Synthesis and Characterization of New 2D Coordination Polymers based on Mn(NCS)₂ and Ni(NCS)₂ with 1, 2‐Bis(4‐pyridyl)‐ethane as Co‐Ligand

Abstract

Reaction of manganese(II) and nickel(II) thiocyanate with 1, 2‐bis(4‐pyridyl)‐ethane (bpa) leads to the formation of literature known compounds of composition M(NCS)2(bpa)2 with M = Mn (1‐Mn) and Ni (1‐Ni). On heating 1‐Mn and 1‐Ni transform into new compounds of composition M(NCS)2(bpa) with M = Mn (2‐Mn) and Ni (2‐Ni). These compounds can also be prepared in solution. In both synthetic routes only microcrystalline powders are obtained with crystals too small for single‐crystal X‐ray diffraction. Therefore, the structures of both compounds were solved and refined from X‐ray powder data. In the crystal structure the transition metal cations are coordinated by two bpa co‐ligands and four thiocyanato anions within slightly distorted octahedra. The metal cations are linked by μ‐1, 3‐bridging thiocyanato anions into chains, that are further connected into layers by the bpa ligands. Magnetic measurements on 2‐Ni shows only Curie‐Weiss paramagnetism. In contrast, for 2‐Mn an antiferromagnetic ordering is observed but on further cooling the susceptibility curves increase indicating for canted antiferromagnetism. Further measurements prove that the increase at lower temperatures can be traced back to a small contamination with 1‐Mn, which is always present independent if this compound is prepared by thermal decomposition or by crystallization from solution. In the course of the crystallization experiments a few single crystals of two additional compounds of composition Mn(NCS)2(bpa)(H2O)2 (3‐Mn) and [Mn(NCS)2]2(bpa)3(CH3OH)2 (4‐Mn) were accidently obtained and characterized by single crystal structure analysis. The results of the magnetic measurements are compared with those for related compounds with different neutral N‐donor ligands.

Thiocyanato Coordination Polymers with Isomeric Coordination Networks – Synthesis, Structures, and Magnetic Properties

“…However, it does not influence the overall result that the chain compound shows only paramagnetic behavior without any magnetic anomalies; this is reasonable because similar compounds based on 1D Ni(NCS) 2 chains show either paramagnetic or metamagnetic behavior. [57,83] …”

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

“…According to a search in the Cambridge Crystallographic database about 100 structures are known, in which two Ni cations are linked by a pair of thiocyanate anions. About twenty of them consist of dimers and the majority of them contains Ni cations linked by pairs of thiocyanate anions into linear chains with the thiocyanate N and S as well as the donor atoms of the co‐ligands in trans position , , , . Most of these chain compounds exhibit N‐donor co‐ligands with additional carboxylate groups and form clathrates with a variety of solvate molecules and were not magnetically investigated , .…”

“…Most of these chain compounds exhibit N‐donor co‐ligands with additional carboxylate groups and form clathrates with a variety of solvate molecules and were not magnetically investigated , . Compared to the huge number of dimers and chains, only a few of them were magnetically characterized, which shows that the exchange is usually ferromagnetic , , , , , . For some of the dimers and very few chains the exchange constant was determined using different approaches , , .…”

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

“…All four compounds showed evidence of three-dimensional antiferromagnetic ordering [Figure ]: a sharp change in (dχ)/(d T ) at T N and a rapid decrease in χ at low temperatures; in all cases, the ZFC and FC susceptibilities did not diverge [Figure S7]. Each compound also shows a rise in the susceptibility at low temperatures ( T < 15 K for M = Fe, Co, Ni and T < 35 K for M = Mn), due to small amounts (<1 wt %) of paramagnetic impurities and defects, as observed in several other magnetic molecular frameworks. ,, …”

“…As electrons are added to the t2g orbitals on moving from Mn 2+ to Ni 2+ , the antiferromagnetic component of the J2 interaction again weakens and becomes zero for M = Ni, resulting in a more ferromagnetic J2. Indeed, for many M(NCS)2 solvate frameworks (those of the form M(NCS)2Lx, where L = ligand), the Ni member of the family orders ferromagnetically along the Ni-NCS-Ni chains, whilst the Mn and Co members order antiferromagnetically, 18,22,[66][67][68] indicating that the exchange interaction along the M-NCS-M chains (i.e. the J2 interaction in the frameworks studied in this work) is ferromagnetic for M = Ni and antiferromagnetic for earlier M in the series, which is consistent with our experimental results.…”