Syntheses and the crystal chemistry of the perfluoridotitanate(IV) compounds templated with ethylenediamine and melamine

Abstract

Chemical reactions between ethane-1,2-diamine [C2H4(NH2)2; ethylenediamine, abbr. en] and 1,3,5-triazine-2,4,6-triamine [C3H6N6; melamine, abbr. mel], with titanium tetrafluoride (TiF4) were carried out in liquid anhydrous hydrogen fluoride (aHF). The latter acted in a dual role: as a reagent and as a solvent. The n(en): n(TiF4) = 2:1, 1:1, 1:3, 1:4, and n(mel): n(TiF4) = 2:1, 1:1, 1:2, 1:3, 1:4 M ratios were studied. Crystallizations of the products from the saturated HF solutions yielded single crystals of [enH2]F2·2HF, previously known [enH2][TiF6] and three new perfluoridotitanate(IV) salts, i.e., [enH2][TiF6]·HF, [enH2]0.5[TiF5] and [melH2][TiF6]·HF. Their crystal structures were determined including the crystal structure of the low-temperature modification of [enH2][TiF6]. The [enH2]0.5[TiF5] phase represents the first example of a structurally characterized perfluoridotitanate(IV) compound with a double charged cation, where instead of the usual octahedral [TiF6]2− monomer, another kind of anion is present, i.e., polymeric chain-like ([TiF5]−)∞ anion. The reactions in en/TiF4/HF and mel/TiF4/aHF systems are not selective enough to enable syntheses of individual [enH2]2+ and [melH2]2+ perfluoridotitanates(IV) in large quantities.