Bis(glycinium) oxalate: evidence of strong hydrogen bonding

Abstract

In the title 2:1 salt, 2C2H6NO2+.C2O4(2-), the glycine molecule is in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The doubly charged oxalate anion lies across a crystallographic inversion centre. One of the reasons why the 1:1 glycinium oxalate salt has a higher melting point than the title compound may be the difference in their hydrogen-bonding patterns. A database search for salts formed between amino acids or substituted amino acids and oxalic acid revealed that, in most of the structures, the conformation about the O=C-OH bond is synplanar. D-Tryptophan oxalate is the only example where the OH group of a semi-oxalate adopts an antiplanar conformation. The 2:1 stoichiometry seen in the present salt is observed only in the salts of DL-serine, DL-aspartic acid and betaine with oxalic acid.

Bis(DL-cysteinium) oxalate

“…The Cambridge Structural Database (CSD, Version 5.29 of January 2008;Allen, 2002) has 18 entries for oxalates of amino acids with the hemi-oxalate ion and with the oxalate ion. The oxalate ion can occupy an inversion centre, as, for example, in the structures of bis(dlaspartic acid) oxalate (Alagar et al, 2003), bis(glycinium) oxalate (Chitra et al, 2006) and bis(dl-serinium) oxalate dihydrate (Alagar et al, 2002). Such structures have an amino acid-oxalate stoichiometry of 2:1.…”

Low-temperature phase transition in glycine–glutaric acid co-crystals studied by single-crystal X-ray diffraction, Raman spectroscopy and differential scanning calorimetry

“…Amino acids are known to form salts with carboxylic acids much more often than co-crystals. Glycine normally forms salts with carboxylic acids, see, for instance, the Cambridge Structural Database (CSD; Allen, 2002) refcodes WOVYOV (Subha Nandhini et al, 2001), WOVYOV01 (Tumanov et al, 2010), WEHZAL (Chitra et al, 2006), RENBAN (Rajagopal et al, 2001), AWIHIY (Losev et al, 2011) etc., with the exception of fumaric acid monohydrate (molar ratio glycine: fumaric acid: water is 2:1:1, refcode GOLZIR; Natarajan et al, 2009), where glycine is present both in the zwitterionic and the protonated form. The glycine-glutaric acid co-crystal is the only known co-crystal of an amino acid with glutaric acid.…”

Comments on the paper: ‘Growth structural, spectral, optical and mechanical studies of gamma bis glycinium oxalate (GBGOx) new NLO single crystal by SEST method’

“…The authors are totally unaware that the product formed in the glycine/oxalic acid system depends on the ratio of glycine:oxalic acid used for crystal growth [7][8][9]. In the present case the authors were also unaware that they were using ammonium oxalate monohydrate (and not glycine) for crystal growth.…”

“…The inappropriate choice of glycine as a precursor for NLO crystal work can be evidenced by the several improperly characterized glycine based compounds, many of which have been extensively commented in the literature [10][11][12][13][14][15][16][17][18][19][20][21][22]. The glycine/oxalic acid system has been the subject of recent research and a total of four compounds (Table 1), crystallizing in centrosymmetric space groups are well documented [7][8][9]. From this reaction system, the authors of the title paper claim to have synthesized a new NLO crystal namely gamma bis glycinium oxalate abbreviated by the code (GBGOx).…”