posted on 2018-01-26, 16:00authored byIgor M. Shlyapnikov, Evgeny A. Goreshnik, Zoran Mazej
Reactions between
AF (A = Li, Na, K, Rb, Cs) and TiF4 (with starting n(AF):n(TiF4) molar ratios in
the range from 3:1 to 1:3) in anhydrous hydrogen fluoride yield [TiF6]2–, [TiF5]−, [Ti4F19]3–, [Ti2F9]−, and [Ti6F27]3– salts. With the exception of the A2TiF6 compounds, which consist of A+ cations
and octahedral [TiF6]2– anions, all of
these materials arise from the condensation of TiF6 units.
The anionic part in the crystal structures of A[TiF5] (A
= K, Cs) and A[TiF5]·HF (A = Na, K, Rb) is composed
of infinite ([TiF5]−)∞ chains built of TiF6 octahedra sharing joint vertices.
Each structure shows a slightly different geometry of the ([TiF5]−)∞ chains. The crystal
structure of Na[Ti2F9]·HF is constructed
from polymeric ([Ti2F9]−)∞ anions that appear as two parallel infinite zigzag
chains comprising TiF6 units, where each TiF6 unit of one chain is connected to a TiF6 unit of the
other chain through a shared fluorine vertex. Slow decomposition of
single crystals of K4[Ti8F36]·8HF
and Rb4[Ti8F36]·6HF (Shlyapnikov, I. M.; et al. Chem. Commun. 2013, 49, 2703) leads to the
formation of [Ti2F9]− (Rb)
and [Ti6F27]3– (K, Rb) salts.
The former displays the same ([Ti2F9]−)∞ double chain as in Na[Ti2F9]·HF, while the anionic part in the latter, ([Ti6F27]3–)∞, represents
the first example of a three-dimensional network built of TiF6 octahedra. The ([Ti6F27]3–)∞ anion was also found in [H3O]3[Ti6F27]. The crystal structure determination
of Cs3[Ti4F19] revealed a new type
of polymeric fluoridotitanate(IV) anion, ([Ti4F19]3–)∞. Similar to the ([Ti2F9]−)∞ anion,
it is also built of zigzag double chains comprising TiF6 units. However, in the former there are fewer connections between
TiF6 units of two neighboring chains than in the latter.