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.

S1. Introduction

Salts of amino acids have attracted attention from different areas of inter­est and, particularly, as possible nonlinear optical (NLO) materials (Fleck & Petrosyan, 2014). Discovering the NLO properties of L-argininium di­hydrogen phosphate monohydrate, (L-ArgH)(H₂PO₄).H₂O (Jiang et al., 1983; Xu et al., 1983a,b), played an important role in triggering a systematic study of the salts of amino acids. Later, the crystal structure of (L-ArgH)(H₂PO₄).H₂O was studied extensively [see references in Fleck & Petrosyan (2014)]. In the L-Arg–H₃PO₄–H₂O system, a new compound, L-Arg.2H₃PO₄, was discovered with a doubly charged L-argininium(2+) cation, i.e. (L-ArgH₂)(H₂PO₄)₂ (Petrosyan et al., 2000). In addition to phosphates, crystals of phosphites of some amino acids with inter­esting physical properties were obtained and investigated. Phosphites of betainium (Fehst et al., 1993), glycinium (Averbuch-Pouchot, 1993a), L-histidinium (Averbuch-Pouchot, 1993b), sarcosinium (Averbuch-Pouchot, 1993c), β-alaninium (Averbuch-Pouchot, 1993d) and L-tryptophanium (Ramos Silva et al., 2005) were obtained and structurally characterized. In addition to these simple salts, a dimeric cation with a phosphite anion, namely, L-alanine L-alaninium phosphite monohydrate, has also been characterized (Smolin et al., 2003). Phosphites of betainium and glycinium display ferroelectric properties (Fehst et al., 1993; Dacko et al., 1996). There is one more report, on L-valinium phosphite (Bendheif et al., 2003), which was later shown (Fleck & Petrosyan, 2014) to be DL-valinium phosphite.

The largest number of amino acid salts is known for L-arginine and L-histidine. However, in contrast with L-histidine, phosphites of L-arginine were not obtained and investigated. Recently, crystals of L-prolinium phosphite (Fleck et al., 2015) were obtained and characterized.

The aim of the present work was to investigate the possibility of salt formation in the L-Arg–H₃PO₃–H₂O system.

S2. Experimental

S2.1. Single-crystal X-ray diffraction

For L-argininium phosphite, (I), full-sphere data up to 0.7 Å resolution (at 296 K) and up to 0.5 Å resolution (at 100 K) were collected using an Oxford Diffraction Gemini R Ultra X-ray diffractometer with a CCD area detector and Mo Kα radiation. An Oxford CryojetHT device was used to cool the sample by N₂ flow.

S2.2. Vibrational spectra

Attenuated total reflection Fourier transform IR spectra (FT–IR ATR) were registered by a Nicolet 5700 spectrometer (ZnSe prism, Happ–Genzel apodization, ATR distortion corrected, number of scans 32, resolution 4 cm^-1). Part of the IR spectrum in the region 500–400 cm^-1 was taken from an FT–IR spectrum registered with a Nujol mull (4000–400 cm^-1, number of scans 32, resolution 2 cm^-1).

Fourier transform Raman spectra were registered by an NXR FT–Raman Module on a Nicolet 5700 spectrometer at room temperature with a resolution of 4 cm^-1. The number of scans and the laser power for the sample of (I) were 512 and 0.34 W, respectively, while for the sample of (II) they were 1024 and 0.37 W, respectively, .

S2.3. Synthesis and crystallization

L-Arginine and phospho­rous acid (H₃PO₃) were purchased from Sigma Chemical Co. Compound formation was investigated by slow evaporation at room temperature of aqueous solutions at different molar ratios of these components. With a 2:1 molar ratio, a glassy precipitate was formed. Good-quality single crystals of (L-ArgH)(H₂PO₃), (I), were obtained from an aqueous solution containing equimolar qu­anti­ties of the components. With a 1:2 molar ratio, another polycrystalline compound, denoted (II), was formed, and with a 1:3 ratio of components, a viscous solution was formed. The crystals of (II) were not of adequate quality for a single-crystal X-ray diffraction experiment and the compound was characterized by vibrational spectroscopy only. Additional work is needed for the optimization of the growth conditions of (II) formed with a 1:2 molar ratio of the components.

S2.4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were located using difference Fourier map and refined freely.

S3. Results and discussion

S3.1. Crystal and molecular structure of L-argininium phosphite, (I), at room temperature (296 K)

The asymmetric unit of L-argininium phosphite, (I), contains one L-argininium(+) cation and one phosphite anion (Fig. 1). Selected geometric parameters are given in Table 2 and the geometric parameters of the hydrogen bonds are given in Table 3. The L-argininium(+) cation is singly charged. The guanidine and α-amino groups are protonated, while the carb­oxy­lic acid group is deprotonated. The C1—O1 and C1—O2 bond lengths (Table 2) are typical for a carboxyl­ate group. The difference in their values ismprobably caused by the formation of hydrogen bonds. Other bond lengths and angles have expected values. The torsion angles ψ¹ [-5.6 (2)°], χ¹ [-65.3 (2)°), χ² [170.9 (2)°], χ³ [56.8 (3)°], χ⁴ [113.1 (3)°] and χ⁵ [-7.2 (4)°] define the conformation of the L-argininium(+) cation, which corresponds to one of 19 previously known conformations of arginine (Saraswathi & Vijayan, 2002). The P—O bond lengths of the phosphite anion have expected values and the differences are also caused by hydrogen bonding. A packing diagram is shown in Fig. 2.

L-Argininium phosphite forms a three-dimensional hydrogen-bonded network. In the directions of the a and c crystallographic axes, the main structural motifs are infinite hydrogen-bonded chains, formed by N—H···O hydrogen bonds between L-argininium(+) cations and phosphite anions. In the direction of the crystallographic b axis are observed infinite chains, formed by O—H···O hydrogen bonds between phosphite anions and N—H···O hydrogen bonds between L-argininium(+) cations. All these chains are linked to each other by hydrogen bonds to form the three-dimensional network.

Various types of inter­action have been encountered in the structures of salts of amino acids with the phosphite anion. The phosphite anions in the structure of β-alaninium phosphite form centrosymmetric dimers, with an O···O distance of 2.567 Å (Averbuch-Pouchot, 1993d). In the structures of L-histidinium phosphite (Averbuch-Pouchot, 1993b) and L-alanine L-alaninium phosphite monohydrate (Smolin et al., 2003), the phosphite anions form hydrogen bonds with the carboxyl­ate groups of the L-histidinium cations and L-alanine zwitterions, with O···O distances of 2.622 and 2.514 Å, respectively. In the structure of L-tryptophanium phosphite (Ramos Silva et al., 2005), the hy­droxy group of the phosphite anion forms a hydrogen bond with the carbonyl O atom of the L-tryptophanium cation, with an O···O distance of 2.713 Å. In the case of phosphites of achiral amino acids [glycinium (Averbuch-Pouchot, 1993a), sarcosinium (Averbuch-Pouchot, 1993c) and betainium (Fehst et al., 1993)], the phosphite anions inter­act with each other and form infinite chains. Based on these cases, one might expect that the phosphite anion would bond with the carbonyl O atom in the case of L-prolinium phosphite and with the carboxyl­ate group in the case of L-argininium phosphite. However, in contrast with this expe­cta­tion, in both cases the phosphite anions form infinite chains via O—H···O hydrogen bonds, with O···O distances of 2.560 (2) and 2.630 (3) Å, respectively.

In the structure of L-argininium phosphite, all the active H atoms form hydrogen bonds with neighbouring anions and the carboxyl­ate groups of symmetry-related cations. The NH₃⁺ group forms one rather strong N1—H1C···O5 hydrogen bond with the phosphite anion and one also rather strong N1—H1A···O1ⁱⁱ [symmetry code: (ii) x, y - 1, z] hydrogen bond with a symmetry-related L-argininium(+) cation. The third contact, N1—H1B···O2ⁱⁱⁱ [symmetry code: (iii) -x + 1, y - 1/2, -z + 1], is inter­mediate between a weak hydrogen bond and a strong van der Waals inter­action. The N6—H6 group forms one more hydrogen bond with atom O1 of the carboxyl­ate group of a neighbouring cation to form an N6—H6···O1^iv [symmetry code: (iv) -x + 2, y - 1/2, -z + 1] medium-strength hydrogen bond, with an N···O distance of 2.811 (2) Å. The guanidyl group also forms two hydrogen bonds [N8—H8A···O5^v and N9—H9B···O4^v; symmetry code: (v) x + 1, y + 1, z] with the same phosphite anion. These hydrogen bonds are similar to the specific inter­action of type A of the guanidyl group considered by Salunke & Vijayan (1981). The guanidyl group forms two more weak hydrogen bonds [N8—H8B···O2^vi and N9—H9A···O4^vii; symmetry codes: (vi) -x + 2, y + 1/2, -z + 1; (vii) -x + 2, y + 1/2, -z + 2] with the carboxyl­ate group and phosphite anion, respectively. Thus, atom O1 forms two relatively strong hydrogen bonds while atom O2 forms two relatively weak hydrogen bonds, and this may be the cause of the difference in the C1—O1 and C1—O2 bond lengths (Table 2). Hydrogen bonds formed by the phosphite anion may also explain the difference in the P1—O4 and P1—O5 bond lengths (Table 2).

S3.2. Crystal and molecular structure of L–argininium phosphite, (I), at 100 K

Crystal structure of L-argininium phosphite at 100 K is quite similar to structure of the title compound at ambient conditions. Molecular geometry and packing are preserved on cooling and only slight distance and angle changes can be detected (see Table 2). The low-temperature experiment allowed us to refine H-atom positions more accurately and to prove that free H-atom refinement at room temperature is reasonable. N6(C5, H6, C7) and N8(C7, H8A, H8B) groups are slightly pyramidal that can be explained by poor delocalization of C7 electrons between three N-atoms leading to N6 and N8 being more sp³ than sp².

S3.3. Vibrational spectra of (L-ArgH)(H2PO3), (I), and the second compound, (II)

The IR and Raman spectra of (I) are shown in Fig. 3. These spectra can be inter­preted on the basis of the crystal structure. One may expect the characteristic stretching vibrational modes of N—H, O—H, C—H and P—H in the high-frequency region 3500–2000 cm^-1. The stretching mode ν(PH) is very characteristic [see Fleck et al. (2015), and references therein). In the Raman spectrum, the most intense line is at 2413 cm^-1. The respective absorption band is at 2407 cm^-1. The stretching vibrational modes of CH and CH₂ groups are very characteristic in the Raman spectrum and are revealed as intense peaks at 2982–2862 cm^-1. These peaks are superimposed on a broad band caused by the stretching vibration of hydrogen-bonded N—H and O—H bonds. According to Nakamoto et al. (1955), ν(NH) stretching modes are expected in the region 3350–2700 cm^-1. Vibrational modes for weakly (N9—H9A···O4^iv) and strongly (N1—H1C···O5) bonded N—H groups (see Table 3) should have the highest and the lowest frequencies in this region correspondingly. The ν(OH) stretching mode for the O3—H7···O4ⁱ hydrogen bond (Table 3) is also expected to be near 2750 cm^-1 (Nakamoto et al., 1955; Novak, 1979).

In addition to the characteristic ν(PH) mode, the presence of the phosphite anion in the structure of (I) is reflected by characteristic absorption bands and Raman lines near 1000 cm^-1 and near 500 cm^-1.

The L-argininium(+) cation is characterized by protonated guanidinium and α-amino groups, as well as by a deprotonated negatively charged carboxyl­ate group. So, in the case of a singly charged L-argininium(+) cation, the characteristic absorption band caused by a carb­oxy­lic acid (COOH) group near 1700 cm^-1 is absent. In the region 1683–1526 cm^-1, there are strong characteristic absorption peaks caused by the asymmetric stretching vibration of the COO^- carboxyl­ate group, the stretching vibrations of C—N bonds in the guanidinium group and the deformation vibrations of the NH₃⁺ group. Some other bands are assigned in Table 4.

The IR and Raman spectra of the second compound, (II), obtained with a 1:2 molar ratio of L-arginine and phospho­rous acid (H₃PO₃), are shown in Fig. 4. Because of the absence of structural data for this compound, we have characterized it by IR and Raman spectra only and will try to extract some structural data based on these spectra. The spectra shown in Figs. 3 and 4 have significant differences. There are three absorption bands and Raman lines in the region of the ν(PH) stretching mode. Another important feature is the presence of the band at 1715 cm^-1 in the Raman spectrum. The respective absorption in the IR spectrum is reflected as a shoulder at 1699 cm^-1 (see the expanded band in the middle of Fig. 4). The third important feature is the presence of very strong and broad absorption in the range 1400–400 cm^-1, which is characteristic for very short and strong O—H···O-type hydrogen bonds. The respective characteristic bands of phosphite anions in both IR and Raman spectra near 1000 and 500 cm^-1 are present. The presence of three ν(PH) lines suggests the presence of three phosphite anions. The band at 1715 cm^-1 (Fig. 4) suggests the presence of a doubly charged L-argininium(2+) cation. This allows us to suppose one of two possible compositions: (L-Arg²⁺)(H₂PO₃^-)(H₂PO₃^-–H₃PO₃) or (L-Arg⁺)(L-Arg²⁺).(H₂PO₃^-)₃. The above-mentioned strong broad absorption band may be caused by a strong hydrogen bond between L-Arg⁺ and L-Arg²⁺, or between L-Arg²⁺ and one of the phosphite anions and also by hydrogen bonds between phosphite anions. The final conclusion on the composition of the compound (II) can be made after single crystals are obtained and crystal structure solved.

S3.4. Nonlinear optical (NLO) activity

We have performed a visual check of the second-harmonic generation (SHG) activity of L-argininium(+) phosphite, (I), and of (II), using a YAG:Nd³⁺ laser. The experimental set-up is described by Petrosyan et al. (2009). These observations showed that L-argininium phosphite displays an SHG signal, although it is weaker than that of the L-argininium phosphate monohydrate (LAP) crystal. For the second compound, (II), we did not observe any noticeable signals. This can be intrinsic property of this compound, but can also result from its poor crystallinity.

S3.5. Conclusions

We have shown the possibility of salt formation in the L-arginine–H₃PO₃–H₂O system. Single crystals of L-argininium(+) phosphite were crystallized from an aqueous solution with equimolar ratio of L-arginine and phospho­rous acid and characterised by single-crystal X-ray diffraction and vibrational spectroscopy. An NLO effect has been observed for this salt. Another compound that can be formed in this system has presumably a different stoichiometry and no NLO properties. This compound is formed from aqueous solution of L-arginine and phospho­rous acid 1:2. Single crystals of this compound could not be obtained yet and it has been characterized by IR and Raman spectroscopy. Two possible compositions, (L-Arg²⁺)(H₂PO₃^-)(H₂PO₃^-–H₃PO₃) or (L-Arg⁺)(L-Arg²⁺).(H₂PO₃^-)₃, have been proposed based on the spectra. The crystals of L-argininium phosphite display SHG activity.

Computing details

For both compounds, data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis PRO (Agilent, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015) and X-STEP32 (Stoe & Cie, 2000); molecular graphics: Mercury (Macrae et al., 2008) and PLATON (Spek, 2009); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The molecular structure of L-argininium phosphite, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Packing diagrams of L-argininium phosphite, viewed along (a) the crystallographic b axis and (b) the crystallographic c axis. Hydrogen bonds are indicated by dashed turquoise lines. Hanging hydrogen bonds have been omitted for clarity.
	Fig. 3. The IR and Raman spectra of L-argininium phosphite, (I).
	Fig. 4. The IR and Raman spectra of L-argininium phosphite, (II).

(I) L-Argininium phosphite

Crystal data

C6H15N4O2^+·H2O3P^−	F(000) = 272
Mr = 256.20	Dx = 1.457 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 9.3993 (3) Å	Cell parameters from 5391 reflections
b = 4.86380 (13) Å	θ = 1.6–31.8°
c = 13.2395 (4) Å	µ = 0.25 mm^−1
β = 105.249 (3)°	T = 296 K
V = 583.95 (3) Å^3	Prism, colourless
Z = 2	0.30 × 0.30 × 0.10 mm

Data collection

Agilent Xcalibur Gemini Ultra diffractometer with Ruby detector	3545 independent reflections
Radiation source: Enhance (Mo) X-ray Source	3247 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
Detector resolution: 10.3457 pixels mm^-1	θmax = 30.5°, θmin = 1.6°
ω scans	h = −13→13
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2012)	k = −6→6
Tmin = 0.989, Tmax = 1.000	l = −18→18
11214 measured reflections

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.032	w = 1/[σ^2(Fo^2) + (0.0445P)^2 + 0.0095P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.082	(Δ/σ)max = 0.001
S = 1.06	Δρmax = 0.23 e Å^−3
3545 reflections	Δρmin = −0.26 e Å^−3
213 parameters	Absolute structure: Flack x determined using 1329 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
1 restraint	Absolute structure parameter: −0.03 (4)

Special details

Experimental. Absorption correction: CrysAlisPro, Agilent Technologies, Version 1.171.35.21 (release 20-01-2012 CrysAlis171 .NET) (compiled Jan 23 2012,18:06:46) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.7086 (2)	1.1903 (4)	0.52044 (15)	0.0281 (4)
C2	0.7771 (2)	1.0539 (4)	0.62700 (14)	0.0259 (4)
H2	0.766 (3)	1.174 (6)	0.682 (2)	0.036 (6)*
C3	0.93853 (19)	0.9765 (6)	0.63652 (14)	0.0311 (4)
H3B	0.948 (3)	0.854 (6)	0.581 (2)	0.040 (7)*
H3A	0.989 (3)	1.136 (7)	0.625 (2)	0.051 (8)*
C4	1.0214 (2)	0.8645 (6)	0.74350 (17)	0.0380 (5)
H4B	1.031 (3)	1.014 (9)	0.793 (3)	0.063 (9)*
H4A	0.971 (3)	0.721 (8)	0.769 (2)	0.055 (8)*
C5	1.1718 (2)	0.7499 (5)	0.74383 (19)	0.0384 (5)
H5A	1.219 (3)	0.704 (8)	0.814 (2)	0.063 (9)*
H5B	1.151 (3)	0.569 (7)	0.693 (2)	0.053 (8)*
C7	1.3887 (2)	1.0592 (5)	0.76994 (15)	0.0303 (4)
N1	0.68993 (19)	0.8053 (4)	0.63668 (14)	0.0284 (3)
H1A	0.709 (3)	0.674 (8)	0.595 (2)	0.052 (8)*
H1B	0.594 (3)	0.861 (7)	0.615 (2)	0.053 (8)*
H1C	0.709 (3)	0.748 (6)	0.711 (2)	0.041 (7)*
N6	1.26517 (17)	0.9509 (5)	0.71067 (13)	0.0352 (4)
H6	1.258 (3)	0.962 (7)	0.641 (2)	0.043 (7)*
N8	1.4703 (2)	1.2148 (5)	0.72271 (16)	0.0394 (4)
H8A	1.542 (3)	1.314 (6)	0.759 (2)	0.040 (7)*
H8B	1.426 (3)	1.292 (8)	0.653 (2)	0.057 (8)*
N9	1.4341 (2)	1.0181 (6)	0.87205 (14)	0.0421 (5)
H9A	1.386 (3)	0.935 (6)	0.908 (2)	0.040 (7)*
H9B	1.518 (3)	1.112 (6)	0.911 (2)	0.054 (8)*
O1	0.76536 (19)	1.4172 (3)	0.50595 (12)	0.0390 (4)
O2	0.60526 (16)	1.0712 (3)	0.45788 (12)	0.0406 (4)
O3	0.7984 (2)	0.7338 (4)	1.01388 (15)	0.0497 (4)
H7	0.768 (4)	0.865 (7)	0.989 (3)	0.059 (10)*
O4	0.71912 (18)	0.2508 (3)	0.97820 (13)	0.0381 (4)
O5	0.7151 (2)	0.5679 (4)	0.82528 (12)	0.0471 (4)
P1	0.78777 (5)	0.48938 (12)	0.93544 (4)	0.03103 (13)
H8	0.921 (2)	0.432 (6)	0.9414 (18)	0.038 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0308 (9)	0.0284 (10)	0.0251 (9)	0.0042 (7)	0.0071 (7)	−0.0001 (7)
C2	0.0272 (8)	0.0261 (9)	0.0241 (8)	−0.0025 (6)	0.0062 (6)	−0.0018 (7)
C3	0.0249 (7)	0.0401 (10)	0.0277 (8)	−0.0030 (9)	0.0060 (6)	0.0009 (9)
C4	0.0269 (9)	0.0560 (14)	0.0300 (10)	−0.0030 (9)	0.0056 (7)	0.0078 (10)
C5	0.0286 (9)	0.0437 (13)	0.0389 (11)	−0.0037 (9)	0.0016 (8)	0.0081 (10)
C7	0.0229 (7)	0.0403 (11)	0.0281 (8)	0.0040 (7)	0.0078 (6)	−0.0006 (8)
N1	0.0252 (7)	0.0302 (8)	0.0287 (8)	−0.0018 (6)	0.0053 (6)	0.0020 (7)
N6	0.0273 (7)	0.0510 (12)	0.0266 (7)	−0.0042 (8)	0.0055 (6)	0.0020 (8)
N8	0.0297 (8)	0.0519 (12)	0.0354 (9)	−0.0060 (8)	0.0065 (7)	0.0063 (9)
N9	0.0315 (8)	0.0659 (15)	0.0273 (8)	−0.0106 (10)	0.0051 (6)	0.0015 (10)
O1	0.0561 (9)	0.0296 (8)	0.0309 (7)	−0.0037 (6)	0.0104 (7)	0.0018 (6)
O2	0.0379 (8)	0.0404 (9)	0.0354 (8)	−0.0003 (6)	−0.0049 (6)	0.0005 (7)
O3	0.0721 (12)	0.0308 (9)	0.0389 (9)	−0.0016 (9)	0.0019 (8)	0.0005 (8)
O4	0.0468 (9)	0.0302 (8)	0.0359 (8)	−0.0056 (7)	0.0085 (6)	0.0026 (6)
O5	0.0554 (9)	0.0549 (11)	0.0298 (8)	−0.0127 (8)	0.0093 (7)	0.0074 (7)
P1	0.0277 (2)	0.0331 (3)	0.0318 (2)	−0.0019 (2)	0.00698 (17)	0.0025 (2)

Geometric parameters (Å, º)

C1—O2	1.242 (2)	C7—N6	1.327 (3)
C1—O1	1.262 (3)	C7—N8	1.344 (3)
C1—C2	1.539 (3)	N1—H1A	0.90 (3)
C2—N1	1.485 (2)	N1—H1B	0.91 (3)
C2—C3	1.536 (3)	N1—H1C	0.99 (3)
C2—H2	0.95 (3)	N6—H6	0.91 (3)
C3—C4	1.526 (3)	N8—H8A	0.87 (3)
C3—H3B	0.96 (3)	N8—H8B	0.98 (3)
C3—H3A	0.94 (3)	N9—H9A	0.84 (3)
C4—C5	1.519 (3)	N9—H9B	0.94 (3)
C4—H4B	0.97 (4)	O3—P1	1.564 (2)
C4—H4A	0.95 (3)	O3—H7	0.74 (3)
C5—N6	1.457 (3)	O4—P1	1.5085 (16)
C5—H5A	0.95 (3)	O5—P1	1.4884 (17)
C5—H5B	1.09 (3)	P1—H8	1.26 (2)
C7—N9	1.322 (3)
O2—C1—O1	126.5 (2)	H5A—C5—H5B	112 (3)
O2—C1—C2	118.40 (18)	N9—C7—N6	122.79 (19)
O1—C1—C2	115.13 (17)	N9—C7—N8	119.4 (2)
N1—C2—C3	110.42 (17)	N6—C7—N8	117.80 (18)
N1—C2—C1	108.85 (15)	C2—N1—H1A	109 (2)
C3—C2—C1	110.30 (15)	C2—N1—H1B	105 (2)
N1—C2—H2	105.1 (16)	H1A—N1—H1B	111 (3)
C3—C2—H2	112.8 (15)	C2—N1—H1C	110.8 (17)
C1—C2—H2	109.2 (16)	H1A—N1—H1C	114 (3)
C4—C3—C2	114.54 (15)	H1B—N1—H1C	108 (2)
C4—C3—H3B	111.0 (16)	C7—N6—C5	126.23 (18)
C2—C3—H3B	111.8 (16)	C7—N6—H6	113.5 (17)
C4—C3—H3A	107.0 (18)	C5—N6—H6	117.0 (19)
C2—C3—H3A	108.1 (17)	C7—N8—H8A	120.5 (17)
H3B—C3—H3A	104 (2)	C7—N8—H8B	119.9 (18)
C5—C4—C3	112.39 (18)	H8A—N8—H8B	113 (3)
C5—C4—H4B	110.5 (18)	C7—N9—H9A	124.8 (18)
C3—C4—H4B	107 (2)	C7—N9—H9B	119.3 (18)
C5—C4—H4A	106.0 (19)	H9A—N9—H9B	115 (2)
C3—C4—H4A	114.2 (18)	P1—O3—H7	114 (3)
H4B—C4—H4A	106 (3)	O5—P1—O4	115.71 (10)
N6—C5—C4	112.8 (2)	O5—P1—O3	112.85 (11)
N6—C5—H5A	107 (2)	O4—P1—O3	107.13 (10)
C4—C5—H5A	106.4 (19)	O5—P1—H8	108.0 (11)
N6—C5—H5B	112.1 (15)	O4—P1—H8	108.6 (13)
C4—C5—H5B	106.3 (15)	O3—P1—H8	103.7 (12)
O2—C1—C2—N1	−5.6 (2)	C2—C3—C4—C5	171.0 (2)
O1—C1—C2—N1	174.44 (16)	C3—C4—C5—N6	56.9 (3)
O2—C1—C2—C3	115.7 (2)	N9—C7—N6—C5	−7.8 (4)
O1—C1—C2—C3	−64.3 (2)	N8—C7—N6—C5	171.6 (2)
N1—C2—C3—C4	−65.2 (3)	C4—C5—N6—C7	113.4 (2)
C1—C2—C3—C4	174.4 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^i	0.90 (3)	1.88 (3)	2.776 (2)	174 (3)
N1—H1B···O2^ii	0.91 (3)	2.34 (3)	2.955 (2)	125 (3)
N1—H1C···O5	0.99 (3)	1.74 (3)	2.704 (2)	164 (3)
N6—H6···O1^iii	0.91 (3)	1.91 (3)	2.811 (2)	170 (3)
N8—H8B···O2^iv	0.98 (3)	1.97 (3)	2.887 (3)	155 (3)
N8—H8A···O5^v	0.87 (3)	2.04 (3)	2.906 (3)	172 (2)
N9—H9B···O4^v	0.94 (3)	1.98 (3)	2.907 (2)	167 (2)
N9—H9A···O4^vi	0.84 (3)	2.20 (3)	3.033 (3)	171 (3)
O3—H7···O4^vii	0.74 (3)	1.93 (4)	2.630 (3)	158 (4)

Symmetry codes: (i) x, y−1, z; (ii) −x+1, y−1/2, −z+1; (iii) −x+2, y−1/2, −z+1; (iv) −x+2, y+1/2, −z+1; (v) x+1, y+1, z; (vi) −x+2, y+1/2, −z+2; (vii) x, y+1, z.

(I_at_100K) L-Argininium phosphite

Crystal data

C6H15N4O2^+·H2O3P^−	F(000) = 272
Mr = 256.20	Dx = 1.480 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 9.33820 (11) Å	Cell parameters from 18784 reflections
b = 4.84411 (5) Å	θ = 1.6–45.5°
c = 13.16136 (14) Å	µ = 0.25 mm^−1
β = 105.0767 (12)°	T = 100 K
V = 574.87 (1) Å^3	Prism, colourless
Z = 2	0.35 × 0.30 × 0.10 mm

Data collection

Agilent Xcalibur Gemini Ultra diffractometer with a Ruby detector	9611 independent reflections
Radiation source: Enhance (Mo) X-ray Source	8864 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
Detector resolution: 10.3457 pixels mm^-1	θmax = 45.3°, θmin = 1.6°
ω scan	h = −18→18
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2014)	k = −9→9
Tmin = 0.943, Tmax = 1.000	l = −26→26
36155 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	All H-atom parameters refined
wR(F^2) = 0.070	w = 1/[σ^2(Fo^2) + (0.0365P)^2 + 0.0027P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max = 0.001
9611 reflections	Δρmax = 0.35 e Å^−3
213 parameters	Δρmin = −0.35 e Å^−3
1 restraint	Absolute structure: Flack x determined using 3802 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.001 (18)

Special details

Experimental. Absorption correction: CrysAlisPro, Agilent Technologies, Version 1.171.37.35 (release 13-08-2014 CrysAlis171 .NET) (compiled Aug 13 2014,18:06:01) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.70837 (8)	1.19147 (14)	0.52118 (5)	0.01141 (9)
C2	0.77713 (7)	1.05358 (14)	0.62795 (5)	0.01082 (9)
H2	0.7710 (19)	1.170 (4)	0.6851 (14)	0.020 (4)*
C3	0.93898 (7)	0.97521 (18)	0.63677 (5)	0.01278 (9)
H3B	0.944 (2)	0.838 (4)	0.5771 (14)	0.025 (4)*
H3A	0.9921 (19)	1.140 (4)	0.6202 (14)	0.026 (4)*
C4	1.02142 (8)	0.85623 (18)	0.74374 (6)	0.01518 (11)
H4B	1.032 (2)	0.983 (5)	0.7968 (14)	0.028 (4)*
H4A	0.964 (2)	0.695 (5)	0.7688 (15)	0.033 (5)*
C5	1.17373 (8)	0.74220 (17)	0.74252 (6)	0.01491 (11)
H5A	1.218 (2)	0.677 (5)	0.8081 (15)	0.032 (5)*
H5B	1.1577 (18)	0.584 (4)	0.6903 (13)	0.022 (4)*
C7	1.39070 (7)	1.05696 (15)	0.77005 (5)	0.01209 (9)
N1	0.68903 (7)	0.80427 (13)	0.63757 (5)	0.01181 (8)
H1A	0.7130 (18)	0.675 (4)	0.5971 (13)	0.019 (4)*
H1B	0.5904 (19)	0.831 (4)	0.6090 (13)	0.023 (4)*
H1C	0.7104 (18)	0.748 (4)	0.7044 (13)	0.021 (4)*
N6	1.26643 (7)	0.94815 (15)	0.70970 (5)	0.01408 (10)
H6	1.2550 (19)	0.963 (5)	0.6428 (14)	0.027 (4)*
N8	1.47319 (7)	1.21606 (16)	0.72327 (5)	0.01551 (10)
H8A	1.541 (2)	1.314 (4)	0.7632 (14)	0.027 (4)*
H8B	1.431 (2)	1.288 (4)	0.6594 (14)	0.025 (4)*
N9	1.43691 (7)	1.01072 (18)	0.87276 (5)	0.01623 (11)
H9A	1.386 (2)	0.941 (4)	0.9079 (14)	0.027 (4)*
H9B	1.5202 (19)	1.101 (4)	0.9057 (13)	0.023 (4)*
O1	0.76640 (7)	1.41960 (12)	0.50692 (4)	0.01508 (9)
O2	0.60350 (7)	1.07295 (13)	0.45793 (5)	0.01543 (9)
O3	0.80137 (8)	0.73601 (14)	1.01865 (5)	0.01838 (10)
H7	0.773 (2)	0.878 (4)	0.9962 (14)	0.027 (4)*
O4	0.71928 (7)	0.24901 (12)	0.98178 (5)	0.01444 (9)
O5	0.71371 (8)	0.57172 (15)	0.82777 (5)	0.01825 (10)
P1	0.78862 (2)	0.49014 (4)	0.93880 (2)	0.01190 (3)
H8	0.9241 (19)	0.431 (4)	0.9427 (13)	0.025 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0125 (2)	0.0110 (2)	0.0107 (2)	0.00142 (18)	0.00285 (18)	−0.00041 (17)
C2	0.0112 (2)	0.0110 (2)	0.01016 (19)	−0.00080 (17)	0.00254 (16)	−0.00029 (17)
C3	0.0101 (2)	0.0165 (2)	0.01141 (19)	−0.0008 (2)	0.00224 (16)	0.0013 (2)
C4	0.0109 (2)	0.0222 (3)	0.0118 (2)	−0.0009 (2)	0.00189 (18)	0.0033 (2)
C5	0.0112 (2)	0.0164 (3)	0.0159 (3)	−0.0009 (2)	0.0014 (2)	0.0021 (2)
C7	0.0098 (2)	0.0153 (2)	0.0114 (2)	0.00078 (18)	0.00325 (17)	0.00016 (18)
N1	0.01081 (19)	0.0124 (2)	0.01208 (19)	−0.00101 (16)	0.00273 (16)	0.00078 (16)
N6	0.0110 (2)	0.0197 (3)	0.01109 (19)	−0.00250 (17)	0.00196 (15)	0.00068 (17)
N8	0.0124 (2)	0.0202 (3)	0.0139 (2)	−0.0023 (2)	0.00338 (18)	0.0030 (2)
N9	0.0130 (2)	0.0245 (3)	0.01065 (18)	−0.0038 (2)	0.00206 (15)	0.0013 (2)
O1	0.0211 (2)	0.01150 (18)	0.01279 (18)	−0.00181 (17)	0.00463 (17)	0.00054 (15)
O2	0.0139 (2)	0.0159 (2)	0.01378 (19)	−0.00021 (17)	−0.00129 (16)	−0.00047 (17)
O3	0.0257 (3)	0.0118 (2)	0.0149 (2)	−0.0011 (2)	0.00033 (19)	−0.00063 (17)
O4	0.0177 (2)	0.01150 (19)	0.01411 (19)	−0.00173 (17)	0.00417 (17)	0.00083 (16)
O5	0.0221 (3)	0.0204 (2)	0.01188 (19)	−0.0047 (2)	0.00376 (18)	0.00272 (18)
P1	0.01080 (6)	0.01254 (7)	0.01235 (6)	−0.00060 (5)	0.00300 (5)	0.00064 (6)

Geometric parameters (Å, º)

C1—O2	1.2480 (9)	C7—N6	1.3326 (9)
C1—O1	1.2661 (9)	C7—N8	1.3465 (10)
C1—C2	1.5375 (9)	N1—H1A	0.889 (18)
C2—N1	1.4852 (9)	N1—H1B	0.910 (17)
C2—C3	1.5331 (9)	N1—H1C	0.892 (17)
C2—H2	0.955 (18)	N6—H6	0.861 (17)
C3—C4	1.5307 (9)	N8—H8A	0.852 (19)
C3—H3B	1.039 (19)	N8—H8B	0.899 (18)
C3—H3A	0.99 (2)	N9—H9A	0.814 (18)
C4—C5	1.5298 (11)	N9—H9B	0.899 (18)
C4—H4B	0.92 (2)	O3—P1	1.5723 (7)
C4—H4A	1.05 (2)	O3—H7	0.77 (2)
C5—N6	1.4580 (10)	O4—P1	1.5146 (6)
C5—H5A	0.91 (2)	O5—P1	1.4997 (6)
C5—H5B	1.016 (19)	P1—H8	1.285 (18)
C7—N9	1.3267 (9)
O2—C1—O1	126.48 (7)	H5A—C5—H5B	109.1 (17)
O2—C1—C2	118.59 (6)	N9—C7—N6	122.86 (7)
O1—C1—C2	114.93 (6)	N9—C7—N8	119.30 (7)
N1—C2—C3	110.44 (6)	N6—C7—N8	117.83 (6)
N1—C2—C1	108.80 (5)	C2—N1—H1A	107.0 (11)
C3—C2—C1	110.24 (5)	C2—N1—H1B	111.8 (12)
N1—C2—H2	105.4 (11)	H1A—N1—H1B	103.9 (15)
C3—C2—H2	110.3 (10)	C2—N1—H1C	110.2 (13)
C1—C2—H2	111.5 (11)	H1A—N1—H1C	110.3 (17)
C4—C3—C2	114.39 (5)	H1B—N1—H1C	113.3 (14)
C4—C3—H3B	110.1 (10)	C7—N6—C5	125.88 (6)
C2—C3—H3B	109.6 (10)	C7—N6—H6	115.7 (13)
C4—C3—H3A	110.1 (11)	C5—N6—H6	115.7 (14)
C2—C3—H3A	108.9 (10)	C7—N8—H8A	117.1 (12)
H3B—C3—H3A	103.1 (14)	C7—N8—H8B	119.1 (12)
C5—C4—C3	111.89 (6)	H8A—N8—H8B	115.7 (18)
C5—C4—H4B	109.5 (11)	C7—N9—H9A	124.4 (13)
C3—C4—H4B	112.1 (13)	C7—N9—H9B	114.8 (11)
C5—C4—H4A	106.6 (11)	H9A—N9—H9B	118.9 (16)
C3—C4—H4A	113.3 (11)	P1—O3—H7	117.5 (14)
H4B—C4—H4A	103.0 (17)	O5—P1—O4	115.52 (4)
N6—C5—C4	112.42 (7)	O5—P1—O3	112.75 (4)
N6—C5—H5A	111.0 (13)	O4—P1—O3	107.45 (3)
C4—C5—H5A	108.2 (12)	O5—P1—H8	107.6 (8)
N6—C5—H5B	108.1 (9)	O4—P1—H8	108.9 (9)
C4—C5—H5B	107.9 (9)	O3—P1—H8	103.9 (9)
O2—C1—C2—N1	−5.48 (9)	C2—C3—C4—C5	171.39 (7)
O1—C1—C2—N1	174.53 (6)	C3—C4—C5—N6	56.21 (9)
O2—C1—C2—C3	115.77 (7)	N9—C7—N6—C5	−7.64 (12)
O1—C1—C2—C3	−64.22 (8)	N8—C7—N6—C5	171.07 (7)
N1—C2—C3—C4	−64.19 (8)	C4—C5—N6—C7	113.22 (8)
C1—C2—C3—C4	175.55 (6)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^i	0.889 (18)	1.868 (18)	2.7563 (9)	176.4 (17)
N1—H1B···O2^ii	0.910 (17)	2.189 (18)	2.9174 (9)	136.6 (17)
N1—H1C···O5	0.892 (17)	1.828 (18)	2.6997 (8)	165.0 (18)
N6—H6···O1^iii	0.861 (17)	1.940 (17)	2.7904 (8)	169 (2)
N8—H8B···O2^iv	0.899 (18)	2.035 (19)	2.8811 (9)	156.4 (18)
N8—H8A···O5^v	0.852 (19)	2.043 (19)	2.8805 (10)	167.0 (16)
N9—H9B···O4^v	0.899 (18)	2.001 (18)	2.8941 (9)	171.9 (18)
N9—H9A···O4^vi	0.814 (18)	2.167 (18)	2.9753 (9)	172.0 (18)
O3—H7···O4^vii	0.77 (2)	1.87 (2)	2.6086 (9)	163.8 (19)

Symmetry codes: (i) x, y−1, z; (ii) −x+1, y−1/2, −z+1; (iii) −x+2, y−1/2, −z+1; (iv) −x+2, y+1/2, −z+1; (v) x+1, y+1, z; (vi) −x+2, y+1/2, −z+2; (vii) x, y+1, z.