Chemistry Reference
In-Depth Information
O
N
N
N
O
N
N
N
N
N
Fe
Cu
Cu
N
N
N
O
N
N
N
O
N
O
N
N
O
N
N
[Cu
I
Fe
II
Cu
I
(
15
)
2
]
4+
N
15
N
N
N
N
O
N
N
N
N
N
N
Cu
O
O
Fe
O
N
O
N
Cu
O
N
N
N
N
N
N
N
N
N
N
16
[Cu
I
Cu
I
Fe
II
(
16
)
2
]
4+
N
N
N
N
N
N
O
O
N
N
N
N
N
N
17
N
N
N
O
Cu
Cu
Cu
N
N
O
N
N
N
O
N
N
N
O
[Cu
II
3
(
15
)(
17
)]
6+
Figure 4.9 Sequence selective formation of helicates and self-assembly of heterostranded
helicates from ligands carrying different metal binding sites.
of these complexes very carefully by different spectroscopic (NMR, UV, fluorescence),
mass spectrometric, and X-ray diffraction techniques [17]. In 2006 they were able to
extend this approach to a triple-stranded trinuclear complex containing two zinc and
one europium ion [18]. and quite recently C. Piguet was able to reveal in collaboration
with T. Riis-Johannessen that it is possible to access triple-stranded trinuclear helicates
with a sequence of 3d-4f-4f-metals in a selective manner using properly designed nitrogen
donor ligands like
14
[19].
For oligopyridine ligands this was first demonstrated by J.-M. Lehn in 1996 [20]. Using
a series of three different ligands
15
-
17
he was able to achieve the selective formation of
sequence selective heterometallic trinuclear complexes (Figure 4.9), as evidenced by
mass spectrometry and X-ray crystal structure analysis. This approach allows also for the
formation of the first heterostranded helicate which is still one of the very rare examples
for this kind of assembly [20,21].
M. Albrecht was then able to show similar sequence selectivity in bimetallic helicate
formation from ligand systems with different oxygen donor ligands (Figure 4.10) like
combinations of catechols and amino phenols [22], catechols and carboxylic acid hydra-
zones [23], 8-hydroxyquinolines and 2-carbamido-8-hydroxyquinolines [24], or catechols
and sulfonic acid hydrazones [25].
Other examples for sequence selectivity appeared from the group of K.N. Raymond
who used ligands like
18
-H
4
containing N-methyl-2,3-dihydroxypyridinone and 2,3-
Search WWH ::
Custom Search