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

摘要

Chemical reactions between guanidinium carbonate or guanidinium chloride and titanium tetrafluoride in anhydrous hydrogen fluoride (aHF) were studied. The obtained products were recrystallized from saturated HF, SO2 and CH3CN solutions. Single-crystal growths resulted in the detection of seven perfluoridotitanate(IV) compounds, which were structurally characterized. Three of them correspond to the phases obtained as the main products of the synthesis in aHF, i.e., [C(NH2)(3)](2)[TiF6], [C(NH2)(3)](4)[Ti4F20], and [C(NH2)(3)][Ti2F9]. When the guanidinium salt/TiF4 molar ratios were greater than 1:2, the resulting products were only sparingly soluble or completely insoluble in aHF. Therefore, single-crystal growths were attempted from other aprotic solvents (SO2 and CH3CN). Single crystals of [C(NH2)(3)](3)[Ti6F27]center dot SO2 were detected in the case of the former and [C(NH2)(3)](4)[H3O](4)[Ti4F20][TiF5](4) in the case of the latter. The presence of [H3O](+) can be explained by a contamination with traces of H2O, which is protonated in the superacid aHF. The same reason applies to the formation of the by-products [H5O2](4)[Ti8F36] and beta-[H3O][Ti2F9]. The crystal structures of the new guanidinium-perfluoridotitanate(IV) compounds consist of oligomeric [Ti4F20](4-), [Ti6F27](3-) and [Ti8F36](4-), as well as polymeric ([TiF5](-))(infinity) and ([Ti2F9](-))(infinity) perfluoridotitanate(IV) anions. The hexameric [Ti6F27](3-) anion with a trigonal prismatic geometry was structurally determined for the first time. The crystal-structure determination of the [C(NH2)(3)](4)[H3O](4)[Ti4F20][TiF5](4) revealed the first example of a mixed-anion perfluoridotitanate(IV) compound containing two different perfluoridotitanate(IV) anions, i.e., oligomeric [Ti4F20](4-) and 1-D polymeric ([TiF5](-))(infinity) anions. The crystal structure of the guanidinium hydrogen difluoride salt [C(NH2)(3)][HF2] is also reported.