Increasing Structural Dimensionality of Alkali Metal Fluoridotitanates(IV)

Abstract

Reactions between AF (A = Li, Na, K, Rb, Cs) and TiF (with starting n(AF):n(TiF) molar ratios in the range from 3:1 to 1:3) in anhydrous hydrogen fluoride yield [TiF], [TiF], [TiF], [TiF], and [TiF] salts. With the exception of the ATiF compounds, which consist of A cations and octahedral [TiF] anions, all of these materials arise from the condensation of TiF units. The anionic part in the crystal structures of A[TiF] (A = K, Cs) and A[TiF]·HF (A = Na, K, Rb) is composed of infinite ([TiF]) chains built of TiF octahedra sharing joint vertices. Each structure shows a slightly different geometry of the ([TiF]) chains. The crystal structure of Na[TiF]·HF is constructed from polymeric ([TiF]) anions that appear as two parallel infinite zigzag chains comprising TiF units, where each TiF unit of one chain is connected to a TiF unit of the other chain through a shared fluorine vertex. Slow decomposition of single crystals of K[TiF]·8HF and Rb[TiF]·6HF ( Shlyapnikov , I. M. ; et al. Chem. Commun. 2013 , 49 , 2703 ) leads to the formation of [TiF] (Rb) and [TiF] (K, Rb) salts. The former displays the same ([TiF]) double chain as in Na[TiF]·HF, while the anionic part in the latter, ([TiF]), represents the first example of a three-dimensional network built of TiF octahedra. The ([TiF]) anion was also found in [HO][TiF]. The crystal structure determination of Cs[TiF] revealed a new type of polymeric fluoridotitanate(IV) anion, ([TiF]). Similar to the ([TiF]) anion, it is also built of zigzag double chains comprising TiF units. However, in the former there are fewer connections between TiF units of two neighboring chains than in the latter.

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

“…Since the frequency of the Raman band belonging to the symmetric in‐phase Ti–F t stretching vibration of perfluoridotitanate(IV) anions increases with both an increasing of the TiF 4 content and a decreasing of the anion charge, it is very useful for the identification of various perfluoridotitanate(IV) anions. The frequency ranges from 599 cm –1 in the case of the [TiF 6 ] 2– anion to 807 cm –1 for the TiF 4 itself , , , . The Raman spectra of guanidinium perfluoridotitanates(IV) recorded in the present research also follow this rule.…”

“…It appears as a monomeric chain of cis ‐connected TiF 6 octahedra. Unlike other determined polymeric pentafluoridotitanate(IV) anions that appear as zig‐zag chains (Figureàa), the ([TiF 5 ] – ) ∞ anion in the crystal structure of [C(NH 2 ) 3 ] 4 [H 3 O] 4 [Ti 4 F 20 ][TiF 5 ] 4 represents a crenelated chain (Figure b). The Ti–F bond lengths are typical for poly[perfluoridotitanate(IV)] compounds ranging from 1.763(1) to 1.877(1) Å and from 1.964(1) to 2.004(1) Å for the Ti–F t and Ti–F b bonds, respectively (Table S17).…”

“…The experimental geometries of the ([TiF 5 ] – ) ∞ anion as appear in a) [H 3 O][TiF 5 ], [NH 4 ][TiF 5 ], A[TiF 5 ] and A[TiF 5 ] · HF (A = Na, K, Rb, Cs) and b) [C(NH 2 ) 3 ] 4 [H 3 O] 4 [Ti 4 F 20 ][TiF 5 ] 4 compounds. Thermal ellipsoids are drawn at the 50 % probability level.…”

“…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.…”

“…The single‐crystal structure of [N(C 2 H 4 NH 3 ) 3 ][TiF 6 ]F was also determined, but was later corrected to [N(C 2 H 4 NH 3 ) 3 ][TiF 4,7 (OH) 1,3 ]F . Examples of the crystal structures of perfluoridotitanate(IV) compounds containing two different perfluoridotitanate(IV) anions were not known before this study , …”