Communication
Dalton Transactions
In summary, a synthetic strategy has been developed and
consequently utilized to prepare
a phenylene-bisoxamate
derived ligand featuring three different types of coordination
sites (H2L1Et). Our synthetic approach can be adopted to
modify other related ligand systems as demonstrated by pre-
paring 1,2-bis(2-hydroxybenzamido)benzene derivatives H2L2
Ac
and H4L2. The novel ligands form stable mononuclear Ni(II)
complexes that were characterized by X-ray crystallography,
NMR and electronic absorption spectroscopy as well as theo-
retical calculations. The obtained ligands represent attractive
building blocks to create multidimensional magnetic materials
in a controllable way that is currently under investigation in
our laboratory.
We thank the Fonds der Chemischen Industrie (Liebig
Fellowships for CS and MMK) and the Deutsche Forschungs-
gemeinschaft (DFG Research Grant KH 279/2-1) for financial
support. Friedrich-Alexander-University Erlangen-Nürnberg
and the Lehrstuhl für Anorganische und Allgemeine Chemie
(Prof. Karsten Meyer) are acknowledged for general support.
Fig. 4 Molecular structure of (TBA)2[NiL2], thermal ellipsoids are drawn at the
50% probability level, two TBA+ cations and a water molecule are omitted.
these three fragments are essentially uncoupled. The metal
coordination site N2O2 is slightly twisted: the Ni1N1N2 plane
shows a dihedral angle of 10° with the Ni1O1O4 plane that is
likely due to a too small ligand cavity to accommodate a low-
spin Ni(II) ion without being distorted. Consequently, the two
salicylamide groups are slightly twisted and not coplanar with
the central phenylene fragment: the C6-rings of the salicyl-
amide groups have dihedral angles of 21° and 22° with the six-
membered central phenylene ring. Thus, significant electronic
coupling is expected between the π-systems of the metal
coordination site and the central phenylene unit in
(TBA)2[NiL2], albeit it is weaker than that in the nearly planar
(TBA)2[NiL1].
Notes and references
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Electronic absorption spectra of (TBA)2[NiL1] and
(TBA)2[NiL2] reveal absorption bands in the near UV and
visible regions that are absent in the spectra of the correspond-
ing metal-free ligands (see ESI†). A strong broad band centered
at 350 nm (ε = 1.56 × 104 M−1 cm−1) and a strong broad band
at 352 nm (ε = 3.14 × 104 M−1 cm−1) accompanied by two
shoulders for (TBA)2[NiL1] and (TBA)2[NiL2], respectively, both
spread into the visible region that results in red colored com-
plexes. Surprisingly, these absorption bands are not due to
MLCT transitions. As determined by time-dependent density
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ligand charge transfer transitions with only a small amount of
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increased overall planarity of the metal coordinated ligands
T. Kuroda-Sowa and M. Munakata, Polyhedron, 2006, 25,
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tronic coupling between the individual π-subsystems of the
ligand after deprotonation. It was obtained in its protected
doubly ethylated form H2L1
ligands in (TBA)2[NiL1] and (TBA)2[NiL2]. Additionally, very
.
Et
weak ligand field d–d transitions at about 450 nm (ε = 4 × 102 13 Y. Sunatsuki, H. Shimada, T. Matsuo, M. Nakamura, F. Kai,
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Dalton Trans.
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