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Synthesis, crystal structure and properties of Cd(NCS)₂ coordination compounds with two different Cd coordination modes

Jochim, Aleksej, Gallo, Gianpiero, Dinnebier, Robert, Näther, Christian
Zeitschrift für Naturforschung 2019 v.74 no.1 pp. 49-58
anions, cadmium, cations, crystal structure, crystallization, crystals, differential scanning calorimetry, ligands, manganese, thermogravimetry, thiocyanates
Reaction of Cd(NCS)₂ with 4-methoxypyridine leads to the formation of four new compounds, of which one crystallizes in two different polymorphs. In Cd(NCS)₂(4-methoxypyridine)₄·(4-methoxypyridine)₂ (1) and Cd(NCS)₂(4-methoxypyridine)₄ (2-I and 2-II) discrete complexes are found, in which the Cd cations are octahedrally coordinated by four 4-methoxypyridine co-ligands and two terminally N-bonded thiocyanate anions. For the polymorphs 2-I and 2-II no single crystals are available and therefore, the corresponding Mn(II) compound (2-I-Mn) was prepared, which is isotypic to 2-I, as proven by a Rietveld refinement. The crystal structure of 2-II was solved and refined from XRPD data. In [Cd(NCS)₂(4-methoxypyridine)₂]ₙ (3), the Cd cations are also octahedrally coordinated but linked into linear chains by pairs of thiocyanate anions with all ligands in trans-position. {[Cd(NCS)₂]₃(4-methoxypyridine)₅}ₙ (4) also consists of chains but two different Cd coordination modes are observed. Two of the three crystallographically independent Cd cations show an octahedral coordination with a trans- or cis-arrangement of the N and S atoms of the anionic ligands, whereas the third one is in a distorted square-pyramidal coordination, with cis-coordination of the thiocyanate N and S atoms. Measurements using simultaneous thermogravimetry and differential scanning calorimetry of 2-I and 2-II show different heating rate dependent mass steps, in which the co-ligands are removed. In some of the residues obtained after the respective TG steps compound 3 was detected but no phase pure samples could be obtained.