V.V. Ghazaryan

Glycine glycinium picrate--reinvestigation of the structure and vibrational spectra.

The crystal of diglycine picrate (glycine glycinum picrate) has been obtained from an aqueous solution containing stoichiometric quantities of the components. The species crystallizes in the monoclinic system (space group P2(1)/c). The crystal structure was determined with high accuracy, IR and Raman spectra are discussed and compared with previous results, and the molecular structure is presented. It was shown that crystals of diglycine picrate obtained from the solution containing equimolar quantities may contain picric acid as impurity, which is the reason for the previously reported observation of second harmonic generation in this centrosymmetric crystal. With this example we want to point out the risk of misinterpretation of SHG signals in general.

New salts of amino acids with dimeric cations

Among salts of amino acids there are compounds with the composition 2A..HX, which consist of dimeric A...A+ cations with short symmetric or asymmetric hydrogen bonds between zwitter-ionic and protonated moieties. These species are materials liable to undergo phase transitions or possess interesting nonlinear optical properties. Here, we report the preparation of 20 new salts with dimeric cations from aqueous solutions, including compounds of glycine, betaine, β- alanine, L-alanine, L-phenylalanine, L-threonine, L-valine, L-leucine and L-proline, with BF4-, ClO4-, Cl-, Br-, HSeO3-, and HC2O4-; as anions. The prepared salts are characterized by IR and Raman spectroscopy. Some of them are grown in form of good quality single crystals, which allowed the determination of their crystal structure.

L-Methioninium picrate.

Single crystals of l-methioninium picrate were obtained by evaporation of aqueous solution containing equimolar quantities of each component. l-Methioninium picrate crystallizes in the monoclinic system (space group P21, Z=2). The asymmetric unit contains one l-methioninium cation and one picrate anion. The carboxyl group of the cation forms an O-H⋯O hydrogen bond with the phenoxy oxygen atom and has an O⋯O distance of 2.669(3)Å. The protonated amino group of the l-methioninium cation forms N-H⋯O hydrogen bonds with the phenoxy oxygen atom of the picrate anion and the carbonyl oxygen atom of the symmetry related cation. The infrared and Raman spectra are recorded and discussed.

Reinvestigation of L-tryptophan picrate: Establishment of the existence of the L-tryptophan L-tryptophanium dimeric cation

A crystal structure redetermination of the L-tryptophan picrate crystal previously studied by Ishida et al. (Chem. Pharm. Bull. 41 (1993) 433-438) showed that it comprises L-tryptophan L-tryptophanium dimeric cation, one picrate anion and picric acid. The O⋯O distance of the O-H⋯O hydrogen bond in the dimeric cation is equal to 2.470(6) Å. The infrared spectrum of the crystal was registered and analyzed. The infrared spectrum of the crystals contains a broad absorption band centered at ca. 1170 cm(-1), which is assigned to the stretching vibration of the O-H bond.

Hexafluorosilicates of alanine

Abstract The existence of three types of salts of amino acid hexafluorosilicates 2 A+ · SiF62–, A2+ · SiF62– and 2(A ··· A+) · SiF62–, where A is an amino acid in zwitterionic state, A+ is a singly charged cation, A2+ is a doubly charged cation and (A ··· A+) is a dimeric cation with a short hydrogen bond, have been established, in the literature (Ghazaryan, V. V.; Fleck, M.; Petrosyan, A. M.: Salts of amino acids with hexafluorosilicate anion. J. Cryst. Growth (2011), doi: 10.1016/j.jcysgro.2011.11.017). Here we report the investigation of hexafluorosilicates of α-alanine. Both L- and DL-alanine form salts according to the main 2 A+ · SiF62– type: 2L-Ala+ · SiF62– · 3 H2O and 2DL-Ala+ · SiF62– · 2 H2O. In addition we found that L-alanine forms a new A+ · (A ··· A+) · SiF62– type of salt: L-Ala+ · (L-Ala ··· L-Ala+) · SiF62– · H2O. Results of structural and vibrational spectroscopic studies are described and discussed.

Mixed salts of amino acids: Syntheses, crystal structure and vibrational spectra of L-histidinium(2+) nitrate-perchlorate and L-histidinium(2+) nitrate-tetrafluoroborate

Abstract Crystals of L-histidinium(2+) nitrate-perchlorate (L-His2+ · NO3– · ClO4–) and L-histidinium(2+) nitrate-tetrafluoroborate (L-His2+ · NO3– · BF4–) have been obtained by crystallization from aqueous solutions. For both compounds, single-crystal XRD analysis as well as ATR FTIR and Raman spectroscopy was performed to determine and investigate the crystal structures, which turned out to be closely related, albeit not isotypic, although symmetry (space group P212121, Z = 4) and unit cell pa rameters of both compounds match to some extent. In each case the asymmetric unit contains a doubly charged L-His2+ cation with the charge counterbalanced by NO3– as well as ClO4– or BF4– anions. The structural differences between both compounds are subtle, mainly expressed in different conformations of the L-histidinium(2+) cations, which leads to different hydrogen bond networks. The L-His2+ cations form O—H···O hydrogen bonds to the nitrate anions and weak N—H···O and N—H···F hydrogen bonds. Powder SHG tests confirm considerable second order nonlinear optical activity for L-His2+ · NO3– · BF4– but not for L-His2+ · NO3– · ClO4–, this discrepancy being a result of the structural difference.

Crystal structure at 296 and 150 K, vibrational spectra and thermal behaviour of sarcosine sarcosinium nitrate

Abstract Crystals of sarcosine sarcosinium nitrate (2 Sar · HNO3) have been grown and characterized at 296 and 150 K by single crystal XRD and vibrational spectroscopy. The species was found to be triclinic (space group P-1, a = 5.320(1) Å, b = 6.578(1) Å, c = 15.957(2) Å, α = 95.448(6)°, β = 95.944(6)°, γ = 93.410(6)°, V = 551.6(1) Å3, and Z = 2 at 296 K), with a dimeric sarcosine ... sarcosinium cation and a nitrate anion in the asymmetric unit. A very strong hydrogen bond connects the molecules within the dimer. In addition, the tensor of thermal expansion was determined for the temperature range of 200 to 290 K. A strong anisotropy was detected, with thermal expansion along the c-axis approximately 14 times as strong as along the a-axis.

L-tryptophan L-tryptophanium chloride.

L-tryptophan L-tryptophanium chloride is a new salt with (A⋯A(+)) type dimeric cation. It crystallizes in the monoclinic system (space group P2(1), Z=2). The asymmetric unit contains one zwitterionic L-tryptophan molecule, one L-tryptophanium cation and one chloride anion. The dimeric cation is formed by a O-H⋯O hydrogen bond with the O⋯O distance equal to 2.5556(18) Å. The infrared and Raman spectra of the crystal are studied and compared with the spectra of L-tryptophanium chloride.

Comment on "A study on structural, optical, mechanical and ferroelectric properties of tri-glycine barium nitrate single crystals"

We argue that the “tri-glycine barium nitrate” crystal reported by R. Ezhil Vizhi and D. Rajan Babu, Ferroelectrics Letters Section 40, 1–10 (2013) is not a new ferroelectric but a dubious crystal.

L-Argininium phosphite – a new candidate for NLO materials

In order to investigate the possibility of salt formation in the L-Arg-H3PO3-H2O system, single crystals of L-argininium phosphite, C6H15N4O2(+)·H2PO3(-), were prepared by evaporation of an aqueous solution containing equimolar quantities of L-arginine and phosphorous acid. The asymmetric unit contains one L-argininium(+) cation and one phosphite [HPO2(OH)](-) anion. The phosphite anions form chains parallel to [010] by O-H...O hydrogen bonding, with an O...O distance of 2.630 (3) Å. The protonated amine and guanidyl groups of the L-argininium(+) cations form N-H...O hydrogen bonds with the carboxylate groups and anions. The IR and Raman spectra are discussed in relation to the crystal structure. The salt displays nonlinear optical (NLO) properties. Another salt was obtained from a solution with a 1:2 molar ratio of components, but was characterized by vibrational spectra only.