V. Pimenta et al. / Journal of Fluorine Chemistry 188 (2016) 164–170
169
Fig. 8. Evolution of the infrared spectra of [NH4]
ꢁ
(Zn4F5(amtetraz)4) 3H2O (4) after treatment at increasing temperatures under air atmosphere.
ꢁ
are consistent with the appearance of a crystalline intermediate
between 140 ꢀC and 280 ꢀC after the loss of NH4F and H2O. At high
temperature, ZnO is formed.
molecules are located. The loss of H2O and NH4F leads to a porous
neutral network with an expected ZnF(amtetraz) formula con-
taining unsaturated metal sites. The crystalline intermediate is
currently studied in order to determine its structure and to
evaluate the gas uptake capacity. Furthermore, we are currently
investigating the luminescence of these new materials as it is
already shown in Zn2+ hybrid materials [31]. Subsequent papers
will focus on these issues.
To evidence the presence and the elimination of ammonium
cations and water molecules in 4 on heating, IR spectra were
collected after heating at increasing temperatures under air and
cooling to room temperature. The spectra show two domains of
vibrational NꢂꢂH and OꢂꢂH energy [30]. The first domain between
3200 and 2810 cmꢂ1 and the second domain around 1400 cmꢂ1 are
respectively assigned to stretching vibrations and bending
vibrations (Fig. 8). When the heating temperature increases
several bands progressively disappear, which is in agreement
4. Experimental
4.1. Synthesis
+
with the elimination of the NH4 and H2O species. At 220 ꢀC, the
ammonium cations and water molecules are totally removed.
The starting reactants were ZnF2 (ꢃ99%, Alfa Aesar), 4%
hydrofluoric acid solution ‘4% HF’ (2.28 mol Lꢂ1) prepared from
‘40% HF’ (HF Riedel de Haen, 22.8 mol Lꢂ1), 5-aminotetrazole
The results obtained for
4 by thermal analyses and IR
spectroscopy confirm the existence of a crystalline intermediate
that is strongly structurally related to 4 after elimination of H2O
and NH4F. X-ray thermodiffraction shows that the structure is
globally maintained and a possible chemical formula for the
intermediate compound is ZnF(amtetraz). It can be assumed that
this phase contains unsaturated zinc coordination sites, known to
exacerbate gas adsorption; the theoretical porosity is estimated to
24%. In order to confirm this hypothetical formulation, the
structure is under determination by an ab initio approach and
complementary solid-state 19F NMR and BET studies are per-
formed. This work and the effect of the solvent on the network
topology will be discussed in a forthcoming of paper.
monohydrate ‘Hamtetraz H2O’ (99%, Alfa Aesar) and acetronitrile
ꢁ
solvent ‘ACN’ (Sigma–Aldrich, 19.0 mol Lꢂ1). All compounds were
solvothermally synthesized under autogenous pressure in Teflon-
lined Parr type autoclaves for 72 h. They were prepared from the
same starting mixture: ZnF2 (78 mg, 0.75 mmol), 4% HF (2.634 mL,
6 mmol), Hamtetraz H2O (78 mg, 0.75 mmol) and ACN (5 mL,
ꢁ
45 mmol) in molar proportions 1/8/1/60. Only the synthesis
temperature was changed to obtain four new complexes from
120 ꢀC to 140 ꢀC. All resulting products were washed with ACN,
filtered and dried at room temperature. For each preparation, X-ray
diffraction was used to find the known phases (EVA software) but
numerous peaks were not indexed. Then, crystals were selected to
identify the new phases. The comparison of simulated and
experimental diffraction patterns show that 1 and 2 are predomi-
nant at 120 ꢀC, 3 at 130 ꢀC and 4 at 140 ꢀC (Fig. S1). It must be noted
that in these conditions, no phase is pure: the crystalline powders
are a mixture of hybrid phases, contaminated with impurities,
3. Conclusion
This paper evidences the temperature effect on the network
dimensionality. In the case of hybrid fluorides associating zinc
cations and aminotetrazole, four new compounds with various
dimensionalities are identified for a narrow domain of synthesis
temperature (120–140 ꢀC): higher the temperature, higher the
network dimensionality and the aminotetrazole decomposition.
ZnF2, ZnF2
ꢁ
4H2O or [NH4] (ZnF3) issued from the aminotetrazole
ꢁ
decomposition at high temperature. In order to obtain pure phases,
several experiments were carried out in a CEM microwave oven
(MARS 5) and Teflon lined autoclaves at T = 160 ꢀC during 1 h.
[NH4]
ꢁ
(Zn4F5(amtetraz)4) 3H2O (4) displays an anionic 3D frame-
ꢁ
work with square cavities in which ammonium cations and water
Despite attempts to achieve phase purity for
1 and 2 by