Supporting information Inorganic Anion Regulates the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules

Inorganic Anions Regulate the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules


Introduction
From both theoretical and applied viewpoints, phase-transition compounds are popular and valuable in increasing the general understanding of structure-property relations and exploring functional materials with novel physical properties [1][2][3][4][5][6][7][8][9][10].Phase-transition crystalline materials are usually accompanied by an abrupt change in some physical properties around the transition temperature.These materials show great applications in molecular sensors, switches, and data storage devices [11][12][13][14][15].In particular, energy harvesting occurs during phase changes; thus, phase-transition materials may serve as energy-saving materials.Designing special inorganic-organic hybrid compounds with molecular dielectrics is an effective method for synthesizing ideal phase-transition materials [16][17][18][19].
Phase-transition inorganic-organic hybrid compounds display novel crystal structures and interesting physical properties, including ferroelectric, dielectric, optical, and piezoelectric properties [20][21][22][23][24].Among them, 15-crown-5 or 18-crown-6 are good candidates, owing to their variable conformation, such as [(RNH 3 )(18-crown-6)][A], where R is an alkyl or aryl group, and A is an anion.The driving force of these phase-transition compounds can be ascribed to the motional changes in the R-NH 3 + guest cation (R = aryl group) or/and anionic units.The use of the R group as a molecular rotor or pendulum unit produces desirable properties [25][26][27][28][29].As a result, the motion of organic ammonium cations changes their dynamic state.This alteration further leads to dielectric changes and ferroelectricity through the phase transitions between the disordered high-temperature phase (HTP) and ordered low-temperature phase (LTP) [30][31][32][33].On the contrary, the asymmetric unit of the supramolecular adduct also contains counter anions.These anions are primarily tetrahedral ions, such as BF 4 − , ClO 4 − , and IO 4 − .These anions easily change position with varied temperatures and weak interactions, because of their higher symmetry and relatively small volume [34,35].In fact, inorganic anions (such as HSO 4 − ) have rarely been explored.Given these findings, in this work we report the syntheses of (4-HNA)(18-crown-6)(HSO 4 ) ( 1) and (4-HNA) 2 (18-crown-6) 2 (PF 6 ) 2 (CH 3 OH) (2) to determine other suitable geometric anions that can regulate a potential phase transition.The structures, phase transitions, and dielectric properties of the two anions are revealed in Scheme 1.

Crystal Structure of 1
The crystal structure of 1 was characterized at different temperatures by X-ray diffraction to confirm whether the phase transition was associated with structural changes.Compound 1 crystallized in the monoclinic space group P21/c with a = 10.450( 6

Crystal Structure of 1
The crystal structure of 1 was characterized at different temperatures by X-ray diffraction to confirm whether the phase transition was associated with structural changes.Compound 1 crystallized in the monoclinic space group P2  1).The crystal structures of 1 are similar between the LTP and HTP structures.This result reveals that the asymmetric unit was composed of one cationic [(4-HNA)(18-crown-6)] + moiety and one anionic HSO 4 − (Figure 1a).The 4-HNA cations were connected to the 18-crown-6 ring to form a supramolecular rotator-stator structure through N-H•  S1).The π-plane of the 4-HNA cation was nearly perpendicular to the mean plane of the oxygen atoms.The N 1 atom of the 4-HNA cations was located higher than the best plane of the oxygen atoms of the crown ring, rather than in the nesting position (Figure 1a).The dihedral angles between the aromatic ring and the crown ether ring were 92.48 • (100 K) and 93.47 • (296 K).In Figure 1b  The crystal structures of 1 are similar between the LTP and HTP structures.This result reveals that the asymmetric unit was composed of one cationic [(4-HNA)(18-crown-6)] + moiety and one anionic HSO4 -(Figure 1a).The 4-HNA cations were connected to the 18-crown-6 ring to form a supramolecular rotator-stator structure through N-H⋯O interactions between the -NH3 + group and the six O (O1, O2, O3, O4, O5, and O6) atoms of 18-crown-6.The average hydrogen-bonding N-O distances of 2.874 and 2.888 Å at 100 K and 296 K, respectively, were almost the same to those of the standard NH3 ﹢ ⋯O distance for the crown ether molecular-based system (Table S1).The π-plane of the 4-HNA cation was nearly perpendicular to the mean plane of the oxygen atoms.The N1 atom of the 4-HNA cations was located higher than the best plane of the oxygen atoms of the crown ring, rather than in the nesting position (Figure 1a).The dihedral angles between the aromatic ring and the crown ether ring were 92.48° (100 K) and 93.47° (296 K).In Figure 1b, the packing diagram of complex 1 is located along the a+c axis.The packing diagram for the LTP (100 K) indicates that the dimer structure of the two HSO4 -anions is linked by O-H⋯O hydrogen bonds that fill in the space to form four [(4-HNA)(18-crown-6)] + supramolecular cations.In addition, the O-H⋯O hydrogen-bonding interaction becomes stronger than the N-H⋯O hydrogen bonds with bond distances of 2.647 Å and 2.657 Å at 100 K and 296 K, respectively.This finding indicates that the movement of H protons was more difficult between the donor (O11) and acceptor atoms (O10).The most significant differences between the structures at 296 K and 100 K were the distances of the two crown ether rings.Compared with the distances at 100 K, those at 296 K changed from 4.208 Å to 4.063 Å. C-H⋯π interactions were noted in the [(4-HNA)(18-crown-6)] + complex cations.The aromatic rings formed two C-H⋯π interactions with distances of 3.195 Å at 100 K and 3.267 Å at 296 K (Figure 2).

Crystal Structure of 2
The crystal structure of 2 was analyzed in HTP (296 K) and LTP (100 K) forms.When the HSO4 - anion was replaced with the PF6 -anion, compound 2 at both 296 K and 100 K crystallized in the monoclinic system with the same space group P21/c.Although the temperature changed, the space group of crystal 2 remained unchanged.Hence, no structural symmetry breaking occurred in this

Crystal Structure of 2
The crystal structure of 2 was analyzed in HTP (296 K) and LTP (100 K) forms.When the HSO 4 − anion was replaced with the PF 6 − anion, compound 2 at both 296 K and 100 K crystallized in the monoclinic system with the same space group P2 1 /c.Although the temperature changed, the space group of crystal 2 remained unchanged.Hence, no structural symmetry breaking occurred in this temperature range.Crystallographic data and details on the collection and refinement for 296 K and 100 K are listed in Table 1.
In contrast to the ordered HSO 4 − anions in 1, the PF 6 − anions in 2 were disordered at both 100 K and 296 K.The molecular structure of 2 with atomic labeling is shown in Figure 3a.The disordered PF 6 − anion and methanol molecules filled the structure between neighboring supramolecular cations (Figure 3b).

Crystal Structure of 2
The crystal structure of 2 was analyzed in HTP (296 K) and LTP (100 K) forms.When the HSO4 - anion was replaced with the PF6 -anion, compound 2 at both 296 K and 100 K crystallized in the monoclinic system with the same space group P21/c.Although the temperature changed, the space group of crystal 2 remained unchanged.Hence, no structural symmetry breaking occurred in this temperature range.Crystallographic data and details on the collection and refinement for 296 K and 100 K are listed in Table 1.
The asymmetric unit of compound 2 consisted of two independent [(4-HNA)(18-crown-6)] + supramolecular cations, two PF6 -anions, and one methanol molecule at 296 K and 100 K (Figure 3a).In contrast to the ordered HSO4 -anions in 1, the PF6 − anions in 2 were disordered at both 100 K and 296 K.The molecular structure of 2 with atomic labeling is shown in Figure 3a.The disordered PF6 - anion and methanol molecules filled the structure between neighboring supramolecular cations (Figure 3b).The most striking structural features in the LTP and HTP forms were the distances of the two crown ether rings.The distances of crystal 2 from the neighboring [(4-HNA)(18-crown-6)] + supramolecular cations were 8.877 Å (100 K) and 9.082 Å (296 K) (Figure 4).Interestingly, it was found that obvious disorder phenomena occur in the HTP phase of the -NO2 group.The O14, O15, O16, O17 atoms of -NO2 group in supramolecular cations are distinctly disordered and occupy two sites (O14A, O14B, O15A, O15B, O16A, O16B, O17A, O17B).The occupation factors of oxygen atoms of -NO2 group are displayed in Table S2, suggesting that biased -NO2 group orientation was achieved in compound 2 (Fig 4b).The -NH3 ﹢ group resided in a perching position, and attained a configuration similar to that of crystal 1; the group was linked by the oxygen atoms of the crown ethers through The most striking structural features in the LTP and HTP forms were the distances of the two crown ether rings.The distances of crystal 2 from the neighboring [(4-HNA)(18-crown-6)] + supramolecular cations were 8.877 Å (100 K) and 9.082 Å (296 K) (Figure 4).Interestingly, it was found that obvious disorder phenomena occur in the HTP phase of the -NO  S2, suggesting that biased -NO 2 group orientation was achieved in compound 2 (Figure 4b).The -NH 3 + group resided in a perching position, and attained a configuration similar to that of crystal 1; the group was linked by the oxygen atoms of the crown ethers through the six N-H• • • O hydrogen bonds.Apparent hydrogen bonding interactions occurred between the nitrogen and oxygen atoms with bond lengths of 2.821-2.956Å and 2.816-2.966Å at 100 K and 296 K, respectively (Table S3).In crystal 2, the distance between two adjacent crown ether rings was nearly twice as long as that in crystal 1 at 100 K and 296 K (Figure 4).In crystal 1, the dimer structure of two HSO 4 − anions occupied a larger space volume, resulting in a relatively closer packing pattern for the [(4-HNA)(18-crown-6)] + supramolecular cation.Furthermore, no C-H• • • π interactions existed in the supramolecular cations.However, weak π• • • π interactions were found between the aromatic rings of the [(4-HNA)(18-crown-6)] + supramolecular cations.These interactions stabilized the crystal packing and formed the alternated inorganic-organic hybrid structure in the bc plane (Figure S1).
nearly twice as long as that in crystal 1 at 100 K and 296 K (Figure 4).In crystal 1, the dimer structure of two HSO4 − anions occupied a larger space volume, resulting in a relatively closer packing pattern for the [(4-HNA)(18-crown-6)] + supramolecular cation.Furthermore, no C-H⋯π interactions existed in the supramolecular cations.However, weak π⋯π interactions were found between the aromatic rings of the [(4-HNA)(18-crown-6)] + supramolecular cations.These interactions stabilized the crystal packing and formed the alternated inorganic-organic hybrid structure in the bc plane (Figure S1).

Differential Scanning Calorimetry
Differential scanning calorimetry (DSC) is commonly used to detect whether a compound displays a phase transition triggered by temperature.This approach is also used to confirm the existence of a heat anomaly during heating and cooling.When a compound undergoes a structural phase transition with a thermal entropy change, reversible heat anomalies are detected during heating and cooling.In the DSC spectrum obtained from crystal 1, a main endothermic peak and a main exothermic peak were observed at heating of 257 K and cooling of 252 K, respectively, with a 5 K hysteresis width (Figure 5a).These exothermic and endothermic peaks clearly reveal the occurrence of a reversible phase transition.The entropy change (∆S) of the phase transition was too low to be estimated from the DSC.The wide heat hysteresis and peak shapes reflect the characteristics of a first-order phase transition.The driving force of the phase transition was confirmed by evaluating the crystal structure across varying temperatures.For example, apparent differences were observed for the distances of two crown ether rings, with values of 4.063 Å at 100 K and 4.208 Å at 296 K. Additionally, the dihedral angle between the aromatic ring and the crown ring slightly changed from 92.48° in the LTP form to 93.47° in the HTP form.
Compared with the DSC measurements for crystal 1, those for crystal 2 were conducted within the temperature range 240-320 K, and revealed two anomalies at 266 K (heating) and 261 K (cooling) (Figure 5b).The thermal hysteresis was about 5 K, and the entropy change (∆S) of the phase transition was also too low to be estimated from the DSC.The almost non-existent hysteresis and small heat anomalies clearly reflect the continuous characteristic of the phase transition and thus effectively show features of a second-order phase transition.The distances of neighboring [(4-HNA)(18-crown-6)] + supramolecular cations were 8.877 Å (100 K) and 9.082 Å (296 K) for crystal 2. For these reasons, crystals 1 and 2 both revealed reversible phase transitions despite containing different anions.This finding implies that the phase transition may have originated from the [(4-HNA)(18-crown-6)] + supramolecular cations, a finding observed in similar compounds.

Differential Scanning Calorimetry
Differential scanning calorimetry (DSC) is commonly used to detect whether a compound displays a phase transition triggered by temperature.This approach is also used to confirm the existence of a heat anomaly during heating and cooling.When a compound undergoes a structural phase transition with a thermal entropy change, reversible heat anomalies are detected during heating and cooling.In the DSC spectrum obtained from crystal 1, a main endothermic peak and a main exothermic peak were observed at heating of 257 K and cooling of 252 K, respectively, with a 5 K hysteresis width (Figure 5a).These exothermic and endothermic peaks clearly reveal the occurrence of a reversible phase transition.The entropy change (∆S) of the phase transition was too low to be estimated from the DSC.The wide heat hysteresis and peak shapes reflect the characteristics of a first-order phase transition.The driving force of the phase transition was confirmed by evaluating the crystal structure across varying temperatures.For example, apparent differences were observed for the distances of two crown ether rings, with values of 4.063 Å at 100 K and 4.208 Å at 296 K. Additionally, the dihedral angle between the aromatic ring and the crown ring slightly changed from 92.48 • in the LTP form to 93.47 • in the HTP form.

Dielectric Property
The variable-temperature dielectric response is another common method for studying phase transitions, especially at relatively high frequency ranges.This method is useful for identifying phase transitions.The temperature-dependent dielectric constant of the powder samples of crystals 1 and 2 were presented at four selected frequencies, namely, 5 KHz, 10 KHz, 100 KHz, and 1 MHz.Strong and significant dielectric anomalies were observed around the Tc.For crystal 1, the dielectric constant slowly increased with rising temperature below 250 K (Figure 6a).Interestingly, when the temperature neared 255 K, the dielectric constant sharply increased to a maximum value of 22.5 at 5 KHz.Then, the dielectric constant abruptly decreased and achieved a minimum value of 11.91 at about 265 K.The sharp peak-like dielectric anomaly further confirms the phase transition in 1, which is consistent with the DSC result.
For crystal 2, the dielectric constant slowly increased, with an abrupt slope at around 265 K during heating (Figure 6b).The maximum dielectric constant value was about 8.14 at 5 KHz; this value corresponds to a high dielectric state.The dielectric constant of 2 achieved a sudden rapid Compared with the DSC measurements for crystal 1, those for crystal 2 were conducted within the temperature range 240-320 K, and revealed two anomalies at 266 K (heating) and 261 K (cooling) (Figure 5b).The thermal hysteresis was about 5 K, and the entropy change (∆S) of the phase transition was also too low to be estimated from the DSC.The almost non-existent hysteresis and small heat anomalies clearly reflect the continuous characteristic of the phase transition and thus effectively show features of a second-order phase transition.The distances of neighboring [(4-HNA)(18-crown-6)] + supramolecular cations were 8.877 Å (100 K) and 9.082 Å (296 K) for crystal 2. For these reasons, crystals Crystals 2017, 7, 224 6 of 9 1 and 2 both revealed reversible phase transitions despite containing different anions.This finding implies that the phase transition may have originated from the [(4-HNA)(18-crown-6)] + supramolecular cations, a finding observed in similar compounds.

Dielectric Property
The variable-temperature dielectric response is another common method for studying phase transitions, especially at relatively high frequency ranges.This method is useful for identifying phase transitions.The temperature-dependent dielectric constant of the powder samples of crystals 1 and 2 were presented at four selected frequencies, namely, 5 KHz, 10 KHz, 100 KHz, and 1 MHz.Strong and significant dielectric anomalies were observed around the T c .For crystal 1, the dielectric constant slowly increased with rising temperature below 250 K (Figure 6a).Interestingly, when the temperature neared 255 K, the dielectric constant sharply increased to a maximum value of 22.5 at 5 KHz.Then, the dielectric constant abruptly decreased and achieved a minimum value of 11.91 at about 265 K.The sharp peak-like dielectric anomaly further confirms the phase transition in 1, which is consistent with the DSC result.
For crystal 2, the dielectric constant slowly increased, with an abrupt slope at around 265 K during heating (Figure 6b).The maximum dielectric constant value was about 8.14 at 5 KHz; this value corresponds to a high dielectric state.The dielectric constant of 2 achieved a sudden rapid increase at room temperature.Compound 2 attained small DSC and dielectric anomalies at about 265 K; this pattern is a feature of a second-order phase transition.The relatively weak dielectric anomaly of crystal 2 relative to that of 1 is presented in the temperature ranges.This finding is probably due to the unchanged electric polarizations of ions and molecules in the crystal lattice.
The temperature-dependent dielectric response of compound 1 and 2 both display one sharp peak-like anomaly upon heating at 255 K and 265 K, respectively.However, there is no distinct dielectric anomaly for 1 and 2 upon cooling.For the cooling and heating processes, the DSC curves for the two crystals exhibit relatively weak exothermic and endothermic peaks.Phase transition occurs in compound 1 and 2, thus leading to dielectric anomalies with the increase in temperature.Because crystal 1 and 2 have undergone phase transitions of temperature variation once with the structural changes, there is no distinct dielectric response with the decrease in temperature.
The variable-temperature crystal structures of 1 and 2 reveal that the phase transition and dielectric anomaly in the same temperature range may be caused by the structural interactions and different crystal packing patterns in the LTP and HTP forms.Crystals 1 and 2 achieved significant differences at 296 K and 100 K, i.e., the distances between the two adjacent crown rings of 2 were 8.877 Å (100 K) and 9.082 Å (296 K).These distances were larger than the values of 4.063 Å (100 K) and 4.208 Å (296 K) in 1.This finding suggests that the inorganic anion tunes the crystal and hence affects the phase-transition points and types.

Materials and Instrument
The chemicals and solvents employed in this work were commercially obtained as chemically pure and used without any further purification.Infrared (IR) spectra were obtained using an Affinity-1 spectrophotometer and KBr pellets in the 4000-400 cm −1 region.Thermogravimetric

Materials and Instrument
The chemicals and solvents employed in this work were commercially obtained as chemically pure and used without any further purification.Infrared (IR) spectra were obtained using an Affinity-1 spectrophotometer and KBr pellets in the 4000-400 cm −1 region.Thermogravimetric analyses (TGA) were performed with a SHIMADZU DTG-60 thermal analyzer in a nitrogen atmosphere from room temperature to 800 K with a heating rate of 10 K/min using aluminum crucibles (Figures S2 and  S3).Elemental analyses were conducted using a Vario EL Elementar Analysensysteme GmbH at the TRW Research Collaboration Center, YanZhou, Shandong.DSC measurements were performed by heating and cooling the samples (16 mg) within the temperature range 210-280 K on a TA Q2000 DSC instrument under nitrogen.Meanwhile, the crystal dielectric constants were measured with a TH2828 Precision LCR meter within the frequency range of 500 Hz-1 MHz, applied voltage of 1.0 V, and temperature sweeping rate of approximately 2 K/min.
X-ray single crystal diffraction: X-ray diffraction experiments were conducted on crystals 1 and 2 using a Bruker CCD diffractometer with Moka radiation (λ = 0.71073 Å) at 100 K and 296 K.The structures of 1 and 2 were elucidated by direct methods and refined by the full-matrix method based on F 2 using the SHELXL 97 software package.All non-hydrogen atoms were anisotropically refined, and the positions of all hydrogen atoms were geometrically generated.CCDC:1529205 (100 K), CCDC:1529207 (296 K) for 1 and CCDC:1529231 (100 K), CCDC:1529232 (296 K) for 2 contain the supplementary crystallographic data for this paper.These data can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif.

Preparation of Compound (4-HNA)(18-crown-6)(HSO 4 ) (1)
Yellow crystals 1 were obtained by evaporating an alcohol solution containing 4-nitroaniline (20 mg), H 2 SO 4 (50 mg), and 18-crown-6 (200 mg) at room temperature for 5 days to a 52% yield (based on 4-nitroaniline).The calculated percentage compositions of C, H, and N for C 18 H 32 N 2 O 12 S were 43.19% C, 6.44% H, and 5.60% N, respectively, whereas the measured percentage compositions were 43.11%, 6.42% H, and 5.76% N, respectively.The IR spectrum of the single crystal 1 is given in Figure S4.Single crystals of 2 were prepared by slowly evaporating a mixture of HPF 6 (50 mg), 4-nitroaniline (20 mg), and 18-crown-6 (200 mg) in methanol solution (50 mL).The methanol solution was allowed to stand for approximately 5 days under room temperature.The single crystals of salt 2 were colorless transparent crystals obtained at 58% yield.The calculated percentage compositions of C, H, and N for C 37 H 66 F 12 N 4 O 17 P 2 were 39.37% C, 5.89% H, and 4.96% N, respectively, whereas the measured percentage compositions were 39.35% C, 5.87% H, and 4.89% N, respectively.The IR spectrum (KBr) of the single crystal 2 is presented in Figure S5.

Conclusions
Two inorganic-organic hybrid crystals based on the [(4-HNA)(18-crown-6)] + supramolecular cation were reported in this study.Variable-temperature crystal structure analyses and thermal measurements (DSC) showed that crystals 1 and 2 exhibited similar crystal packings and underwent reversible phase transitions at 255 K and 265 K, respectively.The dielectric anomalies of crystals 1 and 2 in the temperature-frequency ranges further confirmed the existence of such phase transitions.These results indicated that the phase transitions may be caused by the [(4-HNA)(18-crown-6)] + supramolecular cations.The inorganic anions (PF 6 − and HSO 4 − ) played an important role in the crystal packing and regulated the phase-transition points and types.

Figure 1 .
Figure 1.Crystal structure of crystal 1 at 100 K. (a) Asymmetric unit for crystal 1, dashed lines indicate hydrogen bonds; (b) Unit cell of crystal 1 viewed along the a + c axis.Most hydrogen atoms on carbon atoms are omitted for clarity.

Figure 1 . 10 Figure 2 .
Figure 1.Crystal structure of crystal 1 at 100 K. (a) Asymmetric unit for crystal 1, dashed lines indicate hydrogen bonds; (b) Unit cell of crystal 1 viewed along the a + c axis.Most hydrogen atoms on carbon atoms are omitted for clarity.Crystals 2017, 7, 224 4 of 10

Figure 2 .
Figure 2. Arrangement of the supramolecular cations in 1 at 100 K (a) and 296 K (b) viewed in the a+c plane; the dashed lines show the C-H• • • π interactions.

Figure 2 .
Figure 2. Arrangement of the supramolecular cations in 1 at 100 K (a) and 296 K (b) viewed in the a+c plane; the dashed lines show the C-H⋯π interactions.

Figure 3 .
Figure 3. Asymmetric unit (a) and packing diagram (b) of crystal 2 viewing along the a-axis at 100 K and 296 K.Most of the hydrogen atoms on the carbon atoms are omitted for clarity.

Figure 3 .
Figure 3. Asymmetric unit (a) and packing diagram (b) of crystal 2 viewing along the a-axis at 100 K and 296 K.Most of the hydrogen atoms on the carbon atoms are omitted for clarity.
2 group.The O 14 , O 15 , O 16 , O 17 atoms of -NO 2 group in supramolecular cations are distinctly disordered and occupy two sites (O 14A , O 14B , O 15A , O 15B , O 16A , O 16B , O 17A , O 17B ).The occupation factors of oxygen atoms of -NO 2 group are displayed in Table

Figure 4 .
Figure 4. Arrangement of the supramolecular cations in 2 at 100 K (a) and 296 K (b) viewed along the a-axis; the dashed lines show the distance of the adjacent two crown ether rings.

Figure 4 .
Figure 4. Arrangement of the supramolecular cations in 2 at 100 K (a) and 296 K (b) viewed along the a-axis; the dashed lines show the distance of the adjacent two crown ether rings.

Figure 5 .
Figure 5. DSC curves of crystal 1 (a) and crystal 2 (b) in a heating-cooling cycle.

Figure 5 .
Figure 5. DSC curves of crystal 1 (a) and crystal 2 (b) in a heating-cooling cycle.

Figure 6 .
Figure 6.Dielectric properties for crystal 1 (a) and 2 (b) measured as a function of temperature under a frequency of 5 KHz to 1 MHz.

Figure 6 .
Figure 6.Dielectric properties for crystal 1 (a) and 2 (b) measured as a function of temperature under a frequency of 5 KHz to 1 MHz.

Table 1 .
Crystallographic data and structural refinement details for 1 and 2.