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

Article abstract of DOI:10.1002/ejic.201801207

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]·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 β-[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]^–)_∞ and ([Ti₂F₉]^–)_∞ 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]^–)_∞ anions. The crystal structure of the guanidinium hydrogen difluoride salt [C(NH₂)₃][HF₂] is also reported.

Full text of DOI:10.1002/ejic.201801207

DOI: 10.1002/ejic.201801207
Full Paper
Fluoridotitanates
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
Igor M. Shlyapnikov,*[a,b] Evgeny A. Goreshnik,[a] and Zoran Mazej*[a]
Abstract: Chemical reactions between guanidinium carbonate latter. The presence of [H3O]+ can be explained by a contamina-
or guanidinium chloride and titanium tetrafluoride in anhy- tion with traces of H2O, which is protonated in the superacid
drous hydrogen fluoride (aHF) were studied. The obtained prod- aHF. The same reason applies to the formation of the by-prod-
ucts were recrystallized from saturated HF, SO2 and CH3CN solu- ucts [H5O2]4[Ti8F36] and ꢀ-[H3O][Ti2F9]. The crystal structures of
tions. Single-crystal growths resulted in the detection of seven the new guanidinium-perfluoridotitanate(IV) compounds con-
perfluoridotitanate(IV) compounds, which were structurally sist of oligomeric [Ti4F20]4–, [Ti6F27]3– and [Ti8F36]4–, as well as
characterized. Three of them correspond to the phases ob- polymeric ([TiF5]–)∞ and ([Ti2F9]–)∞ perfluoridotitanate(IV) an-
tained as the main products of the synthesis in aHF, i.e., ions. The hexameric [Ti6F27]3– anion with a trigonal prismatic
[C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20], and [C(NH2)3][Ti2F9]. When geometry was structurally determined for the first time. The
the guanidinium salt/TiF4 molar ratios were greater than 1:2, the crystal-structure determination of the [C(NH2)3]4[H3O]4-
resulting products were only sparingly soluble or completely [Ti4F20][TiF5]4 revealed the first example of a mixed-anion per-
insoluble in aHF. Therefore, single-crystal growths were at- fluoridotitanate(IV) compound containing two different per-
tempted from other aprotic solvents (SO2 and CH3CN). Single fluoridotitanate(IV) anions, i.e., oligomeric [Ti4F20]4– and 1-D
crystals of [C(NH2)3]3[Ti6F27]·SO2 were detected in the case of polymeric ([TiF5]–)∞ anions. The crystal structure of the guan-
the former and [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 in the case of the idinium hydrogen difluoride salt [C(NH2)3][HF2] is also reported.
Introduction
leading to the formation of various inorganic moieties with di-
mensionalities ranging from 0-D to 3-D that are connected to
3-D hybrid organic-inorganic frames via hydrogen bonds.[5] The
mechanism for tailoring hybrid compounds with the formation
of different inorganic anions is still not clear; nevertheless, the
synthesis of new compounds with various templates is essential
for the rational design of new materials.
Hybrid organic-inorganic compounds, i.e., those composed of
an inorganic anionic and an organic cationic part,[1] exhibit
enormous structural diversity. Even the pure inorganic materi-
als, like various silicate and aluminosilicate minerals, as well as
different zeolites, have extremely rich structural motifs of inor-
ganic anions, including monomeric or oligomeric 0-dimensional
(0-D), chain or ribbon 1-dimensional (1-D), layered 2-dimen-
sional (2-D) and of course fascinating 3-dimensional (3-D) struc-
tures.[2,3] The application of organic amines in the synthesis of
such materials expands this field almost infinitely, due to the
almost unlimited variants of size, geometry and the number of
amine groups of N-containing organic compounds.[4] Besides
their charge-balancing role as protonated species during the
formation of the usually negatively charged inorganic frame-
works, they also act as templates (or structure-directing agents),
Perfluoridotitanate(IV) salts, i.e., compounds constructed
from inorganic fluoridotitanate(IV) anions with the general for-
x–
mula [TinF4n+x
]
and various cations, represent an interesting
case of the structural diversity of anions. The elementary build-
ing block in their crystal structures is the Ti4+ cation with an
octahedral coordination of six fluorine ions: [TiF6]2–. In the solid
state these units can remain isolated, leading to trivial hexa-
fluoridotitanate(IV) salts, or they can be linked by sharing fluor-
ine ions, yielding larger oligomeric (0-D geometry) or polymeric
(1-D, 2-D and 3-D) anions. So far, there are 18 structurally char-
acterized fluoridotitanate(IV) anions: oligomeric [TiF6]2–,
[Ti2F10]2–,[6,7] [Ti2F11]3–,[8–10] [Ti4F18]2–,[11–13] [Ti4F19]3–,[14]
[Ti4F20]4–,[10] [Ti5F23]3–,[10] [Ti8F36]4–,[15] [Ti10F45]5–,[16] and poly-
[a] Department of Inorganic Chemistry and Technology, Jožef Stefan Institute,
Jamova cesta 39, 1000 Ljubljana, Slovenia
E-mail: igor.shlyapnikov@ki.si
meric
([TiF5]–)∞,[16–19]
([Ti2F9]–)∞,[10,11,19]
([Ti3F13]–)∞,[16]
zoran.mazej@ijs.si
([Ti4F19]3–)∞,[19] ([Ti6F27]3–)∞,[19] ([Ti7F30]2–)∞,[20] ([Ti9F38]2–)∞,[21]
and two modifications of the ([Ti8F33]–)∞ anion.[21,22] The geom-
etries of the various anions were determined with X-ray experi-
ments on single crystals of pure inorganic and/or hybrid com-
[b] Department of Polymer Chemistry and Technology, National Institute of
Chemistry,
Hajdrihova ulica 19, 1000 Ljubljana, Slovenia
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201801207.
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pounds. Examples of structural determinations of the mixed- as a by-product in the system, XeF2–TiF4.[30] Single crystals of
anion TiIV-fluoride compounds are rare and limited to the phases observed after the crystallization are given in
[NH4]3[TiF7][23] and [NH4][Cu][TiF7]·4H2O[24] consisting of [TiF6]2– Table 1.
and F– anions, Na3HTiF8, consisting of [TiF6]2– and [HF2]– an-
Reactions between [C(NH2)3]2CO3 or [C(NH2)3]Cl and TiF4 in
ions,[25] and [Na]3[NH4][TiF6][SO4]·H2O compounds.[26] The sin-
aHF with a starting molar ratio of n{[C(NH2)3]+}/n(TiF4) = 2:1 led
to the known [C(NH2)3]2[TiF6] phase, which was proved by X-
ray powder-diffraction analysis (Equation (1) and Equation (2)):
gle-crystal structure of [N(C2H4NH3)3][TiF6]F was also deter-
mined,[27] but was later corrected to [N(C2H4NH3)3][TiF4,7
-
(OH)1,3]F.[28] Examples of the crystal structures of perfluorido-
titanate(IV) compounds containing two different perfluorido-
titanate(IV) anions were not known before this study.[19,29]
In this investigation a study of the chemical reactions be-
tween guanidinium carbonate or guanidinium chloride and
titanium tetrafluoride in anhydrous hydrogen fluoride (aHF) is
reported. The obtained products were recrystallized from satu-
rated aHF, SO2 and CH3CN solutions. Single-crystal growths re-
sulted in the detection of seven perfluoridotitanate(IV) com-
pounds, which were then structurally characterized.
[C(NH2)3]2CO3 + TiF4 + 2HF = [C(NH2)3]2[TiF6] + H2O + CO2 (1)
2[C(NH2)3]Cl + TiF4 + 2HF = [C(NH2)3]2[TiF6] + 2HCl
(2)
Crystallization of the products of the reaction between guan-
idinium carbonate and TiF4 with starting molar ratio
n{[C(NH2)3]+}/n(TiF4)
1:1 resulted in mixture of
a
=
a
[C(NH2)3]2[TiF6] and [C(NH2)3]4[Ti4F20] crystals. The Raman spec-
trum and the X-ray diffraction pattern of the powdered mate-
rial, isolated after the reaction between guanidinium carbonate,
TiF4, and aHF, did not reveal any by-products in the mixture
besides the [C(NH2)3]2[TiF6] and [C(NH2)3]4[Ti4F20] compounds.
Crystallization of the product in the reaction between TiF4 and
guanidinium chloride with the same molar ratio of reactants
led to crystals of the [C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20]
{Equation (3) and Equation (4)} and [C(NH2)3][Ti2F9]
{Equation (5)} compounds:
Results and Discussion
Syntheses and Crystallizations of Guanidinium
Poly[perfluoridotitanate(IV)] Compounds
Titanium tetrafluoride and commercially available guanidinium
carbonate and chloride were used as the starting reagents for
the synthesis of the guanidinium poly[perfluoridotitanate(IV)]
compounds. The main parameter varied during the synthesis
was the starting molar ratio between the reagents with values
n{[C(NH2)3]+}/n(TiF4), ranging from 2:1 to 1:4. The masses of the
reactants are given in Table S1.
Five guanidinium poly[perfluoridotitanate(IV)] salts were iso-
lated and structurally characterized, i.e., the previously de-
scribed [C(NH2)3]2[TiF6] and the novel [C(NH2)3][Ti2F9],
2[C(NH2)3]2CO3 + 4TiF4 + 4HF = [C(NH2)3]4[Ti4F20] + 2H2O
+ 2CO2
(3)
(4)
(5)
4[C(NH2)3]Cl + 4TiF4 + 4HF = [C(NH2)3]4[Ti4F20] + 4HCl
[C(NH2)3]Cl + 2TiF4 + HF = [C(NH2)3][Ti2F9] + HCl
Reactions with the starting molar ratio of the reactants
[C(NH2)3]4[Ti4F20], [C(NH2)3]3[Ti6F27]·SO2 and [C(NH2)3]4[H3O]4- n{[C(NH2)3]+}/n(TiF4) = 1:2 and subsequent crystallizations of
[Ti4F20][TiF5]4 compounds. Additionally, two by-products were the obtained products led to mixtures of [C(NH2)3]2[TiF6],
also observed and structurally characterized, i.e., [H5O2]4[Ti8F36] [C(NH2)3]4[Ti4F20], [C(NH2)3][Ti2F9], which were sometimes con-
and ꢀ-[H3O][Ti2F9]. The latter was also independently observed taminated with the ꢀ-[H3O][Ti2F9] phase.
Table 1. The observed single crystals of the poly[perfluoridotitanate(IV)] compounds after crystallization of the products obtained by the chemical reactions
between guanidinium salts and TiF4 with given stoichiometry.
No.
n{[C(NH2)3]+}/n(TiF4)
Phases, detected after the crystallization
Guanidinium carbonate [C(NH2)3]2CO3
1
2
3
4
5
2:1[a]
3:2[a]
1:1[a]
1:2[a]
1:3[a]
[C(NH2)3]2[TiF6][c]
[c]
[C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20
[C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20
]
]
[c]
[C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20], [C(NH2)3][Ti2F9][c]
[H3O][TiF5], [C(NH2)3][Ti2F9][c]
Guanidinium chloride [C(NH2)3]Cl
6
7
8
9
10
11
12
2:1[a]
1:1[a]
1:2[a]
1:3[a]
1:3[b]
1:4[a]
1:4[a]
[C(NH2)3]2[TiF6][c]
[C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20], [C(NH2)3][Ti2F9][c]
[C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20], ꢀ-[H3O][Ti2F9][c]
[C(NH2)3]4[Ti4F20], [C(NH2)3][Ti2F9][c]
insoluble[c]
ꢀ-[H3O][Ti2F9][c]
[C(NH2)3]3[Ti6F27]·SO2, [H5O2]4[Ti8F36
[d]
]
[e]
[C(NH2)3]4[H3O]4[Ti4F20][TiF5]4
13
1:4[b]
insoluble[c]
[a] TiF4 prepared by reaction between TiCl3 and liquid aHF and further fluorination by F2 in aHF. [b] TiF4 prepared by reaction between TiCl4 and liquid aHF.
[c] aHF used as a solvent. [d] SO2 used as a solvent. [e] CH3CN used as a solvent.
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Crystallization of the products of the reactions between both salt/TiF4 mixtures, where the starting molar ratio of the reac-
guanidinium salts and TiF4 {starting molar ratio n([C(NH2)3]+)/ tants was 1:3 and 1:4 (see Raman Spectroscopy). We can as-
n(TiF4) = 1:3} from saturated HF solutions were carried out in sume that in aHF the insoluble phase is mainly [C(NH2)3]3-
two different ways. In the first case the products of the reac- [Ti6F27] or its HF-solvated form. Long-lasting crystallization from
tions were isolated and later attempts were made to re-dissolve the CH3CN solution yielded
a
few crystals of the
them in aHF in an attempt to prepare saturated solutions for [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 phase {Equation (6)}:
single-crystal growths. Since a lot of insoluble material was ob-
served, it can be concluded that the products were only spar-
ingly soluble or almost insoluble in the aHF. The crystallization
yielded only a few single crystals of [C(NH2)3]4[Ti4F20] and
3[C(NH2)3]Cl + 6TiF4 + 3HF = [C(NH2)3]3[Ti6F27] + 3HCl
(6)
The presence of [H3O]+ in [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 and
the formation of [H3O][TiF5], ꢀ-[H3O][Ti2F9] and [H5O2]4[Ti8F36]
can be explained by a contamination with traces of H2O, which
is protonated in the superacid aHF. When guanidinium carb-
onate is used as the starting material, water can also be formed
in situ, since the carbonates react with the aHF to give the
corresponding fluoride, water and carbon dioxide. Therefore, is
a little surprising that no more [H3O]+ phases were observed
when guanidinium carbonate was used as a starting material.
[C(NH2)3][Ti2F9] and several crystals of [H3O][TiF5][17] as the by-
products. In the second case the crystallization was carried out
directly from the reaction mixture, i.e., aHF was added to the
guanidinium salt/TiF4 reaction mixture and after a few days of
intensive stirring the liquid phase was decanted into the nar-
rower arm of double-arm crystallization vessel. After all the liq-
uid phase was evaporated, nothing was left, indicating that the
obtained product (or products) was completely insoluble in the
aHF.
A similar situation occurred when a larger amount of TiF4
was used {n([C(NH2)3]Cl)/n(TiF4) = 1:4}. With the first approach
only a few crystals of ꢀ-[H3O][Ti2F9] were grown; meanwhile,
direct crystallization failed because of the complete insolubility
of the obtained product (or products) in the aHF. Therefore,
other solvents (SO2 and CH3CN) were also tried. Crystallization
from the SO2 solution led to a solvated phase [C(NH2)3]3-
Single-Crystal Structures of [C(NH2)3]2[TiF6],
[C(NH2)3]4[Ti4F20], [C(NH2)3][Ti2F9], [C(NH2)3]3[Ti6F27]·SO2,
[C(NH2)3]4[H3O]4[Ti4F20][TiF5]4, [C(NH2)3][HF2],
[H5O2]4[Ti8F36] and ꢀ-[H3O][Ti2F9]
[Ti6F27]·SO2. Its Raman spectrum was very similar to the Raman The corresponding crystal data and refinement results are sum-
spectra of aHF-insoluble products prepared from guanidinium marized in Table 2.
Table 2. Crystal data and refinement results of [C(NH2)3]2[TiF6], [C(NH2)3]4[Ti4F20], [C(NH2)3][Ti2F9], [C(NH2)3]3[Ti6F27]·SO2, [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4,
[C(NH2)3][HF2], ꢀ-[H3O][Ti2F9] and [H5O2]4[Ti8F36].
Chem. formula
[C(NH2)3]2[TiF6]
[C(NH2)3]4[Ti4F20
]
[C(NH2)3][Ti2F9]
[C(NH2)3]3[Ti6F27]·SO2
CCDC #
Fw [g/mol]
Crystal system
Space group
a [Å]
1865283
282.05
Monoclinic
C2/m
12.8540(6)
7.3700(4)
6.1680(4)
90
1865280
811.83
1865281
326.83
Orthorhombic
Pnma
5.4001(2)
11.9123(5)
14.813(1)
90
1865287
1044.54
Monoclinic
P21/c
18.0595(3)
12.6281(2)
27.7642(5)
90
Triclinic
P1
¯
8.6958(2)
9.7433(2)
9.7533(3)
118.467(3)
111.687(3)
95.516(2)
636.42(3)
1
b [Å]
c [Å]
α [°]
ꢀ [°]
114.599(5)
90
90
90
99.744(2)
90
γ [°]
V [Å3]
531.29(5)
2
952.87(9)
4
6240.5(2)
8
Z
T [K]
200
200
200
150
[a]
R1
0.041
0.020
0.027
0.029
[b]
wR2
0.116
0.058
0.070
0.075
Chem.
formula
[C(NH2)3]4[H3O]4
[Ti4F20][TiF5]4
[C(NH2)3][HF2]
ꢀ-[H3O][Ti2F9]
[H5O2]4[Ti8F36]
CCDC #
Fw [g/mol]
Crystal system
Space group
a [Å]
1865284
1459.40
Monoclinic
P21/c
9.5935(4)
7.4536(4)
30.361(1)
90
90.244(4)
90
2171.0(2)
2
1865279
99.08
Monoclinic
P2/c
5.1338(6)
6.6159(7)
6.7287(7)
90
96.44(1)
90
227.10(4)
2
150
0.036
1865285
285.74
Monoclinic
P21/c
5.3178(2)
16.0786(8)
8.8459(3)
90
91.440(3)
90
756.10(6)
4
1865282
1215.12
Tetragonal
I4/m
11.3935(5)
11.3935(5)
12.4312(9)
90
90
90
1613.7(2)
2
b [Å]
c [Å]
α [°]
ꢀ [°]
γ [°]
V [Å3]
Z
T [K]
150
0.026
0.064
150
0.032
0.083
150
0.040
0.097
[a]
R1
[b]
wR2
0.091
[a] R1 is defined as Σ||Fo| – |Fc||/Σ|Fo|for I > 2σ(I). [b] wR2 is defined as {Σ[w(Fo – Fc2)2]/Σw(Fo2)2}1/2
.
2
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[C(NH2)3]2[TiF6]
guanidinium cations and [TiF6]2– anions appear in the ab-plane
(Figure 2). These layers are parallel to each other and associated
via weak interactions.
The crystal structure of guanidinium hexafluoridotitanate was
previously determined in the Cm space group.[31] Later, it was
recalculated in the centrosymmetric C2/m space group,[32]
which was confirmed by our research. Detailed crystallographic
data are given in Table S2.
The crystal structure is defined by monomeric [TiF6]2– anions
and guanidinium cations [C(NH2)3]+. Six Ti–F bonds have practi-
cally equal lengths [2 × 1.861(2), 4 × 1.860(1) Å]. The asymmet-
ric unit of the anion consists of three atoms – one titanium and
two fluorine. The F2 atoms are situated at general positions, the
F1 atoms are located on the mirror plane m (Wyckoff position
4i) and the Ti1 atoms are situated on the intersection of the
mirror plane and the 2-fold rotation axis (2/m, Wyckoff position
2b).
Each fluorine atom is involved in hydrogen bonding with
guanidinium cations in a way that each F atom forms two con-
tacts with two cations, whereas each cation is hydrogen
bonded to three anions (Figure 1) with N···F distances 2.877(2),
2.901(2) and 2.904(2) Å and N–H···F angles of about 170° (Table
S3). In this way planar hybrid double layers constructed from
[C(NH2)3]4[Ti4F20
]
It crystallizes in the P1 space group with one formula unit per
¯
unit cell and an asymmetric unit that contains 32 atoms. De-
tailed crystallographic data are given in Table S5. The crystal
structure consists of tetrameric [Ti4F20]4– anions and guanidin-
ium [C(NH2)3]+ cations.
The tetrameric [Ti4F20]4– anion is very similar to that deter-
mined in imidazolium salt α-[C3H5N2]4[Ti4F20],[10] and represents
a slightly distorted planar square, made up of four TiF6 octahe-
dra, where each shares two cis vertices (Figure 3). The Ti···Ti
distances are equal to 3.8583(3) and 3.8927(3) Å and the Ti–Ti–
Ti angles are equal to 89.675(7)° and 90.325(8)°. Each titanium
atom is coordinated by two bridging and four terminal fluorine
atoms with the lengths of the Ti–Ft and Ti–Fb bonds ranging
from 1.7731(8) to 1.8512(8) Å and from 1.9537(8) to 2.0144(8) Å,
respectively. All the atoms of the anion are located at general
positions, while there is an inversion centre situated in the mid-
dle of the anion. The other geometric parameters of the
[Ti4F20]4– anion are presented in Table S6.
Figure 3. The crystal structure of the [C(NH2)3]4[Ti4F20] compound. Thermal
ellipsoids are drawn at the 50 % probability level. The atoms, of the asymmet-
ric unit are labelled.
Figure 1. The hydrogen bonding between the [TiF6]2– anions and the guan-
idinium cations in the crystal structure of the [C(NH2)3]2[TiF6] compound.
Thermal ellipsoids are drawn at the 50 % probability level. Symmetry codes:
(i) x, –y, z; (ii) 1 – x, y, –z; (iii) 1 – x, –y, –z; (iv) x, –1 + y, z; (v) 1 – x, –1 +
y, –z; (vi) 0.5 – x, 0.5 – y, –z; (vii) 0.5 – x, –0.5 + y, –z; (viii) 0.5 + x, 0.5 – y, z;
(ix) 0.5 + x, –0.5 + y, z.
Two crystallographically independent cations were found in
the crystal structure of [C(NH2)3]4[Ti4F20], i.e., cations composed
of the crystallographically independent C1, N1, N2, N3 and C2,
N4, N5, N6 atoms. Each cation containing C1 atoms is coordi-
nated with three anions via five N–H···F hydrogen bonds with
N···F distances ranging from 2.892(2) to 3.049(2) Å (Figure 4).
Each cation containing C2 atoms is coordinated with two an-
ions via four N–H···F hydrogen bonds with N···F distances ran-
ging from 2.948(1) to 3.012(2) Å (Figure 5). The distance be-
tween the N6 and F9 atoms is too large to be considered as a
hydrogen bond [3.161(2) Å].[33] Thus, each [Ti4F20]4– anion forms
hydrogen bonds with ten guanidinium cations – with six cat-
ions containing C1, and with four cations containing C2 atoms.
The distances and angles associated with the hydrogen bond-
ing in [C(NH2)3]4[Ti4F20] are given in Table S7.
The packing of the [Ti4F20]4– anions has a similar motif as for
the α-[C3H5N2]4[Ti4F20] imidazolium salt.[10] The two neighbour-
ing anions situated within the one planar layer are pairwise
connected via hydrogen bonds with the guanidinium cations
Figure 2. The double hybrid 2-D layers constructed from the guanidinium
cations and the [TiF6]2– anions. Thermal ellipsoids are drawn at the 50 %
probability level.
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The anions situated in two parallel layers are bridged by both
crystallographically independent guanidinium cations. The po-
sitions of two parallel layers of anions in the crystal structure of
[C(NH2)3]4[Ti4F20] and the sites occupied by both crystallograph-
ically independent guanidinium cations are presented in Fig-
ure 7.
Figure 4. The coordination of the guanidinium cations containing C1 atoms
4–
by the [Ti4F20
]
anions. Thermal ellipsoids are drawn at the 50 % probability
level. Symmetry codes: (i) x, –1 + y, –1 + z; (ii) x, –1 + y, z; (iii) 1 – x, 1 – y,
1 – z; (iv) 2 – x, 2 – y, 1 – z.
Figure 7. The packing of the layers of the anions in the crystal structure of
the [C(NH2)3]4[Ti4F20] compound. Thermal ellipsoids are drawn at the 50 %
probability level. Dashed circles: sites, occupied by the guanidinium cations
containing C2 atoms; chessboarded circles: sites, occupied by the guan-
idinium cations containing C1 atoms.
Figure 5. The coordination of the guanidinium cations containing C2 atoms
4–
by the [Ti4F20
]
anions. Thermal ellipsoids are drawn at the 50 % probability
level. Symmetry codes: (i) x, –1 + y, –1 + z; (iv) 2 – x, 2 – y, 1 – z.
(Figure 6), involving equatorial F3 and axial F8 atoms of anion
and hydrogen atoms, bonded to the N1 atoms of cations [dis-
tances N1···F3 2.914(2) Å and N1···F8 2.892(2) Å].
[C(NH2)3][Ti2F9]
One of the products with the highest rate of titanium synthe-
sized in the system [C(NH2)3]2CO3/[C(NH2)3]Cl–TiF4–HF is guan-
idinium nonafluoridodititanate. It crystallizes in the Pnma space
group. Detailed crystallographic data are given in Table S9. The
crystal structure of [C(NH2)3][Ti2F9] consists of polymeric
([Ti2F9]–)∞ anions and guanidinium cations.
The ([Ti2F9]–)∞ anion is isostructural with the anion deter-
mined in the imidazolium ꢀ-[C3H5N2][Ti2F9] compound.[10] It is
constructed of TiF6 octahedra sharing vertices at the fac-posi-
tion, forming a dimeric zig-zag chain (Figure 8). Each titanium
atom is coordinated with three bridging and three terminal
fluorine atoms, with the Ti–F bonds ranging from 1.771(1) to
1.777(1) Å and from 1.9713(4) to 1.980(1) Å for Ti–Ft and Ti–Fb,
respectively. The Ti–Fb–Ti angles within the individual chains of
dimers are equivalent and equal to 155.01(7)°, which is very
close to the corresponding angles in the structure of ꢀ-
[C3H5N2][Ti2F9] {152.1(1)°}. The Ti–Fb–Ti angles where the tita-
nium atoms belong to two neighbouring single chains of the
dimer are equal to 163.5(1)°, which is similar to the correspond-
ing angles in α-[C3H5N2][Ti2F9] and ꢀ-[C3H5N2][Ti2F9] {162.27(8)°
and 163.1(2)°, correspondingly}[10] within 3σ. Two single
chains of the dimer are symmetry related by a mirror plane,
passing through the bridging F4 atoms, so the TiF6 octahedra
4–
Figure 6. The arrangement of [Ti4F20
]
anions and their connection by the
hydrogen bonds with the guanidinium cations in the structure of the
[C(NH2)3]4[Ti4F20] compound. Thermal ellipsoids are drawn at the 50 % proba-
bility level.
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of the one individual chain eclipse those of the second chain in atoms of the nearest neighbouring TiF6 octahedra, belonging
the structure of [C(NH2)3][Ti2F9], likewise in the ꢀ-[C3H5N2][Ti2F9] to the neighbouring single chains of the dimer with two equal
phase. The other geometric parameters of the ([Ti2F9]–)∞ anion N2···F1 distances [2.969(2) Å]. The hydrogen atoms bonded to
are given in Table S10.
the N1 atoms are linked to two TiF6 octahedra of the individual
chain, which are connected together via an additional TiF6 unit
[the distances N1–F2 and N1–F3 are equal to 3.022(3) and
2.965(3) Å]. The packing of the ([Ti2F9]–)∞ anions has the same
motif as in the crystal structure of the ꢀ-[C3H5N2][Ti2F9] com-
pound,[10] i.e., anionic chains are packed following a slightly
distorted hexagonal motif (Figure 10).
Figure 8. The polymeric ([Ti2F9]–)∞ anion determined in the crystal structure
of the [C(NH2)3][Ti2F9] compound. Thermal ellipsoids are drawn at the 50 %
probability level. Symmetry codes: (i) x, 1.5 – y, z; (ii) –0.5 + x, y, 1.5 – z.
[C(NH2)3]3[Ti6F27]·SO2
Since the product (or products) of the reaction between guan-
idinium chloride and TiF4 with higher molar ratios
(n{[C(NH2)3]Cl}/n(Ti4+) = 1:4) was insoluble in aHF, an attempt
was made to grow single crystals from a saturated SO2 solution.
The crystallization was successful and yielded single crystals of
SO2-solvated [C(NH2)3]3[Ti6F27]. Its crystal structure consists of
two crystallographically independent trigonal prismatic
[Ti6F27]3– anions, six crystallographically unique guanidinium
[C(NH2)3]+ cations and two crystallographically independent
SO2 molecules.
Each terminal fluorine atom is involved in hydrogen bonding
with a guanidinium cation, and all six hydrogen atoms of the
one crystallographically independent cation are hydrogen
bonded to the fluorine atoms of the anion. A pair of H atoms
bonded to a single nitrogen atom is linked with the fluorine
atoms of the neighbouring TiF6 units (Figure 9, Table S11).
Those bonded to the N2 atoms are hydrogen bonded to the F1
The [C(NH2)3]3[Ti6F27]·SO2 compound crystallizes in the
monoclinic P21/c space group with eight formula units per unit
cell. More detailed crystallographic data are given in Table S13.
The crystal structure of the [C(NH2)3]3[Ti6F27]·SO2 compound
represents the first example of the structurally determined
[Ti6F27]3– anion. Both crystallographically independent anions
are very similar to each other and resemble the column-like
structure of TiF4.[34]
The [Ti6F27]3– anions are made up of six TiF6 octahedra: three
TiF6 octahedra form a trimeric ring by sharing cis-vertices, with
the other three octahedra forming the same trimeric ring,
which is connected to the first through the bridging fluorine
atoms forming a trigonal prismatic geometry (Figure 11). Thus,
all the titanium atoms are connected to three terminal and
three bridging fluorine atoms, situated in the fac-positions with
Ti–Ft and Ti–Fb bond lengths of 1.754(1) – 1.788(1) and 1.943(1)
– 2.010(1) Å, respectively. All the geometric parameters of the
[Ti6F27]3– anion are given in Table S14.
Figure 9. The coordination of ([Ti2F9]–)∞ anion by the guanidinium cations.
Thermal ellipsoids are drawn at the 50 % probability level.
Figure 10. The unit cell and the packing of the anions and cations in the
crystal structure of the [C(NH2)3][Ti2F9] compound. Thermal ellipsoids are
drawn at the 50 % probability level.
Figure 11. The experimental geometries of the two crystallographically
unique [Ti6F27
mal ellipsoids are drawn at the 50 % probability level.
]
3– anions in the crystal structure of [C(NH2)3]3[Ti6F27]·SO2. Ther-
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In the structure of the [C(NH2)3]3[Ti6F27]·SO2 the prismatic only four examples of the mixed-anion compounds, i.e.,
anions are ordered in layers lying in the bc-planes. A single layer [NH4]3[TiF7][23] and [NH4][Cu][TiF7]·4H2O,[24] consisting of
consists of anions of the same type (anions with Ti1–Ti6 atoms [TiF6]2– and F– anions, Na3HTiF8 with [TiF6]2– and [HF2]– an-
in one layer and anions with Ti7–Ti12 atoms in another). The ions[25] and [Na]3[NH4][TiF6][SO4]·H2O with [TiF6]2– and [SO4]2–.[26]
relatively small guanidinium cations and SO2 molecules occupy Compounds containing two different perfluoridotitanate(IV) an-
the voids in between the anions (Figure 12). There are a lot ions have not been reported so far. When the product of the
of contacts that could be regarded as weak hydrogen bonds, reaction between guanidinium chloride and TiF4 (n{[C(NH2)3]-
between the fluorine atoms and the hydrogen atoms, bonded Cl}/n(TiF4) = 1:4), synthesized in aHF, was recrystallized from
to the nitrogen atoms. Two crystallographically independent CH3CN during two months, a few single crystals of the
SO2 molecules occupy the voids in the structure. One SO2 mol- [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 compound were grown and its
ecule is slightly distorted with the O–S–O angle equal to crystal structure was determined (Table S15).
115.4(2)° and with shortened S–O bonds [1.378(3) and 1.386(3)
Å]. The second molecule has geometric parameters very close
to the free SO2 molecule [S–O bond lengths 1.408(2) and
1.410(2) Å and O–S–O angle 118.9(2)° in comparison with the
literature values: S–O bond length 1.432 Å and O–S–O angle ca.
119.5°[2]].
The crystal structure consists of guanidinium and oxonium
cations, tetrameric [Ti4F20]4– and polymeric chain-like ([TiF5]–)∞
anions. This is the first example of a mixed-anion compound in
the poly[perfluoridotitanate(IV)] family. Moreover, there are two
types of anions, i.e., oligomeric and polymeric with a 1-D geom-
etry. The tetrameric [Ti4F20]4– anion is similar to that determined
in [C(NH2)3]4[Ti4F20] and α-[C3H5N2]4[Ti4F20].[10] It appears as a
slightly distorted planar square, made up of four TiF6 octahedra,
where each is sharing two cis vertices (Figure 13). The Ti···Ti
distances are equal to 3.8670(6) and 3.8709(6) Å and the Ti–Ti–
Ti angles are equal to 89.87(1)° and 90.13(1)°. Each titanium
atom is coordinated by two bridging and four terminal fluorine
atoms with the lengths of the Ti–Ft and Ti–Fb bonds ranging
from 1.770(1) to 1.892(1) Å and from 1.951(1) to 1.988(1) Å,
respectively. All the atoms of the anion are situated at general
positions, while there is an inversion centre situated in the mid-
dle of the anion. The other geometric parameters of the
[Ti4F20]4– anion are given in Table S16.
Figure 12. The unit cell and the packing of the anions and cations in the
crystal structure of the [C(NH2)3]3[Ti6F27]·SO2 compound. Thermal ellipsoids
are drawn at the 50 % probability level.
During the study of the imidazolium–TiF4–HF system[10] the
formation of [C3H5N2]2[H3O][Ti6F27] was also observed, but it
has not been reported so far. The crystal structure of
[C3H5N2]2[H3O][Ti6F27] also consists of trigonal prismatic
[Ti6F27]3– anions. The compound was later also prepared in
larger quantities by a reaction between imidazole, H2O and TiF4
(starting molar ratio 2:1:6). It crystallises at 150 K in the tetrago-
nal space group P42/nmc with a = 22.1506(4) Å, c = 11.5890(3)
4–
Figure 13. The experimental geometry of the [Ti4F20
]
anion, determined in
the crystal structure of the [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 compound. Thermal
ellipsoids are drawn at the 50 % probability level.
Å, and Z = 8 (CCDC 1865286). Each imidazolium cation is disor-
1
dered and can be described as two parts with the
/ occu-
2
The second anion determined in the crystal structure of
[C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 is the polymeric single-chain an-
ion ([TiF5]–)∞. It appears as a monomeric chain of cis-connected
TiF6 octahedra. Unlike other determined polymeric penta-
fluoridotitanate(IV) anions that appear as zig-zag chains (Figure
14a),[17–19] the ([TiF5]–)∞ anion in the crystal structure of
[C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 represents a crenelated chain
(Figure 14b). The Ti–F bond lengths are typical for poly[perfluor-
idotitanate(IV)] compounds ranging from 1.763(1) to 1.877(1) Å
and from 1.964(1) to 2.004(1) Å for the Ti–Ft and Ti–Fb bonds,
respectively (Table S17).
pancy mutually rotated by 180°. The positions of the oxygen
atoms could not be located (probably because oxonium cations
are distributed over multiple positions). The PLATON procedure
reports on the presence of some voids with a maximum elec-
tron density of less than 2 e/Å3. However, the anionic part corre-
sponds to the same trigonal prismatic [Ti6F27]3– anions as found
in [C(NH2)3]3[Ti6F27]·SO2.
[C(NH2)3]4[H3O]4[Ti4F20][TiF5]4
The packing of oligomeric [Ti4F20]4–, polymeric ([TiF5]–)∞ an-
The existence of [TiF6]2– salts with mixed cations was demon- ions and guanidinium and oxonium cations in the crystal struc-
strated by alkali metal salts.[35–37] On the other hand, there are ture of [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 is presented in Figure 15.
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hydrogen bonds with six [HF2]– anions (Figure 16). The distan-
ces and angles associated with the hydrogen bonding in
[C(NH2)3][HF2] are given in Table S19.
Figure 16. The hydrogen bonds between the [HF2]– anions and guanidinium
cations. Thermal ellipsoids are drawn at the 50 % probability level. Symmetry
codes: (i) 1 – x, 1 – y, 1 – z; (ii) 1 – x, – y, 1 – z; (iii) –1 + x, y, z.
Figure 14. The experimental geometries of the ([TiF5]–)∞ anion as appear in
a) [H3O][TiF5],[17] [NH4][TiF5],[18] A[TiF5] and A[TiF5]·HF (A = Na, K, Rb, Cs)[19]
and b) [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 compounds. Thermal ellipsoids are
drawn at the 50 % probability level.
The packing of [HF2]– anions and guanidinium cations in the
crystal structure of [C(NH2)3][HF2] is presented in Figure 17.
Figure 15. The unit cell and the packing of the anions and cations in the
crystal structure of the [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 compound. Thermal el-
4–
lipsoids are drawn at the 50 % probability level. The oligomeric [Ti4F20
]
anions are shown in purple; the polymeric ([TiF5]–)∞ anions are shown in
yellow.
Figure 17. The packing of the [HF2]– anions and guanidinium cations in the
crystal structure of [C(NH2)3][HF2]. Thermal ellipsoids are drawn at the 50 %
probability level.
[C(NH2)3][HF2]
The dissolving of commercially available guanidinium chloride
in aHF and its further isolation led to a guanidinium hydrogen
difluoride salt [C(NH2)3][HF2]. In spite of its moisture resistance
[H5O2]4[Ti8F36
]
and easy synthesis, its crystal structure has not yet been pub- Besides single crystals of the [C(NH2)3]3[Ti6F27]·SO2 compound
lished. For this purpose, the compound was recrystallized from several crystals of the [H5O2]4[Ti8F36] compound were also
water. The crystals have a strong affinity for twinning. Neverthe- grown (Table S20). The crystal structure is composed of octa-
less, the single-crystal structure has been determined (Table meric [Ti8F36]4– anions and asymmetric [H5O2]+ cations (Figure
S18).
There are a lot of examples of compounds containing poly-
18). The former were previously determined in the crystal struc-
tures of K4[Ti8F36]·8HF and Rb4[Ti8F36]·6HF.[15] The anion deter-
mined in [H5O2]4[Ti8F36] is composed of one crystallographically
independent titanium and five crystallographically independent
fluorine atoms, forming three Ti–Ft bonds with lengths equal to
1.757(1), 1.780(1), 1.784(1) Å and five Ti–Fb bonds with lengths
of 1.956(1), 2 × 1.964(1), 2 × 1.9738(4) Å.
hydrogenfluoride anions [Hn–1Fn]– with the rate of HF polymeri-
zation n ranging from 1 to 7.[38–40] The simplest anion [HF2]– is
built from two fluorine atoms, which are connected by the
strongest known hydrogen bond with F···F distances in the
range 2.26–2.29, Å which is much shorter than the hydrogen
bonds between HF molecules in the solid state [2.49(1) Å[41]],
The [H5O2]+ cations, situated above four faces of the cubic
and the named anions are usually centrosymmetric with rare anion, form hydrogen bonds with the anion, where two sets of
examples of non-centrosymmetric species. The crystal structure bonds can be distinguished: O1–H···F2 and O2–H···F3 with O···F
of [C(NH2)3][HF2] contains a typical centrosymmetric [HF2]– an- distances of 2.735(2) and 2.685(2) Å, respectively.
The packing of the [Ti8F36]4– anions and [H5O2]+ cations in
ion with a F···F distance equal to 2.273(2) Å.
Each difluoride anion forms six hydrogen bonds with six the crystal structure resembles a dense cubic packing (Figure
guanidinium cations, while each guanidinium cation forms six 19).
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pound, the crystal structure of which has been previously deter-
mined at 100 K in the orthorhombic space group (α-
[H3O][Ti2F9]).[11] Unlike the eclipsed structure of the double
chain ([Ti2F9]–)∞ anion in the orthorhombic modification α-
[H3O][Ti2F9] (Figure 20a), the double chain ([Ti2F9]–)∞ anion in
the ꢀ-phase has a gauche conformation of TiF6 octahedra, be-
longing to two monomeric chains of the dimer, and its geome-
try (Figure 20b) resembles the structure of ([Ti2F9]–)∞ in
Cs[Ti2F9][11] and α-[C3H5N2][Ti2F9].[10]
Raman Spectroscopy
Since the frequency of the Raman band belonging to the sym-
metric in-phase Ti–Ft stretching vibration of perfluoridotitan-
ate(IV) anions increases with both an increasing of the TiF4 con-
tent and a decreasing of the anion charge, it is very useful for
the identification of various perfluoridotitanate(IV) anions. The
frequency ranges from 599 cm–1 in the case of the [TiF6]2– anion
to 807 cm–1 for the TiF4 itself.[15,19,21,42] The Raman spectra of
guanidinium perfluoridotitanates(IV) recorded in the present re-
search also follow this rule. The lowest frequency for the in-
phase Ti–Ft stretching is observed in the Raman spectrum of
the [TiF6]2– salt (598 cm–1), followed by the [Ti4F20]4– (710 cm–1)
and ([Ti2F9]–)∞ (744 cm–1) salts. The value (752 cm–1) of the sym-
metric in-phase Ti–Ft stretching of the [Ti6F27]3– anion, deter-
mined in the structure of the solvated [C(NH2)3]3[Ti6F27]·SO2
phase, also fits in that sequence. If the experimental
points n(F–)/n(Ti+) as a function of the Raman frequency of the
single perfluoridotitanate(IV) anion are plotted, they can be
fitted well, leading to a linear function (Figure 21).
Figure 18. The crystal structure of the [H5O2]4[Ti8F36] compound. Thermal
ellipsoids are drawn at the 50 % probability level.
4–
Figure 19. The packing of the [Ti8F36
]
anions and [H5O2]+ cations in the
crystal structure of [H5O2]4[Ti8F36]. Thermal ellipsoids are drawn at the 50 %
probability level.
ꢀ-[H3O][Ti2F9]
After some crystallizations single crystals of ꢀ-[H3O][Ti2F9][30]
were found among the crystallization products. This represents
the second polymorphic modification of the [H3O][Ti2F9] com-
Figure 21. Points n(F–)/n(Ti+) as a function of Raman frequency of the per-
fluoridotitanate(IV) anions.
The Raman spectrum of the [C(NH2)3]3[Ti6F27]·SO2 was re-
corded on a randomly oriented single crystal sealed in a quartz
capillary (Figure 22). The formation of a SO2 adduct and its
stability at room temperature were confirmed by the presence
of vibrational bands, which can be assigned to SO2 molecules:
νas(SO2) at 1328 cm–1, νs(SO2) at 1151 cm–1 and δs(SO2) at
517 cm–1 (weak).[43]
Figure 20. The polymeric ([Ti2F9]–)∞ anions determined in the crystal struc-
tures of a) α-[H3O][Ti2F9][11] and b) ꢀ-[H3O][Ti2F9] compounds. Thermal ellip-
soids are drawn at the 50 % probability level.
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served. It appears as a crenelated chain instead of the more
common zig-zag chain observed in other ([TiF5]–)∞ salts.[19]
Together with [H3O][TiF5], [H3O][Ti2F9], [H3O]2[TiF6],
[H3O]3[Ti6F27], [H3O][H5O2][TiF6] and [H5O2]2[TiF6]·2H2O,[19,29]
the [H5O2]4[Ti8F36] represents a new example of a compound
prepared in the H2O/HF/TiF4 system, showing the diversity of
such a simple system.
According to the IUPAC, the empirical formula is formed just
by the position of the atomic symbols with their appropriate
subscripts to give the simplest possible formula expressing the
composition of a compound.[45] Therefore, when the AF/TiF4
ratio corresponds to 1:2 (AF = represents a single fluoride ion
donor such as KF, XeF6, etc.), the simplest empirical formula is
A[Ti2F9] {e.g., K[Ti2F9], consisting of K+ cations and polymeric
([Ti2F9]–)∞ anions[19]}. In the case of perfluoridotitanates(IV),
many examples have been found that correspond to multipli-
cated versions of the basic A[Ti2F9] formula. The doubled
A2[M4F18][11] and tripled form A3[M6F27][19] and even the four-
and five-times multiplied examples (e.g., A4[M8F36][15] and
A5[M10F45][16]) exist. Additionally, two compounds can contain
anions with the same formula but different geometries. The
[Ti4F19]3– anion in [XeF5]3[Ti4F19][14] is an isolated oligomer
(0-D), meanwhile the corresponding anion in Cs3[Ti4F19][19] is
polymeric (1-D), i.e., ([Ti4F19]3–)∞. Similarly, the anionic part of
[C(NH2)3]3[Ti6F27]·SO2 consists of [Ti6F27]3– oligomers (0-D),
meanwhile in [H3O]3[Ti6F27] there is a three-dimensional net-
work ([Ti6F27]3–)∞ built of TiF6 octahedra (3-D).
Figure 22. The Raman spectrum, recorded on the randomly oriented single
crystal of the [C(NH2)3]3[Ti6F27]·SO2 compound.
Similar Raman spectra (Figure S5), but without the vibra-
tional bands assigned to the SO2 molecules, were recorded on
undissolved material obtained after chemical reactions be-
tween guanidinium salts and TiF4 (1:3 and 1:4; Table 1) in aHF.
This implies that one of the aHF-insoluble products might be
[C(NH2)3]3[Ti6F27] or its HF-solvated phase.
In all the recorded spectra of guanidinium perfluoridotitan-
ate(IV) compounds, vibrational bands that can be assigned to
guanidinium cations are clearly visible. The most intensive ones
are those at 1011–1012 cm–1 assigned to the symmetric stretch-
ing υsCN of the guanidinium cation.[44] Other bands, theoreti-
cally predicted to be more intensive, belong to the NH2-sym-
metric stretching and scissoring[44] and are in reality less inten-
sive due to the formation of hydrogen bonds with perfluor-
idotitanate(IV) anions (Table S21).
The results of the experiments show that with the exception
of the synthesis of [C(NH2)3]2[TiF6] the chemical reactions and
crystallizations between guanidinium carbonate or guanidin-
ium chloride and titanium tetrafluoride in aHF are not very se-
lective and usually a mixture of phases is observed and isolated.
Experimental Section
Conclusions
CAUTION: The anhydrous HF and some fluorides are highly toxic
and must be handled in a well-ventilated hood and a protective
clothing must be worn all the time!
In the [C(NH2)3]+/TiF4 system five guanidinium perfluoridotitan-
ate(IV)
compounds
{[C(NH2)3]2[TiF6],
[C(NH2)3]4[Ti4F20],
[C(NH2)3][Ti2F9], [C(NH2)3]3[Ti6F27]·SO2, [C(NH2)3]4[H3O]4[Ti4F20]-
[TiF5]4} and one guanidinium hydrogen difluoride salt
{[C(NH2)3](HF2)} have been structurally characterized. Addition-
ally, the crystal structures of two by-products ([H5O2]4[Ti8F36]
and ꢀ-[H3O][Ti2F9]) were determined. The crystal structures of
the guanidinium salts consist of monomeric [TiF6]2–, oligomeric
[Ti4F20]4– and [Ti6F27]3–, as well as polymeric ([TiF5]–)∞ and
([Ti2F9]–)∞ perfluoridotitanate(IV) and hydrogen difluoride [HF2]–
anions. The [H3O]+-salts {without [C(NH2)3]+ cations} contain oli-
gomeric [Ti8F36]4– and polymeric ([Ti2F9]–)∞ anions.
Materials and Methods
Reagents: Guanidinium hydrocarbonate (Sigma-Aldrich, 99 %) and
guanidinium hydrochloride (Sigma-Aldrich, ≥ 99 %) were used as
supplied. Titanium tetrafluoride was synthesized by two different
methods. In the first by the reaction between TiCl3 (Sigma-Aldrich,
99.999 %) and aHF and the further fluorination with elemental F2
in aHF. In the second by the reaction between TiCl4 (Acros Organics,
99.9 %) and the liquid aHF at ambient temperature. The purity of
TiF4 was confirmed by the Raman spectroscopy and the elemental
chemical analysis.
The
oligomeric
[Ti6F27]3–
anion
{determined
in
Synthetic and Crystallization Apparatus: Due to high hygroscop-
icity of the TiF4 and the fluoridotitanate(IV) compounds all manipu-
lations with them were carried out under anhydrous conditions.
Non-volatile materials were handled in a M. Braun glove box in an
argon atmosphere, where quantity of water has not exceeded
[C(NH2)3]3[Ti6F27]·SO2 and in [C3H5N2]2[H3O][Ti6F27] during the
study of the imidazole–TiF4–HF system} with its trigonal pris-
matic geometry was structurally determined for the first time.
Its geometry resembles the crystal structure of TiF4.
The crystal structure of [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4 repre- 0.5 ppm. Volatile compounds, such as aHF and F2, were handled on
a vacuum line constructed from nickel and PTFE (polytetrafluoro-
ethylene).
sents the first example of the mixed-anion perfluoridotitan-
ate(IV) compound with both 0-D oligomeric [Ti4F20]4– and 1-D
polymeric ([TiF5]–)∞ perfluoridotitanate(IV) anions found in the
The vessels, used for the syntheses and single-crystal growth, were
same compound. For the latter a new conformation was ob- manufactured from the tetrafluoroethylene–hexafluoropropylene
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5255 © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
block-copolymer (FEP; Polytetra GmbH, Germany) tubes. The reac-
tion vessel was composed from tube (i.d. 16 mm, o.d. 19 mm) that
was heat-sealed on the one end and equipped with a PTFE valve
on another flared end. The crystallization vessel consisted of two
FEP tubes: one 16 mm i.d. × 19 mm o.d. and another 4 mm i.d.
× 6 mm o.d. Each tube was heat-sealed on one end and attached
via the linear PTFE connectors to the connecting PTFE T-part at 90°.
The PTFE valve was attached to the T-part at 180° to the 19 mm
o.d. tube. All PTFE details were covered by the brass parts with
threads that prevented deformation of those details and simplify
their connection between each other and to the vacuum system.
The magnetic stirring bars, isolated by PTFE, were put inside the
reaction vessels. Temperature gradient between two arms of the
crystallization vessels was maintained by cooling a wider arm of a
vessel in the Huber Ministat 230 (to –33 °C) and Thermo Fisher
Scientific EK 90 (to –60 °C) cryostats.
Crystallization of the synthesized compound led to single crystals
of [C3H5N2]2[H3O][Ti6F27] phase.
Characterization Methods
Raman Spectroscopy: Raman spectra with a resolution of 0.5 cm–1
were recorded at room temperature on a Horiba Jobin Yvon La-
bRam-HR spectrometer equipped with an Olympus BXFM-ILHS mi-
croscope. Samples were excited by the 632.8 nm emission line of a
He–Ne laser with regulated power in the range 20–0.0020 mW,
which gives 17–0.0017 mW focused on a 1 μm spot through a 50 ×
microscope objective on the top surface of the sample.
Single crystals or powdered material were mounted in the glove
box in previously vacuum-dried and fluorinated quartz capillaries,
which were initially sealed with Halocarbon 25–5S grease (Halo-
carbon Corp.) inside the glove box and later heat-sealed in an oxy-
gen–hydrogen flame outside the glove box.
Prior to use all the reaction and crystallization vessels were dried
under dynamic vacuum and passivated with elemental fluorine F2
(Solvay Fluor and Derivate GmbH, 99.98 %) at 1 bar for 2 hours.
Anhydrous HF (Linde AG, 99.995 %) was treated with K2NiF6 (Ad-
vance Research Chemicals Inc, 99.9 %) for at least several hours
before use and was usually kept in FEP vessels above K2NiF6.
Single Crystal X-ray Diffraction Analysis: The crystals were im-
mersed in perfluorodecalin (ABCR, 98 %) inside a glove box, se-
lected under a microscope, and mounted on the goniometer head
of the diffractometer in a cold nitrogen stream, created by Oxford
Cryojet cooling system. Some single crystals were put in previously
vacuum-dried and fluorinated quartz capillaries. Although up to 15
crystals from the same batch were screened, the presence of other
crystal phases cannot be definitively ruled out.
Synthesis and Crystal Growth: The syntheses between the guan-
idinium carbonate or the guanidinium chloride and TiF4 were car-
ried out by two ways. In the first one a mixture of titanium tetraflu-
oride TiF4 and guanidinium salt (in a requested ratio) was loaded
into a reaction vessel in a glove box. Around 4–8 ml of aHF was
condensed onto the mixture of reagents at 77 K and reaction mix-
ture was warmed up to ambient temperature. In the second way,
needed amount of guanidinium salt was firstly loaded into a reac-
tion vessel and was treated with aHF to get [C(NH2)3][HnFn+1]. After
Single-crystal data were collected on a Gemini A diffractometer
equipped with an Atlas CCD detector, using graphite monochro-
mated Cu-Ka radiation in the case of ꢀ-[H3O][Ti2F9] and Mo-Ka radi-
ation for all other compounds. The collected diffraction data for
were processed with the CrysAlis PRO program.[46] Analytical ab-
sorption correction was applied to all data sets. The crystal struc-
tures were solved by charge flipping method using Superflip pro-
gram.[47] The electron density map, obtained with Superflip soft-
ware, was analyzed using the EDMA program,[48] which gave an
initial model of the structure. Structure refinements were performed
with SHELXL-2013[49] using Olex crystallographic software.[50] Fig-
ures were prepared using the program DIAMOND 4.4.[51]
that, the required amount of TiF4 was loaded onto [C(NH2)3][HnFn+1
]
in a glove box, around 4–8 ml of aHF was condensed onto the
mixture of reagents at 77 K and obtained mixture was warmed up
to ambient temperature. Reactions were usually left to proceed 1–
3 days at ambient temperature with constant mixing.
In structures of [C(NH2)3]2[TiF6], [C(NH2)3][HF2], ꢀ-[H3O][Ti2F9] and
[H5O2]4[Ti8F36] compounds hydrogen atoms were localized on dif-
ferent Fourier maps and their positions and isotropic thermal pa-
rameters were freely refined. In the case of [C(NH2)3][Ti2F9] salt posi-
tions of H-atoms found from electron density peaks were refined,
their isotropic thermal parameters were constrained. In structures of
[C(NH2)3]4[Ti4F20] and [C(NH2)3]3[Ti6F27]·SO2 hydrogen atoms were
placed on ideal positions and refined as the riding atoms with rela-
tive isotropic displacement parameters. In [C(NH2)3]4[H3O]4-
[Ti4F20][TiF5]4 hydrogen atoms in guanidinium cations were placed
on ideal positions, hydrogen atoms in oxonium cations were local-
ized on different Fourier maps, positions and isotropic thermal pa-
rameters of all hydrogen atoms were refined with constrains.
Reaction of guanidinium carbonate with aHF results in a dense liq-
uid with extremely low vapour pressure. Therefore, no solid could
be recovered from liquid phase by removing of volatiles in a high
vacuum.
Single crystals were grown in crystallization vessels. Synthesized
guanidinium perfluoridotitanate(IV) salt or a required mixture of
guanidium salt and TiF4 were loaded inside the wider arm of the
crystallization vessel in a glove box. Then aHF, SO2, or CH3CN was
condensed onto the sample at 77 K and the vessel was warmed up
to an ambient temperature. When the sample was completely or in
some cases partly dissolved, clear solution was decanted into the
narrower arm. In order to achieve evaporation of the solvent from
the narrower arm, a temperature gradient between two arms of the
crystallization vessel was maintained. In the beginning of the proc-
ess, it was 10 K and later slowly increased to 50 K, in some cases
even up to 80 K. Crystallization continued up to several weeks, or
even two months in case of [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4. Ob-
tained crystals were isolated by pumping away the volatiles and
then transferred to a glovebox.
Associated Content
Supporting Information (see footnote on the first page of this
article): Supporting information is available including crystal data,
refinement results, geometric parameters of perfluoridotitanate(IV)
anions, distances and angles, associated with hydrogen bonding,
Raman spectra and assignments of vibrational bands for per-
fluoridotitanate(IV) anions and guanidinium cation.
Single crystals of imidazolium salt [C3H5N2]2[H3O][Ti6F27] were
sometimes observed as by-product after crystallizations of imidaz- Accession Codes: CCDC 1865283 {for [C(NH2)3]2[TiF6]}, 1865280 {for
ole/TiF4/aHF mixtures.[10] Larger quantity of this compound was
synthesized in aHF by reaction between imidazole (Aldrich, 99 %),
H2O and TiF4 with starting molar ratio n(C3H4N2)/n(H2O)/n(TiF4) =
[C(NH2)3]4[Ti4F20]}, 1865281 {for [C(NH2)3][Ti2F9]}, 1865287 {for
[C(NH2)3]3[Ti6F27]·SO2}, 1865284 {for [C(NH2)3]4[H3O]4[Ti4F20][TiF5]4},
1865279 {for [C(NH2)3][HF2]}, 1865285 {for ꢀ-[H3O][Ti2F9]}, 1865282
2:1:6 [m(C3H4N2) = 0.093 g, m(TiF4) = 0.510 g, m(H2O) = 0.0123 g]. {for [H5O2]4[Ti8F36]}, 1865286 {for [C3H5N2]2[H3O][Ti6F27]} contain the
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The authors declare no competing financial interest.
Most of the syntheses and partial characterization were done by
I. M. S. in the years 2010–2016 at Jožef Stefan Institute during his
Ph.D. study at Jožef Stefan International Postgraduate School, Ljubl-
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within the research program P1-0045 Inorganic Chemistry and
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Keywords: Guanidine · Titanium · Crystal structure ·
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Received: October 2, 2018
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