title: A two-dimensional iron(II) carboxylate linear chain polymer that exhibits a metamagnetic spin-canted antiferromagnetic to single-chain magnetic transition.
abstract: A two-dimensional iron(II) carboxylate coordination polymer, [Fe(pyoa)2]infinity, where pyoa is 2-(pyridin-3-yloxy)acetate, has been prepared by hydrothermal synthesis. Its crystal structure reveals a single iron(II) site with an elongated octahedral coordination environment containing four equatorial carboxylate oxygens and two axial pyridyl nitrogens; the iron(II) sites are linked by syn-anti micro-carboxylates to form chains along the b axis that have an Fe...Fe separation of 4.910 A. The shortest interchain and interlayer Fe...Fe distances are 6.453 and 11.125 A, respectively. The 4.2-295 K Mössbauer spectra of [Fe(pyoa) 2] infinity consist of a single paramagnetic high-spin iron(II) quadrupole doublet. The axial Fe-N bond direction defines the Jahn-Teller axis at an iron(II) site and, consequently, the orientation of the single-ion magnetic anisotropy. Thus, along the b axis in a given chain, the spins are collinear and parallel to the Jahn-Teller axis. The Jahn-Teller axes of adjacent intralayer chains have different orientations with an angle of 79.2 degrees between the axes in adjacent chains in a bc layer. [Fe(pyoa)2]infinity exhibits field-induced metamagnetic behavior such that, in an applied field smaller than the critical field, the iron(II) spin-canted moments experience intrachain ferromagnetic interactions and weak interchain antiferromagnetic interactions; the spin canting yields weak ferromagnetism. In an applied field larger than the critical field, the weak antiferromagnetic interchain interactions are overwhelmed to yield superparamagnetic-like slow-magnetic relaxation with an energy barrier of 23(3) K. Single-crystal magnetic studies reveal a quasi-uniaxial magnetic anisotropy with the a axis as the easy-magnetic axis and the b axis as the hard-magnetic axis; the susceptibility measured along the easy a axis may be fit with the Glauber model to yield an effective intrachain exchange coupling constant of 2.06(8) K. A dynamic analysis of the susceptibility yields a 6.3(1) K energy barrier for intrachain domain wall creation. The observed field-assisted superparamagnet-like behavior is consistent with the dynamics of a single-chain magnet. Thus, [Fe(pyoa)2]infinity is best considered as a "metamagnetic-like" single-chain magnet.
authors.affiliation: MOE Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, China.
authors.forename: Yan-Zhen
authors.initials: YZ
authors.lastname: Zheng
authors.forename: Wei
authors.initials: W
authors.lastname: Xue
authors.forename: Ming-Liang
authors.initials: ML
authors.lastname: Tong
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Chen
authors.forename: Fernande
authors.initials: F
authors.lastname: Grandjean
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Long
mesh_terms: D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D008958:Models, Molecular; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer; D013696:Temperature
chemical_list: D005296:Ferrous Compounds; D008024:Ligands; D011108:Polymers