Speaker: MSc. Alena Shlyaykher, Philipps-Universität Marburg.

Topic: About 200 years ago, ammonium cyanate, [NH4][OCN], was obtained by Liebig and Wöhler as a fluffy, white powder from the reaction of dry ammonia with cyanic acid. They also noticed its rearrangement at room temperature into urea, [NH2]2CO, a compound which has the same sum formula as ammonium cyanate.[1,2] From this the concept of isomerism was deduced and remains unchanged until today.[3] In contrast, the heavier homologue, ammonium thiocyanate, [NH4][SCN], showed higher thermal stability: it only isomerizes into thiourea, [NH2]2CS, when held at ~120 °C for some time.[4–6]Until now, the heavier congener of this series, ammonium selenocyanate, [NH4][SeCN], has scarcely been studied. The first crystallographic data were reported 1913, however, experimental procedures were omitted. In 1982, a detailed synthetical procedure was published, albeit without meaningful further analysis.[7,8] Due to its highly sensitive nature, detailed crystallographic studies and isomerization behavior are a striking gap in this field.We revisit studies of the thermal behavior of [NH4][OCN] and [NH4][SeCN], and report on the hitherto unknown crystal structure of [NH4][SeCN], its behavior towards thermal stress, and reactivity toward Ag[SeCN].[9]

[1] J. D. Dunitz, K. D. M. Harris, R. L. Johnston, B. M. Kariuki, E. J. MacLean, K. Psallidas, W. B. Schweizer, R. R. Tykwinski, J. Am. Chem. Soc. 1998, 120, 13274–13275.
[2] F. Wöhler, Ann. Phys. Chem. 1828, 88, 253–256.
[3] J. J. Berzelius, Jahresbericht Über Die Fortschritte Der Physischen Wissenschaften, Heinrich Laupp, Tübingen, 1832.
[4] J. Waddell, J. Phys. Chem. 1898, 2, 525–535.
[5] G. Peyronel, R. Battistuzzi, G. Marcotrigiano, J. Chem. Soc. 1974, 896.
[6] S. T. Talreja, P. M. Oza, P. S. Rao, Bull. Chem. Soc. Jpn. 1967, 40, 2427–2428.
[7] K. Geisler, E. Nobst, C. Müller, E. Bulka, Z. Chem. 1982, 22, 113–114.
[8] E. von Fedorow, Z. Krist. 1913, 52, 97–136.
[9] A. Shlyaykher, F. Tambornino, Inorg. Chem. 2023, 62, 30, 11943–11953.

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