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

Chapter 4
longer bonds (C1–C2, C2–C3 = 1.397 (3), 1.387 (3) Å) than expected for an average
C=C bond (1.34 Å) but shorter than a single C–C bond of 1.54 Å. 13
An equatorial plane was constructed through O1, O2, O4 and O5 as indicated in
Figure 4.3. The niobium metal centre is slightly elevated above this plane by 0.143
(2) Å. This further illustrates the distorted octahedral geometry of the molecule.
Figure 4.3: Side view of the equatorial plane. Hydrogen atoms have been omitted for clarity.
Displacement ellipsoids are drawn at the 50% probability displacement level.
A similar tantalum crystal structure has been obtained by Davies et al. 14 by using the
same experimental procedure as for [NbCl(acac-κ 2 -O,O’)(OMe)3]. The tantalum
complex, [TaCl2(acac-κ 2 -O,O’)(OMe)2], also exhibits a distorted octahedral
coordination about the metal centre, but is non-isomorphous to the corresponding
niobium complex described here. The tantalum complex contains two chlorido
ligands that occupy trans axial positions while the methoxido and acetylacetonato
ligands are coordinated in the equatorial positions.
13 th
J. C. Kotz, P. Treichel, G. C. Weaver, Chemistry and Chemical Reactivity, 6 Ed, Thomson Learning Inc., 420,
2006.
14
H. O. Davies, T. J. Leedham, A. C. Jones, P. O’Brien, A. J. P. White, D. J. Williams, Polyhedron, 18, 3165, 1999.
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