Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / In this study, the coordination of certain Group 6 and Group 10 & 11 metals to Odonor
and S-donor ligands were investigated. For the most part, this involved the
isolation of new Mo(VI) and W(VI) complexes. By using a distribution diagram that
shows the dependence of the type of species in solution with pH, we attempted to
crystallize new polyoxoanion species of the two metals. It was found that the products
that crystallize are not necessarily dependant upon the relative concentrations of the
species in solution, but rather on the effective packing of the crystal types that are
prepared. During this study a unique W(VI) polyanion, [(CH3CH2)4N]2[W6O19] (4),
was isolated. The Mo(VI) analogue of this compound as well as the dinuclear
Mo(VI)-W(VI) complex have been reported previously, but a pure W(VI) compound
of this type has not been successfully isolated yet. A new polymorph of a known
dimolybdate, K2Mo2O7·H2O (1), was also crystallized, even though dimolybdate
species do not generally occur in solution. This structure, although previously
reported, shows some differences with the one in the literature, in particular large
deviations in unit cell dimensions. Subsequently, as a second component of this study,
a variety of carboxylates were coordinated to Mo(VI) and W(VI) species in an acidic
medium. Two new complexes of Mo(VI) with these carboxylate ligands were
isolated: [(CH3CH2)4N][MoO3(mal)]·H2O (5) (mal = malate) and Na6[Mo2O5(cit)2] (6)
(cit = citrate). The ligands are two- and threefold deprotonated respectively and
coordinate in a polydentate manner to the metal centra. The formation of compound 5
in solution has been known for many years, but the structure of this complex has not
been determined in the solid state until now. Also, the tungsten analogue of compound
6 was reported years ago, but the Mo(VI) complex has not been crystallized before.
Compounds 5 and 6 exhibit a 1:1 and 2:2 metal to ligand ratio respectively, and these
ratios are quite rare in Mo(VI) crystal chemistry. Finally, the dimolybdate complex,
[CH3)3N(CH2)6N(CH3)3][Mo2O7(cit)] (7), was isolated, and its structure determined
and compared to the one in the literature. In the third part of this study, our attention shifted to the group 10 and 11 metals,
platinum and gold. Attempts were made to coordinate unusual ligands with donor
atoms P, Se and/or S to these metal centers. During this investigation, we isolated a
unique Pt(IV) complex, PtCl2(S3C8H7)2 (9). The structure of this compound that was
determined crystallographically involves the coordination of two identical R-SCS2
fragments to the metal ion forming four-membered chelate rings. No compounds of Pt
and Au with the P-Se ligand, P3Se3(C(C6H5)3)3, could be isolated. However, a mixed
valence compound of Au(I,III), [Au(I)Cl(S(CH2C6H5)2)][Au(III)Cl3(S(CH2C6H5)2]
(8), could be isolated and characterized. In this compound Au exhibits two oxidation
states, +1 and +3. Although the complex has been reported previously, the structure
was not described fully, and we now unequivocally determined its crystal structure.
The extended structure shows the formation of chains of alternating Au(I) and Au(III)
centers with a separation of 5.610 Å.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/3111 |
| Date | 03 1900 |
| Creators | Le Roux, Adele |
| Contributors | Luckay, R. C., Raubenheimer, H. G., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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