Na+[Me3NB12Cl11]-·SO2: a rare example of a sodium-SO2 complex.

In the title compound, Na+[Me3NB12Cl11]-·SO2 [systematic name: sodium 1-(trimethylammonio)-undeca-chloro-closo-dodeca-borate sulfur dioxide], the SO2 mol-ecule is η 1-O-coordinated to the Na+ cation. Surprisingly, the SO2 mol-ecule is more weakly bound to sodium than is found in other sodium-SO2 complexes and the SO2 mol-ecule is essentially undistorted compared to the structure of free SO2. The Na+ cation has a coordination number of eight in a distorted twofold-capped trigonal prism and makes contacts to three individual boron cluster anions, resulting in an overall three-dimensional network. Although the number of known η 1-O-coordinated SO2 complexes is growing, sodium-SO2 complexes are still rare.