research papers\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296

New 1:1 and 2:1 salts in the `DL-norvaline–maleic acid' system as an example of assembling various crystal structures from similar supramolecular building blocks

aNovosibirsk State University Pirogova str. 2, Novosibirsk 630090, Russian Federation, and bInstitute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze str. 18, Novosibirsk 630128, Russian Federation
*Correspondence e-mail: arksergey@gmail.com

Edited by A. L. Spek, Utrecht University, The Netherlands (Received 17 October 2016; accepted 14 November 2016; online 1 January 2017)

Mol­ecular salts and cocrystals of amino acids have potential applications as mol­ecular materials with nonlinear optical, ferroelectric, piezoelectric, and other various target physical properties. The wide choice of amino acids and coformers makes it possible to design various crystal structures. The amino acid–maleic acid system provides a perfect example of a rich variety of crystal structures with different stoichiometries, symmetries and packing motifs built from the mol­ecular building blocks, which are either exactly the same, or differ merely by protonation or as optical isomers. The present paper reports the crystal structures of two new salts of the DL-norvaline–maleic acid system with 1:1 and 2:1 stoichiometries, namely DL-norvalinium hydrogen maleate, C5H12NO2+·C4H3O4, (I), and DL-norvalinium hydrogen maleate–DL-norvaline, C5H12NO2+·C4H3O4·C5H11NO2, (II). These are the first examples of mol­ecular salts of DL-norvaline with an organic anion. The crystal structure of (I) has the same C22(12) structure-forming motif which is common for hydrogen maleates of amino acids. The structure of (II) has dimeric cations. Of special inter­est is that the single crystals of (I) which are originally formed on crystallization from aqueous solution transform into single crystals of (II) if stored in the mother liquor for several hours.

1. Introduction

Mol­ecular salts and cocrystals of amino acids are inter­esting mostly due to their potential applications as mol­ecular materials with optical, piezoelectric, ferroelectric and other target physical properties (Fleck & Petrosyan, 2014[Fleck, M. & Petrosyan, A. M. (2014). In Salts of Amino Acids. Crystallization, Structure and Properties. Cham, Switzerland: Springer International Publishing.]). For example, large (several millimetres in each direction) crystals of L-ala­ninium hydrogen maleate [(L-AlaH+M] (Alagar et al., 2001[Alagar, M., Krishnakumar, R. V., Nandhini, M. S. & Natarajan, S. (2001b). Acta Cryst. E57, o855-o857.]b), L-argininium hydrogen maleate dihydrate [(L-ArgH+M·2H2O] (Sun et al., 2007[Sun, Z.-H., Yu, W.-T., Fan, J.-D., Xu, D. & Wang, X.-Q. (2007). Acta Cryst. E63, o2805-o2807.]), L-phenyl­alaninium hydrogen maleate [(L-PheH+M] (Alagar et al., 2001[Alagar, M., Krishnakumar, R. V. & Natarajan, S. (2001c). Acta Cryst. E57, o968-o970.]c), L-histidinium hydrogen maleate hydrate [(L-HisH+M·H2O] (Fleck et al., 2013[Fleck, M., Ghazaryan, V. V., Bezhanova, L. S., Atanesyan, A. K. & Petrosyan, A. M. (2013). J. Mol. Struct. 1035, 407-415.]), L-me­thio­ninium L-me­thio­nine hydrogen maleate (L-Met·L-MetH+·M) (Natarajan et al., 2010[Natarajan, S., Devi, N. R., Dhas, S. A. M. B. & Athimoolam, S. (2010). J. Optoelectron. Adv. Mater. 4, 516-519.]) and glycinium hydrogen maleate [(GlyH+M] (Alagar et al., 2001[Alagar, M., Krishnakumar, R. V., Mostad, A. & Natarajan, S. (2001a). Acta Cryst. E57, o1102-o1104.]a) were obtained and the second harmonic generation (SHG) efficiency, investigated using the Kurtz–Perry powder method (Kurtz & Perry, 1968[Kurtz, S. K. & Perry, T. T. (1968). J. Appl. Phys. 39, 3798-3813.]), was 0.27–1.5 times that of the SGH efficiency of KDP (potassium dideuterium phosphate) (Anbuchezhiyan et al., 2009[Anbuchezhiyan, M., Ponnusamy, S. & Muthamizhchelvan, C. (2009). Spectrochim. Acta Part A, 74, 917-923.]; Devaprasad & Madhavan, 2010[Devaprasad, S. A. & Madhavan, J. (2010). Arch. Appl. Sci. Res. 2, 50-56.]; Yogam et al., 2012[Yogam, F., Vetha Potheher, I., Vimalan, M., Jeyasekaran, R., Rajesh Kumar, T. & Sagayaraj, P. (2012). Spectrochim. Acta Part A, 95, 369-373.]; Gonsago et al., 2012[Gonsago, C. A., Albert, H. M., Karthikeyan, J., Sagayaraj, P. & Pragasam, A. J. A. (2012). Mater. Res. Bull. 47, 1648-1652.]; Vasudevan et al., 2013[Vasudevan, P., Sankar, S. & Gokul Raj, S. (2013). Optik (Stuttgart), 124, 4155-4158.]; Charoen-In et al., 2010[Charoen-In, U., Ramasamy, P. & Manyum, P. (2010). J. Cryst. Growth, 312, 2369-2375.]; Balasubramanian et al., 2010[Balasubramanian, D., Murugakoothan, P. & Jayavel, R. (2010). J. Cryst. Growth, 312, 1855-1859.]; Natarajan et al., 2008[Natarajan, S., Devi, N. R., Britto Dhas, S. D. M. & Athimoolam, S. (2008). Sci. Technol. Adv. Mater. 9, 025012.]). The wide choice of amino acids and coformers makes it possible to design various crystal structures that could be potentially important from a crystal engineering point of view. Moreover, in all the solvates of this system, in particular, hydrates can form on crystallization.

[Scheme 1]

In addition to the abovementioned nonlinear optical pro­perties, the `amino acid–maleic acid' system provides a perfect example of a mol­ecular salt in which the same small organic coformer (maleic acid) can cocrystallize with a large variety of mol­ecules (amino acids). Maleic acid donates a proton to the amino acid and is present as a small and rigid maleate anion in all the crystalline maleates of amino acids. These structures can have various stoichiometries. The diversity of the stoichiometric ratios is determined by several factors:

(i) the symmetry non-equivalence of several amino acid cations;

(ii) the charge of the side chain of the amino acid;

(iii) the binding of several amino acid cations and zwitterions to form complex subunits known as dimeric or trimeric cations.

In particular, it is important to compare the crystal structures of chiral and racemic amino acid salts and cocrystals. Crystals of L- and DL-amino acids often have radically different properties (Chesalov et al., 2008[Chesalov, Yu. A., Chernobay, G. B. & Boldyreva, E. V. (2008). J. Struct. Chem. 49, 627-638.]; Kolesov & Boldyreva, 2007[Kolesov, B. A. & Boldyreva, E. V. (2007). J. Phys. Chem. B, 111, 14387-14397.]; Bordallo et al., 2007[Bordallo, H. N., Kolesov, B. A., Boldyreva, E. V. & Juranyi, F. (2007). J. Am. Chem. Soc. 129, 10984-10985.]; Kolesnik et al., 2005[Kolesnik, E. N., Goryajnov, S. V. & Boldyreva, E. V. (2005). Dokl. Akad. Nauk, 404, 61-64.]), and the same may hold for their salts and cocrystals (Boldyreva, 2014[Boldyreva, E. V. (2014). Z. Kristallogr., 229, 236-245.]; Arkhipov et al., 2013[Arkhipov, S. G., Zakharov, B. A. & Boldyreva, E. V. (2013). Acta Cryst. C69, 517-521.]). Recently, the crystal structure of L-norvalinium hydrogen maleate–L-norvaline has been analyzed and shown to have dimeric L-Nva⋯L-NvaH+ cations (Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.]). In the present paper, we report the structures of racemic salts formed by DL-norvaline and maleic acid having different stoichiometries, namely DL-nor­valinium hydrogen maleate, (I), and DL-norvalinium hydrogen maleate–DL-norvaline, (II).

2. Experimental

2.1. Synthesis and crystallization

Crystals of (I)[link] were obtained by slow evaporation at room temperature from a drop of the saturated aqueous solution containing DL-norvaline and maleic acid in a 1:1 ratio (Rychkov et al., 2014[Rychkov, D. A., Arkhipov, S. G. & Boldyreva, E. V. (2014). J. Appl. Cryst. 47, 1435-1442.]). Inter­estingly, crystallization from an equimolar drop of the solution of DL-norvaline and maleic acid first gives crystals of (I)[link], which, if kept in the mother liquor for a few hours, are transformed into larger crystals of another phase, denoted (II), with a 2:1 stoichiometry of DL-norvaline and maleic acid. One can suppose that phase (I)[link] nucleates and grows faster than phase (II), although the latter is the thermodynamically more stable form. The case is very similar to that observed when crystallizing tolaza­mide polymorphs (I)[link] and (II) (Boldyreva et al., 2015[Boldyreva, E. V., Arkhipov, S. G., Drebushchak, T. N., Drebushchak, V. A., Losev, E. A., Matvienko, A. A., Minkov, V. S., Rychkov, D. A., Seryotkin, Y. V., Stare, J. & Zakharov, B. A. (2015). Chem. Eur. J. 21, 15395-15404.]), as well as to other solution-assisted polymorphic transformations (Munroe et al., 2014[Munroe, A., Croker, D. M., Rasmuson, A. C. & Hodnett, B. K. (2014). Cryst. Growth Des. 14, 3466-3471.]; Kobari et al., 2014[Kobari, M., Kubota, N. & Hirasawa, I. (2014). CrystEngComm, 16, 6049-6058.]). The crystals of (II), grown from a small drop were thin and not suitable for single-crystal X-ray structural analysis. Larger crystals of (II) were obtained using slow evaporation from a crystallization vessel.

2.2. Crystal structure solution and refinement

Crystal data, data collection and structure refinement details are summarized in Table 1[link]. Suitable crystals of (I)[link] and (II) was selected under a microscope in polarized light and mounted by means of MiTeGen MicroGrippers using MiTeGen LV Cryo Oil (LVCO-1) on an Agilent Xcalibur diffractometer. The n-propyl group (including the H atoms) of the DL-norvalinium cation of the structure of (I) (C4A/C5A) is disordered (the minor-disorder sites are labelled C4B/C5B). The occupation ratio of the disordered sites refined to 0.865 (8):0.135 (8). For the C5B/C4B/C3 atoms, the Uij values were restrained to be within 0.02 Å2 (within 0.04 Å2 for the terminal atom). All H atoms were located initially in a difference Fourier map. The positions of all H atoms were subsequently geometrically optimized and refined using a riding model, with the following assumptions and constraints: N—H = 0.89 Å, O—H = 0.82 Å and C—H = 0.93 (anion), 0.98 (methine), 0.97 (methylene) or 0.96 Å (methyl), with Uiso(H) = 1.5Ueq(parent atom) for the methyl and OH groups, and 1.2Ueq(parent atom) otherwise.

Table 1
Experimental details

  (I) (II)
Crystal data
Chemical formula C5H12NO2+·C4H3O4 C5H12NO2+·C4H3O4·C5H11NO2
Mr 233.22 350.37
Crystal system, space group Monoclinic, C2/c Orthorhombic, Pnma
Temperature (K) 293 293
a, b, c (Å) 19.6385 (15), 5.62705 (18), 23.6867 (10) 8.8572 (4), 27.3614 (11), 7.8306 (4)
α, β, γ (°) 90, 108.283 (6), 90 90, 90, 90
V3) 2485.4 (2) 1897.71 (15)
Z 8 4
Radiation type Mo Kα Mo Kα
μ (mm−1) 0.11 0.10
Crystal size (mm) 0.25 × 0.15 × 0.10 0.50 × 0.25 × 0.20
 
Data collection
Diffractometer Agilent Xcalibur Ruby Gemini ultra Agilent Xcalibur Ruby Gemini ultra
Absorption correction Multi-scan (CrysAlis PRO; Agilent, 2014[Agilent (2014). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England.]) Multi-scan (CrysAlis PRO; Rigaku OD, 2015[Rigaku OD (2015). CrysAlis PRO. Rigaku Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.])
Tmin, Tmax 0.866, 1.000 0.948, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections 13186, 2198, 1807 21923, 1975, 1731
Rint 0.051 0.053
(sin θ/λ)max−1) 0.595 0.625
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.068, 0.166, 1.23 0.079, 0.146, 1.14
No. of reflections 2198 1975
No. of parameters 169 216
No. of restraints 12 298
H-atom treatment H-atom parameters constrained H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3) 0.25, −0.15 0.15, −0.20
Computer programs: CrysAlis PRO (Agilent, 2014[Agilent (2014). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England.]), CrysAlis PRO (Rigaku OD, 2015[Rigaku OD (2015). CrysAlis PRO. Rigaku Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]), SHELXT (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2014 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008[Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339-341.]).

The selection of a good-quality single crystal of (I)[link] was not easy because the brittle crystals were easily damaged. The crystal eventually selected for the X-ray diffraction experiment contained four domains. Data reduction was carried out in three different ways: (i) taking into account the reflections from the largest domain only (one orientation matrix and 59% of all reflections); (ii) processing the diffraction data as from a multiple crystal (four different orientation matrices) using reflections from all four domains; (iii) processing the diffraction data as from a multiple crystal using four different orientation matrices but taking into consideration the reflection from largest domain (50% of all reflections). According to the F2/σ(F2) and Rint parameters, the first method gave the best results.

All atoms of (II) (except for the C atom of the carb­oxyl group of the maleate anion, the H atom of the carb­oxyl group of the dimeric DL-norvalinium–DL-norvaline cation and another H atom of the carboxyl group of the maleate anion) are disordered. The sites with smaller occupancies are defined as B. The occupancy ratio for the disordered sites was refined as 0.556 (11):0.444 (11) for the maleate anion and 0.741 (5):0.259 (5) for the dimeric DL-norvalinium–DL-norvaline cation. The amino acid cations at the sites with higher and lower occupancies are stereoisomers. The H1 atom lies on the inversion centre and the H4 atom lies on the mirror plane; therefore, the corresponding site occupancies are equal to 0.5. The C1B—C2B, O1B—C1B, O1—H1 and O4—H4 distances were fixed at 1.480 (2), 1.400 (2), 1.289 (2) and 1.202 (2) Å, respectively. The anisotropic displacement parameters of all the atoms were refined with a rigid-bond restraint. For all non-H atoms, the Uij values were restrained to be within 0.04 Å2 (within 0.08 Å2 for the terminal atom). All H atoms were located initially in a difference Fourier map. The positions of all H atoms (except for the H1 and H4 atoms, for which O—H distances were restrained) were subsequently geometrically optimized and refined using a riding model, with the following assumptions and constraints: N—H = 0.89 Å and C—H = 0.93 (anion), 0.98 (methine), 0.97 (methyl­ene) or 0.96 Å (meth­yl), with Uiso(H) = 1.5Ueq(C,O) for the methyl and OH groups, and 1.2Ueq(C,N) otherwise.

3. Results and discussion

Currently, 25 crystal structures of mol­ecular salts of maleic acid with amino acids have been reported, with 23 having been documented in the Cambridge Structural Database (CSD; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) and two structures having no refcodes [DL-argininium hydrogen maleate (Ravishankar et al., 1998[Ravishankar, R., Chandra, N. R. & Vijayan, M. (1998). J. Biomol. Struct. Dyn. 15, 1093-1100.]) and L-me­thio­ninium L-me­thio­nine hydrogen maleate (Natarajan et al., 2010[Natarajan, S., Devi, N. R., Dhas, S. A. M. B. & Athimoolam, S. (2010). J. Optoelectron. Adv. Mater. 4, 516-519.])]. All these structures can be divided into three classes.

(1) Hydrogen maleates with a 1:1 stoichiometry containing one amino acid and one maleate anion in the asymmetric unit. The majority of all known hydrogen maleates belong to this class.

(2) Hydrogen maleates with a 1:2 stoichiometry containing one amino acid dication and two maleate anions in the asymmetric unit. Currently only one structure can be assigned to this class (see Table 2[link], refcode TENVOZ).

Table 2
Classification of hydrogen maleates according to their stoichiometry

There are also two hydrates belonging to the A+B class, viz. (L-ArgH+M·2H2O (CSD refcode GIHGEK; Sun et al., 2007[Sun, Z.-H., Yu, W.-T., Fan, J.-D., Xu, D. & Wang, X.-Q. (2007). Acta Cryst. E63, o2805-o2807.]) and (L-HisH+M·H2O (CSD refcode TENVUF; Fleck et al., 2013[Fleck, M., Ghazaryan, V. V., Bezhanova, L. S., Atanesyan, A. K. & Petrosyan, A. M. (2013). J. Mol. Struct. 1035, 407-415.]), and two other hydrates related to the nA+nB class, viz. (L-HisH+)2·(M)2·3H2O (CSD refcode VAZJUD; Gonsago et al., 2012[Gonsago, C. A., Albert, H. M., Karthikeyan, J., Sagayaraj, P. & Pragasam, A. J. A. (2012). Mater. Res. Bull. 47, 1648-1652.]) and (L-IleH+)2·(M)2·H2O (CSD refcode VUKQEZ; Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.]).

Composition Stoichiometry class Numerical order CSD refcodes and references to original work
(GlyH+M A+B 1 RENBAN (Rajagopal et al., 2001[Rajagopal, K., Krishnakumar, R. V., Mostad, A. & Natarajan, S. (2001a). Acta Cryst. E57, o751-o753.]a)
(L-AlaH+M     BOQTEG (Alagar et al., 2001[Alagar, M., Krishnakumar, R. V., Nandhini, M. S. & Natarajan, S. (2001b). Acta Cryst. E57, o855-o857.]b)
(L-PheH+M     EDAXIQ (Alagar et al., 2001c[Alagar, M., Krishnakumar, R. V. & Natarajan, S. (2001c). Acta Cryst. E57, o968-o970.])
(DL-PheH+M     VAGVIJ (Alagar et al., 2003[Alagar, M., Subha Nandhini, M., Krishnakumar, R. V., Mostad, A. & Natarajan, S. (2003). Acta Cryst. E59, o209-o211.])
(DL-ValH+M     QURSUR (Alagar et al., 2001a[Alagar, M., Krishnakumar, R. V., Mostad, A. & Natarajan, S. (2001a). Acta Cryst. E57, o1102-o1104.])
(L-SerH+M     REZPET (Arkhipov et al., 2013[Arkhipov, S. G., Zakharov, B. A. & Boldyreva, E. V. (2013). Acta Cryst. C69, 517-521.])
(DL-SerH+M     REZPAP (Arkhipov et al., 2013[Arkhipov, S. G., Zakharov, B. A. & Boldyreva, E. V. (2013). Acta Cryst. C69, 517-521.])
(DL-MetH+M     MOCXUX (Alagar et al., 2002[Alagar, M., Subha Nandhini, M., Krishnakumar, R. V. & Natarajan, S. (2002). Acta Cryst. E58, o396-o398.])
(SarH+M     MIYBAX01 (Ilczyszyn et al., 2003[Ilczyszyn, M., Godzisz, D. & Ilczyszyn, M. (2003). Spectrochim. Acta A Mol. Biomol. Spectrosc. 59, 1815-1828.])
(L-ValH+M     NUZMIG (Rychkov et al., 2016[Rychkov, D., Arkhipov, S. & Boldyreva, E. (2016). Acta Cryst. B72, 160-163.])
(DL-ThrH+M     ETEYOR (Rajagopal et al., 2004[Rajagopal, K., Ramachandran, E., Mostad, A. & Natarajan, S. (2004). Acta Cryst. E60, o386-o388.])
(β-AlaH+M     EDASUX (Rajagopal et al., 2001b[Rajagopal, K., Krishnakumar, R. V. & Natarajan, S. (2001b). Acta Cryst. E57, o922-o924.])
(BacH+M     LUSXII (Báthori & Kilinkissa, 2015[Báthori, N. B. & Kilinkissa, O. E. Y. (2015). CrystEngComm, 17, 8264-8272.])
(L-LysH+M     XADTOL (Pratap et al., 2000[Pratap, J. V., Ravishankar, R. & Vijayan, M. (2000). Acta Cryst. B56, 690-696.])
(DL-ArgH+M     Ravishankar et al. (1998[Ravishankar, R., Chandra, N. R. & Vijayan, M. (1998). J. Biomol. Struct. Dyn. 15, 1093-1100.])
(BetH+M     NASQED01 (Haussühl & Schreuer, 2001[Haussühl, E. & Schreuer, J. (2001). Z. Kristallogr. 216, 616-622.])
(L-HisH22+)·(M)2 An+nB 2 TENVOZ (Fleck et al., 2013[Fleck, M., Ghazaryan, V. V., Bezhanova, L. S., Atanesyan, A. K. & Petrosyan, A. M. (2013). J. Mol. Struct. 1035, 407-415.])
L-Met·L-MetH+·M A2+B 3 Natarajan et al. (2010[Natarajan, S., Devi, N. R., Dhas, S. A. M. B. & Athimoolam, S. (2010). J. Optoelectron. Adv. Mater. 4, 516-519.])
L-Nva·L-NvaH+·M     VUKQID (Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.])
(L-HisH+)2·(M)2 nA+nB (n = 2, 3, etc.) 4 XADTIF (Pratap et al., 2000[Pratap, J. V., Ravishankar, R. & Vijayan, M. (2000). Acta Cryst. B56, 690-696.])
(L-LeuH+)3·(M)3     VUKQAV (Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.])

(3) Hydrogen maleates with dimeric amino acid cations and maleate anions consequently having a 2:1 stoichiometry.

(4) Hydrogen maleates with a 1:1 stoichiometry containing more than one of each chemical species (amino acid cation and maleate anion) in the asymmetric unit (Table 2[link]).

The title salts, (I)[link] and (II), are the first examples of mol­ecular salts of DL-norvaline with a carb­oxy­lic acid (Fig. 1[link]). Maleic acid is known as a common coformer. Due to its compact flat shape, stabilized by an intra­molecular hydrogen bond (Table 3[link]) and the presence of several hydrogen-bond acceptors, maleic acid can easily be embedded into different crystalline environments. Salt (I)[link] crystallizes in the centrosymmetric space group C2/c. The asymmetric unit of (I)[link] contains one norvaline cation and one maleate anion, so that it belongs to the first (most populated) class of the aforementioned classification (Fig. 1[link]) (Table 2[link]).

Table 3
Hydrogen-bond geometry (Å, °) for (I)[link]

D—H⋯A D—H H⋯A DA D—H⋯A
O6—H6⋯O4 0.82 1.60 2.421 (2) 178
O1—H1⋯O5 0.82 1.80 2.612 (3) 171
N1—H1A⋯O2i 0.89 2.11 2.864 (3) 142
N1—H1B⋯O4ii 0.89 2.01 2.898 (3) 172
N1—H1C⋯O3iii 0.89 1.97 2.850 (3) 168
Symmetry codes: (i) [-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]; (ii) [x, -y+1, z+{\script{1\over 2}}]; (iii) [x, -y, z+{\script{1\over 2}}].
[Figure 1]
Figure 1
The asymmetric units of (a) (I)[link] and (b) (II)[link], showing the atom-numbering schemes. Displacement ellipsoids are drawn at the 50% probability level. For (I)[link], only the major-disorder form of the molecules are shown. For (II)[link], half of the maleate anion belongs to the asymmetric unit, as it sits on a mirror plane.

The crystal structure of (I)[link] can be compared with those of two polymorphs of pure DL-norvaline, i.e. at 203 (the β-form) and 183 K (the α-form) (Görbitz, 2011[Görbitz, C. H. (2011). J. Phys. Chem. B, 115, 2447-2453.]). Both compounds have layered structures; the H3N+ group of the norvaline zwitterions are linked to three COO groups of other zwitterions by hydrogen bonds, forming three `head-to-tail' chains. Similar chains (but composed of norvalinium cations) are present also in the structure of (I)[link] [C(5) motifs along the crystallographic b direction]. One can also see C22(6) chains along the b direction formed by hydrogen bonds between the NH3+ group of one norvalinium cation and the COO group of another cation (Fig. 2[link] and Table 4[link]). Almost all the amino acid maleates contain C22(12) chains (Rychkov et al., 2016[Rychkov, D., Arkhipov, S. & Boldyreva, E. (2016). Acta Cryst. B72, 160-163.]), and (I)[link] is no exception; it also has C22(12) chains formed by norvalinium cations and maleate anions assembling along the c direction. In addition, there are C22(12)′ chains in (I)[link] formed by two types of hydrogen bonds: (i) between the COOH group of a norvalinium cation and the COOH group of a maleate anion, and (ii) between the H3N+ group of a norvalinium cation and the COO group of a maleate anion (Fig. 3[link]). The second type of hydrogen bond involves one of the O atoms of the COO group of a maleate anion which is participating in an intra­molecular hydrogen bond within a maleate anion (Fig. 3[link] and Table 3[link]). The C22(6), C22(12) and C22(12)′ chains form half a layer, and two such half-layers are connected by C(5) chains, with each forming a complete layer so that a two-dimensional hydrogen-bonding network parallel to the (100) plane is formed (Fig. 2[link]). The side chains of DL-norvaline are directed to the outer surfaces of the layers and thus adjacent layers interdigitate to give hydro­phobic layers with well-defined channels lie parallel to the hydro­phobic layers (Fig. 4[link]).

Table 4
Hydrogen-bond geometry (Å, °) for (II)[link]

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1A⋯O2i 0.89 1.94 2.807 (8) 165
N1—H1B⋯O3 0.89 2.08 2.92 (4) 157
N1—H1C⋯O3ii 0.89 1.90 2.79 (4) 178
O1—H1⋯O1iii 1.28 (1) 1.28 (1) 2.568 (13) 180 (1)
O4—H4⋯O4iv 1.21 (1) 1.21 (1) 2.418 (9) 173 (8)
Symmetry codes: (i) [-x+{\script{1\over 2}}, -y+1, z-{\script{1\over 2}}]; (ii) [x-{\script{1\over 2}}, y, -z+{\script{1\over 2}}]; (iii) -x+1, -y+1, -z+1; (iv) [x, -y+{\script{3\over 2}}, z].
[Figure 2]
Figure 2
The crystal structure of fragments of (I)[link], showing (a) C22(12) chains linked to each other via C22(6) chains and (b) C22(12)′ chains linked to each other via C(5) chains.
[Figure 3]
Figure 3
The C22(12) and C22(12)′ chains in (DL-NvaH+M, (I).
[Figure 4]
Figure 4
Visualization of the voids in the structures of (a) (I)[link] and (b) (II)[link] using the Mercury program (Macrae et al., 2008[Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466-470.]). The channel along the b direction is highlighted by the dark-red circle. Voids were found using the `contact surface' method with a probe radius of 0.5 Å and a grid size of 0.1 Å. The major-disorder form of the DL-norvalinium cation and DL-norvalinium–DL-norvaline dimeric cation are coloured green, the maleate anion is blue and red dots correspond to the minor-disorder forms of the components.

The mol­ecular salt (II) crystallizes in a centrosymmetric Pnma space group. The unit cell of (II) contains dimeric DL-norvalinium–DL-norvaline cations (a zwitterion of norvaline and a norvalinium cation connected by a strong O—H⋯O hydrogen bond) and maleate anions in the 1:1 ratio. The salt (II)[link] could be assigned to the third class according to Table 2[link]. The structure of (II) contains two C33(17) heteromolecular chains along the crystallographic b direction formed by dimeric DL-norvalinium–DL-norvaline cations and maleate anions. Similar hydrogen-bonded chains were observed in the structure of L-norvalinium hydrogen maleate–L-norvaline (Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.]) (Fig. 5[link]a). Head-to-tail C(5) chains of dimeric DL-norvalinium–DL-norvaline cations propagate along the c direction normal to the C33(17) chains. Another amino acid C22(9) chain along the a direction is formed by the dimeric DL-norvalinium–DL-norvaline cations. These three types of chains have common norvaline mol­ecules and are connected with each other by hydrogen bonds to form a three-dimensional hydrogen-bonded network. Comparing the structures of (I)[link] and (II), one can see that the same components form different types of crystal structures: a layered structure in (I)[link] and a three-dimensional hydrogen-bonded structure in (II). The structure of (II) also has channels along the crystallographic a direction; the volume of the voids in (II) (12.1%, 230.42 Å3) is about a half of that in (I)[link] (Fig. 4[link]).

[Figure 5]
Figure 5
Comparison of the heteromolecular hydrogen-bonded chains in the structures of (a) L-norvalinium hydrogen maleate–L-norvaline (Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.]) and (b) DL-norvalinium hydrogen maleate–DL-norvaline, (II).

The DL-norvaline–maleic acid system is inter­esting from a crystal engineering point of view: the same mol­ecules form salts with different types of crystal structures. DL-Norvaline can form salts with maleic acid with either a layered structure as in (I)[link] or a three-dimensional hydrogen-bonded structure as in (II). The mol­ecular salts (I)[link] and (II) belong to different stoichiometric classes (Table 2[link]). DL-Norvalinium hydrogen maleate, (I)[link], and DL-norvalinium hydrogen maleate–DL-nor­valine, (II), are the first examples of mol­ecular salts of DL-norvaline with a carb­oxy­lic acid. The presence of the dimeric cation of DL-norvaline in the structure of (II) makes it possible to form a three-dimensional network of hydrogen bonds, the structural type which is not common for the maleates of amino acids with a large hydro­phobic side chain. Despite the large number of hydrogen maleates documented in the literature, the prediction of whether a selected L-amino acid or a DL-racemate will cocrystallize with maleic acid is still difficult to make. For example, for norvaline, both L- and DL-norvalinium hydrogen maleates (with different stoichiometries) have been reported (Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.]). For alanine, only L-alaninium hydrogen maleate has been described (Alagar et al., 2001a[Alagar, M., Krishnakumar, R. V., Mostad, A. & Natarajan, S. (2001a). Acta Cryst. E57, o1102-o1104.]), with no maleates of the racemic DL-form reported. In contrast, for threonine, DL-threoninium hydrogen maleate exists (Rajagopal et al., 2004[Rajagopal, K., Ramachandran, E., Mostad, A. & Natarajan, S. (2004). Acta Cryst. E60, o386-o388.]), but no maleate of the L-form has been reported. Moreover, the crystallization of DL-alaninium hydrogen maleate is probably impossible because of the resolution of alanine enanti­omers in a racemic solution on addition of maleic acid with the formation of L-alaninium hydrogen maleate and D-alaninium hydrogen maleate (Asai et al., 1975[Asai, S., Tazuke, H. & Kageyama, H. (1975). US Patent 3897484A; Appl. No. 239786.]). Such `stereoselective' cocrystallization is hard to explain using the traditional synthon approach (Desiraju, 1995[Desiraju, G. R. (1995). Angew. Chem. Int. Ed. Engl. 34, 2311-2327.]). It is quite possible that the number of hydrogen maleates of amino acids obtained is proportional to the time spent searching for them, similar to what McCrone (1965[McCrone, W. C. (1965). Polymorphism, in Physics and Chemistry of the Organic Solid State, Vol. 2, edited by D. Fox, M. M. Labes & A. Weissberger, pp. 725-767. New York: Wiley Interscience.]) supposed for polymorphs.

Another inter­esting point related to the hydrogen maleates of L-amino acids is the presence of dimeric cations in some of the structures. Up to now, this complex structural subunit has been observed in two hydrogen maleates of amino acids, namely in L-norvalinium hydrogen maleate–L-norvaline (Arkhipov et al., 2015[Arkhipov, S. G., Rychkov, D. A., Pugachev, A. M. & Boldyreva, E. V. (2015). Acta Cryst. C71, 584-592.]) and in L-me­thio­ninium L-me­thio­nine hydrogen maleate (Natarajan et al., 2010[Natarajan, S., Devi, N. R., Dhas, S. A. M. B. & Athimoolam, S. (2010). J. Optoelectron. Adv. Mater. 4, 516-519.]). DL-Norvalinium hydrogen maleate–DL-norvaline, (II), is the first example of a racemic maleate containing the dimeric cation of an amino acid.

Supporting information


Computing details top

Data collection: CrysAlis PRO (Agilent, 2014) for (I); CrysAlis PRO (Rigaku OD, 2015) for 2dl_nv_mal. Cell refinement: CrysAlis PRO (Agilent, 2014) for (I); CrysAlis PRO (Rigaku OD, 2015) for 2dl_nv_mal. Data reduction: CrysAlis PRO (Agilent, 2014) for (I); CrysAlis PRO (Rigaku OD, 2015) for 2dl_nv_mal. For both compounds, program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b). Molecular graphics: OLEX2 (Dolomanov et al., 2009) for (I); Mercury (Macrae et al., 2008) for 2dl_nv_mal. For both compounds, software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

(I) DL-Norvalinium hydrogen maleate top
Crystal data top
C5H12NO2+·C4H3O4F(000) = 992
Mr = 233.22Dx = 1.247 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 19.6385 (15) ÅCell parameters from 3032 reflections
b = 5.62705 (18) Åθ = 1.8–25.1°
c = 23.6867 (10) ŵ = 0.11 mm1
β = 108.283 (6)°T = 293 K
V = 2485.4 (2) Å3Block, clear light colourless
Z = 80.25 × 0.15 × 0.1 mm
Data collection top
Agilent Xcalibur Ruby Gemini ultra
diffractometer
2198 independent reflections
Radiation source: Enhance (Mo) X-ray Source1807 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.051
Detector resolution: 10.3457 pixels mm-1θmax = 25.0°, θmin = 1.8°
ω scansh = 2323
Absorption correction: multi-scan
(CrysAlis PRO; Agilent, 2014)
k = 66
Tmin = 0.866, Tmax = 1.000l = 2828
13186 measured reflections
Refinement top
Refinement on F2Primary atom site location: dual
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.068H-atom parameters constrained
wR(F2) = 0.166 w = 1/[σ2(Fo2) + (0.0688P)2 + 1.2674P]
where P = (Fo2 + 2Fc2)/3
S = 1.23(Δ/σ)max < 0.001
2198 reflectionsΔρmax = 0.25 e Å3
169 parametersΔρmin = 0.15 e Å3
12 restraints
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O20.30316 (12)0.1684 (3)0.75497 (7)0.0587 (6)
O40.33415 (13)0.3088 (3)0.45870 (8)0.0634 (6)
O60.34166 (13)0.3563 (3)0.56205 (8)0.0653 (6)
H60.33880.34280.52690.098*
O50.33741 (12)0.1258 (4)0.63532 (8)0.0640 (6)
O30.32140 (14)0.0195 (3)0.39432 (8)0.0733 (7)
O10.35365 (15)0.4538 (4)0.71650 (9)0.0797 (8)
H10.34610.36140.68840.120*
N10.29849 (14)0.4474 (4)0.84537 (9)0.0530 (6)
H1A0.25410.47540.82180.064*
H1B0.30730.53550.87810.064*
H1C0.30300.29430.85530.064*
C90.33889 (16)0.1511 (4)0.58407 (10)0.0472 (7)
C10.33256 (16)0.3576 (5)0.75847 (11)0.0493 (7)
C60.32998 (17)0.0889 (5)0.44513 (11)0.0517 (7)
C20.35023 (16)0.5090 (5)0.81368 (11)0.0513 (7)
H20.34460.67700.80220.062*
C80.33796 (19)0.0648 (5)0.54893 (11)0.0602 (9)
H80.34010.20630.56970.072*
C70.33452 (19)0.0911 (5)0.49233 (12)0.0637 (9)
H70.33500.24800.48020.076*
C30.4257 (2)0.4676 (7)0.85504 (15)0.0804 (11)
H3AA0.43030.54340.89280.097*0.865 (8)
H3AB0.43250.29830.86230.097*0.865 (8)
H3BC0.42170.32990.87840.097*0.135 (8)
H3BD0.45250.41450.82920.097*0.135 (8)
C4A0.4845 (3)0.5576 (11)0.8329 (2)0.1011 (19)0.865 (8)
H4AA0.53010.50920.86080.121*0.865 (8)
H4AB0.48000.48080.79520.121*0.865 (8)
C4B0.473 (2)0.624 (7)0.8964 (16)0.114 (9)0.135 (8)
H4BA0.45270.66380.92740.136*0.135 (8)
H4BB0.51810.54090.91500.136*0.135 (8)
C5A0.4863 (4)0.8168 (15)0.8244 (5)0.143 (3)0.865 (8)
H5AA0.44400.86530.79340.214*0.865 (8)
H5AB0.52800.85780.81350.214*0.865 (8)
H5AC0.48810.89610.86070.214*0.865 (8)
C5B0.488 (4)0.829 (11)0.872 (3)0.166 (18)0.135 (8)
H5BA0.44710.87460.83920.249*0.135 (8)
H5BB0.52850.80540.85810.249*0.135 (8)
H5BC0.49880.95300.90140.249*0.135 (8)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O20.0956 (16)0.0514 (12)0.0351 (10)0.0135 (11)0.0289 (9)0.0092 (8)
O40.1220 (19)0.0344 (10)0.0397 (10)0.0056 (10)0.0336 (10)0.0026 (7)
O60.1231 (19)0.0385 (11)0.0417 (11)0.0051 (11)0.0364 (12)0.0074 (8)
O50.1054 (17)0.0600 (12)0.0355 (10)0.0015 (11)0.0350 (10)0.0014 (8)
O30.139 (2)0.0517 (12)0.0381 (11)0.0037 (12)0.0405 (12)0.0057 (8)
O10.129 (2)0.0787 (16)0.0470 (12)0.0372 (14)0.0501 (13)0.0171 (10)
N10.0863 (18)0.0445 (13)0.0319 (11)0.0082 (11)0.0240 (11)0.0036 (9)
C90.0698 (19)0.0395 (14)0.0354 (14)0.0031 (12)0.0208 (12)0.0009 (10)
C10.0698 (19)0.0502 (17)0.0322 (13)0.0032 (14)0.0221 (12)0.0026 (11)
C60.087 (2)0.0372 (14)0.0364 (14)0.0011 (13)0.0279 (13)0.0007 (11)
C20.072 (2)0.0471 (15)0.0380 (14)0.0066 (13)0.0210 (13)0.0077 (11)
C80.111 (3)0.0333 (14)0.0418 (15)0.0039 (15)0.0321 (15)0.0065 (11)
C70.124 (3)0.0296 (13)0.0429 (15)0.0042 (15)0.0347 (16)0.0041 (11)
C30.082 (3)0.088 (3)0.065 (2)0.002 (2)0.0144 (19)0.0186 (18)
C4A0.072 (3)0.129 (5)0.096 (3)0.002 (3)0.019 (3)0.028 (3)
C4B0.114 (16)0.106 (16)0.104 (16)0.005 (15)0.012 (14)0.044 (14)
C5A0.112 (5)0.122 (6)0.195 (9)0.031 (4)0.050 (6)0.010 (6)
C5B0.15 (3)0.15 (3)0.17 (3)0.03 (3)0.01 (3)0.05 (3)
Geometric parameters (Å, º) top
O2—C11.202 (3)C7—H70.9300
O4—C61.274 (3)C3—H3AA0.9700
O6—H60.8200C3—H3AB0.9700
O6—C91.275 (3)C3—H3BC0.9700
O5—C91.231 (3)C3—H3BD0.9700
O3—C61.226 (3)C3—C4A1.498 (6)
O1—H10.8200C3—C4B1.43 (3)
O1—C11.308 (3)C4A—H4AA0.9700
N1—H1A0.8900C4A—H4AB0.9700
N1—H1B0.8900C4A—C5A1.474 (9)
N1—H1C0.8900C4B—H4BA0.9700
N1—C21.482 (4)C4B—H4BB0.9700
C9—C81.469 (4)C4B—C5B1.36 (7)
C1—C21.507 (4)C5A—H5AA0.9600
C6—C71.490 (4)C5A—H5AB0.9600
C2—H20.9800C5A—H5AC0.9600
C2—C31.517 (5)C5B—H5BA0.9600
C8—H80.9300C5B—H5BB0.9600
C8—C71.329 (4)C5B—H5BC0.9600
C9—O6—H6109.5H3AA—C3—H3AB107.5
C1—O1—H1109.5H3BC—C3—H3BD105.7
H1A—N1—H1B109.5C4A—C3—C2115.2 (3)
H1A—N1—H1C109.5C4A—C3—H3AA108.5
H1B—N1—H1C109.5C4A—C3—H3AB108.5
C2—N1—H1A109.5C4B—C3—C2130.3 (16)
C2—N1—H1B109.5C4B—C3—H3BC104.7
C2—N1—H1C109.5C4B—C3—H3BD104.7
O6—C9—C8120.8 (2)C3—C4A—H4AA108.3
O5—C9—O6121.7 (2)C3—C4A—H4AB108.3
O5—C9—C8117.6 (2)H4AA—C4A—H4AB107.4
O2—C1—O1125.0 (2)C5A—C4A—C3115.9 (5)
O2—C1—C2122.4 (2)C5A—C4A—H4AA108.3
O1—C1—C2112.6 (2)C5A—C4A—H4AB108.3
O4—C6—C7119.1 (2)C3—C4B—H4BA108.7
O3—C6—O4122.4 (2)C3—C4B—H4BB108.7
O3—C6—C7118.5 (2)H4BA—C4B—H4BB107.6
N1—C2—C1107.4 (2)C5B—C4B—C3114 (3)
N1—C2—H2109.3C5B—C4B—H4BA108.7
N1—C2—C3108.9 (2)C5B—C4B—H4BB108.7
C1—C2—H2109.3C4A—C5A—H5AA109.5
C1—C2—C3112.7 (3)C4A—C5A—H5AB109.5
C3—C2—H2109.3C4A—C5A—H5AC109.5
C9—C8—H8114.7H5AA—C5A—H5AB109.5
C7—C8—C9130.6 (2)H5AA—C5A—H5AC109.5
C7—C8—H8114.7H5AB—C5A—H5AC109.5
C6—C7—H7114.6C4B—C5B—H5BA109.5
C8—C7—C6130.8 (2)C4B—C5B—H5BB109.5
C8—C7—H7114.6C4B—C5B—H5BC109.5
C2—C3—H3AA108.5H5BA—C5B—H5BB109.5
C2—C3—H3AB108.5H5BA—C5B—H5BC109.5
C2—C3—H3BC104.7H5BB—C5B—H5BC109.5
C2—C3—H3BD104.7
O2—C1—C2—N126.0 (4)N1—C2—C3—C4A170.8 (3)
O2—C1—C2—C393.9 (4)N1—C2—C3—C4B90 (2)
O4—C6—C7—C85.0 (6)C9—C8—C7—C60.4 (7)
O6—C9—C8—C75.4 (6)C1—C2—C3—C4A70.1 (4)
O5—C9—C8—C7175.1 (4)C1—C2—C3—C4B151 (2)
O3—C6—C7—C8174.1 (4)C2—C3—C4A—C5A63.3 (7)
O1—C1—C2—N1154.9 (3)C2—C3—C4B—C5B57 (5)
O1—C1—C2—C385.1 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O6—H6···O40.821.602.421 (2)178
O1—H1···O50.821.802.612 (3)171
N1—H1A···O2i0.892.112.864 (3)142
N1—H1B···O4ii0.892.012.898 (3)172
N1—H1C···O3iii0.891.972.850 (3)168
Symmetry codes: (i) x+1/2, y+1/2, z+3/2; (ii) x, y+1, z+1/2; (iii) x, y, z+1/2.
(2dl_nv_mal) DL-Norvalinium hydrogen maleate–DL-norvaline (1/1) top
Crystal data top
C5H12NO2+·C4H3O4·C5H11NO2Dx = 1.226 Mg m3
Mr = 350.37Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, PnmaCell parameters from 6447 reflections
a = 8.8572 (4) Åθ = 2.3–27.7°
b = 27.3614 (11) ŵ = 0.10 mm1
c = 7.8306 (4) ÅT = 293 K
V = 1897.71 (15) Å3Block, clear light colourless
Z = 40.5 × 0.25 × 0.2 mm
F(000) = 752
Data collection top
Agilent Xcalibur Ruby Gemini ultra
diffractometer
1975 independent reflections
Radiation source: fine-focus sealed X-ray tube, Enhance (Mo) X-ray Source1731 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.053
Detector resolution: 10.3457 pixels mm-1θmax = 26.4°, θmin = 3.0°
ω scansh = 1111
Absorption correction: multi-scan
(CrysAlis PRO; Agilent, 2014)
k = 3434
Tmin = 0.948, Tmax = 1.000l = 99
21923 measured reflections
Refinement top
Refinement on F2Primary atom site location: dual
Least-squares matrix: fullHydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.079H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.146 w = 1/[σ2(Fo2) + 2.5627P]
where P = (Fo2 + 2Fc2)/3
S = 1.14(Δ/σ)max < 0.001
1975 reflectionsΔρmax = 0.15 e Å3
216 parametersΔρmin = 0.20 e Å3
298 restraints
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.3996 (7)0.5283 (3)0.4353 (8)0.0588 (14)0.733 (5)
O20.2253 (12)0.4842 (4)0.5382 (11)0.0673 (19)0.733 (5)
N10.1895 (3)0.58452 (10)0.2864 (4)0.0436 (9)0.733 (5)
H1A0.2092360.5663960.1947540.052*0.733 (5)
H1B0.2719730.6010060.3163570.052*0.733 (5)
H1C0.1155460.6054550.2625070.052*0.733 (5)
C10.2668 (10)0.5162 (3)0.486 (2)0.053 (2)0.733 (5)
C60.4597 (4)0.69058 (10)0.2591 (5)0.0667 (9)
C30.0925 (9)0.5831 (2)0.5848 (10)0.0563 (15)0.733 (5)
H3A0.0150170.6058210.5479030.068*0.733 (5)
H3B0.0476970.5616150.6692520.068*0.733 (5)
C20.1420 (5)0.55218 (16)0.4302 (6)0.0450 (10)0.733 (5)
H20.0548650.5330110.3920040.054*0.733 (5)
O40.4852 (12)0.70580 (16)0.1052 (7)0.082 (3)0.532 (13)
C40.2156 (11)0.6112 (4)0.6672 (11)0.078 (2)0.733 (5)
H4A0.2580510.6338070.5847840.093*0.733 (5)
H4B0.2950230.5887850.7013210.093*0.733 (5)
C70.4209 (11)0.7257 (3)0.3969 (11)0.055 (2)0.532 (13)
H70.3919430.7114750.4995710.066*0.532 (13)
O4B0.5932 (11)0.70603 (18)0.1975 (19)0.112 (5)0.468 (13)
N1B0.0750 (11)0.5607 (3)0.3297 (13)0.054 (3)0.267 (5)
H1BA0.1166140.5431140.2465740.065*0.267 (5)
H1BB0.0342460.5876710.2856700.065*0.267 (5)
H1BC0.0036940.5432230.3812360.065*0.267 (5)
O1B0.425 (2)0.5365 (8)0.503 (2)0.067 (5)0.267 (5)
O2B0.229 (4)0.4803 (10)0.593 (3)0.066 (5)0.267 (5)
C2B0.1906 (15)0.5742 (4)0.4535 (19)0.054 (3)0.267 (5)
H2B0.2593370.5975570.3990150.064*0.267 (5)
C7B0.3551 (12)0.7257 (3)0.3272 (18)0.068 (3)0.468 (13)
H7B0.2719680.7118380.3812950.082*0.468 (13)
C1B0.271 (3)0.5271 (8)0.473 (7)0.049 (4)0.267 (5)
C3B0.117 (4)0.5995 (9)0.605 (4)0.086 (6)0.267 (5)
H3BA0.0522940.6255990.5638190.103*0.267 (5)
H3BB0.0532070.5761560.6648500.103*0.267 (5)
C4B0.223 (4)0.6193 (12)0.723 (4)0.107 (7)0.267 (5)
H4BA0.2403240.5965310.8154530.129*0.267 (5)
H4BB0.3186020.6251570.6653810.129*0.267 (5)
O30.453 (5)0.6486 (10)0.284 (6)0.073 (7)0.532 (13)
O3B0.440 (5)0.6447 (12)0.290 (6)0.063 (5)0.468 (13)
C50.1602 (13)0.6408 (3)0.8296 (14)0.096 (3)0.733 (5)
H5A0.0893870.6654410.7947060.145*0.733 (5)
H5B0.2452800.6560780.8836800.145*0.733 (5)
H5C0.1124090.6189010.9085340.145*0.733 (5)
C5B0.170 (5)0.6600 (9)0.782 (5)0.129 (11)0.267 (5)
H5BA0.1033000.6743080.6986210.193*0.267 (5)
H5BB0.2513460.6820680.8049350.193*0.267 (5)
H5BC0.1147730.6537310.8850120.193*0.267 (5)
H10.5000000.5000000.5000000.193*
H40.483 (9)0.7500000.115 (11)0.193*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.044 (3)0.052 (3)0.080 (4)0.016 (2)0.004 (2)0.021 (3)
O20.058 (2)0.061 (4)0.083 (6)0.005 (2)0.002 (4)0.030 (4)
N10.0397 (17)0.0352 (15)0.056 (2)0.0090 (13)0.0013 (15)0.0050 (14)
C10.045 (3)0.051 (4)0.061 (5)0.023 (3)0.001 (3)0.019 (5)
C60.064 (2)0.0354 (15)0.101 (3)0.0003 (13)0.0253 (19)0.0043 (17)
C30.048 (3)0.052 (3)0.069 (4)0.018 (2)0.009 (3)0.006 (3)
C20.040 (2)0.034 (2)0.061 (3)0.0051 (18)0.001 (2)0.008 (2)
O40.115 (7)0.047 (2)0.084 (3)0.000 (3)0.028 (4)0.011 (2)
C40.072 (4)0.080 (4)0.081 (5)0.010 (3)0.014 (4)0.023 (4)
C70.066 (5)0.035 (3)0.065 (4)0.001 (3)0.007 (4)0.003 (3)
O4B0.070 (5)0.043 (3)0.223 (12)0.004 (3)0.081 (7)0.000 (4)
N1B0.050 (6)0.041 (5)0.070 (6)0.009 (4)0.002 (5)0.010 (4)
O1B0.044 (6)0.057 (7)0.101 (14)0.013 (5)0.003 (7)0.017 (9)
O2B0.074 (7)0.059 (6)0.064 (11)0.029 (5)0.017 (8)0.050 (7)
C2B0.050 (6)0.029 (5)0.083 (8)0.012 (5)0.006 (6)0.008 (5)
C7B0.048 (5)0.038 (3)0.119 (9)0.000 (4)0.027 (5)0.002 (5)
C1B0.053 (7)0.035 (8)0.059 (10)0.006 (6)0.014 (6)0.026 (7)
C3B0.084 (13)0.090 (14)0.083 (10)0.037 (11)0.002 (9)0.005 (9)
C4B0.127 (15)0.103 (14)0.092 (15)0.041 (12)0.025 (13)0.013 (10)
O30.071 (14)0.023 (4)0.124 (11)0.004 (5)0.026 (9)0.005 (5)
O3B0.050 (6)0.032 (6)0.108 (12)0.002 (6)0.019 (7)0.007 (7)
C50.098 (5)0.094 (7)0.097 (6)0.020 (5)0.004 (4)0.023 (5)
C5B0.20 (3)0.071 (14)0.12 (2)0.029 (16)0.020 (18)0.002 (12)
Geometric parameters (Å, º) top
O1—C11.286 (11)N1B—H1BA0.8900
O1—H11.284 (6)N1B—H1BB0.8900
O2—C11.034 (15)N1B—H1BC0.8900
N1—H1A0.8900N1B—C2B1.457 (17)
N1—H1B0.8900O1B—C1B1.41 (2)
N1—H1C0.8900O1B—H11.20 (2)
N1—C21.492 (6)O2B—C1B1.63 (4)
C1—C21.544 (7)C2B—H2B0.9800
C6—O41.295 (6)C2B—C1B1.481 (18)
C6—C71.486 (8)C2B—C3B1.52 (3)
C6—O4B1.345 (6)C7B—C7Bi1.331 (17)
C6—C7B1.437 (9)C7B—H7B0.9300
C6—O31.17 (3)C3B—H3BA0.9700
C6—O3B1.29 (3)C3B—H3BB0.9700
C3—H3A0.9700C3B—C4B1.42 (3)
C3—H3B0.9700C4B—H4BA0.9700
C3—C21.541 (8)C4B—H4BB0.9700
C3—C41.481 (10)C4B—C5B1.29 (4)
C2—H20.9800C5—H5A0.9600
O4—H41.212 (7)C5—H5B0.9600
C4—H4A0.9700C5—H5C0.9600
C4—H4B0.9700C5B—H5BA0.9600
C4—C51.586 (12)C5B—H5BB0.9600
C7—C7i1.327 (14)C5B—H5BC0.9600
C7—H70.9300
C1—O1—H1110.8 (7)C2B—N1B—H1BA109.5
H1A—N1—H1B109.5C2B—N1B—H1BB109.5
H1A—N1—H1C109.5C2B—N1B—H1BC109.5
H1B—N1—H1C109.5C1B—O1B—H1112.4 (17)
C2—N1—H1A109.5N1B—C2B—H2B108.1
C2—N1—H1B109.5N1B—C2B—C1B100.8 (18)
C2—N1—H1C109.5N1B—C2B—C3B109.4 (15)
O1—C1—C2113.7 (8)C1B—C2B—H2B108.1
O2—C1—O1131.8 (9)C1B—C2B—C3B121 (2)
O2—C1—C2113.5 (9)C3B—C2B—H2B108.1
O4—C6—C7120.5 (4)C6—C7B—H7B114.0
O4B—C6—C7B119.3 (5)C7Bi—C7B—C6131.9 (4)
O3—C6—O4119 (2)C7Bi—C7B—H7B114.0
O3—C6—C7120 (2)O1B—C1B—O2B106 (2)
O3B—C6—O4B120 (2)O1B—C1B—C2B109.0 (19)
O3B—C6—C7B120 (2)C2B—C1B—O2B129 (3)
H3A—C3—H3B107.6C2B—C3B—H3BA109.0
C2—C3—H3A108.6C2B—C3B—H3BB109.0
C2—C3—H3B108.6H3BA—C3B—H3BB107.8
C4—C3—H3A108.6C4B—C3B—C2B113 (3)
C4—C3—H3B108.6C4B—C3B—H3BA109.0
C4—C3—C2114.7 (6)C4B—C3B—H3BB109.0
N1—C2—C1113.0 (6)C3B—C4B—H4BA110.0
N1—C2—C3110.3 (4)C3B—C4B—H4BB110.0
N1—C2—H2108.0H4BA—C4B—H4BB108.4
C1—C2—H2108.0C5B—C4B—C3B108 (3)
C3—C2—C1109.3 (8)C5B—C4B—H4BA110.0
C3—C2—H2108.0C5B—C4B—H4BB110.0
C6—O4—H4105 (4)C4—C5—H5A109.5
C3—C4—H4A109.0C4—C5—H5B109.5
C3—C4—H4B109.0C4—C5—H5C109.5
C3—C4—C5112.7 (8)H5A—C5—H5B109.5
H4A—C4—H4B107.8H5A—C5—H5C109.5
C5—C4—H4A109.0H5B—C5—H5C109.5
C5—C4—H4B109.0C4B—C5B—H5BA109.5
C6—C7—H7114.8C4B—C5B—H5BB109.5
C7i—C7—C6130.4 (3)C4B—C5B—H5BC109.5
C7i—C7—H7114.8H5BA—C5B—H5BB109.5
H1BA—N1B—H1BB109.5H5BA—C5B—H5BC109.5
H1BA—N1B—H1BC109.5H5BB—C5B—H5BC109.5
H1BB—N1B—H1BC109.5
O1—C1—C2—N117.9 (14)N1B—C2B—C1B—O1B147 (3)
O1—C1—C2—C3105.4 (12)N1B—C2B—C1B—O2B83 (4)
O2—C1—C2—N1151.9 (12)N1B—C2B—C3B—C4B173 (2)
O2—C1—C2—C384.9 (15)C2B—C3B—C4B—C5B144 (3)
C2—C3—C4—C5177.9 (7)C1B—C2B—C3B—C4B71 (3)
O4—C6—C7—C7i7.7 (7)C3B—C2B—C1B—O1B92 (3)
C4—C3—C2—N167.1 (8)C3B—C2B—C1B—O2B38 (4)
C4—C3—C2—C157.7 (9)O3—C6—C7—C7i180 (3)
O4B—C6—C7B—C7Bi8.4 (9)O3B—C6—C7B—C7Bi174 (3)
Symmetry code: (i) x, y+3/2, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O2ii0.891.942.807 (8)165
N1—H1B···O30.892.082.92 (4)157
N1—H1C···O3iii0.891.902.79 (4)178
O1—H1···O1iv1.28 (1)1.28 (1)2.568 (13)180 (1)
O4—H4···O4i1.21 (1)1.21 (1)2.418 (9)173 (8)
Symmetry codes: (i) x, y+3/2, z; (ii) x+1/2, y+1, z1/2; (iii) x1/2, y, z+1/2; (iv) x+1, y+1, z+1.
Classification of hydrogen maleates according with their stoichiometry top
Brutto formulaStoichiometry classCSD refcodes (references to original work)
(GlyH+).M-A+B-RENBAN (Rajagopal, Krishnakumar, Mostad & Natarajan, 2001)
(L-AlaH+).M-BOQTEG (Alagar, Krishnakumar, Nandhini & Natarajan, 2001)
(L-PheH+).M-EDAXIQ (Alagar, Krishnakumar & Natarajan, 2001)
(DL-PheH+).M-VAGVIJ (Alagar et al., 2003)
(DL-ValH+).M-QURSUR (Alagar, Krishnakumar, Mostad & Natarajan, 2001)
(L-SerH+).M-REZPET (Arkhipov et al., 2013)
(DL-SerH+). M-REZPAP (Arkhipov et al., 2013)
(DL-MetH+).M-MOCXUX (Alagar et al., 2002)
(SarH+).M-MIYBAX01 (Ilczyszyn et al., 2003)
(L-ValH+).M-NUZMIG (Rychkov et al., 2016)
(DL-ThrH+).M-ETEYOR (Rajagopal et al., 2004)
(β-AlaH+).M-EDASUX (Rajagopal, Krishnakumar & Natarajan, 2001)
(BacH+).M-LUSXII (Báthori & Kilinkissa, 2015)
(L-LysH+).M-XADTOL (Pratap et al., 2000)
(DL-ArgH+).M-(Ravishankar et al., 1998)
(BetH+).M-NASQED01 (Haussühl & Schreuer, 2001)
(L-HisH22+).(M-)2An+nB-TENVOZ (Fleck et al., 2013)
L-Met.L-MetH+.M-A2+B-(Natarajan et al. 2010)
L-Nva.L-NvaH+.M-VUKQID (Arkhipov et al., 2015)
(L-HisH+)2.(M-)2nA+nB-XADTIF (Pratap et al., 2000)
(L-LeuH+)3.(M-)3VUKQAV (Arkhipov et al., 2015)
There are also two hydrates belonging to the A+B- class: (L-ArgH+).M-.2H2O (CSD refcode GIHGEK; Sun et al., 2007), (L-HisH+).M-.H2O (CSD refcode TENVUF; Fleck et al., 2013); and two other hydrates related to the nA+nB- class: (L-HisH+)2.(M-)2.3H2O (CSD refcode VAZJUD; Gonsago et al., 2012), (L-IleH+)2.(M-)2.H2O (CSD refcode VUKQEZ; Arkhipov et al., 2015).
 

Acknowledgements

This work was supported by a grant from the Ministry of Education and Science of Russia (project 1828) (SGA), and by RFBR (grant No. 16-33-60089 mol_a_dk) (to EAL).

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