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

Chapter 2
containing niobium as the niobium species promoted the stabilization of the active
species loaded.
2.6 β-diketone complexes of niobium
Metal β-diketonates are amongst the most studied coordination compounds and their
chemistry has been examined for most of the metals in the periodic table. The ligand
forms chelates with the metal and delocalizes the negative charge over a
“metallacycle”. 53 β-diketones has the potential to be easily derivatized using well-
established procedures. The steric and electronic nature of this ligand type may be
varied to probe the structure and function of interest.
Variation of the R groups influence the properties displayed by metal β-diketonates
and the ability to form higher coordinate species can be achieved by variation of the
terminal R groups on the β-diketone. It has been shown that the stepwise
incorporation of electron-withdrawing trifluoromethyl groups increases the affinity of
the central metal ion for further ligation. 54
Keto Enol
Figure 2.1: Keto-enol tautomerism in β-diketones.
The simplest β-diketone is acetylacetone (2,4-pentanedione, acacH), which tends to
form neutral complexes with niobium. The adopted geometry normally reflects the
preferred geometry of the metal ion involved. Slight basic conditions cause
deprotonation and the resulting acetylacetone anion readily complexes a range of
53
R. C. Mehrotra, R. Bohra, D. P. Gaur, Metal β-diketonates and Allied Derivatives, Academic Press, London,
1978.
54
R. van Eldik, K. Bowman-James, Advances in Inorganic Chemistry, Academic Press, London, 3, 2006.
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