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

Structaral 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) angstrom], and forms a loosely held network of Se-4 and Cl-4 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 center dot center dot center dot N interactions in the solid state. These Se center dot center dot center dot N interactions are much shorter in PhSeCN, 3.023(3)-3.065(4) angstrom, than in PhSeSCN, 3.348(4) angstrom. Weaker Se center dot center dot center dot 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. (c) 2006 Elsevier Ltd. All rights reserved.