Synthesis and Characterisation of [XeF5]3[Ti4F19] Containing a Discrete [Ti4F19]3-Anion

Chromium Oxide Tetrafluoride and Its Reactions with Xenon Hexafluoride; the [XeF5 ]+ and [Xe2 F11 ]+ Salts of the [CrVI OF5 ]- , [CrV OF5 ]2- , [CrV 2 O2 F8 ]2- , and [CrIV F6 ]2- Anions

Molten mixtures of XeF₆ and Cr^VI OF₄ react by means of F₂ elimination to form [XeF₅ ][Xe₂ F₁₁ ][Cr^V OF₅ ]⋅2 Cr^VI OF₄ , [XeF₅ ]₂ [Cr^IV F₆ ]⋅2 Cr^VI OF₄ , [Xe₂ F₁₁ ]₂ [Cr^IV F₆ ], and [XeF₅ ]₂ [Cr^V ₂ O₂ F₈ ], whereas their reactions in anhydrous hydrogen fluoride (aHF) and CFCl₃ /aHF yield [XeF₅ ]₂ [Cr^V ₂ O₂ F₈ ]⋅2 HF and [XeF₅ ]₂ [Cr^V ₂ O₂ F₈ ]⋅2 XeOF₄ . Other than [Xe₂ F₁₁ ][M^VI OF₅ ] and [XeF₅ ][M^VI ₂ O₂ F₉ ] (M=Mo or W), these salts are the only Group 6 oxyfluoro-anions known to stabilize noble-gas cations. Their reaction pathways involve redox transformations that give [XeF₅ ]⁺ and/or [Xe₂ F₁₁ ]⁺ salts of the known [Cr^V OF₅ ]^2- and [Cr^IV F₆ ]^2- anions, and the novel [Cr^V ₂ O₂ F₈ ]^2- anion. A low-temperature Raman spectroscopic study of an equimolar mixture of solid XeF₆ and CrOF₄ revealed that [Xe₂ F₁₁ ][Cr^VI OF₅ ] is formed as a reaction intermediate. The salts were structurally characterized by LT single-crystal X-ray diffraction and LT Raman spectroscopy, and provide the first structural characterizations of the [Cr^V OF₅ ]^2- and [Cr^V ₂ O₂ F₈ ]^2- anions, where [Cr^V ₂ O₂ F₈ ]^2- represents a new structural motif among the known oxyfluoro-anions of Group 6. The X-ray structures show that [XeF₅ ]⁺ and [Xe₂ F₁₁ ]⁺ form ion pairs with their respective anions by means of Xe- - -F-Cr bridges. Quantum-chemical calculations were carried out to obtain the energy-minimized, gas-phase geometries and the vibrational frequencies of the anions and their ion pairs and to aid in the assignments of their Raman spectra.

Reactive p-block cations stabilized by weakly coordinating anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the - naturally subjective -"reactive"-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

Largest perfluorometallate [Ti10F45]5−oligomer and polymeric ([Ti3F13]−)∞and ([TiF5]−)∞anions prepared as [XeF5]+salts

[XeF₅]₅[Ti₁₀F₄₅] consists of the largest known discrete [Ti₁₀F₄₅]⁵⁻anion built from ten TiF₆octahedra, in the shape of a double-star.

Crystal structures and Raman spectra of imidazolium poly[perfluorotitanate(IV)] salts containing the [TiF6]2-, ([Ti2F9]-)∞, and [Ti2F11]3- and the new [Ti4F20]4- and [Ti5F23]3- anions

Reactions between imidazole (Im, C3H4N2) and TiF4 in anhydrous hydrogen fluoride (aHF) in different molar ratios have yielded [ImH]2[TiF6]·2HF, [ImH]3[Ti2F11], [ImH]4[Ti4F20], [ImH]3[Ti5F23], and [ImH][Ti2F9] upon crystallization. All five structures were characterized by low-temperature single-crystal X-ray diffraction. The single-crystal Raman spectra of [ImH]4[Ti4F20], [ImH]3[Ti5F23], and [ImH][Ti2F9] were also recorded and assigned. In the crystal structure of [ImH]2[TiF6]·2HF, two HF molecules are coordinated to each [TiF6](2-) anion by means of strong F-H···F hydrogen bonds. The [Ti2F11](3-) anion of [ImH]3[Ti2F11] results from association of two TiF6 octahedra through a common fluorine vertex. Three crystallographically independent [Ti2F11](3-) anions, which have distinct geometries and orientations, are hydrogen-bonded to the [ImH](+) cations. The [ImH]4[Ti4F20] salt crystallized in two crystal modifications at low (α-phase, 200 K) and ambient (β-phase, 298 K) temperatures. The tetrameric [Ti4F20](4-) anion of [ImH]4[Ti4F20] consists of rings of four TiF6 octahedra, which each share two cis-fluorine vertices, whereas the pentameric [Ti5F23](3-) anion of [ImH]3[Ti5F23] results from association of five TiF6 units, where four of the TiF6 octahedra share two cis-vertices, forming a tetrameric ring as in [Ti4F20](4-), and the fifth TiF6 unit shares three fluorine vertices with three TiF6 units of the tetrameric ring. The [ImH][Ti2F9] salt also crystallizes in two crystal modifications at low (α-phase, 200 K) and high (β-phase, 298 K) temperatures and contains polymeric ([Ti2F9](-))∞ anions, which appear as two parallel infinite zigzag chains comprised of TiF6 units, where each TiF6 unit of one chain is connected to a TiF6 unit of the second chain through a shared fluorine vertex. Quantum-chemical calculations at the B3LYP/SDDALL level of theory were used to arrive at the gas-phase geometries and vibrational frequencies of the [Ti4F20](4-) and [Ti5F23](3-) anions, which aided in the assignment of the experimental vibrational frequencies of the anion series.