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.

Reactions between imidazole (Im, C3H4N2) and TiF4 in anhydrous hydrogen fluoride (aHF) in different molar ratios have yielded [ImH]2[TiF6]·2HF, [ImH]3[Ti2F11], [ImH]4[Ti4F20], [ImH]3[Ti5F23], and [ImH][Ti2F9] upon crystallization. All five structures were characterized by low-temperature single-crystal X-ray diffraction. The single-crystal Raman spectra of [ImH]4[Ti4F20], [ImH]3[Ti5F23], and [ImH][Ti2F9] were also recorded and assigned. In the crystal structure of [ImH]2[TiF6]·2HF, two HF molecules are coordinated to each [TiF6](2-) anion by means of strong F-H···F hydrogen bonds. The [Ti2F11](3-) anion of [ImH]3[Ti2F11] results from association of two TiF6 octahedra through a common fluorine vertex. Three crystallographically independent [Ti2F11](3-) anions, which have distinct geometries and orientations, are hydrogen-bonded to the [ImH](+) cations. The [ImH]4[Ti4F20] salt crystallized in two crystal modifications at low (α-phase, 200 K) and ambient (β-phase, 298 K) temperatures. The tetrameric [Ti4F20](4-) anion of [ImH]4[Ti4F20] consists of rings of four TiF6 octahedra, which each share two cis-fluorine vertices, whereas the pentameric [Ti5F23](3-) anion of [ImH]3[Ti5F23] results from association of five TiF6 units, where four of the TiF6 octahedra share two cis-vertices, forming a tetrameric ring as in [Ti4F20](4-), and the fifth TiF6 unit shares three fluorine vertices with three TiF6 units of the tetrameric ring. The [ImH][Ti2F9] salt also crystallizes in two crystal modifications at low (α-phase, 200 K) and high (β-phase, 298 K) temperatures and contains polymeric ([Ti2F9](-))∞ anions, which appear as two parallel infinite zigzag chains comprised of TiF6 units, where each TiF6 unit of one chain is connected to a TiF6 unit of the second chain through a shared fluorine vertex. Quantum-chemical calculations at the B3LYP/SDDALL level of theory were used to arrive at the gas-phase geometries and vibrational frequencies of the [Ti4F20](4-) and [Ti5F23](3-) anions, which aided in the assignment of the experimental vibrational frequencies of the anion series.

X-ray diffraction study of K4Ti8F36·8HF and Rb4Ti8F36·6HF reveals a novel type of octameric cubic [M8F36](4-) anion built from eight M(IV)F6 octahedra.

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, SO 2 and CH 3 CN 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(NH 2 ) 3 ] 2 [TiF 6 ], [C(NH 2 ) 3 ] 4 [Ti 4 F 20 ], and [C(NH 2 ) 3 ][Ti 2 F 9 ]. When the guanidinium salt/TiF 4 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 (SO 2 and CH 3 CN). Single crystals of [C(NH 2 ) 3 ] 3 [Ti 6 F 27 ]·SO 2 were detected in the case of the former and [C(NH 2 ) 3 ] 4 [H 3 O] 4 [Ti 4 F 20 ][TiF 5 ] 4 in the case of the [a]

A fast, robust, and convenient method for quantitative determination of polyamide-6 (PA6) and polyamide-66 (PA66) in plastic wastes is presented. The method includes a straightforward procedure for complete hydrolysis of polyamides (PAs) into the constituent monomers and their quantitative determination in hydrolyzates by high-performance liquid chromatography on a mixed-mode column, from which the contents of a particular PA are determined. The method was developed on neat PA6 and PA66 as well as their mixture and was further utilized on PA-based composites and postconsumer wastes (carpet and fishing net wastes) containing PA in different amounts. The information on the content of a particular PA type in plastic wastes is important because it determines the maximum recovery of PA constituent monomer(s) by chemical recycling and consequently suitability of waste as a feedstock. Moreover, the proposed method allows for convenient differentiation between PA6 and PA66 in their mixtures, which is difficult to assess with precision by conventional characterization techniques.