A comparison of the solid-state structures of a series of phenylseleno-halogen and pseudohalogen compounds, PhSeX (X = Cl, CN, SCN)

Structural and spectroscopic data on the series of compounds “PhSeX”, where X = Cl, CN or SCN, are reported and compared with previously reported data on “PhSeX” systems (X = Br and I). The chloro-compound displays a “square” motif, Ph4Se4Cl4, in the solid state, linked by long Se–Se bonds [2.993(3)–3.035(3) Å], and forms a loosely held network of Se4 and Cl4 squares in its extended structure. In contrast, the pseudohalogen derivatives, PhSeCN and PhSeSCN, consist of essentially monomeric units, which form chains held together by weak Se⋯N interactions in the solid state. These Se⋯N interactions are much shorter in PhSeCN, 3.023(3)–3.065(4) Å, than in PhSeSCN, 3.348(4) Å. Weaker Se⋯N contacts are also present between the chains. The structure of PhSeSCN described here is the first reported crystallographic study of a selenium thiocyanate compound. Spectroscopic studies suggest that all three compounds exist as monomers in solution. The results reported herein illustrate the subtle differences in the solid-state structures of PhSeX compounds.

Graphical abstractThe solid-state structures of the series of compounds PhSeX (X = Cl, CN, SCN) have been reported. PhSeCl displays a square motif, Ph4Se4Cl4, with four PhSeCl units linked by weak Se–Se bonds. In contrast, the pseudohalogen derivatives PhSeCN and PhSeSCN display essentially monomeric structures, and both exhibit Se⋯N contacts in their extended structures which appear to be the dominant packing force in these compounds. PhSeSCN is the first crystallographically characterised example of a selenium thiocyanate compound.Figure optionsDownload full-size imageDownload as PowerPoint slide