Strengthening the Magnetic Interactions in Pseudobinary First-Row Transition Metal Thiocyanates, M(NCS)₂

Abstract

Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with high operating temperatures. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese (II) thiocyanate, Mn(NCS)2, and iron (II) thiocyanate, Fe(NCS)2. Using magnetic susceptibility measurements on these materials and on cobalt (II) thiocyanate and nickel (II) thiocyanate, Co(NCS)2 and Ni(NCS)2, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, θ, from 29 K for Ni(NCS)2 to −115 K for Mn(NCS)2-a consequence of more diffuse 3d orbitals, increased orbital overlap and increasing numbers of unpaired t2g electrons. We elucidate the magnetic structures of these materials: Mn(NCS)2, Fe(NCS)2 and Co(NCS)2 order into the same antiferromagnetic commensurate ground state, whilst Ni(NCS)2 adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that significantly stronger exchange interactions can be realised in these thiocyanate frameworks by using earlier TMs.

Synthesis, crystal structure and thermal properties of poly[bis[μ2-3-(aminomethyl)pyridine]bis(thiocyanato)cobalt(II)]

“…Which kind of compound is observed depends among other things on the nature of the metal cation, because the synthesis of compounds with bridging anionic ligands is easier with chalcophilic cations such as, for example, Cd II , whereas less chalcophilic metal cations such as Mn II , Fe II and especially Co II and Ni II in several cases lead to the formation of compounds with terminal N-bonded thiocyanate anions. This is of importance because this anionic ligand is able to mediate substantial magnetic exchange (Bassey et al, 2020;Mekuimemba et al, 2018;Palion-Gazda et al, 2015;Mousavi et al, 2020), which can lead to compounds that show a variety of magnetic properties. Co II is of special importance because of its high magnetic anisotropy (Mautner et al, 2018;Neumann et al, 2019).…”

Synthesis, crystal structure and thermal properties of poly[bis[μ-3-(aminomethyl)pyridine-κ2 N:N′]bis(thiocyanato-κN)manganese(II)]

“…Thiocyanate coordination polymers are of interest not only because of their variable structural behaviour, but also because this ligand is able to mediate reasonable magnetic exchange. We and other groups have reported many new compounds in which the metal cations are linked by -1,3bridging thiocyanate anions into chains or layers (Werner et al, 2015;Bassey et al, 2020;Mekuimemba et al, 2018;Palion-Gazda et al, 2015;Neumann et al, 2019;Mousavi et al, 2020). In this context, we became interested in 3-(aminomethyl)pyridine, because this ligand is able to link metal cations via the pyridine and the amino N atom.…”

Synthesis, Crystal Structures and Properties of Polymorphic and Isomeric Nickel(II)thiocyanate Coordination Compounds with 3‐Bromopyridine as Coligand

“…This is a pity, because this ligand is able to mediate reasonable magnetic exchange leading to compounds that can show different magnetic properties. [12][13][14][15][16][17][18][19][20][21] However, in those cases in which compounds with bridging thiocyanate anions are not available from solution, thiocyanate coordination compounds that contain only terminal N-bonded anionic ligands can be heated, which usually leads to a stepwise removal of the coligands, and the irreversible formation of compounds with bridging thiocyanate anions. [3] In most cases, compounds with 1D or 2D thiocyanate networks are obtained.…”