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

3.7.3 Discussion
Chapter 3
A limited amount of structural information of niobium(V) mono coordinated to O,O’-
bidentate complexes is available. Crystals suitable for X-ray crystallography were
obtained for the first three synthesis reactions at -21.0 °C ([NbCl(acac)(OMe) 3],
[Nb(acac)(OEt)2(O)]4, [NbCl(phacac)(OMe)3] and [NbCl2(phacac)(OMe)2]). These
reactions were also duplicated with an increase in the molar equivalents of ligand
added, from two to five, but only the mono coordinated bidentate complexes were
formed every time. All of the synthesized crystals decomposed quickly when
exposed to air and elevated temperatures above 0 °C . Selected crystals had to be
synthesized repeatedly before stable enough samples could be collected for analysis
on the X-Ray diffractometer. Subsequently, elemental analysis could not be
performed due to the sensitive nature of the products. This was also confirmed by 1 H
NMR of the products before and after environmental exposure.
The 1 H NMR results for [NbCl(phacac)(OMe)3] and [NbCl2(phacac)(OMe)2] seems
confusing at first glance, however two crystal structures were obtained from the
same crystal. Hence two different species were observed on the 1 H and 13 C NMR
spectrums. This is an extremely rare occurrence and is discussed in more detail in
Chapter 4 (Section 4.5).
The last three synthesis reactions ([NbCl4(acac)], [NbCl4(hfacac)] and
[NbCl(trop)(OMe)3]) either formed powders or crystals that were not suitable for
analysis on the X-Ray diffractometer. Several attempts were made to recrystallize
the products, but to no avail.
3.7.4 Conclusion
Four new niobium(V) complexes containing O,O’-bidentate ligands have been
obtained and successfully characterized with IR, as well as 1 H-, 13 C- and 93 Nb NMR.
The crystallographic characterisation of these crystals are discussed in detail in the
next chapter.
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