Jahn–Teller Effect in the B₁₂F₁₂ Radical Anion and Energetic Preference of an Octahedral B₆(BF₂)₆ Cluster Structure over an Icosahedral Structure for the Elusive Neutral B₁₂F₁₂

The B₁₂F₁₂^– radical anion was generated by oxidation of [CoCp₂⁺]₂B₁₂F₁₂^2– with AsF₅ in SO₂. In the crystal structure of [CoCp₂⁺]­B₁₂F₁₂^–, the anion displays a lowered symmetry (<i>D</i>_2<i>h</i>) instead of an <i>I_h</i>-symmetric dianion as a result of Jahn–Teller distortion. Moreover, shortening of the B–F bonds and subtle changes of the B–B bonds are observed. DFT calculations show that, for the unknown neutral B₁₂F₁₂, unprecedented structural isomers [e.g., octahedral B₆(BF₂)₆] are energetically favored instead of an icosahedral structure. The structures and energetics are compared with those of the analogous chlorine compounds

Jahn–Teller Effect in the B₁₂F₁₂ Radical Anion and Energetic Preference of an Octahedral B₆(BF₂)₆ Cluster Structure over an Icosahedral Structure for the Elusive Neutral B₁₂F₁₂

The B₁₂F₁₂^– radical anion was generated by oxidation of [CoCp₂⁺]₂B₁₂F₁₂^2– with AsF₅ in SO₂. In the crystal structure of [CoCp₂⁺]­B₁₂F₁₂^–, the anion displays a lowered symmetry (<i>D</i>_2<i>h</i>) instead of an <i>I_h</i>-symmetric dianion as a result of Jahn–Teller distortion. Moreover, shortening of the B–F bonds and subtle changes of the B–B bonds are observed. DFT calculations show that, for the unknown neutral B₁₂F₁₂, unprecedented structural isomers [e.g., octahedral B₆(BF₂)₆] are energetically favored instead of an icosahedral structure. The structures and energetics are compared with those of the analogous chlorine compounds

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 B₁₂F₁₂^2– (Y^2–), 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 Y^2– 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-κ¹<i>O</i>,κ²<i>O</i>′ 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 Y^2–, (ii) SnF₆^2– coordinates somewhat more strongly to K⁺ than does Y^2–, and (iii) B₁₂Cl₁₂^2– coordinates to K⁺ about the same as, if not slightly weaker than, Y^2–