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

Abstract

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.

Guanidinium Perfluoridotitanate(IV) Compounds: Structural Determination of an Oligomeric [Ti6F27]3– Anion, and an Example of a Mixed‐Anion Salt Containing Two Different Fluoridotitanate(IV) Anions

“…The tetrameric [Ti 4 F 20 ] 4– anion is very similar to that determined in imidazolium salt α‐[C 3 H 5 N 2 ] 4 [Ti 4 F 20 ], and represents a slightly distorted planar square, made up of four TiF 6 octahedra, where each shares two cis vertices (Figureà). The Ti ··· Ti distances are equal to 3.8583(3) and 3.8927(3) Å and the Ti–Ti–Ti angles are equal to 89.675(7)° and 90.325(8)°.…”

“…In the solid state these units can remain isolated, leading to trivial hexafluoridotitanate(IV) salts, or they can be linked by sharing fluorine ions, yielding larger oligomeric (0‐D geometry) or polymeric (1‐D, 2‐D and 3‐D) anions. So far, there are 18 structurally characterized fluoridotitanate(IV) anions: oligomeric [TiF 6 ] 2– , [Ti 2 F 10 ] 2– ,, [Ti 2 F 11 ] 3– , [Ti 4 F 18 ] 2– , [Ti 4 F 19 ] 3– , [Ti 4 F 20 ] 4– , [Ti 5 F 23 ] 3– , [Ti 8 F 36 ] 4– , [Ti 10 F 45 ] 5– , and polymeric ([TiF 5 ] – ) ∞ , ([Ti 2 F 9 ] – ) ∞ ,, , ([Ti 3 F 13 ] – ) ∞ , ([Ti 4 F 19 ] 3– ) ∞ , ([Ti 6 F 27 ] 3– ) ∞ , ([Ti 7 F 30 ] 2– ) ∞ , ([Ti 9 F 38 ] 2– ) ∞ , and two modifications of the ([Ti 8 F 33 ] – ) ∞ anion , . The geometries of the various anions were determined with X‐ray experiments on single crystals of pure inorganic and/or hybrid compounds.…”

Hydroxylammonium Tetrafluoridooxidovanadate(V) – (NH3OH)[VOF4]

“…[35][36][37][38] Similarly, the anions in the crystal structure of (NH 3 OH) [VOF 4 ] interact with the cations through a myriad of hydrogen bonds (Table 3). All four hydrogen atoms of the cation are involved in hydrogen (3) a Symmetry transformations for the generation of equivalent atoms:…”

Heat capacity, entropy, dielectric properties and T–p phase diagram of (NH 4 ) 3 TiF 7

“…There exist a lot of fluoride compounds containing [Ti x F 4x+y ] yÀ anions with the vertex-sharing octahedral TiF 6 units, partially studied in [17], which also can be considered as the promising systems to undergo structural transformations. Such a supposition is confirmed by the results of structural studies of some compounds containing [Ti 4 F 20 ] 4À and [Ti 2 F 9 ] À anions at room temperature and 200 K [17].…”