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

Reaction of Cd(NCS) 2 with pyridine in water accidently lead to the formation of crystals of a fourth modification of [Cd(NCS) 2 (pyridine) 2 ] n , which most likely corresponds to form I reported by Taniguchi et al. but which was not structurally characterized by these authors. This modification crystallizes in the monoclinic space group C 2/ c with a = 10.6032(3) Å, b = 15.8676(5) Å, c = 26.2795(8), b = 96.001(2) °and V = 4397.2(2) Å 3 . The structure of this compound is very similar to that of form III reported recently, in which the Cd cations are octahedrally coordinated by two pyridine ligands and four thiocyanato anions. The cations are linked by pairs of anionic ligands into chains, in which the thiocyanato anions are always trans ‐coordinated. Further investigations show that larger amounts of pure form I cannot be prepared because it is always contaminated with form II , in which the thiocyanato anions are cis ‐coordinated. Solvent mediated conversion experiments using mixtures of the trans ‐modifications I and III as well as the cis ‐modification II prove that form III disappears first and therefore, is less stable than the second trans ‐modification I . IR and Raman spectroscopic investigations show, that all forms cannot be distinguished from each other using these methods.