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.