Crystal structure of the new hybrid material bis(1,4-diazoniabicyclo[2.2.2]octane) di-μ-chlorido-bis[tetrachloridobismuthate(III)] dihydrate

The title salt, (C6H14N2)2[Bi2Cl10]·2H2O, bears a close resemblance to its homologous antimonate structure. The crystal structure is formed by an alternating packing of organic and inorganic layers along [001] and contains isolated (Bi2Cl10)4− bioctahedra.


Chemical context
In recent years, many new organic-inorganic hybrid compounds have been synthesized because of their interesting physical behaviour and applications in optoelectronics (Jakubas & Sobczyk, 1990). The main interesting optical activity observed in this kind of compounds is generally the result of the presence of an active ns 2 lone pair (Chaabouni et al., 1998) in the inorganic parts. It can also be the result of an important structural distortion in the organic cations (Ishihara et al., 1990;Lacroix et al., 1994). The combination of the particular properties of the organic and inorganic moieties can induce interesting new properties. In particular for the halogenated bismuth or antimony anionic networks (Ahmed et al., 2001;Jakubas et al., 2005), the anionic arrangement leads to four kinds of dimensionalities: quantum dots (zero-dimensional, 0D) observed in hybrids such as (C 6 H 14 N 2 ) 2 -[Sb 2 Cl 10 ]Á2H 2 O (Ben Rhaiem et al., 2013), quantum wires (one-dimensional, 1D) as is the case in the structure of (C 2 H 7 N 4 O) 2 [BiCl 5 ] (Ferjani et al., 2012), quantum wells (twodimensional, 2D) and a bulk (three-dimensional, 3D) topology. The organic cations are usually filling the empty space left by the inorganic network. Here we report the structure of a new hybrid bismuthate compounds having a 0D dimensionality with respect to its inorganic part.

Structural commentary
The structural unit (Fig. 1) 2+ ] and two water molecules. These components are linked by strong hydrogen bonds. The inorganic moiety is an edge-sharing dioctahedron located site with symmetry 1. The two (DABCOH 2 ) 2+ dications (Fig. 4) in the structural unit are related to the dimeric [Bi 2 Cl 10 ] 4À units by means of N2-H2Á Á ÁCl2 and N2-H2Á Á ÁCl1 interactions.
The bond lengths and angles of the dication are within normal ranges and are comparable to those observed in similar structures. Table 1 summarizes the most important distances in these molecules. The C-N bond lengths vary from 1.479 (11) to 1.508 (12) Å . The C-C bond lengths vary from 1.500 (13) to 1.535 (13) Å . The angles in this molecule are between 109.8 (7) and 110.7 (8) for C-N-C and between 108.1 (8) and 109.2 (8) for N-C-C.

Figure 3
Water-molecule hydrogen-bonding interaction between organic and inorganic parts: (a) in the title compound [symmetry codes: Plot of the molecular entities of (C 6 H 14 N 2 ) 2 [Bi 2 Cl 10 ]. 2H 2 O, showing the atom numbering scheme. Atomic displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radius. [Symmetry codes: (i) Àx + 1, Ày + 1, Àz + 1; (ii) Àx + 2, y + 0.5, Àz + 0.5; (iii) x À 1, Ày + 0.5, z + 0.5.] polyhedra distortion. The final Fourier difference map reveals four large peaks at approximately 1 Å from the bismuth atom that can be attributed to the delocalization of the 6s 2 electron pair as is the case in most other bismuth-based structures. The (C 6 H 14 N 2 ) 2 [Bi 2 Cl 10 ]Á2H 2 O structure is very close to that of (C 6 H 14 N 2 ) 2 [Sb 2 Cl 10 ]Á2H 2 O (Ben Rhaiem et al., 2013). The cell parameters of both structures can be compared after making a necessary transformation (cba) in the Pnnm antimony unit cell to be comparable to the bismuth one (Table 2). Apart from the higher symmetry of the antimony structure, an important distortion is noted in the SbCl 6 octahedra confirmed by the Shannon's distortion index (Shannon,1976) [6.20 (9) Â 10 À3 ], more than three times larger than the one for the title bismuth compound [1.87 (9) Â 10 À3 ] . It is worth noting that the water molecule plays a more efficient role in the bismuth based compound. In (C 6 H 14 N 2 ) 2 [Sb 2 Cl 10 ]Á2H 2 O, the H 2 O molecules are only linked to (DABCOH 2 ) 2+ and in the (C 6 H 14 N 2 ) 2 [Bi 2 Cl 10 ]Á2H 2 O structure they are directly hydrogen bonded to both the organic and inorganic parts (Fig. 3). The atomic radius of bismuth is larger than that for antimony, and thus an increase of the cell volume is expected. In fact, the main increase is observed for the c axis [13.99 (2) Å ] because the metallic coordination polyhedra are aligned along this axis. On the other hand, a roughly equivalent decrease of the b parameter is observed causing the unitcell volume of the two compounds approximately to be the same. A general comparison of the two structures reveals that they have a similar 3D pattern, built up by isolated bioctahedra, (DABCOH 2 ) 2+ cations and water molecules leaving empty the same voids. On the other hand, the water molecule immediate environment is more regular in the Sb structure (Fig. 3b) and the (DABCOH 2 ) 2+ cation is more distorted in the Bi structure (Fig. 3a) explaining the lowering of the symmetry in the title compound.

Figure 4
Hydrogen-bonding environment of the cationic organic part of the title compound.

Figure 5
Projection of the crystal structure of the bismuthate hybrid compound along the c axis, showing the alternation of organic and inorganic layers. molecules stabilize the structure by playing a bridge role between organic and inorganic parts. Furthermore, they ensure the link in the other directions leading to a hydrogenbond-based three-dimensional network. The structure can be seen (Fig. 5) as an alternation of organic and inorganic layers parallel to (100) which are linked by a strong hydrogen-bond pattern (Table 3).

Synthesis and crystallization
(C 6 H 14 N 2 ) 2 [Bi 2 Cl 10 ]Á2H 2 O crystals were obtained at ambient conditions by dissolving Bi(NO 3 ) 3 Á5H 2 O and DABCO (C 6 H 12 N 2 ) in water in a 1:2 molar ratio. The pH of the solution was adjusted to 1 with HCl. The mixture was stirred and kept for several days. Colourless crystals were obtained after a few weeks.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The isotropic displacement parameter of the hydrogen atoms for the water molecule were fixed to be restrained to be approximately 1.5 times those of the parent atom and the water molecule geometries were regularised using distance restraints  Wocadlo, 1995), SHELXS97 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010 program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).