Magneto-structural Correlations in Ni²⁺–Halide···Halide–Ni²⁺ Chains

Abstract

We present the magnetic properties of a new family of S = 1 molecule-based magnets, NiF 2 (3,5-lut) 4 ·2H 2 O and NiX 2 (3,5-lut) 4 , where X = HF 2 , Cl, Br, or I (lut = lutidine C 7 H 9 N). Upon creation of isolated Ni–X···X–Ni and Ni–F–H–F···F–H–F–Ni chains separated by bulky and nonbridging lutidine ligands, the effect that halogen substitution has on the magnetic properties of transition-metal-ion complexes can be investigated directly and in isolation from competing processes such as Jahn–Teller distortions. We find that substitution of the larger halide ions turns on increasingly strong antiferromagnetic interactions between adjacent Ni 2+ ions via a novel through-space two-halide exchange. In this process, the X···X bond lengths in the Br and I materials are more than double the van der Waals radius of X yet can still mediate significant magnetic interactions. We also find that a simple model based on elongation/compression of the Ni 2+ octahedra cannot explain the observed single-ion anisotropy in mixed-ligand compounds. We offer an alternative that takes into account the difference in the electronegativity of axial and equatorial ligands.

Controlling Noncollinear Ferromagnetism in van der Waals Metal–Organic Magnets

“…Considering a Hamiltonian only containing single-ion anisotropy and Heisenberg AFM interactions for the Ni– L– Ni chain, analogous to that used in Pianet et al, gives D J normalL = sin ( γ ) sin ( ϕ − γ ) cos ( ϕ − γ ) . Using the experimental values this implies that D / J L = 0.85(4) for NiCl 2 (btd) and D / J L = 0.90(3) for NiCl 2 (pym), broadly consistent with D observed in similar materials. ,, The DMI and single-ion anisotropy terms will act cooperatively, and so the determined parameters thus correspond to estimates of the maxima rather than the central values. Our DFT calculations and Curie–Weiss analysis suggest that J pym is significantly larger than J btd , which would reduce the observed canting, suggesting that the noncollinear interactions ( D and V ) are in fact smaller for NiCl 2 (btd).…”

Controlling noncollinear ferromagnetism in van der Waals metal-organic magnets

“…Using the experimental values this implies that D/J L = 1.4(1) for NiCl 2 (btd) and D/J L = 0.58(3) for NiCl 2 (pym), broadly consistent with D observed in similar materials. 74 The DMI and single-ion anisotropy terms will act cooperatively, and so the determined parameters thus correspond to estimates of the maxima rather than the central values. Our DFT calculations and Curie-Weiss analysis suggest that J pym is significantly larger than J btd , which would reduce the observed canting, and so the observed opposite trend suggests that the noncollinear interactions (D and V ) are in fact larger for NiCl 2 (btd).…”

Spatially anisotropic S=1 square-lattice antiferromagnet with single-ion anisotropy realized in a Ni(II) pyrazine- n,n′ -dioxide coordination polymer

“…Toward this end, we have studied a variety of coordination-polymer magnetic systems with different dimensionalities, exchange energies, and spin quantum numbers (see, e.g., Refs. [2][3][4][5][6][7][8][9][10][11]). Within the field of quantum magnets, the subfield of two-dimensional (2D) systems is attractive due to the ability to support long-range entangled states [12] and the analogies to theories of high-temperature superconductivity (HTSC).…”