A solution and solid state study of niobium complexes University of ...

6. Evaluation of Study
Synopsis...
A summary of the results obtained and the scientific importance of this M.Sc. study is
given, which is followed by some aspects which might be investigated in future.
6.1 Results Obtained
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This study was aimed at the investigation and identification of various niobium(V)
complexes containing selected O,O’-bidentate ligands that could potentially be used
for the selective separation of niobium from tantalum.
Four new complexes were synthesized and successfully characterized by means of
single crystal X-ray diffraction. Some unique results were obtained; such as the
simultaneous crystallization of [NbCl2(phacac-κ 2 -O,O’)(OMe)2] and [NbCl(phacac-κ 2 -
O,O’)(OMe)3], which is unmarked by any other niobium complexes, and the
formation of the “cage”-like structure of [Nb(acac-κ 2 -O,O’)(OEt)2(µ 2 -O)]4. Only four
other similar, “cage”-like structures have been reported in literature. A comparison
between the novel [NbCl(acac-κ 2 -O,O’)(OMe)3] complex and the [TaCl2(acac-κ 2 -
O,O’)(OMe)2] complex 1 exhibited significant differences in coordination between the
two metal centres. The niobium complex contained only a single chlorido ligand
whereas the tantalum analogue contained two coordinated chlorido ligands. In all of
the complexes synthesised, the chlorido ligands were always placed in axial
positions with an average Nb-Cl bond length of 2.438 (3) Å.
The kinetic study to follow the formation of [NbCl(acac)(OMe)3] revealed that two
reactions occur in methanol as solvent. The initial part of the study involved the
correct identification of the niobium(V) starting reagent, as solvent coordination took
place to form the corresponding niobium-chlorido-methoxido species. This was done
by means of 93 Nb NMR. The first, rate determining reaction comprised of the initial
mono-coordination of the acacH ligand to the niobium(V) centre and the slow,
1 R. Koen, M.Sc. Thesis, University of the Free State, 2012.
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