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Figure 5.11 Molecular structures of the dinuclear complex anions meso -[Ti 2 (6) 3 ] 4 (left), meso -
[Et 4 NTi 2 (6) 3 ] 3 (middle, the encapsulated NEt 4 þ cation is drawn in black) and L,L-[Ti 2 (6) 3 ] 4 .
sulfur atoms in a strongly distorted octahedral fashion. The titanium atoms exhibit oppo-
site absolute configurations (L and D) due to the inversion center present. Consequently
[Ti 2 ( 6 ) 3 ] 4 is an achiral dinuclear triple-stranded meso -complex.
The nonbonding intrastrand N
S separations in the range 3.026-3.043 A
are indica-
tive of the presence of only weak or no N
S hydrogen bonds. This assumption is
confirmed by the observation of Ti-S ortho distances which are not longer than the Ti-S meta
distances, as would be expected in the case of formation of N
H
S ortho hydrogen
bonds [39]. The NMR spectra of (Ph 4 As) 4 [Ti 2 ( 6 ) 3 ] are rather simple, exhibiting only reso-
nances for one ligand strand, which was taken as an indication that the complex anion
adopts the C 3 -symmetry in solution.
Raymond and coworkers described the influence of ammonium templates on the coor-
dination chemistry of an anthracene bridged dicatechol ligand. Molecular modeling stud-
ies showed the capability of the ligand to form both helicates of type [M 2 L 3 ] m and
tetrahedral clusters of type [M 4 L 6 ] n . Reaction of the ligand with Ti or Ga gave dinu-
clear triple-stranded helicates, whereas the presence of a tetraalkylammonium salt caused
the formation of a tetrahedral cluster with one template ion in the interior of its cavity
[44]. Based on these results we investigated the influence of the tetraethylammonium tem-
plate on the reaction of H 4 - 6 with Ti . It was hoped that the ammonium template might
induce the formation of the tetranuclear [Ti 4 ( 6 ) 6 ] 8 cluster anion instead of the dinuclear
complex anion [Ti 2 ( 6 ) 3 ] 4 . The reaction of two equivalents of [Ti(OPr) 4 ]withthree
equivalents of H 4 - 6 in the presence of four equivalents of Et 4 NBr (Scheme 5.3) in metha-
nol yielded a dark red precipitate which was characterized by X-ray diffraction as the
dinuclear complex (Et 4 N) 3 [Et 4 N
H
Ti 2 ( 6 ) 3 ].
Ti 2 ( 6 ) 3 ] crystallized in a centrosymmetric space group.
Figure 5.11 (middle) shows the molecular structure of the anion [Et 4 N
Complex (Et 4 N) 3 [Et 4 N
Ti 2 ( 6 ) 3 ] 3 that
contains one molecule of the tetraethylammonium cation located between the two metal
atoms. The two titanium atoms in the complex anion are each coordinated by three ben-
zene- o -dithiolato moieties differing slightly in their coordination geometry and exhibiting
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