Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The successful preparation and structural characterization of a number of N,N-dialkyl-N’-benzoyl(thio)selenourea
ligands is described; where the intermolecular interactions are characterized by the presence of Resonance Assisted
Hydrogen Bonding (RAHB), π- π interactions between neighbouring benzene residues only being evident amongst
the longer alkyl chain derivatives. The first structural characterization of an asymmetrically substituted N,N-dialkyl-
N’-benzoylselenourea ligand reveals an increased stability of the Z isomer in the solid state, this being reflected by
the sulfur analogue. Attempts to synthesise N,N-dicyclohexyl-N’-benzoylselenourea led to the isolation and
structural characterization of a novel 1,3,5-oxaselenazine salt and dicyclohexylaminobenzoate. The first structural
characterization of a “bipodal” N,N-dialkyl-N’-benzoylselenourea ligand, 3,3,3’,3’-tetrabutyl-1,1’-
isophthaloylbis(selenourea), reveals RAHB in the crystal lattice similar to that exhibited by the “monopodal”
analogue, N,N-dibutyl-N’-benzoylselenourea.
The successful complexation of the N,N-dialkyl-N’-benzoyl(thio)selenourea ligands to a number of different
transition metal ions is reported allowing the preparation of several potential single source precursors. Coordination
through the O and Se/S donor atoms to Pd(II) results in the formation of square planar metal complexes, with a cis
conformation, several of which could be structurally characterized. In particular, the first structural elucidation of an
asymmetrically substituted N,N-dialkyl-N’-benzoylselenourea metal complex, cis-bis(N-benzyl-N-methyl-N’-
benzoylselenoureato)palladium(II) indicates the increased stability of the EZ isomer in the solid state. Structural
elucidation of the novel (N,N-diphenyl-N’-benzoylselenoureato)cadmium(II) reveals a bimetallic complex in the
solid state, where the expected 2:1 ligand : metal ratio is maintained, and the two Cd(II) centres are 5 and 6
coordinated, with O and Se donor atoms. Multinuclear Nuclear Magnetic Resonance (NMR) Spectroscopy has been
employed in the thorough characterisation of the potential single source precursors, 77Se NMR spectroscopy
indicating a decreased shielding of the 77Se nucleus as the “hardness” of the central metal ion increases i.e. Pd(II) >
Zn(II) > Cd(II). Use of 113Cd NMR spectroscopy indicates the preferential binding of N,N-diethyl-N’-
benzoylselenourea to Cd(II) over that of its sulfur analogue, and initial studies suggest a form of chelate metathesis
taking place in solution. 31P NMR spectroscopy is used to gain insight into the formation of cis-bis(N,N-diethyl-N’-
benzoylselenoureato)Pt(II).
Thermolysis of (N,N-diethyl-N’-benzoylselenoureato)cadmium(II) and its sulfur analogue led to the successful
synthesis of CdSe and CdS quantum dots respectively, where thermolysis over a range of temperatures allows a
degree of size control over the resulting nanoparticles. The effect of precursor alkyl chain length on nanoparticle
morphology was investigated for both the N,N-dialkyl-N’-benzoylthio- and –selenoureas. A correlation between the
two for the (N,N-dialkyl-N’-benzoylselenoureato)Cd(II) complexes is described and possible growth mechanisms
are discussed. Preliminary investigations into the use of other N,N-dialkyl-N’-benzoyl(thio)selenourea metal
complexes as single source precursors reveal that both (N,N-diethyl-N’-benzoylselenoureato)Zn(II) and its sulfur
analogue show potential as single source precursors for the formation of ZnO and ZnS nanoparticles respectively.
Initial studies into the use of N,N-dialkyl-N’-benzoyl(thio)selenourea metal complexes as single source precursors
for the synthesis of core-shell nanoparticles is briefly described.
The Aerosol Assisted Chemical Vapour Deposition (AACVD) of several N,N-dialkyl-N’-benzoyl(thio)selenourea
metal complexes is reported, where both (N,N-diethyl-N’-benzoylselenoureato)Cd(II) and its sulfur analogue allow
the deposition of crystalline CdSe and CdS respectively. The AACVD of (N,N-diethyl-N’-
benzoylselenoureato)Zn(II) leads to the deposition of crystalline ZnSe, ZnS being deposited by (N,N-diethyl-N’-benzoylthioureato)Zn(II). The deposition of heazelwoodite (Ni3S2) with varying morphologies results from the
AACVD of cis-bis(N,N-diethyl-N’-benzoylthioureato)Ni(II). Thermal annealing of the amorphous material
deposited by the AACVD of cis-bis(N,N-diethyl-N’-benzoylthioureato)Pd(II), allows the formation of highly
crystalline palladium. The deposition of metallic platinum using cis-bis(N,N-diethyl-N’-benzoylthioureato)Pt(II) is
described as well as the deposition of crystalline Pd17Se15 from cis-bis(N,N-diethyl-N’-benzoylselenoureato)Pd(II).
This, to the best of our knowledge, is the first time that AACVD has been performed, using the N,N-dialkyl-N’-
benzoyl(thio)selenourea metal complexes as single source precursors, in addition, we believe it to be the first time
that palladium selenide has been deposited using the AACVD technique.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1205 |
| Date | 12 1900 |
| Creators | Bruce, Jocelyn Catherine |
| Contributors | Koch, Klaus R., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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