We present an analysis of putative structures of tricyano-1,4-dithiino[c]-isothiazole (TCS3), generated within the sixth crystal structure prediction blind test. Typical packing motifs are identified and characterized in terms of distinct patterns of close contacts and regions of electrostatic and dispersion interactions. We find that different dispersion-inclusive density functional theory (DFT) methods systematically favor specific packing motifs, which may affect the outcome of crystal structure prediction efforts. The effect of crystal packing on the electronic and optical properties of TCS3 is investigated using many-body perturbation theory within the GW approximation and the Bethe–Salpeter equation (BSE). We find that a structure with Pna21 symmetry and a bilayer packing motif exhibits intermolecular bonding patterns reminiscent of π–π stacking and has markedly different electronic and optical properties than the experimentally observed P21/n structure with a cyclic dimer motif, including a narrower band gap, enhanced band dispersion and broader optical absorption. The Pna21 bilayer structure is close in energy to the observed structure and may be feasible to grow.
Supporting information
| Portable Document Format (PDF) file https://doi.org/10.1107/S2052520616009227/xp5006sup1.pdf Supporting tables and figures |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup2.txt The experimental crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, represented in P21/a, which displays a cyclic dimer packing motif. |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup3.txt The experimental crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, represented in P21/n, which displays a cyclic dimer packing motif. This is the structure participants of the blind test that were given as the final experimental structure of target XXII. |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup4.txt A putative crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, which has a catemer packing motif and P21 symmetry. This structure is strongly energetically stabilized by the many-body dispersion (MBD) method. |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup5.txt A putative crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, which has a cyclic dimer packing motif and P21/c symmetry. This structure is the most stable putative crystal structure with a cycle dimer motif other than the experimentally observed structure. |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup6.txt A putative crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, which has P21/c symmetry and molecules which adopt a planar conformation. This structure is energetically destabilized by the PBE0+MBD method, as compared to the PBE+TS and PBE+MBD methods. |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup7.txt A putative crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, which has a bilayer packing motif and P212121 symmetry. This structure is energetically destabilized by the PBE0+MBD method, as compared to the PBE+TS and PBE+MBD methods. |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup8.txt A putative crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, which has a bilayer packing motif and Pna21 symmetry. This is the most energetically stable putative crystal structure found with a bilayer packing motif, and further analysis on it\033s electronic properties is investigated in section 2.3 of the main article. |
| Text file https://doi.org/10.1107/S2052520616009227/xp5006sup9.txt A putative crystal structure of tricyano-1,4-dithiino\[c\]-isothiazole, which has a catemer packing motif and Pna21 symmetry. This structure is strongly energetically stabilized by the many-body dispersion (MBD) method. |