Synthesis, crystal growth, structural and magnetic characterization of NH4MCl2(HCOO), M=(Fe, Co, Ni)

Abstract

An ambient-pressure solution route and an improved solvothermal synthetic method have been developed to produce polycrystalline powders and large single crystals of NH 4 MCl 2 (HCOO) (M = Fe, Co, Ni). The magnetic structure of the 1D linear chain compound NH 4 FeCl 2 (HCOO) has been determined by low-temperature neutron powder diffraction, revealing ferromagnetic intra-chain interactions and antiferromagnetic inter-chain interactions. The newly-reported Co and Ni analogues are isostructural with NH 4 FeCl 2 (HCOO), but there are significant differences in the magnetic properties of each compound; the Ni analogue behaves similarly to the Fe compound but with stronger magnetic coupling, exhibiting antiferromagnetic ordering (T N = 8.5 K) and a broad metamagnetic transition between 2-5 T, while the Co analogue does not order magnetically above 2 K, despite strong antiferromagnetic nearest-neighbor interactions.

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

“…As increasing Δ E Q values correspond to an increasing EFG around the iron atoms, it is therefore possible to assign each doublet to one of the three types of helical chains based on differences in local coordination: Q 1 (Δ E Q = 0.995 mm/s) corresponds to Chain 1, which contains metal centers coordinated by six formate oxygens; Q 2 (Δ E Q = 1.305 mm/s) corresponds to Chain 2, where one formate oxygen is replaced by a neutral water oxygen, leading to a slightly more distorted environment and a larger EFG; Q 3 (Δ E Q = 1.999) corresponds to Chain 3, which is by far the most distorted with four short Fe–O bonds and two long Fe–Cl bonds. This value is also similar to what was observed for FeCl 4 (OOCH) 2 octahedra connected in zigzag chains. , These measurements confirm that none of the iron atoms are in the +3 oxidation state, as would be expected if the covalently bound water in Chain 2 was instead a hydroxide group, and this distinction is further supported by the results of neutron powder diffraction (see below).…”

“…We have previously reported on a series of transition metal-formate-chlorides, NH 4 MCl 2 (OOCH) (M = Fe, Co, Ni), which are characterized by infinite 1D zigzag chains of M 2+ -centered octahedra linked by μ 2 -chloride and syn-syn formate bridges. These compounds order antiferromagnetically at low temperature and exhibit anisotropic metamagnetic transitions. , In this report, we describe an alternative structure in which the linear chains are twisted into helices, which can be formed by removing the monovalent cation from the synthesis. Presented here is the synthesis, structure, and characterization of M 3 (OOCH) 5 Cl­(OH 2 ) (M = Fe, Co, Ni), a series of chiral, polar, homospin topological ferrimagnets.…”

Three coordination frameworks with copper formate based low dimensional motifs: synthesis, structure and magnetic properties

“…3,[8][9][10] The balance between systems that exhibit low dimensional shortrange and three-dimensional long-range order appears particularly finely balanced, which can be tipped by factors such as orbital order. 7,11,12 As found for other frameworks, systems that initially appear likely to be low dimensional can instead exhibit long-range magnetic order due to weak through-space interactions between their low dimensional building blocks. 12,13 Alternatively formate-bridged chains and sheets can interact so weakly that these low dimensional units remain paramagnetic even at very low temperatures.…”

“…7,11,12 As found for other frameworks, systems that initially appear likely to be low dimensional can instead exhibit long-range magnetic order due to weak through-space interactions between their low dimensional building blocks. 12,13 Alternatively formate-bridged chains and sheets can interact so weakly that these low dimensional units remain paramagnetic even at very low temperatures.…”

“…While other formate frameworks are known that are structurally 1D e.g. NH4MCl2(HCO2), where M = Fe, Co and Ni, 9,12 to the best of our knowledge chain mean-field analysis has only been carried out for two formate compounds, (C(NH2))3Cu(HCO2)3 7 and ((CH3)2NH2)Cu(HCO2)3 11 . These both adopt perovskite-like structures and their low dimensional magnetism arises from the orientation of the Jahn-Teller axis of the Cu cations.…”