A two-dimensional iron(II) carboxylate linear chain polymer that exhibits a metamagnetic spin-canted antiferromagnetic to single-chain magnetic transition

作者：Zheng, Yan Zhen; Xue, Wei; Tong, Ming Liang^*; Chen, Xiao Ming; Grandjean, Fernande; Long, Gary J

来源：Inorganic Chemistry, 2008, 47(10): 4077-4087.

DOI：10.1021/ic701879y

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 mu-carboxylates to form chains along the b axis that have an Fe center dot center dot center dot Fe separation of 4.910 angstrom . The shortest interchain and interlayer Fe center dot center dot center dot Fe distances are 6.453 and 11.125 angstrom , respectively. The 4.2-295 K Mossbauer 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 79.20 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.

• 出版日期2008-5-19
• 单位中山大学