Synthesis, structures, magnetic, and theoretical investigations of layered Co and Ni thiocyanate coordination polymers

Abstract

Reaction of cobalt(ii) and nickel(ii) thiocyanate with ethylisonicotinate leads to the formation of [M(NCS)(ethylisonicotinate)] with M = Co (2-Co) and M = Ni (2-Ni), which can also be obtained by thermal decomposition of M(NCS)(ethylisonicotinate) (M = Co (1-Co), Ni (1-Ni)). The crystal structure of 2-Ni was determined by single crystal X-ray diffraction. The Ni(ii) cations are octahedrally coordinated by two N and two S bonding thiocyanate anions and two ethylisonicotinate ligands and are linked by pairs of anionic ligands into dimers, that are connected into layers by single thiocyanate bridges. The crystal structure of 2-Co was refined by Rietveld analysis and is isostructural to 2-Ni. For both compounds ferromagnetic ordering is observed at 8.7 K (2-Ni) and at 1.72 K (2-Co), which was also confirmed by specific heat measurements. Similar measurements on [Co(NCS)(4-acetylpyridine)] that exhibits the same layer topology also prove magnetic ordering at 1.33 K. Constrained DFT calculations (CDFT) support the ferromagnetic interactions within the layers. The calculated exchange constants in 2-Ni were used to simulate the susceptibility by quantum Monte Carlo method. The single-ion magnetic anisotropy of the metal ions has been investigated by CASSCF/CASPT2 calculations indicating significant differences between 2-Ni and 2-Co.

Structural Diversity in Ni Chain Coordination Polymers: Synthesis, Structures, Isomerism and Magnetism

“…This is not surprising for thiocyanate coordination polymers because very small changes in the coordination can have a dramatic influence not only on the exchange but also on the sign of exchange, as recently observed in layered thiocyanate compounds with 4‐acetylpyridine, ethylisonicotinate and 2,6‐dimethylpyrazine. In the former two compounds with Co and Ni dominating ferromagnetic interactions are observed and both compounds show a ferromagnetic transition at significantly different temperatures . In contrast, the compound with 2,6‐dimethylpyrazine shows exactly the same coordination network but dominating antiferromagnetic exchange interactions are found …”

Synthesis, Crystal Structures, and Properties of Ni(NCS)2‐4‐methoxypyridine Coordination Compounds

“…If the precursors consist of discrete complexes with pyridine derivatives as co‐ligands, usually 1D compounds are obtained, in which the metal cations are octahedrally coordinated by two N‐donor co‐ligands as well as four μ‐1,3‐bridging anionic ligands and are linked by pairs of anionic ligands into chains, although examples of 2D networks are also known , . The 1D compounds with Co II are of special interest, because the magnetic exchange along the chain is ferromagnetic and several of these coordination polymers show single chain magnetism , , .…”

Crystal structures of bis[4-(dimethylamino)pyridinium] tetrakis(thiocyanato-κN)manganate(II) and tris[4-(dimethylamino)pyridinium] pentakis(thiocyanato-κN)manganate(II)

“…In this context, we have reported a number of compounds based on M(NCS) 2 moieties (M = Mn, Fe, Co and Ni) that show different magnetic properties including single-chain magnetism (Werner et al, 2015a,b;Rams et al, 2017a,b). In the majority of structures, the metal cations are linked by pairs of -1,3 bridging ligands into chains, but 2D networks are also realized in which the cations are linked by pairs and single anionic ligands into layers (Suckert et al, 2016;Wö hlert et al, 2012aWö hlert et al, , 2013. In some cases, compounds comprising bridging anionic ligands need to be prepared by thermal decomposition of precursors that consist of discrete octahedral complexes with terminal N-bonded thiocyanate anions.…”