Synthesis, Structures and Properties of a Fourth Modification of [Cd(NCS)2(pyridine)2]n

Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds: synthesis, crystal structures and thermal properties

Five new compounds with the compositions [Cd(NCS)2(3-cyanopyridine)2] n  · 3-cyanopyridine (1), [Cd(NCS)2(3-cyanopyridine)2] n  · 1/3 3-cyanopyridine (2), [Cd(NCS)2(3-cyanopyridine)2] n (3), {[Cd(NCS)2]2(3-cyanopyridine)3} n (4), and {[Cd(NCS)2]3(3-cyanopyridine)4} n (5) have been obtained by the reaction of Cd(NCS)2 with 3-cyanopyridine in different solvents. While large amounts of compounds 1–4 could be prepared as powders, only a few single crystals of 5 were accidently obtained. Thermoanalytical investigations have shown that 4 could also be obtained by annealing of 1 or 2 and that under slightly different conditions 5 could be obtained as part of a mixture with 4. The crystal structures of all compounds can be divided in two sets of compounds. Compounds 1, 2 and 3 consist of chains in which the Cd cations show three different coordination environments and in which the coligands are only terminally bonded. In the structures of 4 and 5 similar chains are observed, which are connected into layers via some of the 3-cyanopyridine coligands.

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

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.