Crown Ether Complexes of Alkali‐Metal Chlorides from SO 2

The structures of alkali‐metal chloride SO 2 solvates (Li–Cs) in conjunction with 12‐crown‐4 or 1,2‐disila‐12‐crown‐4 show strong discrepancies, despite the structural similarity of the ligands. Both types of crown ethers form 1:1 complexes with LiCl to give [Li(1,2‐disila‐12‐crown‐4)(SO 2 Cl)] ( 1 ) and [Li(12‐crown‐4)Cl] ⋅ 4 SO 2 ( 2 ). However, 1,2‐disila‐12‐crown‐4 proved unable to coordinate cations too large for the cavity diameter, for example, by the formation of sandwich‐type complexes. As a result, 12‐crown‐4 reacts exclusively with the heavier alkali‐metal chlorides NaCl, KCl and RbCl. Compounds [Na(12‐crown‐4) 2 ]Cl ⋅ 4 SO 2 ( 3 ) and [ M (12‐crown‐4) 2 (SO 2 )]Cl ⋅ 4 SO 2 ( 4 : M =K; 5 : M =Rb) all showed S ‐coordination to the chloride ions through four SO 2 molecules. Compounds 4 and 5 additionally exhibit the first crystallographically confirmed non‐bridging O , O′ ‐coordination mode of SO 2 . Unexpectedly, the disila‐crown ether supports the dissolution of RbCl and CsCl in the solvent and gives the homoleptic SO 2 ‐solvated alkali‐metal chlorides [ M Cl ⋅ 3 SO 2 ] ( 6 : M =Rb; 7 : M =Cs), which incorporate bridging μ‐ O , O′ ‐coordinating moieties and the unprecedented side‐on O , O′ ‐coordination mode. All compounds were characterised by single‐crystal X‐ray diffraction. The crown ether complexes were additionally studied by using NMR spectroscopy, and the presence of SO 2 at ambient temperature was revealed by IR spectroscopy of the neat compounds.