Chemistry Reference
In-Depth Information
Figure 5.14 Schematic representation of
the possible isomers of
the anion [Ti
2
(11)
2
(m-OCH
3
)
2
]
2
.
The observation of six NH resonances, two for each isomer/pair of enantiomers, in the
1
H NMR spectrum of (Ph
4
As)
2
[Ti
2
(
11
)
2
(m-OCH
3
)
2
] demonstrated that three of the four
possible isomers/pairs of enantiomers are formed in solution, which means that at least
one isomer with a parallel and one isomer with an antiparallel orientation of the ligand
strands are present in solution.
The X-ray diffraction analysis of compound (AsPh
4
)
2
[Ti
2
(
11
)(m-OCH
3
)
2
] did not pro-
vide conclusive results [49]. The compound crystallized in the centrosymmetric space
group
P
1with
Z
1. Consequently, the complex dianion must reside on a crystallo-
graphic inversion center. Provided that there is no crystallographic disorder, the complex
dianion with the parallel orientation of the ligand strands, which was detected in solution
by
1
H NMR spectroscopy, cannot lie on an inversion center. The detection of [Ti
2
(
11
)
(m-OCH
3
)
2
]
2
on a crystallographic inversion center could therefore indicate that only
complex anions with an antiparallel orientation of the ligand stands are present in the
crystals of (AsPh
4
)
2
[Ti
2
(
11
)(m-OCH
3
)
2
]. Alternatively, all three isomers present in solu-
tion could co-crystallize in a disordered lattice. Unfortunately, the latter situation was
found. The [Ti
2
(
11
)(m-OCH
3
)
2
]
2
dianionisseverelydisorderedinthesolidstate.All
donor atoms (S and O) coordinated to the titanium atoms are disordered. As a conse-
quence each benzene-
o
-dithiolato group can be replaced with a catecholato group and
vice versa. Therefore, no unambigous assignment can be made regarding the donor atoms
for each titanium atom and the orientation of the ligand strands cannot be determined. The
crystal structure determination only confirms the chemical composition of the dianion to
be [Ti
2
(
11
)
2
(m-OCH
3
)
2
]
2
.
ΒΌ
Search WWH ::
Custom Search