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N
N
N
N
OH
N
N
N
N
N
O
N
N
H
2
C
n
O
N
N
N
N
N
N
N
N
HO
N
MeO
OMe
M
eO
OMe
e
N
L1
n
=1 H
2
n
=2 H
2
L2a
L2b
L3
N
Scheme 6.1 Ligands used for isolating the first lanthanoid helical complexes and helicates.
authors isolated [Ln
2
(L2a)
3
(DMF)
2
] complexes with a dianionic pyrazolonate ligand [3],
the structure of the Sm
III
complex being subsequently published in 1995 [4], while the
second team self-assembled a Eu
III
helicate from a neutral bis(benzimidazolepyridine)
ligand [5] (Figure 6.1); the photophysical properties of the highly charged species
[Eu
2
(L3a)
3
]
6þ
were deciphered the next year [6]. Overall, the bis(benzimidazolepyridine)
framework proved to be quite versatile and its subsequent modifications yielded a wealth
of new exciting molecular objects in which various interactions and properties, magnetic
or spectroscopic, could be tailored. The thermodynamically controlled self-assembly of
Figure 6.1 X-Ray molecular structures of the lanthanoid helical complex [Eu(NO
3
)
2
(L1)]
[2]
and of the first lanthanoid helicates, [Sm
2
(L2a)
3
(DMF)
2
] [4] and [Eu
2
(L3)
3
]
6þ
[5]; see
Scheme 6.1 for ligand formulae.
Redrawn from crystal structure data.
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