Articles
Prediction of the Coordination Scheme of Lanthanide N-Tetrasubstituted
Tetraazamacrocycles: An X-ray Crystallography and Molecular Modeling Study
Claude Lecomte,*
,†
Vale ´ rie Dahaoui-Gindrey,
†
Herve ´ Chollet,
‡,§
Claude Gros,
‡
Anil K. Mishra,
‡
Fre ´ de ´ ric Barbette,
‡
Pluton Pullumbi,
‡
and Roger Guilard*
,‡
Laboratoire de Cristallographie et Mode ´lisation des Mate ´riaux Mine ´raux et Biologiques (LCM
3
B),
URA CNRS No. 809, Universite ´ Henri Poincare ´, Nancy 1, Faculte ´ des Sciences, B.P. 239,
54506 Vandoeuvre le `s Nancy CEDEX, France, and Laboratoire d’Inge ´nierie Mole ´culaire pour la
Se ´paration et les Applications des Gaz (LIMSAG), UMR No. 5633, Universite ´ de Bourgogne,
Faculte ´ des Sciences Gabriel, 6 Bd Gabriel, 21000 Dijon, France
ReceiVed August 2, 1996
X
The synthesis and characterization of three lanthanide (Ce, Gd, Eu) complexes with the 1,4,8,11-tetrakis-(2-
carboxyethyl)-1,4,8,11-tetraazacyclotetradecane ligand (TETP) are described. Crystal structures of [Ce(H
2
TETP)]-
(OH)(H
2
O)‚10H
2
O(1), [Gd(H
3
TETP)](OH)
2
(H
2
O)
2
‚3H
2
O(2), and [Eu(H
3
TETP)](OH)
2
(H
2
O)
2
‚3H
2
O(3) are
reported. Crystal data: (1) monoclinic, C2/c, a ) 29.523(4) Å, b ) 17.492(3) Å, c ) 8.509(1) Å, ) 98.72(1)°,
V ) 4344(1) Å
3
, Z ) 4, R(|F|) ) 0.057 for 2329 data (I/σ(I) g 3), and 213 parameters; (2) monoclinic, C2/c, a
) 15.378(2) Å, b ) 14.172(2) Å, c ) 14.264(2) Å, ) 99.10(1)°, V ) 3069.5(7) Å
3
, Z ) 4, R(|F|) ) 0.075 for
1147 data (I/σ(I) g 3), and 213 parameters; (3) monoclinic, C2/c, a ) 15.32(1) Å, b ) 14.19(1) Å, c ) 14.130(3)
Å, ) 99.41(3)°, V ) 3031(3) Å
3
, Z ) 4, R(|F|) ) 0.085 for 1133 data (I/σ(I) g 3) and 98 parameters. Complexes
2 and 3 are isotypes. In the three complexes, the centrosymmetric TETP macrocycle possesses a [3434]
conformation; two propionate arms are extended, and the others are folded toward two protonated nitrogen atoms.
The lanthanide coordination mode with the TETP ligand does not occur via the four nitrogen atom ring but only
through carboxylic oxygen atoms belonging to four different ligands. Moreover, the four functionalized chains
of the ligand are involved in the coordination polyhedron of the gadolinium and europium ions, but only extended
propionate arms of TETP take part in the cerium ion coordination polyhedron, one of the oxygen atoms of
asymmetric unit being bidentate between two metallic ions. In order to better understand the reactivity and the
coordination scheme observed for these complexes, a theoretical study has been carried out using the molecular
electrostatic potential as a tool to predict sites of the ligands where electrophilic attack should take place. The
overall good agreement between calculated and observed structures permits us to explain the coordination scheme
of this new class of complexes.
Introduction
The continued interest and research for new macrocyclic
ligands stems mainly from their use as models for protein-
metal binding sites in biological systems,
1
as selective com-
plexants of metallic ions,
2-4
i.e. therapeutic reagents for the
treatment of the metal toxicity,
5,6
radioactive waste water
treatment,
7
functional groups for chelating ion-exchange materi-
als,
8
and selective metal extractants in hydrometallurgy,
9
and
to study host-guest interactions.
10
Tetraazamacrocycle ligands
represent a class of macrocycles known for their ability to
complex transition and non-transition metallic cations. The
macrocyclic complexes of lanthanides are now currently used
for other medical applications,
10
in radioimmunotherapy, in
contrast-enhancing agents in magnetic resonance imaging (MRI),
as NMR shift and relaxation reagents, and in many other novel
clinical techniques.
10
The main target in macrocyclic design is to synthesize
macrocycles which are able to discriminate among the different
metal cations. Many factors influence the selectivity of mac-
rocycles toward the lanthanide cations and determine to some
extent the structure of the formed complexes. In this study we
focus on a particular class of macrocyclic ligand which has been
used as complexants of lanthanide ions in aqueous solutions:
namely, the N-tetrapropionate (acetate)-substituted tetraazamac-
* To whom correspondence should be addressed.
†
Universite ´ Henri Poincare ´.
‡
Universite ´ de Bourgogne.
§
Centre du Commissariat a ` l’Energie Atomique de Valduc, France.
X
Abstract published in AdVance ACS Abstracts, July 15, 1997.
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3827 Inorg. Chem. 1997, 36, 3827-3838
S0020-1669(96)00934-2 CCC: $14.00 © 1997 American Chemical Society