title: Structural, electronic, and magnetic properties of quasi-1D quantum magnets [Ni(HF2)(pyz)2]X (pyz = pyrazine; X = PF6(-), SbF6(-)) exhibiting Ni-FHF-Ni and Ni-pyz-Ni spin interactions.
abstract: [Ni(HF(2))(pyz)(2)]X {pyz = pyrazine; X = PF(6)(-) (1), SbF(6)(-) (2)} were structurally characterized by synchrotron X-ray powder diffraction and found to possess axially compressed NiN(4)F(2) octahedra. At 298 K, 1 is monoclinic (C2/c) with unit cell parameters, a = 9.9481(3), b = 9.9421(3), c = 12.5953(4) Å, and β = 81.610(3)° while 2 is tetragonal (P4/nmm) with a = b = 9.9359(3) and c = 6.4471(2) Å and is isomorphic with the Cu-analogue. Infinite one-dimensional (1D) Ni-FHF-Ni chains propagate along the c-axis which are linked via μ-pyz bridges in the ab-plane to afford three-dimensional polymeric frameworks with PF(6)(-) and SbF(6)(-) counterions occupying the interior sites. A major difference between 1 and 2 is that the Ni-F-H bonds are bent (∼157°) 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 π-donation of the HF(2)(-) ligand in 1 owing to the bent Ni-F-H bonds. Magnetic susceptibility data for 1 and 2 exhibit broad maxima at 7.4 and 15 K, respectively, and λ-like peaks in dχT/dT at 6.2 and 12.2 K that are ascribed to transitions to long-range antiferromagnetic order (T(N)). Muon-spin relaxation and specific heat studies confirm these T(N)'s. A comparative analysis of χ vs T 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 (J(1D)) alone is insufficient to explain the data and that residual terms in the spin Hamiltonian, which could include interchain magnetic couplings (J(⊥)), as mediated by Ni-pyz-Ni, and single-ion anisotropy (D), must be considered. While it is difficult to draw absolute conclusions regarding the magnitude (and sign) of J(⊥) and D 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.
authors: Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, Washington 99004, USA. jmanson@ewu.edu
authors: Jamie L
authors: JL
authors: Manson
authors: Saul H
authors: SH
authors: Lapidus
authors: Peter W
authors: PW
authors: Stephens
authors: Peter K
authors: PK
authors: Peterson
authors: Kimberly E
authors: KE
authors: Carreiro
authors: Heather I
authors: HI
authors: Southerland
authors: Tom
authors: T
authors: Lancaster
authors: Stephen J
authors: SJ
authors: Blundell
authors: Andrew J
authors: AJ
authors: Steele
authors: Paul A
authors: PA
authors: Goddard
authors: Francis L
authors: FL
authors: Pratt
authors: John
authors: J
authors: Singleton
authors: Yoshimitsu
authors: Y
authors: Kohama
authors: Ross D
authors: RD
authors: McDonald
authors: Rico E
authors: RE
authors: Del Sesto
authors: Nickolaus A
authors: NA
authors: Smith
authors: Jesper
authors: J
authors: Bendix
authors: Sergei A
authors: SA
authors: Zvyagin
authors: Jinhee
authors: J
authors: Kang
authors: Changhoon
authors: C
authors: Lee
authors: Myung-Hwan
authors: MH
authors: Whangbo
authors: Vivien S
authors: VS
authors: Zapf
authors: Alex
authors: A
authors: Plonczak