Structures of M2(SO2)6B12F12 (M = Ag or K) and Ag2(H2O)4B12F12: Comparison of the Coordination of SO2 versus H2O and of B12F122– versus Other Weakly Coordinating Anions to Metal Ions in the Solid State

The structures of three solvated monovalent cation salts of the superweak anion B12F122– (Y2–), K2(SO2)6Y, Ag2­(SO2)6Y, and Ag2­(H2O)4Y, are reported and discussed with respect to previously reported structures of Ag+ and K+ with other weakly coordinating anions. The structures of K2(SO2)6Y and Ag2­(SO2)6Y 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 MO6F2 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-κ1O,κ2O′ ligands. The structure of Ag2­(H2O)4Y is unique [different from that of K2­(H2O)4Y]. 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-H2O)2­Ag­(μ-H2O)2)]∞ infinite chains between the planes of anions. There are two nearly identical AgO4F2 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 H2O molecules coordinated to a Ag+ ion in the solid state. Comparisons with crystalline H2O and SO2 solvates of other Ag+ and K+ salts of weakly coordinating anions show that (i) N­[(SO2)2­(1,2-C6H4)]−, BF4–, SbF6–, and Al­(OC­(CF3)3)4– coordinate much more strongly to Ag+ than does Y2–, (ii) SnF62– coordinates somewhat more strongly to K+ than does Y2–, and (iii) B12Cl122– coordinates to K+ about the same as, if not slightly weaker than, Y2–.