A Two-Dimensional Iron(II) Carboxylate Linear Chain Polymer that Exhibits a Metamagnetic Spin-Canted Antiferromagnetic to Single-Chain Magnetic Transition

详细信息    查看全文

• 作者：Yan-Zhen Zheng ; Wei Xue ; Ming-Liang Tong ; Xiao-Ming Chen ; Fernande Grandjean ; Gary J. Long
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：May 19, 2008
• 年：2008
• 卷：47
• 期：10
• 页码：4077 - 4087
• 全文大小：5235K
• 年卷期：v.47,no.10(May 19, 2008)
• ISSN：1520-510X

文摘

A two-dimensional iron(II) carboxylate coordination polymer, [Fe(pyoa)₂]_∞, 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 µ-carboxylates to form chains along the b axis that have an Fe···Fe separation of 4.910 Å. The shortest interchain and interlayer Fe···Fe distances are 6.453 and 11.125 Å, respectively. The 4.2−295 K Mössbauer spectra of [Fe(pyoa)₂]_∞ 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° between the axes in adjacent chains in a bc layer. [Fe(pyoa)₂]_∞ 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]_∞ is best considered as a ȁc;metamagnetic-like” single-chain magnet.