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

4.6 Conclusion
Chapter 4
During the course of this project, three novel Nb(V) organometallic complexes have
been synthesized and characterised. Two of these structures have already been
published. 8,17 Comparative research for Nb(V) and Ta(V) structures are aimed at
finding significant coordinative differences for these two metals with similar type
ligands, in this case β-diketonate species. As discussed throughout this chapter,
comparisons of novel compounds with literature sources have been established.
In general, it was observed that these mono-substituted β-diketonate complexes of
Nb(V) finally crystallize in a distorted octahedral coordination polyhedron, which is
also described in literature. 14,22,23,24 Furthermore, these complexes were found to
crystallize in the absence of any solvent or counter ions in the unit cell.
As a general comparison from this work, it is observed that β-diketonate ligands
chelate to the metal centre in a flat plane, with no bending of either the ligand
backbone or at the O,O’-coordination sites. This occurs with an average O–Nb–O
bite angle of 80.5 (1) °. Additionally, the Nb–O b ond distances are never equal for
any of these moieties, as from literature, even in cases where symmetrical β-
diketonate ligands are utilized. 23,24
Table 4.10: Nb–O bond distances with regards to β-diketonate coordination.
Complex Nb–O1 (Å) Nb–O2 (Å)
[NbCl(acac-κ 2 -O,O’)(OMe)3] 2.109 (2) 2.085 (2)
[Nb(acac-κ 2 -O,O’)(OEt)2(µ 2 -O)]4 2.197 (2) 2.088 (2)
[NbCl(phacac-κ 2 -O,O’)(OMe)3]
and
[NbCl2(phacac-κ 2 -O,O’)(OMe)2]
2.094 (3) 2.077 (3)
Only four other niobium “cage” structures, similar to the [Nb(acac-κ 2 -O,O’)(OEt)2(µ 2 -
O)]4 complex, have been reported in literature. 18,19,20,21 These structures all display
relative significant differences in terms of the bridging coordination of the niobium
metal centres.
22
P. Werndrup, M. Verdenelli, F. Chassagneux, S. Parola, V. G. Kessler, J. Mater. Chem., 14, 344, 2004.
23
P. A. Williams, A. C. Jones, P. J. Wright, M. J. Crosbie, J. F. Bickley, A. Steiner, H. O. Davies, T. J. Leedham,
Chem. Vap. Deposition, 8, 3, 110, 2002.
24
A. Antiñolo, F. Carrillo-Hermosilla, J. Fernández-Baeza, S. Garcia-Yuste, A. Otero, E. Palomares, A. M.
Rodriguez, L. F. Sánchez-Barba, J. Organomet. Chem., 603, 194, 2000.
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