Supramolecular architectures featuring Se⋯N secondary-bonding interactions in crystals of selenium-rich molecules: a comparison with their congeners

Supramolecular aggregates featuring Se⋯N contacts have been identified in 88 crystals containing two, three or four selenium atoms, corresponding to 9% of crystals where Se⋯N contacts have the potential to form. Molecules with two selenium atoms make up the majority of examples (58) followed by molecules with three (12) and four (18) selenium atoms. A wide range of supramolecular aggregation patterns has been identified in the 88 crystals featuring Se⋯N contacts with one- (42%) and two- (31%) dimensional aggregation forming the majority compared with zero- (17%) and three- (10%) dimensional aggregation making up the rest. The overwhelming majority of Se⋯N contacts correspond to chalcogen-bonding interactions based on σ-hole interactions. Correlations in intermolecular separations were evident for isostructural crystals which showed that a comparable Te⋯N interaction was stronger than the equivalent Se⋯N interaction, and the Se⋯N interaction was always stronger than the equivalent S⋯N interaction. When compared to crystals of mono-nuclear selenium compounds, a very similar adoption rate was observed in their crystals but with a bias towards smaller aggregation patterns, i.e. 50, 44, 5 and 1% for zero-, one-, two- and three- dimensional, respectively. This observation is clearly consistent with the greater opportunity for multi-nuclear selenium molecules to form more interactions. However, as exemplified by the 18 tetra-nuclear molecules, not all selenium atoms participated in a Se⋯N contact as two, 10, two and four selenium atoms, out of a possible four, formed a Se⋯N contact in their crystals.