Browsing by Author "Koch, Klaus"

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    Determination of platinum, palladium and rhodium, in aqueous media by means of reversed phase-high performance liquid chromatography (RP-HPLC) after complexation with N,N-dialkyl-N'-acylthioureas
    (2000) Mautjana, Nare Alpheus; Koch, Klaus
    The complexes were successfully separated using conventional Reversed Phase-High Performance Liquid Chromatography (RP-HPLC) and a UV detector. A simple method of complexation of platinum(II) and palladium(II) in acidic, aqueous samples was developed. This method involves the mixing of excess ligand (HL") in acetonitrile with aqueous solutions containing traces of platinum(II) and palladium(II) at room temperature followed by salt-induced phase separation prior to RP-HPLC analysis. In the case of rhodium(III), however, complexation was extremely slow and it has not been possible to include this metal in the complexation procedure for platinum(ll) and palladium(II).
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    The effect of stannous chloride on the solvent extraction of tetrachloroplatinate(II) ion by triphenylphosphine
    (1981) Yates, Janet Elizabeth; Koch, Klaus
    The effect of SnCl₂ on the solvent extraction of K₂PtCl₄ in HCl into CH2Cl2 using triphenylphosphine (PPh₃) has been studied in detail. It has been found that SnCl₂ dramatically increases the rate and efficiency of extraction. Our studies show that the percentage Pt extraction depends upon the time allowed for extraction, the Pt(II)/PPh₃ ratio, the Pt(II)/Sn(II) ratio and the HCl concentration in a complicated way.
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    Progressive design and self-assembly of supramolecular architectures : based on metallamacrocyclic nickel(II) complexes with bipodal tetra-alkylaroylbis (thioureas)
    (2004) Hallale, Oren; Bourne, Susan A; Koch, Klaus
    Rationally designed bipodal3,3,3',3'-tetraalkyl-l,1'-benzoylbis(thioureas) are used as pre-programmed cheiating ligands to form metallamacrocyclic square planar nickel(ll) complexes via self-assembly. Metal : ligand stoichiometries of either 2:2 or 3:3 can be achieved by using meta- or para- substituted ligands. The metallamacrocyclic complexes are subsequently converted into octahedral adducts via the addition of monodentate nitrogen donor ligands. Metallamacrocycles are further employed as secondary building units in the self-assembly of I-dimensional double- or tripleconnected coordination polymers. The synthesis of these polymers is achieved with the use of exo-bidentate nitrogen donor ligands.
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    Selective preconcentration of platinum and rhodium from hydrochloric acid media containing tin (II) chloride using polyurethane foam
    (1987) Jones, Lynn; Koch, Klaus
    The potentially quantitative and selective sorption of chloro-(trichlorostannato)-platinum(II) and -rhodium (III/I) complex anions by polyurethane foams has been examined. Quantitative separation of platinum(II) from iridium and ruthenium has been achieved. Rhodium( III) is similarly sorbed by polyurethane foam in the presence of sufficient tin(II) chloride and-its clean separation from iridium has been achieved using this method. Ruthenium, although not significantly sorbed under the same conditions as platinum and rhodium, appears to inhibit the extraction of the rhodium(III/I)-tin(II) species. A procedure has been developed for the quantitative recovery of both platinum and rhodium. The polyurethane foams are dissolved in hot nitric acid, followed by flame AAS. Near-quantitative recovery of these metals has been achieved by means of foam stripping using a suitable eluent. The rate of formation of the chloro-(trichlorostannato)platinum( II) complex anions is rapid when PtCl₄²⁻ is treated with an excess of tin( II) chloride. On the other hand, the reaction of cis-Pt(NH₃)₂Cl₂ with stannous chloride is very slow and forcing conditions are required to achieve quantitative sorption of the platinum(II)-tin( II) species by polyurethane foams for this complex The potential of the foam to selectively extract platinum from solutions containing certain base metals was studied. Results obtained show that in all cases complete extraction of platinum was achieved. Of the base metals investigated, namely Fe( III), Co( II), Ni(II), Cu(II) and Zn(II), only copper(II) co-extracts to a small extent with the noble metal.
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    Synthesis of mixed ligand, water soluble square planar platinum (II) complexes and an investigation of their association with haematin and potential to inhibit the formation of synthetic malaria pigment
    (2002) Swan, Paul Lombard; Egan, Timothy J; Koch, Klaus
    To establish their potential as a template for novel anti-malarial drugs, a series of planinum (II) complexes were synthesised, their association with haematin determined in 40 aqueous DMSO, pH 7.4 at 25°C and their ability to inhibit the formation of β-haematin (synthetic malaria pigment) was investigated. The compounds synthesised and investigated contained a platinum (II) ion coordinated to acylthiourea and diimine ligands. The diimines used included both substituted and unsubstituted 2,2’-bipyridines and 1,10-phenanthrolines. 2-phenyl pyridine was also utilised as a ligand. It has been shown that the uncoordinated planar ligands interact weakly with haematin with a log K in the range of 1.9 and 3.3 while the twisted or more sterically hindered ligands show no observable association with porphyrin. A series of complexes having platinum coordinated which was reflected in association constant log K values in the range of 4.8 to 5.8. Using a 1,10-phenanthroline ligand in place of a 2,2-bipyridine ligand increased the association constant of the platinum complex, resulting in this series of complexes having log K values in the range of 5.8 to 6.2. It has been shown that when platinum (II) is coordinated to diimines, it is the electron withdrawing properties of the metal which result in the strong association between the diimine containing complex and haematin. Finally both the complex containing platinum cis to two acylthiourea ligands as well as a platinum complex containing 2-phenyl pyridine were shown to have no observable interaction with haematin.
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    Synthesis of N-alkyl-and N,N-dialkyl-N'-acyl- and N'-aroythioureas, and aspects of their co-ordination chemistry with Pt(II)and Pd(II)
    (2000) Miller, Jörn Derrick Schuster; Koch, Klaus
    The synthesis of simple, and also bipodal N-substituted N'-acyl- and N'-aroylthiourea ligands has been investigated, along with aspects of their co-ordination chemistry to Pt(II) and Pd(II). The ligands are commonly produced by reacting a secondary or primary amine with an acyl or aroyl isothiocyanate. This synthesis requires nucleophilic addition of the amine to the thiocarbonyl carbon of the acyl or aroyl isothocyanate. However, a competitive side-reaction frequently occurs because the amine nucleophile can attack the carbonyl carbon of the isothiocyanate reagent instead. This leads to substitution of the isothiocyanate moiety and the formation of an N-substituted amide.
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    The solvent extraction and separation of the tetrachloroplatinate (2) and -palladate (2) ions in the presence of stannous chloride into methylisobutylketone
    (1983) Ahmed, Nazir; Koch, Klaus
    The potentialities of extracting platinum(!!) and palladium(II) selectively as complexes of [M(SnCl3)nCl4-nJ2 - (M=Pt,Pd) was examined. A study was made of the effect of SnCl2 on the solvent extraction of K2PtCl4 and K2PdCl4 from solutions containing various concentrations of HCL into methylisobutylketone (MIBK) /hexane mixtures. It was found that increasing SnCl2 concentrations dramatically increases the efficiency of extraction of platinum into the organic phase. In the presence of a five-molar excess of SnCl2, platinum is quantitatively extracted. In contrast, palladium is not quantitatively extracted under similar conditions. Our studies show that the percentage extraction of platinum and palladium depends upon the Sn(II) :M(II) ratio, the HCL, H+ and c1- concentrations and the equilibration time as well. Studies were also carried out to investigate the possibility of separating platinum and palladium by varying the amount of SnCl2 present. Results obtained showed that the separation was dependant on the HCL concentration of the aqueous phase and the composition of the organic phase. The effects of macro amounts of palladium and excess tin on the separation process was also examined. A preliminary study of the effect of four base metals on the separation was undertaken.