buffer of pH 5.0+/-0.05 and at 40 degrees C. Addition of 200microg ml(-1) diethylenetriaminepentaacetic acid (DTPA) conferred high selectivity for the proposed method. Following the recommended procedure, Mo(VI) could be determined with a linear calibration graph up to 2.5ng ml(-1) and a detection limit, based on the 3S(b)-criterion, of 0.027ng ml(-1). The unique sensitivity and selectivity of the implemented method allowed its direct application to the determination of Mo(VI) in natural and industrial waste water. The method was validated by comparison with the standard ETAAS method. Moreover, published catalytic-spectrophotometric methods for the determination of molybdenum were reviewed.

Supramolecular structures of oxovanadium(IV) polymeric complexes containing quinoline azodyes

A novel series of oxovanadium(IV) monomeric and polymeric complexes with 5-(4′ derivatives phenylazo)-8-hydroxy-7-quinolinecarboxaldehyde (HLn) has been synthesized and characterized. The composition, structural, chemical and electronic properties were investigated by elemental analysis followed by 1H-NMR to determine the effect of substituents on the intramolecular hydrogen bond. The electronic properties and model of bonding of ligands as well as complexes were investigated by UV-Vis and IR spectroscopy. Comparison with reference data along with electronic and IR spectroscopies allow identification of the molecular structures for the polymeric complexes, where a six coordinate square planar with an oxygen atom in the apical position was proposed. Data from the above combined techniques reveal the formation of two isomeric forms. The polymeric structure results from intermolecular V=O…V=O interactions, whereas the ligands act as a monobasic bidentate chelating agent coordinating through CO and OH groups by replacing a proton from the latter group.

Potentiometric and thermodynamic studies of 5-(4'-sulfonylazidophenylazo)-3-phenyl-2-thioxothiazolidin-4-one and its metal complexes

The proton dissociation constant of 5-(4′-sulfonylazidophenylazo)-3-phenyl-2-thio- xothiazolidin-4-one (SPT) and the stability constants of its complexes with some metal ions were calculated potentiometrically in 0.1 M KCl and 40% (v/v) ethanol–water mixture. The order of stability was found to be Mn2+ < Co2+ < Ni2+ < Cu2+ < Zn2+. The effect of temperature on the dissociation of SPT and the stability of its complexes were studied. The corresponding thermodynamic functions were derived and discussed. The dissociation process is unspontaneous, endothermic, and entropically unfavorable. The formation of the metal complexes was found to be spontaneous, endothermic and entropically favorable.

Supramolecular modeling in novel polymeric complexes of ruthenium and uranium derived from azoquinoline containing hydrogen bonds

Novel polymeric complexes of Ru3+ and with 5-(2−-alkyl phenylazo)-8-quinolinol (LnH2) have been prepared and characterized by elemental and thermogravimetric analysis (TGA), 1H and 13C NMR, magnetic susceptibility and electronic spectral techniques. The important infrared (IR) bands and the main 1H and 13C NMR signals are assigned and discussed relative to the proposed molecular structure of the polymeric complexes. The spectra show that all complexes are octahedral with chloride attached to the metal. The spectral data were utilized to compute the important ligand field parameters B, β and Dq. The B-values suggest covalency in the metal-ligand σ-bond and the Dq-values indicate a medium strong ligand field. β depends greatly on the electronegativity of the donor atoms and the ligand structure and also the effect of the o-substituent groups. The ligands are dibasic (bis-bidentate chelating agent), coordinating through CN, N=N, COOH, OH and SH groups by replacement of a proton from the last three groups. The bond lengths and the force constants of the U–O bond were calculated from the IR data related to the electronic properties of the substituents. Considerable interest has been focused on the synthesis of azo compounds and polymeric metal complexes. The stability of these complexes has also been investigated. O-azo-quinolinols intramolecular OH–N hydrogen bonds have been detected and discussed.

Role of a Novel Mixed-Valence-Ligand on the Structures of Supramolecular Polymeric Complexes

The design of supramolecular polymer complexes of ruthenium, rhodium and uranium based on the homopolymer N-acryloyl-1-ethyl-2-thiourea (AETH) has been pursued. AETH shows three types of coordination behaviour. It acts as a neutral bidentate ligand coordinating through its thiocarbonyl sulphur and carbonyl oxygen atoms in both the mixed valence paramagnetic trinuclear polymer complexes ((1) and (2)) and mononuclear polymer complexes ((3)–(5)). On the other hand, it behaves as a monobasic bidentate ligand coordinating through CS and enolic (C–O) bonds in the mixed ligand poly-chelates (PAETH), which are obtained from the reaction of AETH with RuCl3 · x H2O in the presence of N-heterocyclic base consisting of polymer complexes ((7) and (8)). The mononuclear compound (6) acts as a monobasic and neutral bidentate ligand coordinating through CO and imino atoms. Monomeric distorted octahedral or trimeric chlorine-bridge pseudo-octahedral structures are proposed for these polymer complexes. The stoichiometries of the poly-chelates are 1:1, 1:2 and 3:2 (metal/homo-polymer) and exhibit six-coordinations. The amine homo-polymer exchange reactions of coordination poly-chelate in symmetrical and unsymmetrical bidentate homo-polymer complexes have been investigated and the ligand field parameters were also calculated. The homo-polymer and its polymer complexes have been characterized using a variety of physiochemical techniques.

Solvent-free hydrogenation of cyclohexene over Rh-TUD-1 at ambient conditions

Rhodium nanoparticles (≈3–5 nm) were incorporated into the 3D mesoporous TUD-1 material by using sol–gel technique. The prepared catalyst shows high activity in the liquid phase conversion of cyclohexene to cyclohexane at room temperature (298 K), 1 atm H2 pressure, and under solvent-free conditions. Rhodium nanoparticles exhibited high stability, reusability and negligible leaching.

Potentiometric and Thermodynamic Studies of 2-Acrylamidosulfamethazine and Its Metal Complexes in Monomeric and Polymeric Forms

Abstract2-Acrylamidosulfamethazine (ASM) was synthesized and characterized by elemental analyses and IR spectroscopy. Proton-monomeric ligand dissociation and metal-monomeric ligand stability constants of ASM with some metal ions were determined potentiometrically in 0.1 M KCl and 40% (v/v) ethanol–water mixture. In the presence of 2,2′-azobisisobutyronitrile as an initiator, the dissociation and stability constants of ASM were determined in polymeric form (PASM). The influence of temperature on the dissociation of ASM and the stability constants of their complexes in monomeric and polymeric forms were precisely studied. The pKH value of PASM was found to be higher than ASM, which indicates that the vinyl group in the monomeric form decreases the electron density on nitrogen and hence reduces the N–H bond strength. The stability constants of the metal complexes in polymeric form are higher than those of the monomeric form. This reveals that the ligand in a polymeric form may be considered as a better complexing agent.