title: Towards direct correlations between spin-crossover and structural features in iron(II) complexes.
abstract: The [Fe(PM-BiA)(2)(NCS)(2)] complex, where PM is N-2-pyridylmethylene and BiA is 4-aminobiphenyl, crystallizes in two polymorphs. The two phases, denoted (I) and (II), undergo a spin-crossover when the sample is cooled and present distinct spin-transition features as (I) shows a very abrupt spin transition, while (II) exhibits a gradual transition. The two forms of the complex are used to investigate the correlations that exist between the spin-transition features and structural features. This article presents the crystal structures of polymorph (II) at room temperature (high spin) and at 120 K (low spin), including a comparison with those of polymorph (I). This study reveals that the packing, in a first approximation, is similar in both forms. In order to look at the crystal structures in more detail, a new angular parameter, denoted theta(NCS), as well as a particular type of intermolecular hydrogen-bond interaction, which involves the S atoms of the NCS ligands, are investigated. Interestingly, this angle and this intermolecular interaction can be directly connected to the cooperativity of the spin transition. Such a result is extended to all the SCO iron(II) complexes belonging to the same family of the general formula [Fe(PM-L)(2)(NCS)(2)].
authors.affiliation: Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), UPR CNRS 9048, Université Bordeaux I, 87 Av. de Docteur Schweitzer, F-33608 Pessac, France. marchivi@icmcb.u-bordeaux.fr
authors.forename: Mathieu
authors.initials: M
authors.lastname: Marchivie
authors.forename: Philippe
authors.initials: P
authors.lastname: Guionneau
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Létard
authors.forename: Daniel
authors.initials: D
authors.lastname: Chasseau