Synthesis, crystal structure and thermal properties of catena-poly[[bis­(4-methyl­pyridine)­nickel(II)]-di-μ-thio­cyanato], which shows an alternating all-trans and cis–cis–trans-coordination of the NiS2Np2Nt2 octa­hedra (p = 4-methyl­pyridine, t = thio­cyanate)

In the crystal structure of the title compound, Ni(NCS)₂(C₆H₇N)₂ (C₆H₇N = 4-methyl­pyridine), the Ni^II cations are in an octa­hedral coordination and are linked by pairs of anionic ligands into corrugated chains in which the cations show alternating all-trans and cis–cis–trans coordination geometries. Upon heating, the title compound transforms into Ni(NCS)₂(C₆H₇N), which is isotypic to its Cd analog as proven by a Rietveld refinement.

The title compound, [Ni(NCS)₂(C₆H₇N)₂]_n, was prepared by the reaction of Ni(NCS)₂ with 4-methyl­pyridine in water. Its asymmetric unit consists of two crystallographically independent Ni^II cations, of which one is located on a twofold rotational axis whereas the second occupies a center of inversion, two independent thio­cyanate anions and two independent 4-methyl­pyridine co­ligands in general positions. Each Ni^II cation is octa­hedrally coordinated by two 4-methyl­pyridine coligands as well as two N- and two S-bonded thio­cyanate anions. One of the cations shows an all-trans, the other a cis–cis–trans configuration. The metal centers are linked by pairs of μ-1,3-bridging thio­cyanate anions into [101] chains. X-ray powder diffraction shows that a pure crystalline phase has been obtained and thermogravimetry coupled to differential thermoanalysis reveals that the title compound loses half of the 4-methyl­pyridine coligands and transforms into Ni(NCS)₂(C₆H₇N). Nearly pure samples of this compound can be obtained by thermal annealing and a Rietveld refinement demonstrated that it is isotypic to its recently reported Cd analog [Neumann et al., (2020#). CrystEngComm.22, 184–194] In its crystal structure, the metal cations are linked by one μ-1,3(N,S)- and one μ-1,3,3(N,S,S)-bridging thio­cyanate anion into single chains that condense via the μ-1,3,3(N,S,S)-bridging anionic ligands into double chains.