Resumen:
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[EN] Understanding the origin of cooperativity and the
equilibrium temperature of transition (T1/2) displayed by the
spin-crossover (SCO) compounds as well as controlling these
parameters are of paramount importance for ...[+]
[EN] Understanding the origin of cooperativity and the
equilibrium temperature of transition (T1/2) displayed by the
spin-crossover (SCO) compounds as well as controlling these
parameters are of paramount importance for future applications.
For this task, the occurrence of polymorphism, presented by a
number of SCO complexes, may provide deep insight into the
influence of the supramolecular organization on the SCO
behavior. In this context, herein we present a novel family of
mononuclear octahedral FeII complexes with formula cis-
[Fe(bqen)(NCX)2], where bqen is the chelating tetradentate
ligand N,N¿-bis(8-quinolyl)ethane-1,2-diamine and X = S, Se.
Depending on the preparation method, these compounds
crystallize in either the orthorhombic or the trigonal symmetry
systems. While the orthorhombic phase is composed of a
racemic mixture of mononuclear complexes (polymorph I), the trigonal phase contains only one of the two possible enantiomers
(¿ or ¿), thereby generating a chiral crystal (polymorph II). The four derivatives undergo SCO behavior with well-differentiated
T1/2 values occurring in the interval 90¿233 K. On one hand, T1/2 is about 110 K (polymorph I) and 87 K (polymorph II) higher
for the selenocyanate derivatives in comparison to those for their thiocyanate counterparts. These differences in T1/2 are ascribed
not only to the higher ligand field induced by the selenocyanate anion but also to a remarkable difference in the structural
reorganization of the [FeN6] coordination core upon SCO. Likewise, the higher cooperativity observed for the thiocyanate
derivatives seems to be related to their stronger intermolecular interactions within the crystal. On the other hand, T1/2 is about 53
K (thiocyanate) and 29 K (selenocyanate) higher for the trigonal polymorph II in comparison to those for the orthorhombic
polymorph I. These differences, and the small changes observed in cooperativity, stem from the slightly different hetero- and
homochiral crystal packing generated by the cis-[Fe(bqen)(NCX)2] molecules, which determines subtle adaptations in the
intermolecular contacts and the FeII coordination core.
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Agradecimientos:
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We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), Generalitat Valenciana (PROM-ETEO/2016/147), ...[+]
We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), Generalitat Valenciana (PROM-ETEO/2016/147), and EU Framework Program for Research and Innovation (RISE project number 734322). FJ.V.-M. thanks MINECO for a predoctoral FPI grant
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