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

Article abstract of DOI:10.1016/j.ica.2019.02.027

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.

Full text of DOI:10.1016/j.ica.2019.02.027

Accepted Manuscript
Research paper
Syntheses and the crystal chemistry of the perfluoridotitanate(IV) compounds
templated with ethylenediamine and melamine
Igor M. Shlyapnikov, Evgeny A. Goreshnik, Zoran Mazej
PII:
S0020-1693(19)30028-3
https://doi.org/10.1016/j.ica.2019.02.027
ICA 18790
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
7 January 2019
20 February 2019
21 February 2019
Please cite this article as: I.M. Shlyapnikov, E.A. Goreshnik, Z. Mazej, Syntheses and the crystal chemistry of the
perfluoridotitanate(IV) compounds templated with ethylenediamine and melamine, Inorganica Chimica Acta
(
2019), doi: https://doi.org/10.1016/j.ica.2019.02.027
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Syntheses and the crystal chemistry of the perfluoridotitanate(IV)
compounds templated with ethylenediamine and melamine
a,b
a
a,*
Igor M. Shlyapnikov, * Evgeny A. Goreshnik, Zoran Mazej
a
Department of Inorganic Chemistry and Technology, Jožef Stefan Institute, Jamova cesta 39,
SI–1000 Ljubljana, Slovenia
b
Department of Polymer Chemistry and Technology, National Institute of Chemistry,
Hajdrihova ulica 19, SI–1000 Ljubljana, Slovenia
*
E-mail: zoran.mazej@ijs.si, igor.shlyapnikov@ki.si
Abstract
Chemical reactions between ethane-1,2-diamine [C
en] and 1,3,5-triazine-2,4,6-triamine [C ; melamine, abbr. mel], with titanium
tetrafluoride (TiF ) 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(TiF ) = 2:1, 1:1, 1:3, 1:4, and
n(mel) : n(TiF ) = 2:1, 1:1, 1:2, 1:3, 1:4 molar ratios were studied. Crystallizations of the
products from the saturated HF solutions yielded single crystals of [enH ]F ·2HF, previously
known [enH ][TiF ] and three new perfluoridotitanate(IV) salts, i.e., [enH ][TiF ]·HF,
enH ] and [melH ][TiF ]·HF. Their crystal structures were determined including the
crystal structure of the low-temperature modification of [enH ][TiF ]. The [enH
phase represents the first example of a structurally characterized perfluoridotitanate(IV)
2 4 2 2
H (NH ) ; ethylenediamine, abbr.
3
6 6
H N
4
4
4
2
2
2
6
2
6
[
2
]
0.5[TiF
5
2
6
2
6
2 5
]0.5[TiF ]
2
−
6
compound with a double charged cation, where instead of the usual octahedral [TiF ]
−
monomer, another kind of anion is present, i.e., polymeric chain-like ([TiF
5
] )
∞
anion. The
reactions in en/TiF
4
/HF and mel/TiF
4
/aHF systems are not selective enough to enable
2
+
2+
syntheses of individual [enH
2
2
] and [melH ] perfluoridotitanates(IV) in large quantities.
Keywords: ethylenediamine, melamine, titanium, fluorides, structure elucidation, hybrid
compounds
1

1
. Introduction
Perfluoridotitanates(IV) form an extensive class of the inorganic and hybrid compounds
1
,2,3
with a great structural diversity of the anions in the solid state.
Majority of them are the
2
−
2
[
TiF
isolated, the TiF
geometry) or polymeric (1-D: chains, columns; 2-D: layers, slabs; 3-D: three-dimensional
framework) poly[perfluoridotitanate(IV)] anions. In principle two octahedral TiF units can
6
] salts where the anionic parts consist of the isolated TiF
6
octahedra. Besides being
6
octahedra could be linked together yielding larger oligomeric (0-D
6
share one, two or three fluorine atoms resulting in vertex-, edge- or face-sharing geometries of
−
the linked octahedra. The latter example would represent the isolated [Ti
2
F
9
] anion, predicted
4
5
just theoretically. All the experimental attempts to prepare such salts failed so far. Instead of
−
the isolated [Ti
2
F
9
] anions, the compounds formulated as ATi
2
F
9
(A = single charged cation)
−
consist of the polymeric ([Ti
2
F
9
] )
∞
double chain-like anions. In the case of larger cations the
2
−
5
formula is doubled (i.e., A Ti
2
4
F18) and the compounds contain isolated [Ti
4
F
18] oligomers.
In the last decade we have successfully prepared a whole range of new
perfluoridotitanates(IV) compounds. Many of them consist of previously unknown
3
− 6
4− 7 , 8
4 4
poly[perfluoridotitanate(IV)] anions as for example oligomeric [Ti F19] , [Ti F20] ,
3
− 7
3− 8
4− 8,
9
5− 10
−
2,5,7,8
[Ti
5
F
23] , [Ti
6
F
27] , [Ti
8
F
36] ,
[Ti10
F
45] ,
and polymeric ([Ti
2 9 ∞
F ] ) ,
−
10
3−
2
3−
2
([Ti
3
F
13] )
∞
, ([Ti
4
F
19] )
∞
, and ([Ti
6
F
27] )
∞
. In all cases, single charged cations (organic or
inorganic) of various size and geometry were used as counter cations. The examples of the
2
−
hybrid perfluoridotitanates(IV) containing dications are scarce and mostly limited to [TiF
6
]
salts. One of the structurally characterized hybrid phase of diprotonated cation is
1
1
ethylenediammonium hexafluoridotitanate(IV), [enH
enH
known.
As previously evidenced, the [enH
2
][TiF
6
].
Besides it, the
−
[
2
][TiF4.3(OH)1.7], where part of the fluorine atoms is replaced by OH groups, is also
1
2
2
][TiF
around 130 K. In order to determine the crystal structure of the low-temperature phase (T <
30 K) and to check the possibility of the existence of other possible perfluoridotitanate(IV)
salts of ethylenediammonium (abbr. en), crystallizations between various ratios of en and TiF
in an anhydrous hydrogen fluoride (aHF) were carried out. Additionally, reactions between
,3,5-triazine-2,4,6-triamine (melamine; abbr. mel) and TiF in aHF were investigated. The
melamine was chosen because its corresponding protonated cation can occur in three forms:
6
] undergoes a first-order phase transition at
1
1
1
4
1
4
1
3
4 4
singly, doubly or triply protonated. Syntheses in en/TiF /aHF and mel/TiF /aHF systems
resulted in the detection of seven perfluoridotitanate(IV) compounds. Four of them were
2

structurally characterized. These are low temperature form of [enH
enH ] and HF containing compounds [enH ][TiF ]·HF and [melH
latter two are new examples of compounds containing HF species. Previously known
2
][TiF
6
] (β-modification),
[
2
]
0.5[TiF
5
2
6
2
][TiF ]·HF. The
6
1
4
1
5
examples with first row transition metals (3d) are A
2
CrF
6
·2HF (A = Na, K), A
2
CrF
6
·4HF (A
1
5
15
16
2
=
Rb, Cs),
imH) TiF ·2HF (im = imidazolium), NaTi
O)
K
3
Cr
2
F
11·2HF,
K
2
MF
6
·HF (M = Ti, Cr), ATiF
5
·HF (A = Na, K, Rb),
7
2
9
9
(
(
[
2
6
2
F
9
·HF,
K
4
Ti
8
F36·8HF, Rb
4
Ti
8
F
36·6HF,
1
7
14
H
3
3
[Cr(SbF
6
)
6
](Sb
2
F
11)·HF and CoSr
5
(AsF
6
)
128HF. Additionally, crystal structure of
enH
2
]F
2
·2HF has been determined within this study. Besides of cationic part and HF
molecules its crystal structure consists also of so called »independent« or »lone« fluoride ions
1
8
as previously reported in many anhydrous and hydrated metal fluorides. Results of both
studies (en/TiF /aHF and mel/TiF /aHF) are reported in this paper.
4
4
2
. Experimental section
CAUTION: Anhydrous HF and some fluorides are highly toxic and must be handled in a
well-ventilated hood and protective clothing must be worn all the time!
2
.1. Materials and Methods
.1.1. Reagents.
2
Ethane-1,2-diamine (Sigma-Aldrich, 99 %) was kept above the molecular sieves. 1,3,5-
triazine-2,4,6-triamine (Sigma-Aldrich, 99 %) was used as supplied. Anhydrous HF (Linde
AG, 99.995 %) was kept above K
used after at least four hours of treatment. Titanium tetrafluoride was synthesized by two
different methods: 1) by a reaction between TiCl (Sigma-Aldrich, 99.999 %) and aHF and
subsequent fluorination with elemental F in aHF; 2) by a reaction between TiCl (Acros
was confirmed
2 6
NiF (Advance Research Chemicals Inc, 99.9 %) and was
3
2
4
Organics, 99.9%) and liquid aHF at ambient temperature. The purity of TiF
using Raman spectroscopy and elemental chemical analysis.
4
2
.1.2. Synthetic and crystallization apparatus.
4
Because of the high hygroscopicity of TiF and fluoridotitanate(IV) compounds all
manipulations 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 0.5 ppm. Volatile compounds, such as aHF and F
line constructed of nickel and PTFE (polytetrafluoroethylene).
2
, were handled on a vacuum
3

Vessels, used for syntheses and single crystal growth, were manufactured from
tetrafluoroethylene-hexafluoropropylene block-copolymer (FEP; Polytetra GmbH, Germany)
tubes. Detailed information about reaction and crystallization vessels is given in ESI in
Figures S1 and S2.
Prior to use all reaction and crystallization vessels were dried under dynamic vacuum
and passivated with elemental fluorine F
bar for 2 hours.
.1.3. Synthesis and crystal growth.
Syntheses between ethylenediamine and melamine with TiF
ways. The first approach was used for reactions with starting n(en) : n(TiF
2
(Solvay Fluor and Derivate GmbH, 99.98 %) at
1
2
4
were carried out by two
) = 2:1 and 1:1
4
molar ratio. The approximate amount of ethylenediamine was condensed into the
preliminarily dried reaction vessel and its mass was further accurately determined. After that
the required amount of TiF
was condensed to the ethylenediamine at 77 K and after the solution was warmed up to
ambient temperature, it was poured to the reaction vessel filled with TiF . Reactions were
4
was loaded into another reaction vessel. Around 4–8 ml of aHF
4
usually left to proceed 1–3 days at ambient temperature with constant mixing. At the end the
liquid phase was decanted from the insoluble residue to another reaction vessel, all volatiles
were pumped out and isolated solids characterized.
In aHF soluble phases were loaded into crystallization vessels, the aHF was condensed
to the samples at 77 K and the vessel was warmed up to an ambient temperature. When the
samples were completely dissolved, clear solutions were decanted into the narrower arm of
the vessel. In order to achieve evaporation of the aHF from the narrower arm, a temperature
gradient between two arms of the crystallization vessel was maintained. In the beginning of
the process, it was 10 degrees and later slowly increased to 50 K. The obtained crystals were
isolated by pumping away the volatiles and then transferred to a glovebox.
The second synthetic approach was used for the reactions with higher starting rate of
4 4
TiF , i.e., with starting n(en) : n(TiF ) = 1:3 and 1:4 molar ratios. The approximate amount of
ethylenediamine (~20 µL) was added by automatic pipette into a few centimeters long FEP
tube (4 mm i.d.  6 mm) in a glove box. The tube was equipped with PTFE valve. After the
mass of reactant was accurately determined, the PTFE valve was removed and the whole tube
inserted inside the wider arm (16 mm i.d.  19 mm o.d) of crystallization vessel containing
4
requested amount of TiF . Whole procedure was done in glove box. On the vacuum system,
approximately 10–13 mL of aHF was condensed to the reagents and the content of the vessel
mixed well. After several days the liquid phase was decanted into the narrower arm of double-
4

arm crystallization vessel and the crystallization process began. Both, the products recovered
from decanted solutions and in aHF insoluble remains were characterized.
In attempts to synthesize melaminium perfluoridotitanate(IV) compounds, calculated
4
amounts of the solid reactants (melamine and TiF ) were loaded to the reaction vessels in the
glove box. Approximately 10-13 ml of aHF was condensed onto the reagents, the reactions
were left to proceed for several days and finally the liquid phase was decanted to the narrower
arm of the crystallization vessel. Both, the products recovered from decanted solutions and in
aHF insoluble remains were characterized. Additional experiments were done to dissolve in
aHF insoluble melamine/TiF
4 2 3
phases in SO and CH CN in an attempt to prepare saturated
solutions for single-crystal growths.
4 4
The masses of the reactants for all ethylenediamine/TiF /aHF and melamine/TiF /aHF
reactions are given in Tables S1 and S2.
2
.2. Characterization Methods
.2.1. Raman spectroscopy.
Raman spectra with a resolution of 0.5 cm were recorded at room temperature on a
2
−1
Horiba Jobin Yvon LabRam-HR spectrometer equipped with an Olympus BXFM-ILHS
microscope. 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.
Powdered materials were mounted in the glove box in previously vacuum-dried and
fluorinated quartz capillaries, which were initially sealed with Halocarbon 25-5S grease
(Halocarbon Corp.) inside the glove box and later heat-sealed in an oxygen−hydrogen flame
outside the glove box.
2
.2.2. Single crystal X-ray diffraction analysis.
Single crystal X-ray diffraction data were collected on a Rigaku AFC7 diffractometer
equipped with a Mercury CCD area detector for [enH
compounds and on “Agilent Gemini A” diffractometer equipped with Atlas CCD detector for
β-[enH ][TiF ], [enH ] and [enH ]F ·2HF compounds. In all cases graphite-
monochromated Mo K
00 K for β-[enH ][TiF
2 6 2 6
][TiF ]·HF and [melH ][TiF ]∙HF
2
6
2
]
0.5[TiF
5
2
2
α
radiation (λ = 0.7107 Å) was used. Diffraction data were collected at
1
2
6
] and at 200 K for the other four compounds.
Crystals were immersed in perfluorodecalin (Fluorochem, Cat. Code: 003283, melting
point 263 K) inside a glove box, selected under a microscope, and mounted on the goniometer
head of the diffractometer in a cold nitrogen stream, created by Oxford Cryojet cooling
5

system. Although up to 15 crystals from the same batch were screened, the presence of other
crystal phases cannot be definitively excluded.
The diffraction data, collected on the Rigaku AFC7 diffractometer, were processed
1
9
using Rigaku CrystalClear software.
Data, collected on the “Agilent Gemini A”
2
0
diffractometer were processed with the CrysAlis PRO program. The crystal structures of
2
1
[
enH
implemented in teXan software.
enH ]F ·2HF were solved by charge flipping method using the Superflip program (Olex
crystallographic software ). The electron density map, obtained with the Superflip software,
2 6 2 6
][TiF ]·HF and [melH ][TiF ]∙HF were solved by direct methods using SIR-92 ,
2
2
2 6 2 5
Structures of β-[enH ][TiF ], [enH ]0.5[TiF ] and
2
3
[
2
2
2
4
2
5
was analyzed with the EDMA program, which gave initial models of the structures. Final
2
6
refinement was done with SHELXL-2013,
implemented in Olex crystallographic
2
4
27
software. Figures were prepared using the program DIAMOND 4.4. The thermal ellipsoids
in figures are drawn at the 50 % probability level. Hydrogen atoms are presented by circles of
arbitrary size.
2 2
All hydrogen atoms in the structure of [enH ]F ·2HF were found on a difference Fourier
map, their positional and isotropic thermal parameters were refined. Hydrogen atoms
belonging to melaminium or ethylenediaminium cations in all other structures were placed on
ideal positions and refined as the riding atoms with relative isotropic displacement
parameters. Positions of hydrogen atoms belonging to HF molecules in structures of
2 6 2 6
[enH ]TiF ·HF and [melH ][TiF ]·HF were found on difference Fourier maps, their positional
and isotropic thermal parameters were refined.
2
+
Carbon atoms of [enH
2 2 6
] cation in the structure of β-[enH ][TiF ] are moderately
disordered, resulting in strong elongation of respective thermal ellipsoids. All attempts to split
2
+
2
the positions of carbon atoms in [enH ] cation resulted in unstable refinement and unrealistic
bonds lengths.
3
. Results and discussion
3
.1. Syntheses and crystallizations of ethylenediammonium perfluoridotitanate(IV)
compounds
Ethylenediammonium poly[perfluoridotitanate(IV)] compounds were synthesized by the
chemical reactions between liquid ethylenediamine C
2
H
4
(NH
2
)
2
(en) and titanium
tetrafluoride TiF in an excess of an anhydrous hydrogen fluoride (aHF). The latter acted in a
4
4
dual role: as a reagent and as a solvent. Starting n(en) : n(TiF ) molar ratios of reagents were
6

4
equal to 2:1, 1:1, 1:3 and 1:4. In all en/TiF /aHF reactions two phases – liquid and insoluble
solid material – were always observed (Scheme 1). In the 2:1 and 1:1 reaction systems the
liquid phases were firstly separated from insoluble residues. After that, volatiles were pumped
away, solid products recovered and finally characterized. Part of the sample, isolated from
solution, was re-dissolved in aHF in attempt to grow single crystals. In the case of reactions
4
with larger amounts of TiF (1:3 and 1:4) the liquid phase was decanted from one arm of the
crystallization vessel into another one without prior isolation in an attempt to grow single
crystals.
soluble
2 6 2 5 2 2
[enH ][TiF ](·HF), [enH ]0.5[TiF ], [enH ]F ·2HF
4
en + nTiF + HF
n = 0.5, 1
2 5 2 9
[enH ][TiF ][Ti F ]
insoluble
soluble
Ø
4
en + nTiF + HF
n = 3, 4
2 5 2 9 2 2 9
[enH ][TiF ][Ti F ], [enH ]0.5[Ti F ]
insoluble
Scheme 1. Products of reactions between ethylenediamine and TiF
serving as a reagent and also as a solvent) with different starting molar ratios of reactants,
i.e., n(en) : n(TiF ) = 2:1, 1:1, 1:3, and 1:4.
4
in an anhydrous aHF
(
4
Raman spectra of the solids, recovered from the HF solutions prepared by reactions
between en and TiF (molar ratios: 2:1 and 1:1) in aHF, were almost identical (Figure 1).
They show vibrational bands, that can be assigned to [TiF
4
2
−
−1
−1
6
] anions (609 cm , 284 cm and
−1 7,8
2+
28
weak at 487 cm ) and [enH
2
] cations. Subsequent crystallization of the soluble phase of
1
1
2
:1 system yielded single crystals of [enH
2
]F
2
·2HF, [enH
2
][TiF
6
]
as well as traces of
2
9
+
[H
3
O][TiF
5
] phase, as a by-product. The formation of [H
3
O] compounds was a result of a
contamination of reactants with traces of water, which is protonated in the superacid aHF with
+
the formation of [H
3
O] cations. The second system, with the starting n(en) : n(TiF
4
) = 1:1
molar ratio, revealed single crystals of three phases: prevailing [enH
2
][TiF
6
] and its solvated
7

form [enH
2
][TiF
6
2 5
]·HF and only a few crystals of [enH ]0.5[TiF ], containing polymeric zigzag
−
chain-like ([TiF
5
] )
∞
anion.
Figure 1. Raman spectra of in HF soluble materials, isolated after reactions between
-1
ethylenediamine and TiF
4
in 2:1 and 1:1 molar ratios. The vibrational bands at 609 cm ,
-1
-1
2−
4
6
87 cm and 284 cm belong to [TiF ] anion.
Chemical reactions between ethylenediamine and larger amounts of titanium
tetrafluoride [n(en) : n(TiF ) = 1:3 and 1:4 molar ratios] yielded products which were
insoluble in aHF. Their Raman spectra (Figure 2) do not show the presence of TiF (Figure
S14). Raman spectrum of insoluble solid obtained in a reaction with n(en):n(TiF ) = 1:3 molar
ratio is similar to the Raman spectra of insoluble residues after reactions between en and TiF
4
4
4
4
−1
with 2:1 and 1:1 molar ratios (Figure 2). There are two vibrational bands at 706 cm and
−1
7
50 cm , that can be assigned to a symmetric Ti–F stretching modes of
2
,5,7,8,9,10
perfluoridotitanate(IV) anions.
On the basis of previous results those bands can be
2
+
−
assigned as belonging to [enH
2
]
compound which consists of polymeric ([TiF
5
] )
∞
and
−
([Ti
2
F
9
] )
∞
anions. Raman spectrum of the solid residue after a reaction of en with TiF
4
(molar
8

−1
ratio 1:4) in aHF, shows strong vibrational band at 759 cm , that can be assigned to
−
([Ti
2
F
9
] )
∞
anion, e.g., the formation of [enH
2
]0.5[Ti
2
F
9
] or its HF-solvated form (Figure 2).
−1
This indicates that the compound obtained in 1:3 system (vibrational bands at 706 cm and
−1
7
50 cm ) is most probably not a mixture of [enH
2
]0.5[TiF
5
2 2 9
] and [enH ]0.5[Ti F ] phases but
more likely a mixed-anion [enH ][TiF ][Ti F ] compound. In the former case, the band
2 5 2 9
−
−1
assigned to ([Ti
product [enH
systems with larger contents of TiF
way of single crystal growth to get the final answer about their composition.
2
F
9
] )
∞
anion (at 750 cm ) should be observed at the same position as in 1:4
−1
2
]
0.5[Ti
2
F
9
] (759 cm ; Figure 2). Since the products obtained in en/TiF
4
/aHF
4
are insoluble in aHF it will be necessary to find another
2 5 2 9
[enH ][TiF ][Ti F ]
2 2 9
[enH ]0.5[Ti F ]
Figure 2. Raman spectra of in aHF insoluble residues after reactions between
ethylenediamine and TiF in 2:1, 1:1, 1:3 and 1:4 molar ratios. The marked intense bands
correspond to a symmetric Ti–F stretching [ν (Ti–F)] of perfluoridotitanate(IV) anions
4
s
−
−
(
5 ∞ 2 9 ∞
[TiF ] ) and ([Ti F ] ) .
9

3
.2. Syntheses and crystallizations of 1,3,5-triazine-1,3-diium-2,4,6-triamine
poly[perfluoridotitanate(IV)] compounds
Possible formation of the previously unknown perfluoridotitanate(IV) salts of 1,3,5-
triazine-2,4,6-triamine (mel; melamine) was screened by carrying out chemical reaction
between melamine and TiF
with different starting n(mel) : n(TiF
and Scheme 2). The product of the reaction with the highest rate of melamine, n(mel) :
n(TiF ) equal to 2:1, was completely soluble in HF. The Raman spectrum of the isolated solid,
after pumping away HF, revealed the formation of the hexafluoridotitanate(IV) and hydrogen
4
in an anhydrous HF (serving as a reagent and also as a solvent)
4
) molar ratios (2:1, 1:1, 1:2, 1:3, 1:4 and 1:5; Table S2
4
-1
difluoride salts of melamine. The vibrational band at ~560 cm (Figure 3) confirms the
−
30
presence of [HF
2
] anion. This vibrational band is not present in pure melamine but it
appears after its treatment with aHF (Figure 3). In the superacidic aHF melamine is
x+
−
x 2 x
protonated leading to [melH ] ([HF ] ) (x = 1, 2 or 3). Without the single crystal structure
determination the degree of protonation (i.e., single-, double- or triple-protonated) cannot be
exactly known. Subsequent crystallization of the product from the saturated HF solution
4
(obtained by n(mel) : n(TiF ) = 2:1 molar ratio) led to the single crystals of the solvated
[
melH ][TiF ]·HF phase. The product of the second reaction, with starting n(mel) : n(TiF )
2
6
4
2
−
6
molar ratio equal to 1:1, was mostly composed from the [TiF ] phase as proved by Raman
spectroscopy. A small amount of the insoluble phase precipitated from the HF solution after
one day of mixing. The crystallization of the product from the saturated HF solution [n(mel) :
n(TiF
4
) = 1:1] yielded small single crystals of the [melH
In the course of the reactions with higher ratios of TiF
:3, 1:4 and 1:5] there was always a lot of insoluble solid visible. The HF solutions above the
solid residues were decanted to the narrower arms of the crystallization vessels. Only the
crystals of the solvated phase [melH ][TiF ]·HF grew from the decanted solutions obtained in
the melamine/TiF systems with starting n(mel) : n(TiF ) = 1:3 and 1:4 molar ratios
Scheme 2). The quality of single crystals grown during crystallization of the soluble product
2
][TiF
6
]·HF phase.
4
[n(melamine) : n(TiF ) = 1:2,
4
1
2
6
4
4
(
in the system with 1:2 molar ratio of reactants, was too poor for a crystal structure
determination. The crystallization from the decanted solution obtained by reaction with
4
reactant ratio n(mel) : n(TiF ) = 1:5 resulted in the precipitation of the fine powder only.
1
0

soluble
x+
−
[
2 6 x 2 x
melH ][TiF ]·HF, [melH ] ([HF ] )
4
mel + nTiF + HF
n = 0.5, 1, 2, 3, 4, 5
x 5 x x 2 9 x
[melH ][TiF ] , [melH ][Ti F ]
insoluble
Scheme 2. Products of reactions between 1,3,5-triazine-2,4,6-triamine and TiF4 in an
anhydrous aHF (serving as a reagent and also as a solvent) with different starting molar ratios
4
of reactants, i.e., n(mel) : n(TiF ) = 2:1, 1:1, 1:2, 1:3, 1:4 and 1:5.
The insoluble products formed after the reactions [n(mel) : n(TiF
4
) = 1:2, 1:3, 1:4 and
1
:5] were isolated separately and studied by means of Raman spectroscopy (Figure 3). The
−1
most intensive vibrational band at 690 cm corresponds to the protonated melamine
13
vibrations. The other two intensive bands, found in the range typical for the symmetric in-
2
,5,7,8,9,10
phase Ti-F
t
stretching vibrations of perfluoridotitanate(IV) anions,
are determined at
−1
7
13 and 755 cm . These vibrational bands can be assigned to the polymeric anions
−
2,8,10,29,31
−
2,5,7,8,32
(
[TiF
5
5
] )
∞
∞
and ([Ti
2
F
9
] )
∞
,
respectively. The phase with the single-chain like
−
([TiF
] )
anion predominates in the products with lower rate of TiF
4
(Figure 3; reactions
−
with 1 : 2 and 1 : 3 molar ratios). The compound containing the double-chain like ([Ti
2
F
9
] )
∞
anion appears in larger amounts in the products of the reactions with greater amounts of TiF
Figure 3; reactions with 1:4 and 1:5 molar ratios). On the basis that the intensities of
vibrational bands (Figure 3; ratios 1:2, 1:3, 1:4 and 1:5) vary and are found at the same
4
(
−1
−
positions (713 and 755 cm ) we can assume that we have a mixture of ([TiF
5
] )
∞
and
−
−
−
(
[Ti F ] ) salts and not a ([TiF ] ) /([Ti F ] ) mixed-anion compound. The vibrational band
2 9 ∞ 5 ∞ 2 9 ∞
−1
at around 555 cm in the Raman spectra of the 1:2 to 1:5 products (Figure 3) is not necessary
−
connected with the presence of [HF
2
] anion. It more likely belongs to the vibrations of
−
2
([TiF
5
] )
∞
chain as previously observed in ATiF
5
(A = K, Rb, Cs).
Attempts to grow single crystals of in aHF insoluble phases from aprotic solvents, as
and CH CN, failed. Either powdered (using SO ) or either low crystalline or powdered
and sticky material was recovered (using CH CN).
SO
2
3
2
3
1
1

2
−
−
[TiF
6
]
([TiF
5 ∞
] )
−
2
[HF ]
−
(
[Ti F ] )
2 9 ∞
melamine
5
59
melamine + HF
6
16
2
: 1
1
: 1
: 2
7
13
1
1
7
55
: 3
1
: 4
: 5
1
100
200
300
400
500
600
700
800
900 1000
-
1
Wavenumber / cm
Figure 3. Raman spectra of in aHF insoluble residues recorded after reactions between
melamine and TiF (1:2, 1:3, 1:4 and 1:5 molar ratios) in aHF. Raman spectra of melamine,
melamine treated with aHF, melaminium [TiF
of the product of the reaction between 2:1 molar ratio of melamine and TiF
given. The marked intense bands correspond to a symmetric Ti–F stretching [ν
4
2
−
6
] salt (1:1 molar ratio), and Raman spectrum
in aHF, are also
(Ti–F)] of
4
s
2
−
−
−
6 5 ∞ 2 9 ∞
perfluoridotitanate(IV) anions [TiF ] , ([TiF ] ) and ([Ti F ] ) .
3
.3. Single crystal structures of ethylenediammonium perfluoridotitanates β-
(NH ][TiF ], [C (NH ][TiF ]·HF, and [C (NH ].
The corresponding single crystal structure data of ethylenediammonium, i.e., [enH
compounds, isolated from the C (NH /TiF /aHF systems are summarized in Table 1.
[
C
2
H
4
3
)
2
6
2
H
4
3
)
2
6
2
H
4
3 2 5
) ]0.5[TiF
2
+
2
] ,
2
H
4
2
)
2
4
1
2

Table 1. Crystal data and refinement results of β-[enH
2
][TiF
6
], [enH
2
][TiF
6
]·HF,
·
[
enH
2
]
0.5[TiF
5
] and [enH
2
]F
2
·2HF
Chem.
formula
CCDC #
[enH
2 2
]F
2HF
β-[enH
2
][TiF
6
]
[enH
2
][TiF
6
]·HF
2 5
[enH ]0.5[TiF ]
1885310
223.97
1885309
244.03
1885308
347.84
1885312
140.14
Monoclinic
I2/m
5.2645(4)
4.6185(4)
12.787(1)
90
97.141(7)
90
308.48(4)
2
w
F (g/mol)
Crys. system
Space group
a (Å)
Triclinic
P 1
Triclinic
P 1
Monoclinic
1
P2 /c
5.8601(4)
5.9228(4)
10.6118(7)
94.706(5)
92.210(5)
93.383(5)
366.09(4)
2
5.8821(8)
5.9338(8)
11.958(2)
91.353(6)
96.867(6)
98.318(7)
409.67(9)
2
5.7801(3)
15.447(1)
5.4825(3)
90
92.433(5)
90
b (Å)
c (Å)
α (°)
β (°)
γ (°)3
V (Å )
Z
489.06(5)
2
T (K)
100
0.043
0.116
200
0.046
0.130
200
0.033
0.086
200
0.031
0.088
a
R
1
b
wR
is defined as Σ║F
o c o
wR is defined as [Σ[w(F –F ) ]/Σw(F ) ] .
2
a
b
R
1
o
│–│F
c
║/Σ│F
o
│for I > 2σ(I).
2
2 2
2 2 ½
2
3
.3.1. Crystal structure of β-[enH ][TiF ].
2 6
One of the products of the chemical reaction between ethylenediamine (en) and TiF
with starting n(en) : n(TiF 2:1 molar ratio was ethylenediaminium
hexafluoridotitanate(IV). The α-[enH ][TiF ] crystallizes in the monoclinic A2/a space group
a = 10.655 Å, b = 8.7081 Å, c = 7.9704 Å, β = 95.032 ° at ambient temperature). As
previously evidenced by thermal investigations by differential scanning microcalorimetry and
dielectric measurements a first order phase transition in [enH ][TiF ] is present at around
30 K, but the crystal structure of the low-temperature phase has not been reported until
now. To fill this gap the single crystal of [enH ][TiF ] was cooled down from 200 K to 100 K
in two hours on the goniometer of the diffractometer. The phase transition led to a symmetry
decrease. Its low-temperature modification, β-[enH ][TiF ], crystalizes in the triclinic P1
4
4
)
=
2
6
1
1
(
2
6
1
1
1
2
6
2
6
space group. Detailed crystallographic data are given in Table S3.
The crystal structure of the low-temperature phase consists of two crystallographically
2
−
independent octahedral [TiF
6
]
anions (one of them is disordered) and one
2
+
crystallographically independent ethylenediammonium cation, [enH
2
]
(Figure 4). The
] is the same as for
anions. Titanium atoms are in octahedral coordination of six
2
−
geometry of the [TiF
6 2 6
] anion in the crystal structure of β-[enH ][TiF
2
−
previously reported [TiF
6
]
1
3

fluorine atoms with the Ti–F bond lengths ranging from 1.846(2) to 1.873(4) Å. The F–Ti–F
angles differ from 90 ° by up to 0.8 ° (Table S4). The geometry of the ethylenediammonium
cation in the β-phase slightly differs from that in the α-phase: one C–N and the C–C bonds are
slightly elongated, and another C–N bond is shortened in the low-temperature modification
comparatively to the high-temperature modification. The C–C–N angles and N–C–C–N
torsion angles are practically identical in both modifications.
2
−
2+
The packing of the [TiF
6
] anions and the [enH
2
] cations in the unit cells of α- and β-
[
enH
2
][TiF ] compounds is presented in Figure 4. The packing observed in the high-
6
temperature modification is very similar (Figure 4) with the only one clearly visible
difference – disordering of one anion in the low-temperature modification.
The hydrogen atoms, bonded to nitrogen atoms are involved in hydrogen bonding with
2
−
the [TiF
6
]
anions. The hydrogen bonding pattern in both structures is very similar: each
2
+
[
enH ] cation forms hydrogen-bonds with six anions, while the shortest H···F distance in
2
the high-temperature modification is 1.971 Å, whereas in the low-temperature modification
the shortest H···F distance is 1.818 Å.
Figure 4. The unit cells of α-[enH
2
][TiF
6
2 6
] (upper) and β-[enH ][TiF ] (lower) compounds.
2
−
Two disordered positions of the [TiF
6
] anions are shown.
1
4

3
.3.2. Crystal structure of [enH
Among single crystals, grown during the crystallization of the products of the chemical
reaction between ethylenediamine (en) and TiF in aHF with the n(en) : n(TiF ) = 1:1 molar
ratio from aHF, several single crystals of monosolvated hexafluoridotitanate(IV) phase
enH ][TiF ]·HF were observed. It crystallizes in the triclinic P1 space group (Table S5).
The crystal structures of solvated and non-solvated α- and β-[enH ][TiF ] phases consist
] the hexafluoridotitanate anion is
more symmetrical with three independent Ti–F bonds with very similar lengths (1.848 Å,
2 6
][TiF ]·HF.
4
4
[
2
6
2
6
2
−
6 2 6
of octahedral [TiF ] anions. In the case of α-[enH ][TiF
1
1
1
.849 Å and 1.859 Å). The F···Ti···F angles in the octahedra differ from 90 ° by up to 0.5 °.
In the crystal structure of [enH ][TiF ]·HF, where HF molecules are incorporated in the
crystal structure, hydrogen bonds between HF and the anion appear, leading to the distortion
2
6
2
−
6 6
of the [TiF ] anion. In TiF unit all seven atoms (one Ti and six F) are crystallographically
independent with the Ti–F bond lengths ranging from 1.834(2) to 1.913(2) Å (Figure S4).
The longest Ti–F bond is between Ti and F3 atom, where the latter is involved in hydrogen
bonding with HF. The shortest bond is between Ti atom and F5 atom, which is situated in
trans- position to the F3 atom involved in hydrogen bonding. Other geometric parameters of
2
−
the [TiF
In the crystal structure of [enH
all hydrogen atoms (bonded to nitrogen atoms) of [enH
bonding. The F3···F7 distance, between the F3 atom of [TiF
molecule involved in hydrogen bonding, equals to 2.384(4) Å (Figure 5). Such hydrogen
6
] anion are given in Table S6.
2
−
2
][TiF
6
]·HF, all fluorine atoms of the [TiF
6
] anion and
2
+
2
] cations are involved in hydrogen
2
−
6
] anion and F7 atom of HF
2
−
bonding between HF molecules and [TiF
6
6
]
anions in hybrid compounds was previously
7
observed in imidazolium salt [imH] [TiF
2
]·2HF. Corresponding F···F distances between
7
fluorine atoms involved in hydrogen bonding are comparable (2.374(6) Å) to those observed
in the crystal structure of [enH
HF under dynamic vacuum and makes single crystals of [enH
atmosphere at ambient temperature. The remaining five fluorine atoms of the [TiF
2
][TiF
6
]·HF. Such strong hydrogen bonding prevents release of
2
][TiF ]·HF stable in inert
6
2
−
6
] anion
2
+
form hydrogen bonds with five [enH
2
] cations on the way that each F atom is coordinated to
2
+
2+
one H atom of each [enH
2 2
] cation. Additionally, one of the [enH ] cations is hydrogen
bonded (N2–H∙∙∙F7) to F7 atom of the HF molecule (Figure S5).
2
+
Two crystallographically independent [enH
2
]
cations are determined in the crystal
2
+
structure of [enH
six hydrogen bonds with the six [TiF
2
.712(4) to 2.796(4) Å (Figure S6). Each [enH ] cation, consisting of N2 and C2 atoms, is
2 6 2
][TiF ]·HF. Each [enH ] cation, constructed of N1 and C1 atoms, forms
2
−
6
]
anions with the N···F distances ranging from
2
+
2
1
5

2
−
hydrogen bonded with the four [TiF
Å and weakly hydrogen bonded with two HF molecules with the N···F distance equal to
.051(4) Å. Detailed parameters of hydrogen bonding are depicted in Table S7.
The packing of the structural units in the unit cell of the [enH ][TiF ]·HF compound is
6
] anions with the N···F distances 2.788(4) and 2.846(2)
3
2
6
presented in Figure 5. As in the crystal structures of all hybrid poly[perfluoridotitanate(IV)]
compounds, inorganic anions and organic cations are interconnected in 3-D structure by
hydrogen bonding. The HF molecules are located inside the voids.
2 6
Figure 5. The unit cell of [enH ][TiF ]·HF compound viewed along the b-axis. The atoms of
the asymmetric unit are labeled.
3
2 5
.3.3. Crystal structure of [enH ]0.5[TiF ].
Single crystals of another ethylenediammonium poly[perfluoridotitanate(IV)]
compound were observed as a minor product after the crystallization of the reaction mixture
of ethylenediamine and TiF
corresponds to [enH
4
in aHF with the n(en) : n(TiF
4
) = 1:1 molar ratio. New phase
2
]
0.5[TiF
5
] compound. It crystallizes in the P2
1
/c space group with four
formula units per unit cell. Detailed crystallographic data are given in Table S8.
The crystal structure of ethylenediammonium bis[pentafluoridotitanate(IV)] consists of
2
+
one crystallographically independent ethylenediammonium [enH
2
]
cation and polymeric
octahedra,
−
([TiF
5
] )
∞
anions in the form of monomeric zig-zag chain of slightly distorted TiF
6
linked by cis-vertices (Figure 6). Bond distances between titanium and terminal fluorine
1
6

atoms, ranging from 1.780(1) to 1.850(2) Å, are considerably shorter than the bond lengths
between titanium and bridging fluorine atoms (2.023(1) – 2.028(1) Å). Other geometric
−
parameters of the ([TiF
5
] )
∞
are given in Table S9. The observed bond lengths are in good
−
agreement with the Ti–F bond lengths in previously reported ([TiF
5
] )
∞
salts (Table S11), i.e.,
2
9
31
2
10
[
[
[
H
3
O][TiF
C(NH
enH
5
], [NH
4
][TiF
5
], A[TiF
5
]·HF (A = Na, K, Rb, Cs), [XeF
5
][TiF
5
]
and
8
2
)
3
]
4
[H O] [Ti
3
4
4
F
20][TiF
5
]
4
.
All Ti–F –Ti angles in the crystal structure of
b
2
]
0.5[TiF
5
] are equivalent and equal to 138.31(7) °.
−
All terminal fluorine atoms of the ([TiF
5
] )
∞
anion are involved in hydrogen bonding
octahedra are
2
+
with the [enH
hydrogen bonded with F1, F2 and F3 atoms to the same hydrogen atom of the [enH
with the N···F distances ranging from 2.783(3) to 2.897(3) Å (Figures 6 and S7). Two TiF
units, separated by the third one, are connected via Ti–F4···H–N hydrogen bonds with the
2
]
cations (Table S10). Three nearest neighbouring TiF
6
2
+
2
] cation
6
2
+
same [enH
2
]
cation, where one hydrogen bond is stronger and one weaker (the N···F
distances equal to 2.839(3) and 3.047(3) Å, respectively).
−
Figure 6. The unit cell of [enH
2
]0.5[TiF
5
] compound and coordination of the ([TiF
5 ∞
] ) anions
2
+
by [enH
2
] cations. Symmetry codes: (i) x, 1.5−y, −0.5+z; (ii) x, y, −1+z; (iii) −1+x, y, z.
1
7

2
+
Each [enH
2
5
] cation forms hydrogen bonds with four TiF chains (Figures 6 and S8).
−
The polymeric ([TiF
5
] )
∞
anions are closely packed and connected together by hydrogen
2
+
bonding with the [enH
2
] cations (Figure S9).
3
.4. Single crystal structure of melaminium perfluoridotitanate [C
The crystallizations of the melaminium poly[perfluoridotitanate(IV)] compounds from
the saturated aHF solutions led to small single crystals. Among the crystallized products of
the reactions between melamine and TiF in aHF with the n(mel) : n(TiF ) = 2:1, 1:1, 1:2, 1:3
and 1:4 molar ratios, only the single crystals of [melH ][TiF ]·HF phase were of sufficient
quality for X-ray diffraction analysis. The corresponding single crystal structure data of
3 8 6 6
H N ][TiF ]∙HF
4
4
2
6
[
melH
2
][TiF
6
]·HF are given in Table 2.
2 6
Table 2. Crystal data and refinement results of [melH ][TiF ]·HF.
Chem. formula
CCDC #
3 8 6 6
[C H N ][TiF ]∙HF
1885311
310.06
Triclinic
P 1
w
F (g/mol)
Crystal system
Space group
a (Å)
6.694(1)
b (Å)
c (Å)
α (°)
β (°)
7.4705(8)
9.865(2)
86.65(3)
87.27(3)
74.47(2)
474.2(1)
2
γ (°)
3
V (Å )
Z
T (K)
200
0.063
0.178
a
R
1
b
wR
2
a
R
1
is defined as Σ║F │–│F ║/Σ│F │for I > 2σ(I).
o c o
b
2
2 2
2 2 ½
2 o c o
wR is defined as [Σ[w(F –F ) ]/Σw(F ) ] .
The hexafluoridotitanate(IV) salt of melaminium crystallizes from the saturated aHF
solution as a monosolvate in a triclinic P1 space group with two formula units per unit cell.
The detailed crystallographic data are given in Table S14. In the superacidic aHF medium,
two nitrogen atoms of melamine, belonging to the aromatic ring, are protonated yielding
2
+
2−
[C
3
H
8
N
6
]
cations. The charge balance is maintained by well-known octahedral [TiF
6
]
]
2
−
anions. The crystal structure also includes HF molecules coordinated to anions. The [TiF
6
anion is slightly distorted (Figure 7). The Ti–F bond lengths range from 1.824(2) to
1
8

1
.923(2) Å. The longest Ti–F bond includes F7 atom involved in hydrogen bonding with HF
molecule. This bond is longer than the corresponding Ti–F bond in the crystal structure of the
enH ][TiF ]·HF compound (1.912(2) Å). Other geometric parameters are given in Table
S15.
[
2
6
2 6
Figure 7. Part of the crystal structure of [melH ][TiF ]·HF. The atoms of the asymmetric unit
are labeled.
Hydrogen bonding in the crystal structure of [melH
fluorine atoms of the anion and all hydrogen atoms of the cation (Figures 7, S12, S13, and
Table S16). Each of the three fluorine atoms of TiF unit (F2, F3 and F4) forms one hydrogen
cation. The hydrogen bond between N3 and F3 atoms with the
2 6
][TiF ]·HF involves all terminal
6
2
+
2
bond with one [melH ]
shortest N···F distance causes significant elongation of the Ti–F3 bond (1.854(2) Å) in
comparison to the Ti–F4 and Ti–F2 bonds, where hydrogen bond between N2 and F4 atoms is
weaker and that between N1 and F2 is the weakest. Other two fluorine atoms, F5 and F6, are
2
+
coordinated each to the one [melH
includes the hydrogen atom of –NH
bonded to the N4 or N5 nitrogen atoms in the aromatic ring (Figure S12). Those hydrogen
2
] cation via two hydrogen bonds. One of hydrogen bonds
2
group (N1 and N2) and another – the hydrogen atom
1
9

bonds cause equivalent elongations of the Ti–F5 and Ti–F6 bonds. The remaining F7 fluorine
2
−
2+
atom of the [TiF
6 2
] anion also forms two hydrogen bonds: one with the [melH ] cation and
one with HF molecule (Figure 7). The (Ti–)F7···F1(–H) distance between the F7 fluorine
2
−
atom belonging to the [TiF
It is longer than corresponding distances in ethylenediaminium [enH
imidazolium [imH] [TiF ]·2HF salts (2.384(4) and 2.374(6) Å, respectively). Nevertheless,
the hydrogen bond between the anion and HF molecule is strong enough to make crystals of
melH ][TiF ]·HF compound stable under dynamic vacuum and in inert atmosphere at
ambient temperature.
6
] anion and the F1 fluorine atom of HF molecule is 2.490(3) Å.
2
][TiF ]·HF and
6
2
6
[
2
6
2
+
2−
All [melH
2
]
cations are coordinated with six [TiF
groups (Figure S13). On such way the [melH
anions and HF molecules of the [melH ][TiF ]·HF are connected through
6
]
anions via hydrogen bonds,
2
+
involving all hydrogen atoms of –NH
2
2
]
2
−
cations, [TiF
6
]
2
6
multiple hydrogen bonds into 3-D network. Anions and cations are packed so that the
alternation of cationic and anionic layers along the b-axis can be observed (Figure 8).
2
+
2−
Figure 8. Alternating layers of [melH
2
]
cations, HF molecules and [TiF
6
]
anions in
[
melH ][TiF ]·HF.
2
6
2
0

3
.5. Single crystal structure of fluoride [C
Single crystals of ethylenediammonium fluoride disolvate [enH
from saturated solution prepared by dissolution of the products of the reaction between TiF
and excess of ethylenediamine [n(en) : n(TiF ) = 2:1 molar ratio]. The [enH ]F ·2HF
2 4 3 2 2
H (NH ) ]F ·2HF
2
2
]F ·2HF were grown
4
4
2
2
crystallizes in the I2/m space group with the two formula units per unit cell. Detailed
crystallographic data are given in Table S12.
In [enH
2
]F
2
·2HF, the F···F distances between (H−)F1 and lone F2 atom (Figure S10)
−
2
are slightly elongated [2.322(1) Å] in comparison to the usual F···F distances in the [HF ]
3
3
anion [2.213(4) – 2.277(6) Å]. The H atom is much closer to the F1 atom than to the F2
atom [H1c···F1 and H1c···F2 bond lengths are 0.95(4) and 1.38(4) Å, respectively, Figure
S10]. Additionally, the hydrogen bond pattern reveals formation of strong hydrogen bonds
between cations and the lone fluorine atom F2 and only weak between cations and the F1
−
−
atom. There are no strict borders between [HF
2
] and [F ·HF] formulations. In some works,
−
2 2 2
the FHF moiety with similar geometry as in [enH ]F ·2HF, is rather described as [HF ]
3
4
anion. Nevertheless in the [enH
2 2
]F ·2HF compound the FHF moieties are better described
as HF molecules hydrogen-bonded to lone fluoride ligands, following previous researches
3
3
based on both crystallographic and NMR spectroscopic studies of the similar systems.
−
2+
Each F anion (F2 atom) forms four strong hydrogen bonds with three [enH
2
] cations
and one HF molecule (Figure S10). The N···F2 distances are 2.709(1) and 2.871(2) Å. The
3
5
2+
F1 atoms of the HF molecule are involved in very weak hydrogen bonding with the [enH
2
]
cations with N···F1 distances 2.927(1) and 3.013(2) Å and more acute N–H–F angles between
2
+
9
2
2 and 106 °. All six hydrogen atoms of each [enH ] cation, bonded to nitrogen atoms, form
−
hydrogen bonds with six different F anions (Figure S11). The distances and angles,
associated with the hydrogen bonding in [enH
2
]F
2
·2HF are depicted in Table S13.
2
]F ·2HF, the
Because of the described hydrogen bonding in the crystal structure of [enH
2
ethylenediammonium cations, fluoride anions and HF molecules are interconnected into an
infinite 2-D layers by strong hydrogen bonds, that are connected between themselves by weak
hydrogen bonds with HF molecules (Figure 9).
2
1

2 2
Figure 9. Part of the crystal structure of [enH ]F ·2HF. Strong hydrogen bonds are shown by
black dashed lines; weak hydrogen bonds are shown by grey dashed lines.
4
. Conclusions
The chemical reactions between ethane-1,2-diamine (en) and 1,3,5-triazine-2,4,6-
triamine (mel) with TiF in anhydrous hydrogen fluoride (aHF) are not selective enough to
4
synthesize individual phases of ethylenediammonium or melaminium perfluoridotitanates(IV)
in larger quantities. In aHF insoluble phases are, besides of corresponding cations, probably
−
−
composed of polymeric perfluoridotitanate(IV) ([TiF
5
] )
∞
and/or ([Ti
2
F
9
] )
) = 2:1 and 1:1], the
][TiF
]·HF and
∞
anions. With
increasing amount of ethylenediammine or melamine [n(en/mel) : n(TiF
4
2
−
formation of [TiF
6
] anions is favored, resulting in aHF soluble products. The [enH
and most likely [melH ][TiF ]) salt and their solvated forms [enH ][TiF
melH ][TiF ]·HF can be recovered from such solutions.
On the basis of Raman spectra and crystallographic data we can assume that at least five
different phases ([enH ][TiF ], [enH ][TiF ]·HF, [enH ], [enH ][TiF ][Ti ],
]) exist in the en/TiF /aHF system and at least three ([melH ][TiF ]·HF,
], [melH ]) in the mel/TiF /aHF system.
2
6
]
(
[
2
6
2
6
2
6
2
6
2
6
2
]0.5[TiF
5
2
5
2 9
F
[
enH
2
]0.5[Ti
2
F
9
4
2
6
[
melH
2
]
0.5[TiF
5
2
]0.5[Ti
2
F
9
4
2
2

2 5
The [enH ]0.5[TiF ] compound represents the first example of structurally characterized
perfluoridotitanate(IV) phase with a double charged cation, where instead of the usual
2
−
octahedral [TiF
6
]
monomer, another kind of anion is present, i.e., polymeric chain-like
−
([TiF
5
] )
∞
.
Acknowledgements
Most of the syntheses and partial characterization were done by I.M.S. in the years
2
010–2016 at Jožef Stefan Institute during his Ph.D. study at Jožef Stefan International
Postgraduate School, Ljubljana, Slovenia. The authors acknowledge the financial support
from the Slovenian Research Agency (research core funding No. P1-0045, Inorganic
Chemistry and Technology).
Conflicts of interest
The authors declare no competing financial interest.
Appendix A. Supplementary data
Supplementary data associated with this article are available including crystal data,
refinement results, geometric parameters of perfluoridotitanate(IV) anions, and distances and
angles, associated with the hydrogen bonding.
CCDC 1885308 – 1885312 contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or
by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033.
1
2
3
4
. Doble charged organic cations template perfluoridotitanate(IV) compounds
. Polymeric ([TiF5]-)∞ anions as a counterions for a double charged cation
. Low-temperature modification of ethylenediaminium hexafluoridotitanate is determined
-
2-
. HF molecules form strong hydrogen bonds with F and [TiF
6
] anions
2
3

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