Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX2(pyz)2 (X = Cl, Br, I, NCS; pyz = Pyrazine)

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• 作者：Junjie Liu ; Paul A. Goddard ; John Singleton ; Jamie Brambleby ; Francesca Foronda ; Johannes S. Möller ; Yoshimitsu Kohama ; Saman Ghannadzadeh ; Arzhang Ardavan ; Stephen J. Blundell ; Tom Lancaster ; Fan Xiao ; Robert C. Williams ; Francis L. Pratt ; Peter J. Baker ; Keola Wierschem ; Saul H. Lapidus ; Kevin H. Stone ; Peter W. Stephens ; Jesper Bendix ; Toby J. Woods ; Kimberly E. Carreiro ; Hope E. Tran ; Cecelia J. Villa ; Jamie L. Manson
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：April 4, 2016
• 年：2016
• 卷：55
• 期：7
• 页码：3515-3529
• 全文大小：814K
• ISSN：1520-510X

文摘

The crystal structures of NiX₂(pyz)₂ (X = Cl (1), Br (2), I (3), and NCS (4)) were determined by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN₄X₂ units that are bridged by pyz ligands. The 2D layered motifs displayed by 1–4 are relevant to bifluoride-bridged [Ni(HF₂)(pyz)₂]EF₆ (E = P, Sb), which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1–4 and cause a staggered packing of adjacent layers. Long-range antiferromagnetic (AFM) order occurs below 1.5 (Cl), 1.9 (Br and NCS), and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3, and 4 were measured by electron-spin resonance with no evidence for zero–field splitting (ZFS) being observed. The magnetism of 1–4 spans the spectrum from quasi-two-dimensional (2D) to three-dimensional (3D) antiferromagnetism. Nearly identical results and thermodynamic features were obtained for 2 and 4 as shown by pulsed-field magnetization, magnetic susceptibility, as well as their Néel temperatures. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. Compound 3 is characterized as a 3D AFM with the interlayer interaction (J_⊥) being slightly stronger than the intralayer interaction along Ni–pyz–Ni segments (J_pyz) within the two-dimensional [Ni(pyz)₂]²⁺ square planes. Regardless of X, J_pyz is similar for the four compounds and is roughly 1 K.