Acta Chim. Slov. 2003, 50, 239-250. 239 INFRARED AND RAMAN SPECTRA OF MELAMINIUM BIS(4-HYDROXYBENZENESULFONATE)DIHYDRATE Mariusz K. Marchewka Institute ofLow Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroclaw 2, P.O. Box 937, Poland E-mail: mkm@int.pan.wroc.pl Received 12-06-2002 Abstract Room temperature powder infrared and Raman measurements for the new melaminium salt, 2,4,6-triamino-l,3,5-triazine-l,3-diium bis (4-hydroxybenzenesulfonate) dihydrate, C3H8N62+-2C6H504S"-2H20, crystal were carried out. The vibrational spectra corroborate the X-ray data recently published by Janczak et al. Some spectral features of this new crystal refer to corresponding ones for other melamine complexes. No detectable signal was observed during powder test for second harmonic generation. DSC performed for the crystal shows no phase transition in the studied temperature range (113-293 K). Introduction Following the dimer of cyanamide, the trimer i.e. melamine (2,4,6-triamino-l,3,5-triazine) is interesting for crystal engineering or supramolecular chemistry. In order to better understand the behaviour of melamine molecule, the vibrational characterization of a new melaminium salt of 4-hydroxybenzenesulfonic acid was performed. The organic salts of 4-hydroxybenzenesulfonic acid are interesting because some of them exhibit nonlinear optical properties like second harmonic generation. This phenomenon was already observed by author in the čase of other crystals containing SO3 groups i. e. melamine with aminomethanesulfonic acid, aniline with /?-toluenesulfonic acid and L-lysine with /?-toluenesulfonic acid." The structural and vibrational studies of the crystals comprising similar organic or inorganic parts can be useful in elucidation of the role of these molecular units in the generation of second harmonic frequency of light (SHG). Therefore it seemed to be worthwhile to characterize title crystal with the help of infrared, Raman, calorimetric and preliminary second harmonic powder measurements. A few papers with assignments of internal vibrations of melamine molecule were already published.4"10 The fundamental frequency assignment for melamine and M. K. Marchewka: Infrared and Raman Spectra of Melaminium Bis(4-Hydroxybenzenesulfonate)... 240 Acta Chim. Slov. 2003, 50, 239-250. melamine && were done almost 50 years ago in the classical paper of Jones and Orville-Thomas.5 Some of aforementioned works were devoted to the band assignment for melamine and hexa-methoxymethyl melamine. Few of the fundamentals were assigned in the paper of Meier et al.1 He also presented the form of some of the normal modes of methylol melamine. The crystal structure of the melaminium bis(4-hydroxybenzenesulfonate) dihydrate was determined at room temperature recently.n According to data presented there the title crystal comprises doubly protonated melaminium (2+) residues, dissociated /7-phenolsulfonate anions and water molecules. Generally, the solid-state complexation of melamine with different organic and inorganic (mineral) acids has an interesting aspect concerning the formed hydrogen bond system. Such a system comprises most frequently the N-H—O and O-H—O tvpes.11"14 This phenomenon has features of self-organization process widely reported in literature. Sulfonates are hydrophilic. The title crystal, grown from an aqueous solution, contains water molecules and has complicated hydrogen bond networks, similar to the i c i o others. "I0 The S03 groups, which are present in title crystal, play an important role in e.g. the complexation of polymer electrolytes. NMR studies performed on complex of poly(propylene oxide) with sodium trifluoromethanesulfonate19 confirmed the vibrational spectroscopic studies, showing that CF3S03~ anion is involved in a great deal of cation-anion association. Results and discussion Assignment of the bands The bands observed in the measured region 4000-380 cm"1 arise from the vibrations of protons in the hydrogen bonds, the internal vibrations of the /7-phenolsulfonate anions, the internal vibrations of melaminium cations and from the vibrations of water molecules. The bands below 200 cm"1 in the Raman spectrum arise from the lattice vibrations of the crystal. The vibrations of melaminium residues. For the melamine alone, some bands found in our infrared and Raman spectra were not observed by Schneider et al. For infrared bands they are as follows: 2982ssh, 2828s, 2678m, 2332w, 2195w, 1761w, M. K. Marchewka: Infrared and Raman Spectra of Melaminium Bis(4-Hydroxybenzenesulfonate)... Acta Chim. Slov. 2003, 50, 239-250. 241 1308m, 872w, 75 lw, 442wsh, and for Raman: 881vw, 822vw, 570vw, 250vw, 156vs, 149s, 139m, 124vs, 110w and lOOvs. Only one band observed by Schneider in melamine powder infrared spectrum, le. at 1075wb, is not present in our spectrum. 3500 3000 2500 2000 1500 Wavenumbers [cm-1] 1000 500 Fig. 1. Room temperature powder FT-IR and FT-Raman spectra of melaminium bis(4-hydroxybenzenesulfonate) dihydrate crystal. Very weak Raman band at 983 cm" originates from triazine ring N in-plane radial vibration. This is suitable Raman group frequency. This vibration does not couple with the substituent groups and can be found in the 969-992 cm"1 region. Such a band is present in fact in the FT-Raman spectra of ali other complexes obtained by author. In the complex of melamine with: acrylic acid at 981 cm"1 a very weak band, butyric acid at 982 cm"1 a very weak band, glutaric acid at 977 cm"1 a weak band, arsenic acid at 978 cm"1 a very weak band, phthalic acid at 984 cm"1 a very weak band, glycolic acid at 985 cm"1 a very weak band and perchloric acid at 982 cm"1 a weak band. M. K. Marchewka: Infrared and Raman Spectra of Melaminium Bis(4-Hydroxybenzenesulfonate)... 242 Acta Chim. Slov. 2003, 50, 239-250. Table 1. Wavenumbers (cm"1) and relative intensities of the bands observed in the powder infrared and Raman spectra of the melaminium bis(4-hydroxybenzenesulfonate) dihydrate crystal. FT-IR FT-Raman Assignment Reference 3573m H20 asym stretch 3493m H20 sym stretch 3438msh NH2 asym stretch 3401s NH2 asym stretch 3373s NH2 sym stretch 3232ssh 3206ssh 3212vwb O-H-0 stretch, 2.91 and 3.00 A 3162vssh 3176vw Combination tone: NH2 bend + side-chain asym C-N stretch, 5 3118vsb 3118vwb N-H-0 stretch, 2.85-2.94 A 3072w C-H stretch 3060vwsh C-H stretch 2837mb N-H-0 stretch, 2.79 A 2674mb Combination tone: NH2 asym stretch - side chain out-of-plane C-N bend and N-H-0 stretch, 2.70 A 5 1727s NH2 bend 1694vs 1699vw NH2 bend 1685vs NH2 bend 1672vs 1661vw NH2 bend 1639ssh NH2 bend 1622m Ring: quadrant stretch; 6 NCN bend + ring def 23 1600m 1601w H20 def 1588m 1585w H20 def 1561wsh 1565vw Side-chain asym C-N stretch, 5 ring: quadrant stretch, 6 NCN bend + ring def and NH2 sciss 23 1512msh NH2 def 1504vs 1505vw NH2 def 1442m Ring stretch, 5 ring and side-chain C-N stretch 23 1397m 1370m Ring: semi-circle stretch + exogenous C-N contract 6 1354m Ring: semi-circle stretch 9 1335m 1342vw Ring: semi-circle stretch 9 1303m Ring: semi-circle stretch + exogenous C-N contract 6 1299m Ring: semi-circle stretch + exogenous C-N contract 6 1283m C-H def 1254msh Table 1. Continued on i fhe nextpage. M. K. Marchewka: Infrared and Raman Spectra of Melaminium Bis(4-Hydroxybenzenesulfonate)... Acta Chim. Slov. 2003, 50, 239-250. 243 Table 1. Continuedfrom the previous page. 1243m SO3 asym stretch 1179vs 1184vw SO3 asym stretch 1173vs 1174vw SO3 asym stretch 1144s 1141vwsh 1129vs 1125m SO3 asym stretch 1119vssh 1116w 1107s 1107vwsh 1086msh NH2 tors 1036s 1037w SO3 sym stretch 1031s 1030w SO3 sym stretch 1006s 1006vw NH2 swing and SO3 asym stretch 982m 983vw Triazine ring N, in-phase radial 975msh 975vw 963m Ring breath 918w Ring breath 890w Ring breath 864w 846wsh CCC def 839wsh 837w Ring def. (out-of-plane) 833m CNC def 827msh 822w 819wsh 819w 810w Ring-sextant out-of-plane bend 805w 778m 779vw Side-chain out-of-plane C-N bend. ring-sextant out-of-plane bend 736msh 730vwb Ring def. (out-of-plane) 702s CCO def 692msh 687vs 635w Ring breath and NH2 bend and C-S stretch 607mb H20 twist 580ssh 578wsh SO3 asym def 575s 572w Ring bend, NH2 and CNH bend 564ssh 563vw SO3 asym def 553msh NH2 swing and S03 def 530m Side-chain in-plane C-N bend and SO3 sym def 439wb 451vwb SO3 sym def 23 9 23 23 23 23 5 9 23 23 5 23 23 5 Table 1. Continued on the next page. Table 1. Continuedfrom the previous page. M. K. Marchewka: Infrared and Raman Spectra ofMelaminium Bis(4-Hydroxybenzenesulfonate)... 244 Acta Chim. Slov. 2003, 50, 239-250. 387wsh NH2tors and S03 ročk 380w Ring: quadrant out-of-plane 300w 244vw 218vw Side-chain out-of-plane bend 204vw 135ssh Lattice vibration 119s Lattice vibration 98vs Lattice vibration Abbreviations: s - strong, w - weak, v - very, sh - shoulder, b - broad, m - medium, tors - torsional, asym - asymmetric, sym - symmetric, bend - bending, ročk - rocking, def - deformation, swing - swinging, twist - tvvisting, stretch - stretching, breath - breathing, scis - scissoring, contract - contracting. The medium band located at 833 cm"1 in the infrared spectrum of title crvstal was attributed to CNC deformations of melamine ring. The most intense band in FT-Raman spectrum is at 687 cm"1. This band is also a very characteristic one for ali melamine complexes. It originates from the svmmetric vibrations of sym-triazine ring. The location of this band was analysed by author in several crvstals and the results are derived in Table 2. As it follows from the data presented in Table 2, the complexation of melamine causes, in ali cases, the rising of the frequency of analysed vibration compared to the value for melamine alone. For some melamine bands the precise assignment remains an open question. The vibrations of p-phenolsulfonate anions. For isolated SO3 group with C3V symmetry one expect four normal modes: V3(E) =1291 cm"1 (asym stretch), vi(Ai) = 1053 cm"1 (sym stretch), V4(E) = 551 cm"1 (asym def) and vii^-i) = 535 cm"1 (sym def). In the studied crvstal, the sulfonate group has a slightly distorted tetrahedral geometryu. Due to the lowering of the symmetry from an ideal C3V configuration and the crystal field effect, the splitting can be observed for double degenerated V3 and V4 modes. In the infrared spectra of the /?-phenolsulfonic acid, three very strong bands at 1218, 1172 and 1125 cm" are present , which unambiguously originate from asymmetric stretching vibrations of SO3 groups. M. K. Marchewka: Infrared and Raman Spectra ofMelaminium Bis(4-Hydroxybenzenesulfonate)... 23 9 23 Acta Chim. Slov. 2003, 50, 239-250. 245 Table 2. The position of the Raman band originating from the symmetric ring breathing vibration in different crystalline complexes of melamine. In melamine either purchased or recrystalized from water solution this band is located at 676 cm"1. Position of the band in Position of the band in Proton donor non-deuterated deuterated crystal Reference crystal [cm"1] [cm"1] m-nitrophenol 679 3 boric acid 680 3 L-tartaric acid 683 653 24 2,5-dinitrophenol 684 652 3 iodic acid 684 3 trichloroacetic acid 684 3 terephthalic acid 684 3 phthalic acid 685 25 phosphoric acid 685 26 arsenic acid 686 3 selenic acid 686 651 27 p-toluenesulfonic acid 686 3 glycolic acid 686 3 butyric acid 687 28 valeric acid 687 3 maleic acid 687 3 glutaric acid 687 3 sulphuric acid 688 29 perchloric acid 688 3 methanesulfonic acid 688 3 selenous acid 688 3 phosphorous acid* 689 3 (form with vP-H band at 2358 cm"1) phosphorous acid* 689 3 (first crystallization) hydrochloric acid 690 30 acetic acid 690 31 malic acid 690 3 acrylic acid 690 3 phosphorous acid* 691 654 3 (after recrystallization) nitric acid 691 653 3 oxalic acid 692 3 citric acid 695 32 different forms of crystals were obtained with phosphorous acid. M. K. Marchewka: Infrared and Raman Spectra ofMelaminium Bis(4-Hydroxybenzenesulfonate)... 246 Acta Chim. Slov. 2003, 50, 239-250. Thus the bands observed in the infrared spectra of title compound at 1243, 1179, 1173 and 1129 cm"1 were attributed to these vibrations. It was worthwhile noticing that in the crystalline complex of L-lysine with /?-phenolsulfonic acid similar bands are observed in the infrared spectrum at 1242, 1165 and 1120 cm"1. Similarlv, three strong bands at 1036, 1031 and 1006 cm"1 in infrared spectrum of title crvstal originate from svmmetric stretching vibrations of SO3 groups. Quite similar pattern is observed at 1027, 1022 and 1003 cm" in the complex of L-lysine mentioned above. The strong band at 564 cm"1 observed in infrared spectrum having a very weak Raman counterpart at 563 cm"1 was attributed to SO3 deformation vibrations. Similar strong band can be noticed at 568 cm" in the infrared spectrum of the L-lysine complex mentioned above. The strong band observed in infrared spectrum at 702 cm"1 can be assigned to CCO deformation of phenol ring. In the infrared spectrum of L-lysine complex the corresponding band was found at 695 cm"1. Additionally, the CCC deformations of phenol ring give the weak band at 846 cm"1 that corresponds to the band at 850 cm"1 in the complex of L-lysine with/?-phenolsulfonic acid. Sun et al. published the structure and FT-IR spectra of caesium 4-methyl-benzenesulfonate and the spectra of 4-methylbenzenesulfonic acid monohydrate. Our assignments for anion are in good correspondence with presented in the paper mentioned above. The vibrations of water molecules The eight water molecules in the elementary unit celi11 of the title crystal are involved as donors in hydrogen bonds with S03~ groups and as acceptors in hydrogen bonds with hydroxyl group of phenol ring and amino group from melaminium residue. These hydrogen bonds are relatively weak, with the lengths of 2.905, 2.997, 2.786 and 2.846 A, respectively. Two medium intensity bands at 3573 and 3493 cm"1 in infrared spectrum were assigned to the antisymmetric and symmetric stretching vibrations of water molecules. Their Raman counterparts are not visible on the spectrum presented in Fig. 1 because the inherent scattering intensity of these modes is low like in ali H-bond systems. The bands corresponding to in-plane deformation vibrations were found at 1600 and 1588 cm"1 (infrared, medium intensity) and at 1601 and 1585 cm"1 (Raman, weak bands). M. K. Marchewka: Infrared and Raman Spectra of Melaminium Bis(4-Hydroxybenzenesulfonate)... Acta Chim. Slov. 2003, 50, 239-250. 247 The infrared medium and broad band located at 607 cm" was assigned to rocking vibrations of water molecules. The hydrogen bonds vibrations. Janczak and Perpetuo11 found that there are two types of hydrogen bonds in the crystal under study: O-H—O with the length of 2.786 A and four of N-H-0 type with the lengths of 2.699, 2.846, 2.901 and 2.945 A, respectively. The vibrations of the latter one manifest themselves as perturbed amino group vibrations of the dissociated melaminium di-cation. Moreover, the hvdrogen atoms of water molecules are involved in O-H—O hvdrogen bonds with the lengths of 2.997 and 2.905 A. The shoulder at 3438 cm"1 and the band at 3401 cm"1 observed in infrared spectra originate from the asvmmetric stretching vibrations of three NH2 groups. Ali six protons of these groups are engaged in weak interactions mentioned above. The svmmetric stretching vibrations of these groups give a very strong and broad band in infrared spectrum, located at 3737 cm"1. Weak interactions through hvdrogen bonds give broad and intense absorption around ca. 3100 cm"1 with several submaxima. The proposed assignments for particular hydrogen bonds are given in Table 1. Lattice vibrations. Only two bands and one shoulder are observed in the FT-Raman spectrum in the range of lattice vibrations i. e. for the wavenumbers lower than 200 cm"1. A very strong band is present at 98 cm"1 and the strong band at 119 cm"1 with a strong shoulder at ca. 135 cm"1. It seemed worthwhile mentioning here, that the lattice dynamics was studied for bis(4-chlorophenyl)sulfone by Criado, and the calculated infrared and Raman frequencies were compared with experimental data. Second harmonic generation The measurements were performed before the structure was known. During the powder SHG test of the crystal presented here no detectable signal was observed. It is in consistency with the X-ray experiments giving centrosymmetric Pbcn space group (No. 60) of orthorhombic system. For centrosymmetric crystals second harmonic frequency 99 of light should not be observed. M. K. Marchewka: Infrared and Raman Spectra of Melaminium Bis(4-Hydroxybenzenesulfonate)... 248 Acta Chim. Slov. 2003, 50, 239-250. DSC calorimetric studies DSC measurements performed for melaminium bis(4-hydroxybenzenesulfonate) dihydrate crystal do not indicate the occurrence of the phase transition in the studied temperature range (113-293 K). Conclusions Most infrared and Raman bands corresponding to calculated vibrations of melamine molecule reported in literature were tentatively assigned. Generally, vibrational spectra support structural data. Low temperature phase transition was not observed. SHG signal was not detected confirming centrosymmetric structure of the complex. Experimental Preparation. The starting compounds, melamine (Aldrich, 99%) and 4-phenolosulfonic acid (FERAK LABORAT GMBH BERLIN, pure) were used as supplied and prepared in the ratio of 1:3. The dissolved acid was added to the hot solution of melamine (2g) with the use of dropper. After the solution was cooled to room temperature, it remained clear without any precipitants. Then the solution was purified with the aid of active carbon. The solution slowly evaporated during a few days till the colourless and transparent crystals appeared. Spectroscopic measurements. The vibrational measurements were carried out at room temperature. Infrared spectra were taken on a Bruker IFS-88 spectrometer in the region 4000-80 cm"1. Resolution was set up to 2 cm"1, signal/noise ratio was established by 32 scans, weak apodisation. Powder Fourier Transform Raman (FT-Raman) spectra were taken with an FRA-106 attachment to the Bruker IFS-88 spectrometer equipped Ti with Ge detector cooled to liquid nitrogen temperature. Nd" :YAG air-cooled diode pumped laser of power ca. 200mW was used as an exciting source. The incident laser excitation is 1064 nm. The scattered light was collected at the angle of 180° in the region 3600-80 cm"1, resolution 2 cm"1, 256 scans. The polycrystalline powders were obtained by grinding in agate mortar with pestle. Samples, as suspensions in oil, were put between KBr plates. The powder infrared M. K. Marchewka: Infrared and Raman Spectra of Melaminium Bis(4-Hydroxybenzenesulfonate)... Acta Chim. Slov. 2003, 50, 239-250. 249 spectra were taken in Nujol and Fluorolube emulsions to eliminate the bands originating from used oils. The infrared spectrum of/>phenolosulfonic acid was obtained as a film without oils. Differential scanning calorimetry measurements. DSC was carried out on a Perkin Elmer DSC-7 calorimeter equipped with a CCA-7 low temperature attachment with a heating/cooling rate of 20 K/min. The sample of the mass ca. 26 mg was sealed in the aluminium caps. SHG powder test. Preliminary SHG experiment was carried out on powder sample, which was simply irradiated at 1064 nm by a Q-switched pulsed Nd:YAG laser. Acknowledgement I am grateful to Dr M. Drozd for DSC measurements and Dr S. Debrus for performing SHG test. This work was fmancially supported by the KBN (project No. 7 T09A014 20). References 1. K. C. Russell, J.-M. Lehn, N. Kyritsakas, A. DeCian, J. Fisher, New J. Chem. 1998, 2, 123-128. 2. R. F. M. Lange, E. W. Meijer, Macromol. Symp. 1996, 702, 301-308. 3. M. K. Marchewka, unpublished results. 4. R. J. Meier, A. Tiller, S. A. M. Vanhommerig, J. Phys. Chem. 1995, 99, 5457-5464. 5. W. J. Jones, W. J. Orville-Thomas, Trans. Faraday Soc. 1959, 55, 203-210. 6. P. J. Larkin, M. P. Makowski, N. B. Colthup, L. A. Food, Vibrational Spectroscopy 1998,17, 53-72. 7. R. J. Meier, J. R. Maple, M. J. Hwang, A. T. Hagler, J. Phys. Chem. 1995, 99, 5445-5456. 8. J. R. Schneider, B. Schrader, J. Mol. Struct. 1975, 29, 1-14. 9. P. J. Larkin, M. P. Makowski, N. B. Colthoup, Spectrochim. Acta 1999, A55, 1011-1020. 10. M. P. Fernandez-Liencres, A. Navarro, J. J. Lopez-Gonzalez, M. Fernandez-Gomez, J. Tomkinson, GJ. Kearley, Chem. Phys. 2001, 266, 1-17. 11. J. Janczak, G. J. Perpetuo, Acta Cryst. 2001, C57, 873-875. 12. J. Janczak, G. J. Perpetuo, Acta Cryst. 2001, C57, 1120-1122. 13. J. Janczak, G. J. Perpetuo, Acta Cryst. 2001, C57, 1431-1433. 14. J. Janczak, G. J. Perpetuo, Acta Cryst. 2001, C57, 123-125. 15. Y. Ohki, Y. Suzuki, T. Takeuchi, A. Ouchi, Buli. Chem. Soc. Jpn. 1988, 61, 393-396. 16. Y. Ohki, Y. Suzuki, M. Nakamura, Buli. Chem. Soc. Jpn. 1985, 58, 2968-2971. 17. P. Starynowicz,^cto Cryst. 1992, C48, 1414-1416. 18. J. W. Bats, P. Coppens, Acta Cryst. 1975, B31, 1467-1472. 19. J. P. Manning, C. B. Frech, B. M. Fung, R. E. Frech, Polymer 1991, 32, 2939-2946. 20. B. Sun, Y. Zhao, J.-G. Wu, Q.-C. Yang, G.-X. Xu, J. Mol. Struct. 1998, 471, 63-66. 21. A. Criado, J. Phys. Soc. Jpn. 1995, 64, 2470-2477. 22. V. G. Dmitriev, G. G. Gurzadyan, D. N. Nikogosyan, Handbook ofNonlinear Optical Crystals, 2nd edition, Springer, 1997. 23. Y.-L. Wang, A. M. Mebel, C.-J. Wu, Y.-T. Chen, C.-E. Lin, J.-C. Jiang, J. Chem. Soc. Faraday Trans. 1997, 93, 3445-3451. M. K. Marchewka: InfraredandRaman Spectra ofMelaminium Bis(4-Hydroxybenzenesulfonate)... 250 Acta Chim. Slov. 2003, 50, 239-250. 24. M. K. Marchewka, J. Baran, A. Pietraszko, A. Haznar, S. Debrus, H. Ratajczak, SolidState Sciences 2003,5, 509-518. 25. M. K. Marchewka, submitted to Materials Letters. 26. M. K. Marchewka, submitted to Cryst. Res. Technol. 27. M. K. Marchewka, J. Janczak, S. Debras, J. Baran, H. Ratajczak, Solid State Sciences 2003, 5, 643-652. 28. M. K. Marchewka, H. Ratajczak, Buli. Pol. Acad. Sci. Chem. 2002, 3, 335-345. 29. M. K. Marchewka, J. Chem. Res. 2003, in press. 30. M. K. Marchewka, Mat. Sci. Eng. 2002, B95, 214-221. 31. M. K. Marchewka, submitted to Buli. Korean Chem. Soc. 32. M. K. Marchewka, A. Pietraszko, J. Phys. Chem Solids 2003, in press. Povzetek Posneli smo infrardeče in Ramanske spektre polikristaliničnih, do sedaj še nepoznanih melaminskih soli C3H8N62+-2C6H504S"-2H20. Ugotovili smo, da vibracijski spektri podpirajo rezultate dobljene iz spektrov narejenih z difrakcijo X-žarkov, ki jo je nedavno tega objavil Janczak s sodelavci. Nekateri vibracijski trakovi v spektrih na novo sintetiziranih spojin se ujemajo s trakovi drugih melaminskih kompleksov, vendar so testi pokazali, da spojine ne izsevajo višjih harmonskih nihanj. V temperaturnem območju 113-293 K spojine ne kažejo fazne spremembe, kot to potrjujejo DSC merjenja. M. K. Marchewka: Infrared and Raman Spectra ofMelaminium Bis(4-Hydroxybenzenesulfonate)...