Structures of M₂(SO₂)₆B₁₂F₁₂ (M = Ag or K) and Ag₂(H₂O)₄B₁₂F₁₂: Comparison of the Coordination of SO₂ versus H₂O and of B₁₂F₁₂^2– versus Other Weakly Coordinating Anions to Metal Ions in the Solid State

The structures of three solvated monovalent cation salts of the superweak anion 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–.