A new dabco-templated metal sulfate: 1,4-diazoniabicyclo[2.2.2]octane hexaaquacadmium bis(sulfate)

The title double molecular salt, (C6H14N2)[Cd(H2O)6](SO4)2, is an isostructure of its Mn and Co analogues. The CdII atom adopts a near-regular CdO6 octahedral coordination geometry. The crystal structure can be described as an alternation of cationic and anionic layers along [010], and numerous O—H⋯O and N—H⋯O hydrogen bonds are observed. No thermal anomalies corresponding to possible phase transitions were observed in DSC (differential scanning calorimetry) measurements and the 93 K structure is almost the same as the room-temperature structure.

The title double molecular salt, (C 6 H 14 N 2 )[Cd(H 2 O) 6 ](SO 4 ) 2 , is an isostructure of its Mn and Co analogues. The Cd II atom adopts a near-regular CdO 6 octahedral coordination geometry. The crystal structure can be described as an alternation of cationic and anionic layers along [010], and numerous O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds are observed. No thermal anomalies corresponding to possible phase transitions were observed in DSC (differential scanning calorimetry) measurements and the 93 K structure is almost the same as the room-temperature structure.

Experimental
Crystal data (C 6
Data collection: RAPID-AUTO (Rigaku, 2000); cell refinement: RAPID-AUTO; data reduction: RAPID-AUTO ; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL and DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: SHELXTL.  (Yahyaoui et al., 2007;Rekik et al., 2006Rekik et al., , 2007Naili et al., 2006;Zhao et al., 2005). The related Fe, Ni, Cu compounds were found to undergo reversible phase transitions resulting from the ordering of the dabcodiium cations (Yahyaoui et al., 2007;Naili et al., 2006;Rekik et al., 2006). Similarly, Dabcodiium hexaaquacopper(II) bis(selenate), (H 2 dabco)Cu(H 2 O )6 (SeO 4 ) 2 , as a new member of this series, was recently found to undergo a paraelectric-to-ferroelctric phase transition with striking dielectric response (Zhang et al., 2009). It seems the structures and related structural phase transitions are sensitive to both the metal ions and the counterpart anions. So far, the metal ions in this series of compounds are limited to the first row transition metal. We herein report the structure of a new member of this series with the second transition metal ion, Dabcodiium hexaaquacadmium(II) bis(sulfate), (C 6 H 14 N2) [Cd(H 2 O) 6 ](SO 4 ) 2 (I).
The [Cd(H 2 O) 6 ] 2+ octahedron is slightly irregular according to the Cd-OW distances and the OW-Cd-OW angles (Table   1). Each [Cd(H 2 O) 6 ] 2+ octahedron is surrounded by five sulfate groups H-bonded in a bidentate manner and two sulfate groups in a monodentate mode to the octahedron (Fig. 3).
The dabconium moieties can be viewed as template, and are stabilized in the hydrogen bonding network through N-H···O bonds (Fig. 2, Table 2).They occupy general positions and are fully ordered. The C-C and N-C distances range from 1.507 (3) to 1.512 (4) Å, from 1.481 (3) to 1.496 (3) Å respectively. As is the case in the Mn or Co isostructure. In the dabconium templated sulfates, phase transition was observed only for those with disordered dabcodiium cations. To confirm whether there is a phase transition, we performed DSC measurement. No thermal anomaly was observed in the temperature from 148 to below 373 K. Near 373 K the heat flow increases rapidly, indicating there is not a highertemperature phase transition but decomposition. The structure determined at 93 K is shown to have the same structure at room temperature. The negative results prove the disordered dabcodiium play the key role in the phase transtions as well as packing modes of the structures. independent sulfate anions have normal geometry, as seen in other dabcodiium-templated sulfates (Yahyaoui et al., 2007;Rekik et al., 2006Rekik et al., , 2007Naili et al., 2006;Zhao et al., 2005). As can be seen in Fig. 2 and 5, the sulfate anions play an important role in the structure connectivity. They are stacked in a manner that they form anionic layers parallel to the cationic ones parallel to the (ac) plane. Then cationic and anionic layers alternate along the b axis in a ABAB fashion and linked by N-H···O and OW-H···O. (Fig. 5). The crystal structure is then described as an alternation of cationic and anionic layers along [010].

Experimental
An aqueous solution of dabcodiium sulfate was prepared by neutralization of dabco with equimolar amount of sulfuric acid in water. To this solution, an aqueous solution containing equimolar amount of CdSO 4 was added. The resulting solution was allowed to evaporate at room temperature and colourless blocks of (I) were obtained after two weeks, Yield: 70%.

Refinement
All H atoms were found in the difference maps. Those from coordinated water molecules was refined isotropically. The bond distances of O-H and distance between two H atoms from each water molecules was restrained to be 0.85 and 1.37 Å with the default deviation respectively. However, those bonded to C and N atoms were placed at ideal positions and refined using a 'riding′ model with U iso = 1.2 U eq (C or N).

Figure 1
View of the asymmetric unit of I with displacement ellipsoids drawn at the 30% probability level.

1,4-diazoniabicyclo[2.2.2]octane hexaaquacadmium bis(sulfate)
Crystal data (C 6  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.