title: Spin crossover of ferric complexes with catecholate derivatives. Single-crystal X-ray structure, magnetic and Mössbauer investigations.
abstract: Complexes of general formula [(TPA)Fe(R-Cat)]X.nS were synthesised with different catecholate derivatives and anions (TPA = tris(2-pyridylmethyl)amine, R-Cat2- = 4,5-(NO2)2-Cat2- denoted DNC(2-); 3,4,5,6-Cl4-Cat2- denoted TCC2-; 3-OMe-Cat(2-); 4-Me-Cat(2-) and X = BPh4-; NO3-; PF6-; ClO4-; S = solvent molecule). Their magnetic behaviours in the solid state show a general feature along the series, viz., the occurrence of a thermally-induced spin crossover process. The transition curves are continuous with transition temperatures ranging from ca. 84 to 257 K. The crystal structures of [(TPA)Fe(DNC)]X (X = PF6-; BPh4-) and [(TPA)Fe(TCC)]X.nS (X = PF6-; NO3- and n= 1, S = H2O; ClO4- and n= 1, S = H2O; BPh4- and n= 1, S = C3H6O) were solved at 100 (or 123 K) and 293 K. For those two systems, the characteristics of the [FeN(4)O(2)] coordination core and those of the dioxolene ligands appear to be consistent with a prevailing Fe(III)-catecholate formulation. This feature is in contrast with the large quantum mixing between Fe(III)-catecholate and Fe(II)-semiquinonate forms recently observed with the more electron donating simple catecholate dianion. The thermal spin crossover process is accompanied by significant changes of the molecular structures as shown by the average variation of the metal-ligand bond distances which can be extrapolated for a complete spin conversion from ca. 0.123 to 0.156 A. The different space groups were retained in the low- and high-temperature phases.
authors.affiliation: Laboratoire de Chimie Inorganique, UMR 8613, ICMMO, Bâtiment 420, Universite Paris-Sud, 91405 Orsay, France.
authors.forename: S
authors.initials: S
authors.lastname: Floquet
authors.forename: A J
authors.initials: AJ
authors.lastname: Simaan
authors.forename: E
authors.initials: E
authors.lastname: Rivière
authors.forename: M
authors.initials: M
authors.lastname: Nierlich
authors.forename: P
authors.initials: P
authors.lastname: Thuéry
authors.forename: J
authors.initials: J
authors.lastname: Ensling
authors.forename: P
authors.initials: P
authors.lastname: Gütlich
authors.forename: J-J
authors.initials: JJ
authors.lastname: Girerd
authors.forename: M-L
authors.initials: ML
authors.lastname: Boillot
mesh_terms: D002396:Catechols / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D008958:Models, Molecular; D015204:Spectroscopy, Mossbauer; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D002396:Catechols; D005290:Ferric Compounds; D008024:Ligands; D014867:Water; C034221:catechol