Crystal structure, Hirshfeld surface analysis and DFT study of 2,2''-({[(1,1')-(diselanedi-yl)bis-(2,1-phenyl-ene)]bis-(methane-ylyl-idene)}bis-(aza-neylyl-idene))bis-[3',6'-bis-(di-ethyl-amino)-4a',9a'-di-hydro-spiro-[isoindoline-1,9'-xanthen]-3-one].

The title compound, CHNOSe, is a spiro bicyclic diselenide, made up of two [SeCHCH=N-N(CO)CH(C)CHNEt(O)CHNEt] units related by a twofold crystallographic symmetry element bis-ecting the diselenide bond. The compound crystallizes in a non-centrosymmetric polar space group (tetra-gonal, 2) and the structure was refined as an inversion twin. The two diethyl amine groups and their attached phenyl groups of the xanthene ring are disordered over two orientations, with occupancies of 0.664 (19)/0.336 (19) and 0.665 (11)/0.335 (11), respectively. The dihedral angles between the mean planes of the central isoindoline and the phenyl rings are 26.8 (2) and 2.5 (4)°, respectively. The mean plane of the central xanthene ring forms dihedral angles of 2.0 (5), 8.8 (5), 1.7 (5) and 7.9 (6)° with the peripheral phenyl rings. The isoindoline and xanthene rings subtend a dihedral angle of 89.8 (2)°. The mol-ecular conformation is stabilized by an intra-molecular C-H⋯O hydrogen bond generating an (6) ring motif. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds together with C-H⋯π (ring) inter-actions, forming a three-dimensional network. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H⋯H (68.1%), C⋯H/H⋯C (21.2%) and O⋯H/H⋯O (8.7%) contacts. The optimized structure calculated using density functional theory (DFT) at the B3LYP/6 - 31 G() level is compared with the experimentally determined mol-ecular structure in the solid state. The HOMO-LUMO behaviour was used to determine the energy gap and the mol-ecular electrostatic potential (MEP) of the compound was investigated.