title: Structural and magnetic investigations of the mixed-valence Fe(II,III) two-dimensional layer complex, [Fe2(II) Fe2(III)(HCOO)10(C6H7N)6]n.
abstract: The structure of the complex, [Fe2(II)Fe2(III)(HCOO)10(C6H7N6)n, (1) exhibits a neutral two-dimensional layer network of alternating iron(II) and iron(III) ions, bridged equatorially by formate groups. All iron atoms are octahedrally coordinated, with iron(III) coordinating axially to one gamma-picoline and one formate group, while the iron(II) centers interact axially with two gamma-picoline groups, above and below the layer plane. The complex crystallizes in the triclinic space group P1 at all studied temperatures [at 120 K, the cell dimensions are: a = 10.228(1), b = 12.071(1), c = 12.072(1) A, alpha = 89.801(2), beta = 71.149(2), gamma = 73.371(2) degrees]. An intralayer antiferromagnetic exchange interaction of J = -2.8 cm(-1) between iron(II) and iron(III) was observed in the magnetic studies. Decreasing the temperature to close to 20 K causes a magnetic-ordering phenomenon to occur and a low-temperature phase with a long-range antiferromagnetic spin orientation appears. The magnetic phase transition was confirmed by Mössbauer spectroscopic studies at temperatures above and below the critical temperature. Structural information of 1 from synchrotron X-ray diffraction data collected at room temperature and 16 K suggests that the antiferromagnetic ordering is caused by an enhanced pi-pi interaction between chi-picoline groups from adjacent layers.
authors.affiliation: Department of Chemistry, University of Aarhus, Langelandsgade 140, 8000 Aarhus C, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Overgaard
authors.forename: Eva
authors.initials: E
authors.lastname: Rentschler
authors.forename: Grigore A
authors.initials: GA
authors.lastname: Timco
authors.forename: Finn K
authors.initials: FK
authors.lastname: Larsen
mesh_terms: D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D008280:Magnetics; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer; D013696:Temperature
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D009942:Organometallic Compounds