Crystal structure of (C9H17N2)3[Bi2I9]

The crystal structure of (C9H7N2)3Bi2I9 contains dinuclear [Bi2I9]3− anions, formed by two face-sharing octahedra, and protonated 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) cations.


Supramolecular features
The [Bi 2 I 9 ] 3À dinuclear units are packed in columns parallel to the [010] direction (Fig. 2), separated by the protonated DBUH + cations. There are no short IÁ Á ÁI distances between the [Bi 2 I 9 ] 3À anions, implying that there are limited interactions that could lead to extended electronic delocalization.
As shown in Table 1, there is hydrogen bonding between the amine functional groups in the DBU moieties and the [Bi 2 I 9 ] 3À dinuclear units. It should be noted that H30 does not form a hydrogen bond. This may be related to the fact that N30 is almost equidistant to I2, I5, I7 and I11. In addition, there are also short contacts of the type C-HÁ Á ÁI. Hirshfeld surface analysis was performed using Crystal Explorer 17 (Turner et al., 2017), with standard resolution of the d norm surfaces. A number of short HÁ Á ÁI contacts are highlighted in red in the Hirshfeld surfaces for the DBU cations and the [Bi 2 I 9 ] 3À anion (Fig. 3). Examination of the fingerprint plots for the DBUH + cations (see supporting information), resolved 2 of 4 James et al. View of the packing of the title compound along [010]. Key: bismuth, green polyhedra; iodine, large orange spheres; carbon, small grey spheres; nitrogen, small blue spheres. H atoms have been omitted for clarity.

Figure 1
The asymmetric unit of (C 9 H 7 N 2 ) 3 Bi 2 I 9 with displacement ellipsoids drawn at the 50% probability level. H atoms have been omitted for clarity. Only one orientation of the disordered DBUH + ring is shown.

Figure 3
Hirshfeld surfaces, mapped with d norm , of the three crystallographically independent DBUH + cations and the [Bi 2 I 9 ] 3À anion. The red areas correspond to regions where contacts are shorter than the sum of the van der Waals radii. into HÁ Á ÁH and HÁ Á ÁI contacts, reveals that approximately 30% of the surface area corresponds to HÁ Á ÁI contacts, with the remaining area corresponding to HÁ Á ÁH interactions.

Optical properties and thermal stability
UV-vis diffuse reflectance data ( Fig. 4) were collected on hand-picked single crystals, using a Perkin Elmer Lambda 35 UV-vis spectrometer. BaSO 4 was used as a standard. The optical band gap, which was estimated from the absorption edge, is 2.1 eV. Thermogravimetric analysis (TGA) was carried out using a TA-TGA Q50 instrument. Measurements (see supporting information) carried out under a flowing nitrogen atmosphere indicate that (C 9 H 7 N 2 ) 3 Bi 2 I 9 is stable up to 300 C.

Synthesis and crystallization
A mixture of BiI 3 (1.1790 g, 2 mmol), KI (0.4490 g, 3 mmol), DBU (0.150 mL, 1 mmol) and ethanol (10 mL) was placed inside the Teflon liner of a 23 mL Parr autoclave. The autoclave was heated in an oven at 443 K for 6 days, using a heating and cooling rate of 0.1 K min À1 . Following filtration, the collected solid product consisted of a mixture of red powder and crystals of the title compound. The powder X-ray diffraction pattern of the product (see supporting information), collected using a Bruker D8 Advance powder diffractometer (Cu K 1 , = 1.5406 Å ), was in excellent agreement with the simulated diffraction pattern, based on the singlecrystal structure determination. Elemental analysis: Calculated values (%) for C 27 H 51 N 6 Bi 2 I 9 : C, 16. 06;H,2.55;N,4.16. Found: C,16.07;H,2.42;N,4.09. IR ( max ) cm À1 : 2920, 2850 (C-H); 1640 (C N).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )