Structure, Growth and Characterization of Ammonium 5-Sulfosalicylic Acid Monohydrate Crystal①

LV Yng-Yng YE Li-Wng XU Zhi-Hung CAO You-Jie SU Gen-Bo ZHUANG Xin-Xin②

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Structure, Growth and Characterization of Ammonium 5-Sulfosalicylic Acid Monohydrate Crystal①

LV Yang-Yanga, bYE Li-WangaXU Zhi-HuangaCAO You-Jiea, bSU Gen-BoaZHUANG Xin-Xina②

a(350002)b(100039)

Ammonium 5-sulfosalicylic acid monohydrate (NH4·C7H5O6S·H2O, ASSA) was synthesized and optical grade crystal with dimensions of 45mm × 20mm× 18mmwas obtained from aqueous solution by the cooling solution method. The crystal structure was confirmed by X-ray single-crystal diffraction method and the empirical composition is C7H11NO7S with formula weight 253.23. The crystal belongs to monoclinic space group21/with= 11.884(9),= 7.306(5),= 12.152(9) ?,= 104.851(13)°,= 1019.8(13) ?3,= 4,D= 1.649 g/cm3,= 0.340 mm-1,(000) = 528, the final= 0.0307 and= 0.0866 for 7494 observed reflections (> 2()).Elemental analysis, IR and1H-NMR spectrum were used to characterize the compound. Thermal analysis showed that one coordination water molecule was contained and dehydration temperature of ASSA crystal was 106℃. Optical transmission and fluorescence spectrum revealed that the ASSA crystal exhibited a strong absorption in ultraviolet region with the sharp absorption edge located at 340 nm and a significant blue fluorescent emission band at 442 nm.

ammonium 5-sulfosalicylic acid monohydrate, crystal growth, crystal structure, fluorescence spectrum;

1 INTRODUCTION

Recently, as a kind of salicylic derivatives, 5-sulfo- salicylic acid (C7H6O6S·2H2O, H3SSA) is currently of increasing interest not only due to its structural but also due to its biological applications, spectroscopic behavior and proton conductivity[1-7]. As a kind of organic ligand, H3SSA possesses three substituent groups: -COOH, -SO3H and -OH, which make it prove a particularly useful synthon for molecular assembly through hydrogen bonding associations. In the H3SSA anion formed in the reaction with Lewis bases, all of these substituent groups provide hydrogen-bonding donor or acceptor atoms with potential for primary, secondary and tertiary structure extension[8]. In addition, H3SSA possesses endogenous fluorescence[9]and good solubility in water, so it is often used as indicator and color developing reagent of fluorescence me- thod, for example as fluorescent indicator to de- termine the amount of lanthanum, terbium and europium[10]. Moreover, some of the functional deri- vatives from H3SSA have been reported, which possess special fluorescence and are employed for potential applications like fluoroimmuno-assays and fluorescence microscopy[11, 12]. In the previous study of our own laboratory, an optical crystal, a kind of H3SSA derivatives, disodium sulfosalicylate NaO3S- C6H3(OH)COONa·3H2O, which exhibits a strong purple-blue fluorescent emission band at 420 nm upon excitation at 355 nm, has been grown from aqueous solution by the cooling solution method[13].

For researching novel materials with excellent fluorescence properties, we started to elaborate com- pounds constructed from H3SSA. Herein, we report the synthesis, crystal structure and fluorescence property of a compound: ammonium 5-sulfosalicylic acid monohydrate (ASSA). The structure of the crystal was firstly allocated as the deposition number CCDC 920446 to our request and later reported by Graham Smith[14]. The researches of crystal growth and optical property were not yet being pursued.In our paper, the compound was synthesized in solution and the large optical-grade single crystal was ob- tained. The crystal structure was determined using the X-ray diffraction method, and the optical pro- perties were characterized with spectroscopic tech- niques.

2 EXPERIMENTAL

2. 1 Synthesis of the material

All starting materials used were of analytical grade and experiments were carried out in ultra-pure water.

ASSA was synthesized by mixing equal molar of NH4HCO3(0.1 mol, 7.91 g) and C7H6O6S·2H2O (0.1 mol, 25.42 g) in 100 mL of ultra-pure water at 50 ℃. The chemical reaction could be indicated as follows:

NH4HCO3+ C7H6O6S·2H2O →

NH4·C7H5O6S·H2O + 2H2O + CO2

The hot solution was stirred for 1 h until the concentration to ca. 50 mL, and then filtered through moistened filter membrane with pore size of 0.15mm. After evaporating off the solvent for several days at room temperature, colorless crystals of ASSA were obtained. Elemental analysis was carried out on a Vario MICRO CHNOS elemental analyzer. Anal. Calcd. (%) for ASSA (M= 253), C, 33.20; H, 4.35; N, 5.53. Found (%): C, 33.22; H, 4.46; N, 5.56.

2. 2 Crystal growth

The temperature dependence of the solubility of ASSA in water was determined by means of tradi- tional weight analysis. The solubility versus tempe- rature curve is shown in Fig. 1 and can also be ex- pressed as

= 91.25394 – 2.65012+ 0.04204t

Fig. 1 . Solubility curve of ASSA in water

The solubility of ASSA in water increases gra- dually with increasing the temperature and the cooling solution method can be used for growing crystals[15].

The saturated solution at 50 ℃ was prepared in a 2500 mL glass crystallizer and filtered through a filter film with pore size of 0.15m at 60 ℃. After overheating the hot-filtered solution for 24 hours, the temperature was reduced to 5 ℃ higher than the saturation point. Then a 3mm × 3mm× 1mmself- nucleated seed crystalline mounted on a platform, which helda reversible rotation rate of about 40 rpm, was placed into the solution. Once immersed in the supersaturated solution, the seed started to grow up by cooling the solutionat a rate of 1.2 ℃/day. After 72 h, a transparent ASSA single crystal with the size of about 45mm× 20mm× 18mmwas obtained (Fig. 2).

3 RESULTS AND DISCUSSION

3. 1 Crystal structure

The crystal structure of the title compound was confirmed by X-ray single-crystal diffraction me- thod. A single as-grown crystal with approximate dimensions of 0.60mm × 0.60mm× 0.40mm was mounted on a glass fibre in a random orientation. The unit cell determination and diffraction data were collected at 293(2) K on an Enraf-Nonius CAD4 X- ray diffractometer equipped with graphite-mono- chromatizedMo-radiation (= 071037 ?) by using an-2scan mode in the range 3.51<<27.52°. Lorentz polarization corrections and an empirical absorption were applied to the data. The structure was solved by direct methods and refined by full- matrix least-square method with SHELXTL-97 program package[16]. Single-crystal X-ray analysis revealed that the crystal belongs to the monoclinic space group21/with= 11.884(9),= 7.306(5),= 12.152(9) ?,= 104.851(13)°,= 1019.8(13) ?3,= 4,D= 1.649 g/cm3and= 0.340 mm-1. The refinement converted to/= 3.1/8.7% for reflections with> 2() and/= 3.2/8.8% for all reflections. Figs. 3 and 4 show the molecular structure and the packing of molecules in a unit cell, respectively. In ASSA crystal structure, each asym- metric unit contains one ammonium cation, one 5- sulfosalicylate anion and one water molecule (Fig. 3). The -SO3H groups are deprotonated, but the -OH and -COOH groups are neutral. A large number of oxygen acceptors and water hydrogen-donor sites mean a lot of hydrogen-bonding associations which stabilize the crystal structure. All atoms of the Sali- cylate part are virtually coplanar, and the carboxyl acid and phenolic groups are tied together through an intramolecular hydrogen bond O(1)–H(1A)···O(2).The ammonium cations and water molecules are squeezed between the parallel layers of 5-sulfo- salicylate anions. NH4+ions are bonded with O of -SO31-and -COOH by N–H···O hydrogen bonds N–H(1)···O(2), N–H(3)···O(5) and N–H(4)···O(6), respectively. Water molecules are stabilized by inter- molecular O–H···O hydrogen bonds formed be- tween O(11)–H(5)···O(4) and O(3)–H(7)···O(11) of adjacent molecules.

Fig. 2 . ASSA crystal

Fig. 3 . Molecular structure of ASSA

Fig. 4 . Packing of the molecules in a unit cell

3. 2 IR spectrum

IR spectrum of the compound was recorded on a Spectrum One spectrophotometer in the range of 4,000～400 cm-1by using KBr pellets at room temperature (Fig. 5). In the 3500～3000 cm-1region of IR spectrum, the broad band centered at 3531 cm-1was characteristic of O–H stretching vibrations and hydrogen bond. In the region where O–H deformation vibrations occurred, two absorption bands were observed at 1477 and 1301 cm-1. The asymmetric and symmetric stretching vibrations of carboxyl acid group were viewed at 1664 and 1345 cm-1, respectively. Two peaks, which were asso- ciated to the stretching vibration of -SO3, are centered at 1207 and 1027 cm-1. Due to the N–H stretching and deformation vibrations in ammonium cation, two bands were found at 3180 and 1408 cm-1, respectively. The bands at 3083, 1610 and 1449 cm-1were attributed to C–H stretching vibrations and C=C stretching vibrations of phenol ring. A number of C–H deformation bands occur in the regions of 1275～960 and 900～650 cm-1. The bands traced at 1128, 1080, 948, 854, 796 and 714 cm-1were con- signed to C–H bending vibrations.

Fig. 5 . IR spectrum of ASSA

3. 31H-NMR spectrum

1H-NMR spectrum of the compound was per- formed on an AVANCE III spectrometer at 400 MHz by using D2O as a solvent and TMS as the standard at room temperature. As shown in Fig. 6, in the1H-NMR spectrum of ASSA, the peaks of 7.06 (d,= 8.8 Hz, 1H), 7.86 (dd,= 8.8 Hz, 1H) and 8.26 (d,= 2.4 Hz, 1H) ppm were found. The three proton peaks, in the equally integral areaof the correspon- ding chemical shift range, were attributed tothe H atom of C–H placed next to phenolic group, the H atom of C–H neighbored next to the sulfonic acid group, and the H atom of C–H squeezed between the sulfonic and carboxyl acid groups in ASSA, respec- tively. Proton bands of H atoms of phenolic group, carboxyl acid group and ammonium cation were separated from the respective HOD bands by drawing smooth curve at high magnetic field side, because the active hydrogen atoms were reacted with solvent D2O through proton exchange reaction.

3. 4 Thermal analysis

Thermalanalysiswasinvestigatedby a NET- ZSCHSTA449C thermal analyzer. The sample was heated from 40 to 300 ℃ at a rate of 10 ℃/min under nitrogenous atmosphere with high pure Al2O3powder as a reference material.As given in Fig. 7, in differential thermal analyses (DTA) curve, two en- dothermic peaks at 114 and 266 ℃ were performed, which correspond to the loss of one coordination water molecule and decomposition components of the rest. Weight loss of 6.96% (calculated: 7.11%) is found from 106 to 245 ℃. Thermogravimetric curve showed that the dehydration temperature of ASSA crystal was about 106 ℃, and the main framework began to collapse at about 245 ℃. The result indi- cated that the ASSA crystal is considered as a better organic crystal material with superior stable thermal stability.

Fig. 6 .1H-NMR spectrum of ASSA

Fig. 7 . DTA/TG curves of ASSA

3. 5 Optical property

Investigations for optical properties of the crystal were performed. The optical transmission spectrum was recorded on a PE-lambda 900 spectrometer with performing wavelength ranging from 200 nm to 760 nm. The fluorescence spectrum was studied by using a FLS920 fluorescence spectrometer with wave- length from 350 nm to 820 nm. A crystal with size of 10mm × 10mm× 1.5mm was polished for optical measurements.

Fig. 8 shows the room temperature transmittance of as-grown ASSA crystal as a function of the wave- length. In the wavelength range of 370～760 nm, the transmission intensity of the crystal was over 80%, while it had a strong absorption in ultraviolet region with the sharp absorption edge located at 340 nm.

The emission spectrum of as-grown ASSA crystal is shown in Fig. 9, which is excited by the wave- length of 320 nm at room temperature. The signi- ficant emission band was centered at 442 nm, which originated from*→transition of the compound.Compared with free H3SSA which showed an emi- ssion band at 384 nm in the solid state under the same situations, compound ASSA played an impor- tant role in red shift of the emission. It was con- ceivable that the removal of proton from sulfonic acid group and the building of N–H···O hydrogen bonds betweenammonium cation and 5-sulfo- salicylate anion decrease the*→gap,thus resul- ting in a red shift in emission band. In order to understand the energy transfer process well, the ex- citation of ASSA crystal was also measured, as shown in Fig. 9. For the emission band of ASSA crystal, the excitation peaks were located at 212, 280 and 348 nm,respectively ascribed to the intramo- lecular hydrogen bond O–H···O between the car- boxyl acid and phenolic group, which made the compound undergo a fast intramolecular hydrogen atom transfer reaction in the first excited singlet state to give a tautomer structure that exhibits a fluorescence with a large Stokes shift[17].

Fig. 8 . Optical transmission spectrum of ASSA crystal

Fig. 9 . Fluorescence spectra of H3SSA and ASSA crystals

4 CONCLUSION

In summary, the compound ASSA was synthe- sized and the large single crystal (45mm × 20mm× 18mm) has been grown at temperature range (40～50) by cooling solution method. The crystal structure, growth, thermal stability and optical pro- perty have been characterized. The dehydration temperature was about 106 ℃. And itexhibited a significant blue fluorescent emission band at 442 nm upon excitation at 320 nm, which makes it promi- sing for application in the fields of fluorescent materials.

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23 May 2014; accepted 16 December 2014 (CCDC 920446)

① This work was carried out under the sponsorship and financial support from the Key Laboratory of Optoelectronic Materials Chemistry and Physics, Chinese Academy of Sciences

. Zhuang Xin-Xin, born in 1967, professor. Phone: +86 0591 83709359. E-mail: zxx@fjirsm.ac.cn

10.14102/j.cnki.0254-5861.2011-0386