title: Remarkable steric effects and influence of monodentate axial ligands l on the spin-crossover properties of trans-[FeII(N4 ligand)L] complexes.
abstract: Iron(II) complexes obtained from tetradentate, rigid, linear N4 ligands have been investigated to appraise the influence of steric effects and the impact of trans-coordinated anions on the spin-transition behavior. As expected, the well-designed ligands embrace the metal center, resulting in octahedral iron(II) complexes where the basal plane is fully occupied by the pyridine/pyrazole N4 ligand, while anions or solvent molecules are exclusively axially coordinated. Precursor complexes, namely, [Fe(bpzbpy)(MeOH)2](BF4)2 (where bpzbpy symbolizes the ligand 6,6'-bis(N-pyrazolylmethyl)-2,2'-bipyridine) and [Fe(mbpzbpy)(MeOH)2](BF4)2 (where mbpzbpy symbolizes the ligand 6,6'-bis(3,5-dimethyl-N-pyrazolmethyl)-2,2'-bipyridine), have been used for the in situ preparation of a series of structural analogues via the exchange of the weakly coordinated trans methanol molecules by various anions, such as thiocyanate, selenocyanate, or dicyanamide. The magnetic properties of all seven iron(II) compounds thus obtained have been investigated. Two iron(II) complexes, i.e., [Fe(bpzbpy)(NCS)2] and [Fe(bpzbpy)(NCSe)2], exhibit gradual spin-crossover (SCO) properties typical of isolated mononuclear species with weak cooperative interaction. These two SCO materials have been studied by Mössbauer spectroscopy, and the light-induced excited spin state trapping effect has been investigated, revealing the possibility to induce the spin-transition both by temperature variation and by light irradiation. A correlation between steric/anion effect and SCO behavior is suggested.
authors: Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
authors: José Sánchez
authors: JS
authors: Costa
authors: Kristian
authors: K
authors: Lappalainen
authors: Graham
authors: G
authors: de Ruiter
authors: Manuel
authors: M
authors: Quesada
authors: Jinkui
authors: J
authors: Tang
authors: Ilpo
authors: I
authors: Mutikainen
authors: Urho
authors: U
authors: Turpeinen
authors: C Matthias
authors: CM
authors: Grunert
authors: Philipp
authors: P
authors: Gütlich
authors: Hanane Zhor
authors: HZ
authors: Lazar
authors: Jean-François
authors: JF
authors: Létard
authors: Patrick
authors: P
authors: Gamez
authors: Jan
authors: J
authors: Reedijk