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

Abstract

The structures of three solvated monovalent cation salts of the superweak anion B 12 F 12 2– (Y 2– ), K 2 (SO 2 ) 6 Y, Ag 2 (SO 2 ) 6 Y, and Ag 2 (H 2 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 K 2 (SO 2 ) 6 Y and Ag 2 (SO 2 ) 6 Y are isomorphous and are based on expanded cubic close-packed arrays of Y 2– anions with M(OSO) 6 + complexes centered in the trigonal holes of one expanded close-packed layer of B 12 centroids (⊙). The K + and Ag + ions have virtually identical bicapped trigonal prism MO 6 F 2 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-SO 2 -κ 1 O,κ 2 O ′ ligands. The structure of Ag 2 (H 2 O) 4 Y is unique [different from that of K 2 (H 2 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-H 2 O) 2 Ag(μ-H 2 O) 2 )] ∞ infinite chains between the planes of anions. There are two nearly identical AgO 4 F 2 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 H 2 O molecules coordinated to a Ag + ion in the solid state. Comparisons with crystalline H 2 O and SO 2 solvates of other Ag + and K + salts of weakly coordinating anions show that (i) N[(SO 2 ) 2 (1,2-C 6 H 4 )] −, BF 4 –, SbF 6 –, and Al(OC(CF 3 ) 3 ) 4 – coordinate much more strongly to Ag + than does Y 2–, (ii) SnF 6 2– coordinates somewhat more strongly to K + than does Y 2–, and (iii) B 12 Cl 12 2– coordinates to K + about the same as, if not slightly weaker than, Y 2– .