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

Chapter 2
diketonate ligand in the equatorial plane. The average Nb-O(dbm) bond length
was determined as 2.07 Å.
Figure 2.9: Structure of trans-[NbCl2(OEt)2(dbm)].
2.6.4 Bridged niobium β-diketonate complexes:
Formation of metal-metal bonded dimers is common to d 1 metal centres such as
Nb(IV) and Ta(IV), especially as their tetrahalide structures. 66
2.6.4.1 [Nb2(µ-S2)2(acac)4] and [Nb2(µ-S2)(acac)4]
In 1999 Sokolov et al. 67 published two crystal structures in their efforts to
synthesise niobium clusters with bridging chalcogen atoms. The key stage in
this chemistry was the transformation of the inert polymeric NbS2Cl2 into
soluble salts of [Nb2S4(NCS)8] 4- by the reaction with molten KNCS at 180 °C.
The Nb(IV) oxidation state is stabilized in dimeric complexes. In their study
they investigated the coordination chemistry of these [Nb2(µ-S2)2] 4+ cores with
various β-diketone ligands. 68 [Nb2(µ-S2)(acac)4] crystallized in the triclinic
spacegroup Pī and [Nb2(µ-S2)2(acac)4] crystallized in the monoclinic
spacegroup C2/c. The average Nb-O(acac) bond lengths for [Nb2(µ-S2)2(acac)4]
was determined as 2.14 Å and for [Nb2(µ-S2)(acac)4] as 2.10 Å. The average
Nb-Nb distance for both complexes was determined as 2.89 Å.
66
M. Sokolov, A. Virovets, V. Nadolinnyi, K. Hegetschweiler, V. Fedin, N. Podberezskaya, V. Fedorov, Inorg.
Chem., 33, 3503, 1994.
67
M. Sokolov, H. Imoto, T. Saito, V. Fedorov, Dalton Trans., 85, 1999.
68
M. Sokolov, O. Gerascko, A. Virovets, V. Fedorov, K. Hegetschweiler, Inorg. Chim. Acta, 271, 222, 1998.
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