Crystal structure of strontium and barium acesulafame (6-methyl-4-oxo-4H-1,2,3-oxathiazin-3-ide 2,2-dioxide)

Strontium and barium acesulfames crystallize in nearly identical isotypic forms, with barium–oxygen interatomic distances being longer due to the larger ionic radius of the barium(II) ion. The conformation of the acesulafame ions is a distorted envelope with an out-of-plane S atom. Metal and acesulfame ions are assembled in infinitive chains along the [100] axis. These chains are connected via hydrogen bonds into a three-dimensional network.


Chemical context
Acesulfame is one of the most common sweeteners; usually it is used in the form of a potassium salt. Salts with all alkali metals, ammonium, magnesium, and calcium ions, as well as its protonated molecular form, are also known. The almost identical crystal structures of the strontium and barium salts are reported here.

Figure 1
The numbering scheme of strontium acesulfame monohydrate, shown with 50% probability displacement elipsoids.

Figure 3
Overlay of the two acesulafame ions in the Sr structure.

Supramolecular features
Each acesulfame anion is connected to three strontium (or barium) ions via a bridging O atom of the amide carbonyl group, an N atom of this group, and one of the O atoms of a sulfonyl group. Each metal ion is directly connected to six acesulfame anions. As a result, metal ions and acesulfame anions form infinite chains along the [100] axis (Fig. 5). The O atoms of the two sulfonyl groups that are not connected to metal ions form, instead, strong hydrogen bonds with both H atoms of the water molecule. These hydrogen bonds (Tables 3  and 4) connect each chain to four neighboring parellel chains, thus creating a three-dimensional assembly (Fig. 6). There are also two short C-HÁ Á ÁO contacts (Tables 3 and 4) which may additionally stabilize the crystal structures.

Figure 5
The infinite chain of metal ions and acesulafame anions along the [100] axis. The view is along the [010] vector.
with transition-metal ions and various salts of bulky organic cations.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. All H atoms of water molecules are refined in isotropic approximation. All other H atoms are refined with riding coordinates; methyl H atoms are refined as rotating idealized methyl groups and with U iso (H) = 1.5U iso (C). Crystal structure of strontium and barium acesulafame (6-methyl-4oxo-4H-1,2,3-oxathiazin-3-ide 2,2-dioxide) Alexander Y. Nazarenko

Poly[aquabis(µ 3 -6-methyl-2,2-dioxo-1,2λ 6 ,3-oxathiazin-4-olato)strontium(II)] (Sr)
Crystal data  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.