Magnetic Order Through Super-Superexchanges in the Polar Magnetoelectric Organic鈥揑norganic Hybrid Cr[(D3N-(CH2)2-PO3)(Cl)(D2O)]

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• 作者：Gwilherm N茅nert ; Hyun-Joo Koo ; Claire V. Colin ; Elvira M. Bauer ; Carlo Bellitto ; Clemens Ritter ; Guido Righini ; Myung-Hwan Whangbo
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：January 18, 2013
• 年：2013
• 卷：52
• 期：2
• 页码：753-760
• 全文大小：573K
• 年卷期：v.52,no.2(January 18, 2013)
• ISSN：1520-510X

文摘

The crystal and magnetic structures of the organic鈥搃norganic hybrid compound Cr(II) ammoniumethylphosphonate chloride monohydrate, Cr[D₃N-(CH₂)₂-PO₃)(Cl)(D₂O)] (1), have been studied by temperature-dependent neutron powder diffraction and superconducting quantum interference device (SQUID) magnetometry. The compound represents a rare example of a magnetoelectric polar organic鈥搃norganic hybrid solid, containing high spin Cr²⁺ ions (S = 2) and is a canted antiferromagnet (weak ferromagnet) below T_N = 5.5 K. The neutron powder diffraction pattern recorded at T = 10 K, shows that the partially deuterated compound crystallizes in the same non centrosymmetric monoclinic space group P2₁ (No. 4) with the following unit-cell parameters: a = 5.24041(4) 脜, b =13.93113(8) 脜, c = 5.26081(4) 脜, and 尾 = 105.4347(5)掳. Powder neutron diffraction of a partially deuterated sample has enabled us, for the first time, to locate the water molecule. At low temperature, the compound presents a canted antiferromagnetic state characterized by k = 0 resulting in the magnetic symmetry P2₁鈥? This symmetry is in agreement with the previously reported large magnetodielectric effect. The crystal structure of (1) can be described as being built up of triangular lattice planes made up of [Cr(II)O₄Cl] square pyramids which are separated by ammonium ethyl groups along the b axis. The transition from paramagnetic to weakly ferromagnetic state results from super-superexchanges only. Surprisingly, while the overall magnetic behavior is antiferromagnetic, the Cr(II)O₄Cl planes are ferromagnetic, and the strongest antiferromagnetic coupling is via the ammonium ethyl groups. Our density functional calculations confirm these aspects of the spin exchange interactions of (1) and that the spin exchange interactions between Cr(II) ions are considerably weak compared with the single-ion anisotropy of Cr^II.