Thermal conversion of a pyridine solvate to a de-solvate facilitated by rearrangement of chalcogen bonds. The solvate and non-solvate structures of N-(2-nitro-4-(3-oxobenzo[d][1,2]selenazol-2(3H)-yl)phenyl)picolinamide

The pyridine solvate of benzisoselenazolinone 1.pyridine is characterised by planar sheets of the benzisoselenazolinone 1 pierced by channels of pyridine molecules at an angle of 133°, the pyridine molecules are held in place by N⋯Se chalcogen bonding to the isoselenazolinone moiety. These channels, which extend through the structure to the surface of the crystal, provide a means for escape of pyridine from the lattice when the crystal is heated to ca. 100 °C. Upon loss of the pyridine from these channels the remaining molecules undergo rearrangement to fill the space and in doing so the N⋯Se chalcogen bond in 1.pyridine is replaced by a CO⋯Se chalcogen bond to give the non solvate 1(ex.DMF). The geometry of the chalcogen bond requires that the two benzisoselenazolinone ring systems which are essentially coplanar in 1.pyridine twist by an angle of 138° resulting in the formation of highly corrugated sheets in the non solvate.