NH₄FeCl₂(HCOO): Synthesis, Structure, and Magnetism of a Novel Low-Dimensional Magnetic Material

Solvothermal synthesis was used to create a low-dimensional iron­(II) chloride formate compound, NH₄FeCl₂­(HCOO), that exhibits interesting magnetic properties. NH₄FeCl₂­(HCOO) crystallizes in the monoclinic space group <i>C</i>2/<i>c</i> (No. 15) with <i>a</i> = 7.888(1) Å, <i>b</i> = 11.156(2) Å, <i>c</i> = 6.920(2) Å, and β = 108.066(2)°. The crystal structure consists of infinite zigzag chains of distorted Fe²⁺-centered octahedra linked by μ₂-Cl and syn-syn formate bridges, with interchain hydrogen bonding through NH₄⁺ cations holding the chains together. The unique Fe²⁺ site is coordinated by four equatorial chlorides at a distance of 2.50 Å and two axial oxygens at a distance of 2.08 Å. Magnetic measurements performed on powder and oriented single-crystal samples show complex anisotropic magnetic behavior dominated by antiferromagnetic interactions (<i>T</i>_N = 6 K) with a small ferromagnetic component in the direction of chain propagation. An anisotropic metamagnetic transition was observed in the ordered state at 2 K in an applied magnetic field of 0.85–3 T. ⁵⁷Fe Mössbauer spectroscopy reveals mixed hyperfine interactions below the ordering temperature, with strong electric field gradients and complex noncollinear arrangement of the magnetic moments

A Series of Chiral, Polar, Homospin Topological Ferrimagnets: M₃(OOCH)₅Cl(OH₂) (M = Fe, Co, Ni)

An isostructural series of transition metal-formate-chloride-hydrate compounds, M₃(OOCH)₅Cl­(OH₂) (M = Fe, Co, Ni), have been synthesized using a solvothermal method. These compounds crystallize in the chiral and polar space group <i>P</i>3₁ and are comprised of three different types of helical chains of edge-sharing M²⁺-centered octahedra. All three compounds undergo 3D ferrimagnetic ordering at low temperature, and the iron and cobalt analogues exhibit field-induced metamagnetic transitions. The magnetic structure was determined by neutron powder diffraction, revealing ferromagnetic intrachain coupling and antiferromagnetic interchain interactions, with the three chains arranged in a two-up/one-down triangular lattice. As all three chains contain one type of metal in the same spin state, these compounds are rare examples of homospin topological ferrimagnets

A Series of Chiral, Polar, Homospin Topological Ferrimagnets: M₃(OOCH)₅Cl(OH₂) (M = Fe, Co, Ni)

An isostructural series of transition metal-formate-chloride-hydrate compounds, M₃(OOCH)₅Cl­(OH₂) (M = Fe, Co, Ni), have been synthesized using a solvothermal method. These compounds crystallize in the chiral and polar space group <i>P</i>3₁ and are comprised of three different types of helical chains of edge-sharing M²⁺-centered octahedra. All three compounds undergo 3D ferrimagnetic ordering at low temperature, and the iron and cobalt analogues exhibit field-induced metamagnetic transitions. The magnetic structure was determined by neutron powder diffraction, revealing ferromagnetic intrachain coupling and antiferromagnetic interchain interactions, with the three chains arranged in a two-up/one-down triangular lattice. As all three chains contain one type of metal in the same spin state, these compounds are rare examples of homospin topological ferrimagnets