Structural, Electronic, and Magnetic Properties of Quasi-1D Quantum Magnets [Ni(HF2)(pyz)2]X (pyz = pyrazine; X = PF6鈥?/sup>, SbF6鈥?/sup>) Exhibit

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• 作者：Jamie L. Manson ; Saul H. Lapidus ; Peter W. Stephens ; Peter K. Peterson ; Kimberly E. Carreiro ; Heather I. Southerland ; Tom Lancaster ; Stephen J. Blundell ; Andrew J. Steele ; Paul A. Goddard ; Francis L. Pratt ; John Singleton ; Yoshimitsu Kohama ; Ross D. McDonald ; Rico E. Del Sesto ; Nickolaus A. Smith ; Jesper Bendix ; Sergei A. Zvyagin ; Jinhee Kang ; Changhoon Lee ; Myung-Hwan Whangbo ; Vivien S. Zapf ; Alex Plonczak
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：July 4, 2011
• 年：2011
• 卷：50
• 期：13
• 页码：5990-6009
• 全文大小：1590K
• 年卷期：v.50,no.13(July 4, 2011)
• ISSN：1520-510X

文摘

[Ni(HF₂)(pyz)₂]X {pyz = pyrazine; X = PF₆^{鈥?/sup> (1), SbF₆鈥?/sup> (2)} were structurally characterized by synchrotron X-ray powder diffraction and found to possess axially compressed NiN₄F₂ octahedra. At 298 K, 1 is monoclinic (<i>Ci>2/<i>ci>) with unit cell parameters, <i>ai> = 9.9481(3), <i>bi> = 9.9421(3), <i>ci> = 12.5953(4) 脜, and 尾 = 81.610(3)掳 while 2 is tetragonal (<i>Pi>4/<i>nmmi>) with <i>ai> = <i>bi> = 9.9359(3) and <i>ci> = 6.4471(2) 脜 and is isomorphic with the Cu-analogue. Infinite one-dimensional (1D) Ni-FHF-Ni chains propagate along the <i>ci>-axis which are linked via 渭-pyz bridges in the <i>abi>-plane to afford three-dimensional polymeric frameworks with PF₆鈥?/sup> and SbF₆鈥?/sup> counterions occupying the interior sites. A major difference between 1 and 2 is that the Ni鈥揊鈥揌 bonds are bent (157掳) in 1 but are linear in 2. Ligand field calculations (LFT) based on an angular overlap model (AOM), with comparison to the electronic absorption spectra, indicate greater 蟺-donation of the HF₂鈥?/sup> ligand in 1 owing to the bent Ni鈥揊鈥揌 bonds. Magnetic susceptibility data for 1 and 2 exhibit broad maxima at 7.4 and 15 K, respectively, and 位-like peaks in d蠂<i>Ti>/d<i>Ti> at 6.2 and 12.2 K that are ascribed to transitions to long-range antiferromagnetic order (<i>Ti>_N). Muon-spin relaxation and specific heat studies confirm these <i>Ti>_N鈥檚. A comparative analysis of 蠂 vs <i>Ti> to various 1D Heisenberg/Ising models suggests moderate antiferromagnetic interactions, with the primary interaction strength determined to be 3.05/3.42 K (1) and 5.65/6.37 K (2). However, high critical fields of 19 and 37.4 T obtained from low temperature pulsed-field magnetization data indicate that a single exchange constant (<i>Ji>_1D) alone is insufficient to explain the data and that residual terms in the spin Hamiltonian, which could include interchain magnetic couplings (<i>Ji>), as mediated by Ni-pyz-Ni, and single-ion anisotropy (<i>Di>), must be considered. While it is difficult to draw absolute conclusions regarding the magnitude (and sign) of <i>Ji> and <i>Di> based solely on powder data, further support offered by related Ni(II)-pyz compounds and our LFT and density-functional theory (DFT) results lead us to a consistent quasi-1D magnetic description for 1 and 2.}