Structures of M 2 (SO 2 ) 6 B 12 F 12 (M = Ag or K) and Ag 2 (H 2 O) 4 B 12 F 12 : Comparison of the Coordination of SO 2 versus H 2 O and of B 12 F 12 2- versus Other Weakly Coordinating Anions to Metal Ions in the Solid State.

The structures of three solvated monovalent cation salts of the superweak anion B12 F12 2- (Y2- ), K2 (SO2 )6 Y, Ag2 (SO2 )6 Y, and Ag2 (H2 O)4 Y, are reported and discussed with respect to previously reported structures of Ag+ and K+ with other weakly coordinating anions. The structures of K2 (SO2 )6 Y and Ag2 (SO2 )6 Y are isomorphous and are based on expanded cubic close-packed arrays of Y2- anions with M(OSO)6 + complexes centered in the trigonal holes of one expanded close-packed layer of B12 centroids (⊙). The K+ and Ag+ ions have virtually identical bicapped trigonal prism MO6 F2 coordination spheres, with M-O distances of 2.735(1)-3.032(2) Å for the potassium salt and 2.526(5)-2.790(5) Å for the silver salt. Each M(OSO)6 + complex is connected to three other cationic complexes through their six μ-SO2 -κ1 O,κ2 O' ligands. The structure of Ag2 (H2 O)4 Y is unique [different from that of K2 (H2 O)4 Y]. Planes of close-packed arrays of anions are offset from neighboring planes along only one of the linear ⊙···⊙···⊙ directions of the close-packed arrays, with [Ag(μ-H2 O)2 Ag(μ-H2 O)2 )]∞ infinite chains between the planes of anions. There are two nearly identical AgO4 F2 coordination spheres, with Ag-O distances of 2.371(5)-2.524(5) Å and Ag-F distances of 2.734(4)-2.751(4) Å. This is only the second structurally characterized compound with four H2 O molecules coordinated to a Ag+ ion in the solid state. Comparisons with crystalline H2 O and SO2 solvates of other Ag+ and K+ salts of weakly coordinating anions show that (i) N[(SO2 )2 (1,2-C6 H4 )]- , BF4 - , SbF6 - , and Al(OC(CF3 )3 )4 - coordinate much more strongly to Ag+ than does Y2- , (ii) SnF6 2- coordinates somewhat more strongly to K+ than does Y2- , and (iii) B12 Cl12 2- coordinates to K+ about the same as, if not slightly weaker than, Y2- .