Paper
CrystEngComm
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(1) and [C3N2H5 ]2[I422] (3) including preparation, crystal
instrument in the temperature range 300–700 K with a ramp
rate 2 K min21 the scans was performed in flowing nitrogen
(flow rate: 1 dm3 h21).
The complex electric permittivity, e* = e9 2 ie99 was measured
between 100 and 290 K by the Agilent E4980A Precision LCR
Meter in the frequency range between 135 Hz and 2 MHz. The
overall error was less than 5%. The single crystal samples had
dimensions ca. 2 6 2 6 0.5 mm3. Silver electrodes were
printed on opposite faces. The dielectric measurements were
carried in a controlled atmosphere (N2).
structures in various phases, thermal and dielectric properties.
Structural characterization is presented also for
a new
substituted imidazolium compound; [C3N2H3I2 ][I2] (2). The
molecular motions in (1) and (3) are studied by means of
proton magnetic resonance measurements (1H NMR) (for
+
more information, see ESI ). The molecular mechanism of the
phase transitions in the crystals under investigation is also
proposed.
3
Single crystal X-ray diffraction crystallographic data were
collected on a KM4 diffractometer with CCD detector and
graphite-monochromated Mo Ka radiation (l = 0.71073 Å).
Low temperature was maintained using an open flow unit
(Oxford Cryosystem). The CrysAlis software version 1.171.32
was used for data processing.13 An empirical absorption
correction was applied using spherical harmonics implemen-
ted in SCALE3 ABSPACK scaling algorithm. The structure was
solved by direct methods and refined against F2 by means of
SHELX-97 program package.14 All non-hydrogen atoms were
refined anisotropically. H atoms were included in geometric
positions and treated as riding atoms. The Uiso(H) were
constrained to be xUeq (carrier atom), where x = 1.2.
Structural phase transitions observed with temperature
lowering led to twinning of the (1) and (3) crystals. In (3)
symmetry changed from orthorhombic to monoclinic which
resulted in crystal twinning with two dominating domains,
with partially overlapped diffraction peaks. Refinement of the
structure was performed using the data from both domains
and HKLF 5 instruction.
In the case of (1) two structural transformations were
encountered. During the cooling cycle the crystal symmetry
changed from trigonal to triclinic (at 180 K) and with further
cooling to a monoclinic one (113/123 K cooling–heating).
Lowering of the crystal class led to non-merohedral twinning
of the sample. Six triclinic crystal domains were encountered
at 150 K from the splitting of diffraction peaks. Partial
overlapping of the peaks together with weak intensities did
not allow satisfactory indexing, thus the crystal structure of
this intermediate phase has not been determined. Below 113 K
the symmetry of (1) increased to monoclinic and the number
of domains was reduced to three. The structure refinement
was based on the diffraction intensities from one dominating
crystal domain, indexing 60% of the measured diffraction
peaks. All peaks were completely separated. Table 1 contains
crystal data and structure refinement results of measured
crystals.
Experimental section
Materials and instrument
Synthesis of the complexes. All compounds were obtained in
the reaction between imidazole amine and iodic acid, however,
both synthesis-reactions were carried out in different condi-
tions (temperature and molar ratio) applied for each com-
pound.
(1) crystals were prepared at ambient temperature by
dissolving imidazole in the 20% HI solution. Single crystals
were grown by slow evaporation from the solution. The
crystalline product was twice recrystallized. Single transparent
crystals were grown by slow evaporation from an aqueous
solution and characterized by an elemental analysis: C: 18.37%
(theor. 18.39%), N: 14.25% (theor. 14.29%), H 2.49% (theor.
2.57%).
(2) crystals were prepared by dissolving imidazole in the
20% HI solution. Subsequently, the mixture was stirred (at 320
K for about 30 min). After a few days, tiny minuscule
transparent solids were formed by a slow evaporation from
the colorless solution. Nevertheless, due to small amounts of
obtained material (only X-ray diffraction measurements were
undertaken) we were not able to make the physicochemical
characterization of this material. We obtained successfully the
4,5-diiodoimidazolium iodide crystals only during the first
crystallization. The following crystallization produced exclu-
sively the (1) crystals.
(3) crystals were prepared at ambient temperature by
dissolving imidazole in concentrated (57%) HI. Single crystals
were grown by slow evaporation from the solution. The dark,
navy blue, needle like crystals were characterized by an
elemental analysis: C: 11.18% (theor. 11.16%), N: 8.55%
(theor. 8.68%), H 1.59% (theor. 1.56%).
General details
All the solvents and starting materials for the synthesis were
purchased commercially and were used as received.
DSC traces were obtained using a Perkin Elmer model 8500
differential scanning calorimeter calibrated using n-heptane
and indium. Hermetically sealed Al pans with the polycrystal-
line material were prepared in a controlled-atmosphere N2
glovebox. The measurements were performed between 100 and
470 K. The thermal hysteresis was estimated from the scans
performed at various rates (20, 10 and 5 K min21) extrapolated
Results and discussion
Thermal properties
The DSC runs of (1) (Fig. 1(a)) revealed two PTs at 180/185 K
and 113/123 K (cooling–heating) of the first order type. The
PTs are reversible, however, the enthalpy effects differ on
cooling and heating significantly. The entropy values were
estimated to be ca. 7 J mol21 K21 for the I « II PT and 2 J
to
a
scanning rate of
0
K
min21
.
Simultaneous
Thermogravimetric Analysis (TGA) and Differential Thermal
Analysis (DTA) were performed on a Setaram SETSYS 16/18
5634 | CrystEngComm, 2013, 15, 5633–5640
This journal is ß The Royal Society of Chemistry 2013
Weclawik, Magdalena
