with their neighbouring molecules. In such case, the NH3+ group
behaves as a molecular rotor at room temperature, but the
rotation may be eventually hindered at a lower temperature.5
Anilinium halides6 exhibit some unexpected crystallographic
features connected to the phase transitions. The infrared spectra
of anilinium chloride, bromide and iodide were measured at 295
K and at 83 K. While in the case of anilinium chloride6 there were
no changes at both temperatures, the spectra of the bromide and
the iodide exhibited changes indicating a phase transition. The
structure of anilinium bromide is orthorhombic above 298 K and
becomes monoclinic below 83 K. The crystal structure of anili-
nium iodide has not been studied using the X-ray diffraction
techniques, but both the room and the low temperature spectra
are very similar to the spectra of anilinium bromide.6,10 X-Ray,
neutron and NMR studies have shown that in the high-temper-
ature phase (space group Pccn, orthorhombic-phase I) of anili-
aqueous solutions (2 mol lꢀ1) of the pertinent inorganic acid. All
crystals crystallize from the pertinent solution of a 1 : 1 molar
ratio. The obtained colourless or slightly yellow solutions were
kept in the dark at room temperature. The prepared crystals were
filtered off and dried in air. The N-deuterated analogue of
an2SO4 (d-an2SO4) was prepared by repeated crystallization of
an2SO4 salt from D2O solutions kept in the desiccator over
KOH.
Single-crystal X-ray diffraction data of an2SeO4,
an2SeO4$2H2O and an2SO4 have been collected on a Oxford
Diffraction four-circle diffractometer Gemini with mirror-colli-
mated CuKa radiation and CCD detector Atlas. The phase
problem was solved by the direct methods (SIR2002, see ref. 22)
and the non-hydrogen atoms were refined anisotropically using
the full-matrix least-squares refinement (Jana2006, see ref. 23).
All the hydrogen atoms were discernible in the difference Fourier
maps and could be refined to a reasonable geometry. According
to a common practice the hydrogens were nevertheless kept in
ideal positions during the refinement. The isotropic atomic
displacement parameters of the hydrogen atoms were evaluated
+
nium bromide the NH3 group is disordered over two alternate
positions with an equal probability and it becomes ordered in the
low-temperature phase (P21/c, monoclinic-phase II).6,11 The
orientational ordering of the molecular group directs the freezing
of a phonon mode near the phase transition.12
ꢂ
ꢂ
as 1.2Ueq of the parent atom (C–H ¼ 0.96 A and N–H ¼ 0.87 A).
The basic crystallographic data, information about measurement
and refinement details are summarised in Table 1.†
The salts of selenic acid13 form a broad family of hydrogen
bonded crystals which have been intensively studied by struc-
tural, spectroscopic, optical, dielectric and thermal methods.14–16
For instance, the compound with the complex hydrogen bond
network, tetrakis(2,4,6-triamino-1,3,5-triazin-1-ium) bis(sele-
nate) trihydrate,8 with symmetry P1 possesses the second
harmonic generation efficiency deff ¼ 0.4dKDP (KDP; i.e.
KH2PO4). Since the influence of the strong hydrogen bonds17 on
the nonlinear optical properties of the molecule can be consid-
ered, the vibrational spectra can be helpful in the elucidation of
the role of such hydrogen bonds in the crystals exhibiting
nonlinear optical properties.
The infrared spectra were recorded using DRIFTS and nujol
mull (KBr windows) techniques on a Nicolet 6700 FTIR spec-
trometer with 2 cmꢀ1 resolution and Happ–Genzel apodization
in the 400–4000 cmꢀ1 region.
The Raman spectra of the polycrystalline samples of all the
compounds were recorded on a Labram HR spectrometer
(Horiba Jobin Yvon) interfaced to an Olympus microscope
(objective 50ꢁ). The power of He–Ne laser (633 nm) impinging
on the sample was between 1 and 3 mW. The spectrometer was
calibrated by the F1g mode of Si at 520.2 cmꢀ1, and the resolution
The basic step in the crystal engineering process of these NLO
materials is selection of the appropriate organic molecule. This
work follows up the study of materials for the second-harmonic
generation (SHG) based on hydrogen-bonded salts of organic
cations, amino-1,2,4-triazolium18,19 and biguanidium,20,21 and
deals with the systems capable of forming an intermolecular
hydrogenbond variety. Our effortwas applied to finalize the study
of the novel inorganic salts of anilinium and to determine the non-
linear optical properties for compounds known in the literature.
Novel salts of anilinium—anilinium selenate (an2SeO4) and
anilinium selenate dihydrate (an2SeO4$2H2O)—have resulted
from the search for such materials. Unfortunately, the anilinium
selenate dihydrate (an2SeO4$2H2O) is centrosymmetric and
therefore not suitable for the second harmonic generation. The
prepared hydrogen-bonded salts were studied by the single-
crystal X-ray diffraction, FTIR and Raman spectroscopies, the
differential scanning calorimetry and the second harmonic
generation measurements. The aim of the present work was also
to determine the efficiency of the second harmonic generation of
other anilinium salts—anilinium sulfate (an2SO4) and anilinium
chloride (anCl) for the first time.
of the spectrometer was about 1 cmꢀ1
.
Low-temperature FTIR and FT Raman measurements were
carried out on a Nicolet 6700 FTIR spectrometer equipped with
FT Raman Nexus module in a low-temperature cell cooled by
liquid nitrogen in the 298–100 K interval. The temperature was
controlled by a Fe-Const. thermocouple. The analog signal was
processed on a PC using the AX5232 temperature measurement
board. The nujol mull method with KBr windows was used for
FTIR spectra recording.
The DSC measurements were carried out on Perkin Elmer
Pyris Diamond DSC and DSC 7 instruments in the 93–453 K
temperature region (nitrogen or helium atmosphere—20 ml
minꢀ1). For each of the compounds, a heating or cooling rate of
10 K minꢀ1 was applied to measure approximately 20 mg of
a finely ground sample placed in hermetically sealed aluminium
pans.
The UV-Vis spectra of aqueous solutions of an2SeO4,
an2SeO4$2H2O, and an2SO4 were recorded in the 190–800 nm
range using a Lambda 19 UV/Vis/NIR spectrometer, Perkin
Elmer.
SHG measurements were performed using a Q-switched Nd–
YAG laser (6 ns pulses at 20 Hz, l ¼ 1064 nm). For the quan-
titative determination of the SHG efficiency, the intensity of the
transmitted laser light at 532 nm generated in the sample was
measured by a photomultiplier and a boxcar averager and the
signal was compared with that one generated in KDP. For
Experimental
Crystals of an2SeO4, an2SeO4$2H2O, an2SO4 and anCl were
prepared from solutions obtained by addition of aniline to
4132 | CrystEngComm, 2011, 13, 4131–4138
This journal is ª The Royal Society of Chemistry 2011