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metal binding sites. Furthermore, helicates usually show a high degree of self-sorting
when chiral racemic ligands are used in which the ligand strands are designed properly,
meaning that the formation of the metal complexes does not induce too much steric stress
in the assembly.
Using these principles new ligands can be designed that allow the preparation of
oligonuclear complexes of defined length, shape, and stereoselectivity which can be
decorated with additional functional groups in defined positions. This, however, is
the prerequisite to access functional helicates and actually some functions have
already been realized: they have been demonstrated to act as templates in the synthe-
sis of molecular knots [76], they can be used as a new building and ordering princi-
ple for mesogenic materials [77], they have been shown to interact with DNA in a
specific manner [78], they have been used as receptors [79] (although not yet making
use of their chirality), the principle of diastereoselective formation of helicates has
been employed for the resolution of racemic ligands using an immobilized enantio-
merically pure template [80], and they have been demonstrated to be efficient pro-
moters of chemical reactions [81]. However, one can definitely envision more to
come in the bright future of helicate chemistry.
References
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with growth-factor activity. I. Isolation and characterization.
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2. (a) Carrano, C.J. and Raymond, K.N. (1978) Synthesis and characterization of iron complexes
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J. Chem.
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4. (a) van Stein, G.C., van der Poel, H., van Koten, G.
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R
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(
S
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5
H
4
N)-C(H)¼N]
2
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2
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3
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3
)
2
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3
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107,109
Ag-
1
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1
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2
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2þ
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et al.
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Strucutral investigations of silver(I) and copper(I) complexes with neutral N
4
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X-ray crystal and molecular structure of the dimer [Ag{m-(
R,S
)-1,2-(py-2-CH
N)
2
Cy}
2
]
(O
3
SCF
3
)
2
and
1
H,
13
C, and INEPT
109
Ag and
15
N NMR solution studies.
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106
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5. Scarrow, R.C., White, D.L., and Raymond, K.N. (1985) Ferric ion sequestering aents. 14.
1-hydroxy-2(1
H
)-pyridinone complexes: properties and structure of a novel Fe-Fe dimer.
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6. Lehn, J.-M., Rigault, A., Siegel, J.
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cates from oligobipyridine ligands and copper(I) cations: Structure of an inorganic double
helix.
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84
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