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Increasing Structural Dimensionality of Alkali Metal Fluoridotitanates(IV)

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journal contribution
posted on 2018-01-26, 16:00 authored by Igor 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.

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