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New chemical analogs of triglycine sulfate
Journal of Crystal Growth ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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New chemical analogs of triglycine sulfate V.V. Ghazaryan a, M. Fleck b, A.M. Petrosyan a,n a b
Institute of Applied Problems of Physics, NAS of Armenia, 25 Nersessyan Str., 0014 Yerevan, Armenia Institute of Mineralogy and Crystallography, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria
art ic l e i nf o
Keywords: A1. Crystal structure A2. Growth from solution B1. Salts of amino acids Hexafluorosilicate
a b s t r a c t Triglycine sulfate (TGS) and its analogs can be presented by the molecular structure AH(A⋯AH)Y, where A is an amino acid (glycine in TGS) in zwitter-ionic form, AH is a protonated cationic amino acid, (A⋯AH) is a dimeric cation, where A and AH are connected by a short hydrogen bond, and Y is a divalent anion. Doing research on amino acid hexafluorosilicates we obtained a series of salts with different compositions, including four hexafluorosilicate salts which chemically are analogs of triglycine sulfate. Those are GlyH(Gly⋯GlyH)SiF6 (I), SarH(Sar⋯SarH)SiF6 2H2O (II), L-AlaH(L-Ala⋯L-AlaH)SiF6 H2O (III) and L-ProH(LPro⋯L-ProH)SiF6 H2O (IV). We have already published our results on crystals (II) and (III). In this work we report our results on the crystals (I) and (IV). & 2013 Elsevier B.V. All rights reserved.
1. Introduction Triglycine sulfate (TGS), known since 1956 [1], is technologically a very important ferroelectric crystal. Two more of its analogs, triglycine selenate (TGSe) [1] and triglycine tetrafluoroberyllate (TGBeF4) [2] are known too. Their molecular structure can be presented as AH(A⋯AH)Y, where A is an amino acid (in present case glycine) in zwitter-ionic form, AH is a protonated cationic amino acid, (A⋯AH) is a dimeric cation, where A and AH are connected by short hydrogen bond, and Y is a divalent (SO24 , SeO24 , BeF24 ) anion. Later, new analogs of TGS, namely tri-Lvaline sulfate [3] and tri-L-valine selenate [4], were discovered. Recently we started a systematic investigation of salts of amino acids with hexafluorosilicate anion (SiF26 ) [5]. In the course of this work we discovered four more new analogs of TGS formed by the same mechanism: GlyH(Gly⋯GlyH)SiF6 (I), SarH(Sar⋯SarH)SiF6 2H2O (II), L-AlaH(L-Ala⋯L-AlaH)SiF6 H2O (III) and L-ProH(L-Pro⋯ L-ProH)SiF6 H2O (IV). Our results on the investigation of crystals of salts of L-alanine (III) and sarcosine (II) were recently published [6,7]. In the present work we report our results on the investigation of crystals of salts of glycine (I) and L-proline (IV) in comparison with salts of sarcosine (II), L-alanine (III) and TGS. Crystals of salts of optically active amino acids (III, IV) necessarily crystallize in noncentrosymmetric structures (species III has even polar symmetry), while crystals of salts of achiral amino acids (I, II) often crystallize in centrosymmetric structures (see Table 1 and [6,7]). The O⋯O distances in the structures of (I, II, III) are
n
Corresponding author. Tel.: þ 374 10 241106; fax: þ374 10 281861. E-mail addresses: [email protected], [email protected] (A.M. Petrosyan).
close to the respective distance in TGS (2.470(9) Å) [8], while in the case of (IV) this distance is significantly shorter (see Table 2). As observed for TGS, TGSe and TGBeF4, phase transitions are possible in related crystals as well. A phase transition was observed in the structure of tri-L-valine selenate at 138 K [4], also a structural centrosymmetric–noncentrosymmetric phase transition was observed in (II) near 180 K. Crystallization conditions of (I, IV) crystals are discussed as well as their infrared and Raman spectra. 2. Experimental As initial reagents we used the amino acids glycine and L-proline, and hexafluorosilicic acid (in the form of 34% solution) purchased from “Sigma-Aldrich” Co. It was possible to obtain several salts with hexafluorosilicic acid. In case of glycine these are 2Gly H2SiF6, 2Gly H2SiF6 2H2O, 3Gly H2SiF6, and in case of L-proline these are 2L-Pro H2SiF6 H2O, 3L-Pro H2SiF6 H2O. The crystals 3Gly H2SiF6 and 3L-Pro H2SiF6 H2O have been obtained from aqueous solutions containing stoichiometric quantities of components by slow evaporation at room temperature. Needle-like crystals were obtained. Polyethylene vessels were used for chemical inertness. For identification of obtained salts we used the methods of IR and Raman spectroscopy. Crystal and molecular structures of salts obtained in the form of single crystals have been determined by single-crystal X-ray diffraction method. The qualities of the crystals were not perfect, several specimen had to be investigated manually and via XRD to find suitable pieces. Preparation was necessary in all the cases, still the crystal quality was not as good as expected. Nevertheless, the structural parameters could be determined to a satisfactory degree, and data from the spectroscopic study confirmed this. Details of structure determination and
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Table 1 Crystal data and details of the refinement for the 3Gly H2SiF6 and 3LPro H2SiF6 H2O.
Formula Mr CCDC numbersa Crystal system Space group a [Å] b [Å] c [Å] α [deg] β [deg] γ [deg] V [Å3] Z Dcalcd [g cm–3] μ(MoKα) [cm–1] F(000) hkl range T [K] Reflections measured Reflections unique Data with Fo 4 4s(Fo) Rint Parameters refined R(F)b (for Fo 44s(Fo)) wR(F2)b (all reflections) Weighting parameters a/b Flack parameter [12] GoF (F2)b Δρfin (max/min) [e Å 3]
3Gly H2SiF6
3L-Pro H2SiF6 H2O
C6H17F6N3O6Si 369.32 954452 Monoclinic P21/n 5.6134(11) 12.900(3) 19.554(4) 90 91.31(3) 90 1415.6(5) 4 1.733 0.269 760 7 8, 7 19, 7 29 296(2) 16826 4904 3358 0.0321 209 0.083 0.200 0.042/1.338 1.361 0.93/ 0.77
C15H31F6N3O7Si 507.52 954453 Orthorhombic P212121 5.7740(2) 10.0468(3) 38.3966(12) 90 90 90 2227.4(1) 4 1.513 0.197 1064 8/6, 714, –57/41 296(2) 23551 7577 5477 0.0279 304 0.061 0.183 0.097/0.514 0.11(7) 1.053 0.61/ 0.55
a The CCDC data sets 954452 and 954453 contain the supplementary crystallographic data. These data can be obtained free of charge via http://www.ccdc.cam. ac.uk/conts/retrieving.html, or from the Cambridge crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336 033; or e-mail: [email protected]. b R1¼ Σ∣∣Fo∣ ∣Fc∣∣⧸Σ∣Fo∣, wR2¼ [Σw(Fo2 - Fc2)2/ ΣwFo4]1/2, w¼ 1/[s2(Fo2)þ(a P)2 þ b P], P¼ (Fo2 þ 2Fc2)/3
registration of the spectra are given in detail in our previous publication [7].
3. Results and discussion 3.1. Structure As an achiral amino acid glycine salt 3Gly H2SiF6 may and crystallizes in the centrosymmetric space group P21/n of the monoclinic system (Table 1). The asymmetric unit contains one glycine, two glycinium moieties, and one hexafluorosilicate anion, all in general position (Fig. 1). Gly þ (B) and Gly(C) moieties are bounded with O1B–H1B⋯O1C hydrogen bond with a distance of 2.458(3) Å, thus forming dimeric cation. The other oxygen atom of moiety (C) forms N1A–H11A⋯O2C hydrogen bond with NH3þ group of moiety (A). COOH group of Gly þ (A) cation is connected with fluorine atom of anion through O1A–H1A⋯F4 hydrogen bond (2.586(3) Å). Other hydrogen bonds are of N–H⋯F type. 3L-Pro H2SiF6 H2O crystallizes in the orthorhombic system with P212121 space group (Table 1). The asymmetric unit contains one L-proline, two L-prolinium moieties, one hexafluorosilicate anion, and one water molecule, all in general position. There is an O1B–H1B⋯O1C hydrogen bond between L-Pro þ (B) and L-Pro (C) moieties with a distance of 2.420(4) Å, which is the shortest distance of any dimeric hydrogen bond in salts with 3:1 composition. L-Pro þ (A) moiety also forms O–H⋯O type hydrogen bond, but with the water molecule and with a significantly longer distance of 2.553(4) Å. Besides, the water molecule acts as a donor in the O1W–H1W⋯F4 hydrogen bond (2.680(3) Å) with the hexafluorosilicate anion. Intramolecular H-bonds exist in all of proline moieties between NH2 þ group of cycle, and one of the oxygen atoms of carboxyl or of carboxylate groups. The hexafluorosilicate anions accept N–H⋯F type hydrogen bonds from NH2þ groups of all of proline moieties, and one O–H⋯F type hydrogen bond, which is mentioned above.
Table 2 Hydrogen bond details (in Å and deg) in the 3Gly H2SiF6 and 3L-Pro H2SiF6 H2O. D–H⋯A
D–H
H⋯A
D⋯A
oD–H–A
3Gly H2SiF6 O1A–H1A⋯F4 i 0.888(19) 1.70(2) 2.586(3) 173(5) N1A–H11A⋯O2C ii 0.89 2.04 2.929(4) 179 N1A–H12A⋯F3 0.89 1.91 2.800(3) 174 ii N1A–H13A⋯F1 0.89 2.07 2.797(4) 139 O1B–H1B⋯O1C ii 0.91(2) 1.55(2) 2.458(3) 173(6) i N1B–H11B⋯F5 0.89 1.98 2.866(5) 178 N1B–H12B⋯F3 iii 0.89 2.08 2.815(3) 140 N1B–H13B⋯F5 iv 0.89 2.24 2.945(4) 137 N1C–H11C⋯F2 0.89 2.20 2.948(5) 141 N1C–H12C⋯F2 v 0.89 2.12 2.800(4) 133 vi N1C–H13C⋯F6 0.89 1.94 2.788(6) 159 Symmetry codes: (i) x 1/2, yþ 1/2, z þ1/2; (ii) x 1, y, z; (iii) xþ 1/2, yþ 1/2, z þ1/2; (iv) xþ 1/2, y 1/2, z þ3/2; (v) x, y, z þ1; (vi) x þ1, y, z þ 1. 3L-Pro H2SiF6 H2O O1A–H1A⋯O1W i N1A–H11A⋯F2 ii N1A–H12A⋯F1 N1A–H12A⋯F5 O1B–H1B⋯O1C N1B–H11B⋯F3 ii N1B–H12B⋯O2B N1B–H12B⋯F1 N1B–H12B⋯F6 N1C–H11C⋯F3 iii N1C–H12C⋯F1 iii O1W–H1W⋯F4 Symmetry codes: (i) x 1, y 1, z; (ii) x 1,
0.954(19) 0.90 0.90 0.90 0.963(19) 0.90 0.90 0.90 0.90 0.90 0.90 0.88(5) y, z; (iii) xþ 1/2, yþ 1/2, z.
1.60(2) 1.97 2.12 2.20 1.46(2) 1.87 2.15 2.24 2.43 2.36 2.22 1.82(5)
2.553(4) 2.755(3) 2.919(3) 2.977(3) 2.420(4) 2.751(3) 2.659(3) 2.930(3) 3.139(4) 2.916(3) 2.921(4) 2.680(3)
173(5) 144 147 144 176(5) 168 115 134 136 120 134 162(5)
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Fig. 1. Molecular structures of 3Gly H2SiF6 (a) and 3L-Pro H2SiF6 H2O (b).
As found in other amino acid hexafluorosilicate salts (and amino acid salts in general), the three dimensional structure is stabilized by the hydrogen bond network, which involves the 2 anions (SiF6 in these cases). In previous instances [9], we have shown that the hydrogen bonds extending towards the F atoms in the anion determine the rigidity of the position of this group, ranging from very well defined positions up to complete disorder of the anion. This proposition is also supported by the data found in the title compounds. Although the fluorine atoms show some displacement, no disorder was found (we have tried refinement with disordered SiF6 anions, without success), as a rather large number of hydrogen bonds extend towards the hexafluorosilicate groups (Table 2). The hydrogen bond network as a dominant factor involved in the packing of the building units is shown in the packing diagrams of 3Gly H2SiF6 and 3L-Pro H2SiF6 H2O (Fig. 2) 3.2. Vibrational spectra The infrared and Raman spectra of 3Gly H2SiF6 are presented in Fig. 3. The presence of Gly þ cations is reflected by the band at 1747 cm 1 and the line at 1748 cm 1, caused by the stretching vibrations of CQO bonds. In case of the zwitterionic Gly moiety, one can find the Raman line at 1676 cm 1 due to the asymmetric stretching vibration of COO– group. The strongest Raman line with peaks at 3030, 3022 and 2988 cm 1 is the result of stretching vibrations of CH2 groups. The same vibration can be seen in the IR spectrum in the form of a shoulder at 2991 cm 1. It is overlapped with the broad and very strong band of stretching vibrations of N–H bonds, centered at 3165 cm 1, and having a shoulder at 3222 cm 1. In the Raman spectrum it has corresponding middle intensity line with a shoulder at 3170 cm 1 and a peak at 3222 cm 1. The most characteristic ν3 vibration of SiF26 anion is
3
Fig. 2. Packing diagrams of 3Gly H2SiF6 (a) and 3L-Pro H2SiF6 H2O (b). Hydrogen bonds are indicated by dashed lines.
present in the IR spectrum as the most intensive band at 703 cm 1. The ν4 mode also is present in the IR spectrum as a band at 475 cm 1. In the Raman spectrum one can find the lines at 660 and 477 cm 1, caused by the ν1 and ν2 vibrations, respectively. The infrared and Raman spectra of 3L-Pro H2SiF6 H2O are presented in Fig. 4. Like in Gly þ cations in L-Pro þ cations COOH carboxyl group is presented, which can be easily found by the presence of a band above 1700 cm 1 caused by the stretching vibration of CQO group. In this case one can find the band at 1722 cm 1 and corresponding line at 1724 cm 1. In the zwitterionic proline moiety COO carboxylate group exists, the asymmetric stretching vibrations of which are observed as the shoulder at 1674 cm 1 in the IR spectrum, and as the line at 1674 cm 1 in the Raman spectrum. Stretching vibrations of O–H bonds of water molecules are observed as the band with peaks at 3465 cm 1 and 3430 cm 1, and the line at 3456 cm 1. Stretching vibrations of C–H bonds are well presented in the Raman spectrum as the lines with peaks at 3039, 3008, 3000, 2943 and 2888 cm 1. Corresponding bands are weak and not seen in the IR spectrum, because they are overlapped with bands of stretching vibrations of N–H bonds in the region 3200–2100 cm 1. The strongest band in the IR spectrum at 695 cm 1 is caused by the ν3 vibration of SiF26 anion. The strong and narrow band at 481 cm 1 is caused by the ν4 vibration. The ν1 vibration is active in the Raman spectrum and is present as a line at 653 cm 1.
4. Conclusion In this work, we present two new hexafluorosilicate salts, namely GlyH(Gly⋯GlyH)SiF6 (I) and L-ProH(L-Pro⋯L-ProH)
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Fig. 3. Infrared and Raman spectra of 3Gly H2SiF6.
SiF6 H2O (IV), which we compare with two previously published salts, namely SarH(Sar⋯SarH)SiF6 2H2O (II), L-AlaH (L-Ala⋯L-AlaH)SiF6 H2 O (III). All four are formed by the same
mechanism as triglycine sulfate, i.e. AH(A⋯AH)Y, where A is an amino acid in zwitter-ionic form, AH is a protonated cationic amino acid, (A⋯AH) is a dimeric cation, where A and AH are
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Fig. 4. Infrared and Raman spectra of 3L-Pro H2SiF6 H2O.
connected by short hydrogen bond, and Y is a divalent anion. In these crystals, the zwitterionic amino acid moiety and one of two cations form a dimeric cation through O–H⋯O hydrogen
bond. The O⋯O distances of dimeric hydrogen bonds are 2.458 (3), 2.466(2), 2.553(2) and 2.420(4) Å in the crystal structures of (I), (II), (III) and (IV), respectively.
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Acknowledgment This work was made possible in part by a research Grant condmatex-3154 from the Armenian National Science and Education Fund (ANSEF) based in New York, USA.
[2] [3] [4] [5] [6] [7] [8] [9]
S. Hoshino, T. Mitsui, F. Jona, R. Pepinsky, Phys. Rev. 107 (5) (1957) 1255–1258. I. Němec, Ph.D. thesis, Charles University in Prague, Faculty of Science, 1998. I. Němec, Z. Mička, J. Mol. Struct. 563-564 (2001) 289–294. V.V. Ghazaryan, M. Fleck, A.M. Petrosyan, J. Cryst. Growth 362 (2013) 162–166. V.V. Ghazaryan, M. Fleck, A.M. Petrosyan, Z. Kristallogr. 227 (2012) 646–655. M. Fleck, V.V. Ghazaryan, A.M. Petrosyan, Solid State Sci. 14 (2012) 952–963. R.R. Choudhury, R. Chitra, PRAMANA-J. Phys. 71 (2008) 911–915. M. Fleck, V.V. Ghazaryan, A.M. Petrosyan, Z. Kristallogr. 228 (2013) 240–249.
References [1] B.T. Matthias, C.E. Miller, J.P. Remeika, Phys. Rev. 104 (3) (1956) 849–850.
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Contents lists available at ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
New chemical analogs of triglycine sulfate V.V. Ghazaryan a, M. Fleck b, A.M. Petrosyan a,n a b
Institute of Applied Problems of Physics, NAS of Armenia, 25 Nersessyan Str., 0014 Yerevan, Armenia Institute of Mineralogy and Crystallography, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria
art ic l e i nf o
Keywords: A1. Crystal structure A2. Growth from solution B1. Salts of amino acids Hexafluorosilicate
a b s t r a c t Triglycine sulfate (TGS) and its analogs can be presented by the molecular structure AH(A⋯AH)Y, where A is an amino acid (glycine in TGS) in zwitter-ionic form, AH is a protonated cationic amino acid, (A⋯AH) is a dimeric cation, where A and AH are connected by a short hydrogen bond, and Y is a divalent anion. Doing research on amino acid hexafluorosilicates we obtained a series of salts with different compositions, including four hexafluorosilicate salts which chemically are analogs of triglycine sulfate. Those are GlyH(Gly⋯GlyH)SiF6 (I), SarH(Sar⋯SarH)SiF6 2H2O (II), L-AlaH(L-Ala⋯L-AlaH)SiF6 H2O (III) and L-ProH(LPro⋯L-ProH)SiF6 H2O (IV). We have already published our results on crystals (II) and (III). In this work we report our results on the crystals (I) and (IV). & 2013 Elsevier B.V. All rights reserved.
1. Introduction Triglycine sulfate (TGS), known since 1956 [1], is technologically a very important ferroelectric crystal. Two more of its analogs, triglycine selenate (TGSe) [1] and triglycine tetrafluoroberyllate (TGBeF4) [2] are known too. Their molecular structure can be presented as AH(A⋯AH)Y, where A is an amino acid (in present case glycine) in zwitter-ionic form, AH is a protonated cationic amino acid, (A⋯AH) is a dimeric cation, where A and AH are connected by short hydrogen bond, and Y is a divalent (SO24 , SeO24 , BeF24 ) anion. Later, new analogs of TGS, namely tri-Lvaline sulfate [3] and tri-L-valine selenate [4], were discovered. Recently we started a systematic investigation of salts of amino acids with hexafluorosilicate anion (SiF26 ) [5]. In the course of this work we discovered four more new analogs of TGS formed by the same mechanism: GlyH(Gly⋯GlyH)SiF6 (I), SarH(Sar⋯SarH)SiF6 2H2O (II), L-AlaH(L-Ala⋯L-AlaH)SiF6 H2O (III) and L-ProH(L-Pro⋯ L-ProH)SiF6 H2O (IV). Our results on the investigation of crystals of salts of L-alanine (III) and sarcosine (II) were recently published [6,7]. In the present work we report our results on the investigation of crystals of salts of glycine (I) and L-proline (IV) in comparison with salts of sarcosine (II), L-alanine (III) and TGS. Crystals of salts of optically active amino acids (III, IV) necessarily crystallize in noncentrosymmetric structures (species III has even polar symmetry), while crystals of salts of achiral amino acids (I, II) often crystallize in centrosymmetric structures (see Table 1 and [6,7]). The O⋯O distances in the structures of (I, II, III) are
n
Corresponding author. Tel.: þ 374 10 241106; fax: þ374 10 281861. E-mail addresses: [email protected], [email protected] (A.M. Petrosyan).
close to the respective distance in TGS (2.470(9) Å) [8], while in the case of (IV) this distance is significantly shorter (see Table 2). As observed for TGS, TGSe and TGBeF4, phase transitions are possible in related crystals as well. A phase transition was observed in the structure of tri-L-valine selenate at 138 K [4], also a structural centrosymmetric–noncentrosymmetric phase transition was observed in (II) near 180 K. Crystallization conditions of (I, IV) crystals are discussed as well as their infrared and Raman spectra. 2. Experimental As initial reagents we used the amino acids glycine and L-proline, and hexafluorosilicic acid (in the form of 34% solution) purchased from “Sigma-Aldrich” Co. It was possible to obtain several salts with hexafluorosilicic acid. In case of glycine these are 2Gly H2SiF6, 2Gly H2SiF6 2H2O, 3Gly H2SiF6, and in case of L-proline these are 2L-Pro H2SiF6 H2O, 3L-Pro H2SiF6 H2O. The crystals 3Gly H2SiF6 and 3L-Pro H2SiF6 H2O have been obtained from aqueous solutions containing stoichiometric quantities of components by slow evaporation at room temperature. Needle-like crystals were obtained. Polyethylene vessels were used for chemical inertness. For identification of obtained salts we used the methods of IR and Raman spectroscopy. Crystal and molecular structures of salts obtained in the form of single crystals have been determined by single-crystal X-ray diffraction method. The qualities of the crystals were not perfect, several specimen had to be investigated manually and via XRD to find suitable pieces. Preparation was necessary in all the cases, still the crystal quality was not as good as expected. Nevertheless, the structural parameters could be determined to a satisfactory degree, and data from the spectroscopic study confirmed this. Details of structure determination and
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Table 1 Crystal data and details of the refinement for the 3Gly H2SiF6 and 3LPro H2SiF6 H2O.
Formula Mr CCDC numbersa Crystal system Space group a [Å] b [Å] c [Å] α [deg] β [deg] γ [deg] V [Å3] Z Dcalcd [g cm–3] μ(MoKα) [cm–1] F(000) hkl range T [K] Reflections measured Reflections unique Data with Fo 4 4s(Fo) Rint Parameters refined R(F)b (for Fo 44s(Fo)) wR(F2)b (all reflections) Weighting parameters a/b Flack parameter [12] GoF (F2)b Δρfin (max/min) [e Å 3]
3Gly H2SiF6
3L-Pro H2SiF6 H2O
C6H17F6N3O6Si 369.32 954452 Monoclinic P21/n 5.6134(11) 12.900(3) 19.554(4) 90 91.31(3) 90 1415.6(5) 4 1.733 0.269 760 7 8, 7 19, 7 29 296(2) 16826 4904 3358 0.0321 209 0.083 0.200 0.042/1.338 1.361 0.93/ 0.77
C15H31F6N3O7Si 507.52 954453 Orthorhombic P212121 5.7740(2) 10.0468(3) 38.3966(12) 90 90 90 2227.4(1) 4 1.513 0.197 1064 8/6, 714, –57/41 296(2) 23551 7577 5477 0.0279 304 0.061 0.183 0.097/0.514 0.11(7) 1.053 0.61/ 0.55
a The CCDC data sets 954452 and 954453 contain the supplementary crystallographic data. These data can be obtained free of charge via http://www.ccdc.cam. ac.uk/conts/retrieving.html, or from the Cambridge crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336 033; or e-mail: [email protected]. b R1¼ Σ∣∣Fo∣ ∣Fc∣∣⧸Σ∣Fo∣, wR2¼ [Σw(Fo2 - Fc2)2/ ΣwFo4]1/2, w¼ 1/[s2(Fo2)þ(a P)2 þ b P], P¼ (Fo2 þ 2Fc2)/3
registration of the spectra are given in detail in our previous publication [7].
3. Results and discussion 3.1. Structure As an achiral amino acid glycine salt 3Gly H2SiF6 may and crystallizes in the centrosymmetric space group P21/n of the monoclinic system (Table 1). The asymmetric unit contains one glycine, two glycinium moieties, and one hexafluorosilicate anion, all in general position (Fig. 1). Gly þ (B) and Gly(C) moieties are bounded with O1B–H1B⋯O1C hydrogen bond with a distance of 2.458(3) Å, thus forming dimeric cation. The other oxygen atom of moiety (C) forms N1A–H11A⋯O2C hydrogen bond with NH3þ group of moiety (A). COOH group of Gly þ (A) cation is connected with fluorine atom of anion through O1A–H1A⋯F4 hydrogen bond (2.586(3) Å). Other hydrogen bonds are of N–H⋯F type. 3L-Pro H2SiF6 H2O crystallizes in the orthorhombic system with P212121 space group (Table 1). The asymmetric unit contains one L-proline, two L-prolinium moieties, one hexafluorosilicate anion, and one water molecule, all in general position. There is an O1B–H1B⋯O1C hydrogen bond between L-Pro þ (B) and L-Pro (C) moieties with a distance of 2.420(4) Å, which is the shortest distance of any dimeric hydrogen bond in salts with 3:1 composition. L-Pro þ (A) moiety also forms O–H⋯O type hydrogen bond, but with the water molecule and with a significantly longer distance of 2.553(4) Å. Besides, the water molecule acts as a donor in the O1W–H1W⋯F4 hydrogen bond (2.680(3) Å) with the hexafluorosilicate anion. Intramolecular H-bonds exist in all of proline moieties between NH2 þ group of cycle, and one of the oxygen atoms of carboxyl or of carboxylate groups. The hexafluorosilicate anions accept N–H⋯F type hydrogen bonds from NH2þ groups of all of proline moieties, and one O–H⋯F type hydrogen bond, which is mentioned above.
Table 2 Hydrogen bond details (in Å and deg) in the 3Gly H2SiF6 and 3L-Pro H2SiF6 H2O. D–H⋯A
D–H
H⋯A
D⋯A
oD–H–A
3Gly H2SiF6 O1A–H1A⋯F4 i 0.888(19) 1.70(2) 2.586(3) 173(5) N1A–H11A⋯O2C ii 0.89 2.04 2.929(4) 179 N1A–H12A⋯F3 0.89 1.91 2.800(3) 174 ii N1A–H13A⋯F1 0.89 2.07 2.797(4) 139 O1B–H1B⋯O1C ii 0.91(2) 1.55(2) 2.458(3) 173(6) i N1B–H11B⋯F5 0.89 1.98 2.866(5) 178 N1B–H12B⋯F3 iii 0.89 2.08 2.815(3) 140 N1B–H13B⋯F5 iv 0.89 2.24 2.945(4) 137 N1C–H11C⋯F2 0.89 2.20 2.948(5) 141 N1C–H12C⋯F2 v 0.89 2.12 2.800(4) 133 vi N1C–H13C⋯F6 0.89 1.94 2.788(6) 159 Symmetry codes: (i) x 1/2, yþ 1/2, z þ1/2; (ii) x 1, y, z; (iii) xþ 1/2, yþ 1/2, z þ1/2; (iv) xþ 1/2, y 1/2, z þ3/2; (v) x, y, z þ1; (vi) x þ1, y, z þ 1. 3L-Pro H2SiF6 H2O O1A–H1A⋯O1W i N1A–H11A⋯F2 ii N1A–H12A⋯F1 N1A–H12A⋯F5 O1B–H1B⋯O1C N1B–H11B⋯F3 ii N1B–H12B⋯O2B N1B–H12B⋯F1 N1B–H12B⋯F6 N1C–H11C⋯F3 iii N1C–H12C⋯F1 iii O1W–H1W⋯F4 Symmetry codes: (i) x 1, y 1, z; (ii) x 1,
0.954(19) 0.90 0.90 0.90 0.963(19) 0.90 0.90 0.90 0.90 0.90 0.90 0.88(5) y, z; (iii) xþ 1/2, yþ 1/2, z.
1.60(2) 1.97 2.12 2.20 1.46(2) 1.87 2.15 2.24 2.43 2.36 2.22 1.82(5)
2.553(4) 2.755(3) 2.919(3) 2.977(3) 2.420(4) 2.751(3) 2.659(3) 2.930(3) 3.139(4) 2.916(3) 2.921(4) 2.680(3)
173(5) 144 147 144 176(5) 168 115 134 136 120 134 162(5)
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Fig. 1. Molecular structures of 3Gly H2SiF6 (a) and 3L-Pro H2SiF6 H2O (b).
As found in other amino acid hexafluorosilicate salts (and amino acid salts in general), the three dimensional structure is stabilized by the hydrogen bond network, which involves the 2 anions (SiF6 in these cases). In previous instances [9], we have shown that the hydrogen bonds extending towards the F atoms in the anion determine the rigidity of the position of this group, ranging from very well defined positions up to complete disorder of the anion. This proposition is also supported by the data found in the title compounds. Although the fluorine atoms show some displacement, no disorder was found (we have tried refinement with disordered SiF6 anions, without success), as a rather large number of hydrogen bonds extend towards the hexafluorosilicate groups (Table 2). The hydrogen bond network as a dominant factor involved in the packing of the building units is shown in the packing diagrams of 3Gly H2SiF6 and 3L-Pro H2SiF6 H2O (Fig. 2) 3.2. Vibrational spectra The infrared and Raman spectra of 3Gly H2SiF6 are presented in Fig. 3. The presence of Gly þ cations is reflected by the band at 1747 cm 1 and the line at 1748 cm 1, caused by the stretching vibrations of CQO bonds. In case of the zwitterionic Gly moiety, one can find the Raman line at 1676 cm 1 due to the asymmetric stretching vibration of COO– group. The strongest Raman line with peaks at 3030, 3022 and 2988 cm 1 is the result of stretching vibrations of CH2 groups. The same vibration can be seen in the IR spectrum in the form of a shoulder at 2991 cm 1. It is overlapped with the broad and very strong band of stretching vibrations of N–H bonds, centered at 3165 cm 1, and having a shoulder at 3222 cm 1. In the Raman spectrum it has corresponding middle intensity line with a shoulder at 3170 cm 1 and a peak at 3222 cm 1. The most characteristic ν3 vibration of SiF26 anion is
3
Fig. 2. Packing diagrams of 3Gly H2SiF6 (a) and 3L-Pro H2SiF6 H2O (b). Hydrogen bonds are indicated by dashed lines.
present in the IR spectrum as the most intensive band at 703 cm 1. The ν4 mode also is present in the IR spectrum as a band at 475 cm 1. In the Raman spectrum one can find the lines at 660 and 477 cm 1, caused by the ν1 and ν2 vibrations, respectively. The infrared and Raman spectra of 3L-Pro H2SiF6 H2O are presented in Fig. 4. Like in Gly þ cations in L-Pro þ cations COOH carboxyl group is presented, which can be easily found by the presence of a band above 1700 cm 1 caused by the stretching vibration of CQO group. In this case one can find the band at 1722 cm 1 and corresponding line at 1724 cm 1. In the zwitterionic proline moiety COO carboxylate group exists, the asymmetric stretching vibrations of which are observed as the shoulder at 1674 cm 1 in the IR spectrum, and as the line at 1674 cm 1 in the Raman spectrum. Stretching vibrations of O–H bonds of water molecules are observed as the band with peaks at 3465 cm 1 and 3430 cm 1, and the line at 3456 cm 1. Stretching vibrations of C–H bonds are well presented in the Raman spectrum as the lines with peaks at 3039, 3008, 3000, 2943 and 2888 cm 1. Corresponding bands are weak and not seen in the IR spectrum, because they are overlapped with bands of stretching vibrations of N–H bonds in the region 3200–2100 cm 1. The strongest band in the IR spectrum at 695 cm 1 is caused by the ν3 vibration of SiF26 anion. The strong and narrow band at 481 cm 1 is caused by the ν4 vibration. The ν1 vibration is active in the Raman spectrum and is present as a line at 653 cm 1.
4. Conclusion In this work, we present two new hexafluorosilicate salts, namely GlyH(Gly⋯GlyH)SiF6 (I) and L-ProH(L-Pro⋯L-ProH)
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Fig. 3. Infrared and Raman spectra of 3Gly H2SiF6.
SiF6 H2O (IV), which we compare with two previously published salts, namely SarH(Sar⋯SarH)SiF6 2H2O (II), L-AlaH (L-Ala⋯L-AlaH)SiF6 H2 O (III). All four are formed by the same
mechanism as triglycine sulfate, i.e. AH(A⋯AH)Y, where A is an amino acid in zwitter-ionic form, AH is a protonated cationic amino acid, (A⋯AH) is a dimeric cation, where A and AH are
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Fig. 4. Infrared and Raman spectra of 3L-Pro H2SiF6 H2O.
connected by short hydrogen bond, and Y is a divalent anion. In these crystals, the zwitterionic amino acid moiety and one of two cations form a dimeric cation through O–H⋯O hydrogen
bond. The O⋯O distances of dimeric hydrogen bonds are 2.458 (3), 2.466(2), 2.553(2) and 2.420(4) Å in the crystal structures of (I), (II), (III) and (IV), respectively.
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Acknowledgment This work was made possible in part by a research Grant condmatex-3154 from the Armenian National Science and Education Fund (ANSEF) based in New York, USA.
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Please cite this article as: V.V. Ghazaryan, et al., Journal of Crystal Growth (2013), http://dx.doi.org/10.1016/j.jcrysgro.2013.11.054i