Na(+)[Me(3)NB(12)Cl(11)](-)·SO(2): a rare example of a sodium-SO(2) complex.

In the title compound, Na(+)[Me(3)NB(12)Cl(11)](-)·SO(2) [systematic name: sodium 1-(trimethylammonio)-undeca-chloro-closo-dodeca-borate sulfur dioxide], the SO(2) mol-ecule is η (1)-O-coordinated to the Na(+) cation. Surprisingly, the SO(2) mol-ecule is more weakly bound to sodium than is found in other sodium-SO(2) complexes and the SO(2) mol-ecule is essentially undistorted compared to the structure of free SO(2). 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 SO(2) complexes is growing, sodium-SO(2) complexes are still rare.