Role of the Main and Auxiliary Ligands in the Nuclearity of Cu-Ln Complexes

Article abstract of DOI:10.1002/ejic.201901150

Trianionic ligands with an inner N₂O₂, an outer O₂O₂ or O₂O coordination site and an oxygen atom coming from an amide function not involved in these sites yield dinuclear Cu-Ln complexes that self-ass

Full text of DOI:10.1002/ejic.201901150

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Accepted Article
Title: Role of the main and auxiliary ligands in the nuclearity of Cu-Ln
complexes
Authors: Jean-Pierre Costes, Maria-Jesus Rodriguez Douton, Sergiu
Shova, and Laure Vendier
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10.1002/ejic.201901150
European Journal of Inorganic Chemistry
Role of the main and auxiliary ligands in the
nuclearity of Cu-Ln complexes
Jean-Pierre Costes,*,† Maria-Jesus Rodriguez Douton,§ Sergiu Shova,‡ Laure
Vendier†
† LCC-CNRS, Université de Toulouse, CNRS, Toulouse, France
email : jean-pierre.costes@lcc-toulouse.fr
§
Laboratorio NEST, Istituto Nanoscience-CNR & Scuola Normale Superiore,
Piazza San Silvestro 12, 56127 Pisa, Italy
‡ « Petru Poni » Institute of Macromolecular Chemistry, Aleea Gr. Ghico Voda 41 A,
Iasi 700487, Romania
Abstract
Trianionic ligands with an inner N2O2, an outer O2O2 or O2O coordination site and an oxygen
atom coming from an amide function not involved in these sites yield dinuclear Cu-Ln
complexes that self-assemble into tetranuclear species with an alternate arrangement of Cu
and Ln ions. This alternate Cu-Gd arrangement impedes Cu-Cu and Gd-Gd interactions that
could be antiferromagnetic and favours presence of ferromagnetic Cu-Gd interactions whose
strength depends on the nature of the bridge, phenoxo bridge made of a single oxygen atom or
amidato bridge made of three NCO atoms. Depending on the ligands the phenoxo bridges can
be single (CuOGd) or double (CuO2Gd) while the amidato one is always a single
(CuNCOGd) bridge. A particular complex involving a trinuclear Cu-Gd-Cu arrangement
through two amidato bridges confirms that the Cu-Gd interaction through the amidato bridge
is always weaker than the interaction through the phenoxo bridge. It has been possible to
obtain complexes with an alternate Cu-Gd arrangement involving more than two Cu-Gd
entities when two amidato bridges are present. These two amidato bridges may come from a
main ligand, as in the case of tetraanionic ligands possessing two amide functions, or from
two different ligands involving one amide function that are assembled by a Gd ion through
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10.1002/ejic.201901150
European Journal of Inorganic Chemistry
their phenoxo functions. Note that the presence of auxiliary ligands with a good chelating
ability for the Gd ion, as the diketonato ligands, allows isolation of tetranuclear species only,
whatever the number of amide functions.
Introduction
We have previously shown that trianionic compartmental ligands with two
coordination sites, an inner N2O2 and an outer O2O2 site able to coordinate the 3d and the 4f
ions respectively, along with one oxygen atom of an amide function not involved in these
coordination sites, yield dinuclear CuLn entities that self-assemble in tetranuclear Cu2Ln2
complexes, as a consequence of a head to tail assembling of two dinuclear species. In the case
of Cu2Gd2 entities, the complexes possess a S = 8 spin ground state due to the presence of two
active ferromagnetic interactions, one through the double phenoxo bridge and the second one
through the amide bridge.1 In order to change the spin state of these 3d-4f entities, we2 and
other research teams3,4 have tried to modify the ligands and also to introduce different counter
ions around the 4f ions. The use of different ligands with outer O2O2 or O2O sites does not
improve the nuclearity of the samples, as shown in the structurally characterized complexes
already published.1-4 In these later complexes, the 4f ions are surrounded by eight or nine
oxygen atoms. A way to change the nuclearity would consist in increasing the number of
oxygen atoms interacting magnetically with the copper ions in the coordination sphere of the
4f ion. There are two ways to do it: first, using dianionic or trianionic ligands possessing one
amide function and an outer coordination site reduced to one phenoxo oxygen atoms directly
connected to the copper ion and second, using tetraanionic ligands with two amide functions.
The later solution has the advantage to increase the attraction of the 4f ion for the negatively
charged dianionic 3d complex and to decrease the number of auxiliary anionic species around
the 4f ion. In the former solution, it is expected that the Ln ion could link two copper
complexes in order to yield trinuclear Cu-Ln-Cu entities instead of the dinuclear Cu-Ln ones,
which, by self-assembling through the amidato functions, should be able to yield, at least,
hexanuclear complexes. In this paper the two solutions will be examined, along with the role
held by the auxiliary ligands needed for reaching the electroneutrality of the isolated entities.
Results and discussion
Syntheses.
It has previously shown5-7 that compartmental Schiff base ligands having two
coordination sites sharing two oxygen atoms coming from two phenol functions were able to
yield strictly heterodinuclear 3d-4f complexes. In a following step we have described new
2
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10.1002/ejic.201901150
European Journal of Inorganic Chemistry
ligands which possess, beside the inner N2O2 and outer O2O2 sites, an oxygen atom able to
self-assemble the dinuclear complexes in order to yield species of higher nuclearity.1,2,8 This
behaviour is favoured by the introduction of an amide function that repels the oxygen atom of
that function out of the N2O2 coordination site after deprotonation and complexation of the
nitrogen amide atom (see Scheme 1). Previous results indicate that a change in the number of
coordinating atoms in the outer site which encapsulates the 4f ion, 1-3,8 from O2O2 to O2O, or
Scheme 1.
a modification of auxiliary ligands or anions linked to the 4f ion,2,8 does not alter the
nuclearity of the resulting complexes. In order to get 3d-4f complexes of different or higher
nuclearities, we tried to change the main ligands coordinating the 3d and 4f ions and used the
so-called “half-unit” ligands resulting from reaction of a diamine with the phenyl ester of
salicylic acid or 3-methoxy-salicylic acid such as LH2, L1H2, L2H2, L3H2, which are reported
3
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