L-Argininium bis­(di­hydrogen phosphate)

In the crystal structure of the title compound, C₆H₁₆N₄O₂²⁺·2H₂PO₄⁻, the argininium residue has a gauche II-trans-trans-trans conformation. The argininium residue forms N—H...O and O—H...O hydrogen bonds with the phosphate anions; the latter form O—H...O hydrogen bonds with each other. Three-centered hydrogen bonding is also observed.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.044
• wR factor = 0.132
• Data-to-parameter ratio = 7.3

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level A:



PLAT_305  Alert A Isolated Hydrogen Atom (Outside Bond Range ??)       H(9)


 Alert Level C:



WEIGH_01  Alert C Extra text has been found in the
          _refine_ls_weighting_scheme field. This should be in the
          _refine_ls_weighting_details field.
          Weighting scheme given as calc w = 1/[\s^2^(Fo^2^)+(0.1002P)^2^+0.238
          Weighting scheme identified as calc

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           67.92
         From the CIF: _reflns_number_total               1567
         Count of symmetry unique reflns         1569
         Completeness (_total/calc)             99.87%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present          yes
          WARNING: Large fraction of Friedel related reflns may
                   be needed to determine absolute structure


 1 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

Arginine is known to possess non-linear optical properties (Jiang et al., 1983). The crystal structure of L-arginine dihydrate (Karle & Karle, 1964), L-arginine chloride (Mazumdar et al., 1969), L-arginine hydrochloride monohydrate (Dow et al., 1970), L-arginine phosphate monohydrate (Aoki et al., 1971), L-arginine perchlorate (Monaco et al., 1987; Srinivasan & Rajaram, 1997) and L-arginine diarsenate (Zalkin et al., 1989), L-argininium dinitrate (Ramaswamy et al., 2001) and a triclinic polymorph of L-argininium chloride (Sridhar et al., 2002) have been reported. In the present study, the crystal structure of L-argininum bis(dihydrogen phosphate), (I), has been determined.

The asymmetric unit of (I) contains one argininium residue and two dihydrogen phosphate anions. The C—O distances and O—C—C bond angles clearly show the presence of the COOH group. Futhermore, the guanidyl group is protonated to form a guanidinium ion. The backbone conformation angles, χ¹ and χ², are in cis and trans forms, respectively. The side-chain angle ψ¹ has the most favoured gauche II conformation, while the other three conformation angles ψ², ψ³ and ψ⁴ have the trans-trans-trans form. The P—O distances agree well with the values for normal single- and double-bond distances (Table 1).

The phosphate anions play a vital role in forming hydrogen bonds with the argininium residue and with each other (Table 2). All the phosphate O atoms are involved in hydrogen bonding. Interestingly, three-centered hydrogen bonding is observed, involving the η¹ N atom (N3) and phosphate O atoms.

S2. Experimental

The title compound was crystallized by slow evaporation of an aqueous solution of L-arginine and orthophosphoric acid in a stoichiometric ratio of 1:2.

S3. Refinement

In the absence of significant anomalous scattering effects, and with no Friedel pairs, the absolute configuration could not be determined crystallographically. The H atoms of the phosphate anions were located in difference Fourier maps and refined isotropically. All other H atoms were placed in geometrically calculated positions and included in the refinement in the riding-model approximation, with U_iso values set at 1.2U_eq of the carrier atom.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CAD-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the title compound, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A packing diagram of the title compound, viewed down the b axis.

L-argininium bis(dihydrogen phosphate)

Crystal data

C6H16N4O2^2+·2H2PO4^−	Dx = 1.672 Mg m^−3
Mr = 370.20	Cu Kα radiation, λ = 1.54180 Å
Orthorhombic, P212121	Cell parameters from 25 reflections
a = 6.9910 (2) Å	θ = 15.2–23.8°
b = 9.6760 (5) Å	µ = 3.28 mm^−1
c = 21.735 (2) Å	T = 293 K
V = 1470.26 (16) Å^3	Plate, colorless
Z = 4	0.3 × 0.2 × 0.2 mm
F(000) = 776

Data collection

Enraf-Nonius CAD-4 diffractometer	1548 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 67.9°, θmin = 4.1°
ω–2θ scans	h = −8→0
Absorption correction: ψ scan (North et al., 1967)	k = −11→0
Tmin = 0.367, Tmax = 0.519	l = −26→0
1567 measured reflections	2 standard reflections every 60 min
1567 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.044	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.132	Calculated w = 1/[σ^2(Fo^2) + (0.1002P)^2 + 0.2388P] where P = (Fo^2 + 2Fc^2)/3
S = 1.27	(Δ/σ)max = 0.002
1567 reflections	Δρmax = 0.57 e Å^−3
216 parameters	Δρmin = −0.82 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.047 (3)

Special details

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
P1	0.80681 (13)	0.37460 (9)	0.53565 (4)	0.0193 (3)
O3	0.7445 (4)	0.3503 (3)	0.60100 (12)	0.0300 (7)
O4	1.0137 (3)	0.4192 (3)	0.52937 (12)	0.0226 (6)
O5	0.6760 (4)	0.4833 (3)	0.50331 (12)	0.0302 (7)
H5	0.596 (7)	0.519 (5)	0.524 (2)	0.023 (12)*
O6	0.7961 (4)	0.2402 (3)	0.49577 (18)	0.0370 (7)
H6	0.680 (8)	0.198 (5)	0.492 (2)	0.033 (13)*
P2	0.86870 (13)	0.91646 (9)	0.36808 (4)	0.0185 (3)
O7	0.8041 (4)	0.8017 (3)	0.32634 (11)	0.0282 (7)
O8	0.9260 (4)	0.8732 (3)	0.43213 (10)	0.0235 (6)
O9	1.0382 (4)	0.9917 (3)	0.33515 (12)	0.0282 (6)
H9	1.105 (8)	1.066 (6)	0.372 (2)	0.041 (14)*
O10	0.7080 (4)	1.0301 (3)	0.37063 (13)	0.0297 (7)
H10	0.616 (10)	1.043 (8)	0.389 (4)	0.08 (2)*
O1	2.0545 (4)	−0.1214 (3)	0.64127 (13)	0.0318 (7)
H1	2.1419	−0.1763	0.6473	0.048*
O2	1.9592 (5)	−0.2794 (3)	0.57282 (14)	0.0392 (8)
C1	1.9410 (5)	−0.1696 (4)	0.59857 (16)	0.0228 (8)
C2	1.7750 (5)	−0.0727 (4)	0.58508 (16)	0.0205 (7)
H2	1.8267	0.0151	0.5699	0.025*
N1	1.6597 (5)	−0.1375 (3)	0.53498 (14)	0.0222 (7)
H1A	1.5613	−0.0830	0.5257	0.033*
H1B	1.6164	−0.2193	0.5476	0.033*
H1C	1.7327	−0.1490	0.5018	0.033*
C3	1.6549 (5)	−0.0437 (4)	0.64168 (15)	0.0232 (8)
H3A	1.7370	−0.0061	0.6735	0.028*
H3B	1.6034	−0.1304	0.6568	0.028*
C4	1.4900 (6)	0.0562 (4)	0.63093 (17)	0.0243 (8)
H4A	1.5364	0.1389	0.6106	0.029*
H4B	1.3946	0.0135	0.6047	0.029*
C5	1.4024 (6)	0.0931 (5)	0.69191 (18)	0.0304 (9)
H5A	1.3697	0.0090	0.7138	0.036*
H5B	1.4957	0.1429	0.7164	0.036*
N2	1.2309 (5)	0.1781 (4)	0.68503 (15)	0.0288 (8)
H2A	1.2237	0.2333	0.6541	0.035*
C6	1.0861 (5)	0.1738 (4)	0.72423 (16)	0.0212 (7)
N3	1.0996 (5)	0.1038 (4)	0.77659 (16)	0.0325 (8)
H3C	1.2034	0.0605	0.7854	0.039*
H3D	1.0045	0.1018	0.8017	0.039*
N4	0.9217 (5)	0.2377 (4)	0.71153 (17)	0.0334 (9)
H4C	0.9089	0.2823	0.6776	0.040*
H4D	0.8285	0.2343	0.7373	0.040*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0166 (5)	0.0189 (5)	0.0225 (5)	−0.0009 (4)	0.0018 (3)	−0.0022 (3)
O3	0.0296 (14)	0.0323 (14)	0.0281 (14)	0.0049 (12)	0.0036 (13)	0.0095 (12)
O4	0.0174 (13)	0.0223 (12)	0.0282 (13)	−0.0033 (11)	0.0018 (10)	−0.0044 (10)
O5	0.0260 (15)	0.0406 (16)	0.0241 (13)	0.0120 (14)	0.0030 (12)	0.0022 (12)
O6	0.0251 (14)	0.0288 (14)	0.0570 (19)	−0.0033 (13)	0.0012 (14)	−0.0181 (14)
P2	0.0160 (5)	0.0230 (5)	0.0166 (5)	−0.0011 (4)	0.0002 (3)	−0.0007 (3)
O7	0.0283 (14)	0.0332 (14)	0.0231 (11)	−0.0076 (13)	−0.0001 (12)	−0.0051 (11)
O8	0.0233 (12)	0.0275 (13)	0.0197 (11)	−0.0028 (12)	−0.0027 (10)	0.0019 (10)
O9	0.0259 (15)	0.0353 (13)	0.0232 (12)	−0.0071 (13)	0.0073 (12)	−0.0025 (11)
O10	0.0271 (15)	0.0342 (15)	0.0279 (13)	0.0127 (13)	0.0059 (12)	0.0066 (12)
O1	0.0256 (14)	0.0296 (13)	0.0402 (15)	0.0053 (13)	−0.0123 (13)	−0.0079 (13)
O2	0.0426 (17)	0.0333 (16)	0.0418 (17)	0.0179 (14)	−0.0130 (15)	−0.0173 (14)
C1	0.0217 (17)	0.0251 (18)	0.0217 (15)	0.0015 (16)	0.0025 (15)	−0.0005 (15)
C2	0.0211 (17)	0.0195 (15)	0.0210 (15)	−0.0007 (15)	0.0003 (14)	−0.0009 (14)
N1	0.0225 (15)	0.0236 (14)	0.0205 (13)	0.0019 (14)	0.0000 (13)	−0.0003 (12)
C3	0.0235 (18)	0.0263 (17)	0.0197 (15)	0.0023 (16)	0.0011 (15)	−0.0024 (14)
C4	0.0221 (18)	0.0274 (17)	0.0235 (16)	0.0008 (16)	0.0021 (14)	−0.0002 (15)
C5	0.0238 (19)	0.043 (2)	0.0241 (16)	0.0088 (19)	0.0033 (16)	−0.0002 (17)
N2	0.0302 (17)	0.0286 (16)	0.0277 (16)	0.0089 (16)	0.0033 (15)	0.0057 (14)
C6	0.0224 (17)	0.0223 (16)	0.0190 (15)	0.0008 (15)	0.0038 (14)	−0.0034 (14)
N3	0.0254 (16)	0.044 (2)	0.0278 (16)	0.0072 (16)	0.0040 (14)	0.0085 (15)
N4	0.0275 (19)	0.042 (2)	0.0306 (17)	0.0131 (18)	0.0025 (14)	0.0059 (16)

Geometric parameters (Å, º)

P1—O3	1.504 (3)	C1—C2	1.521 (5)
P1—O4	1.515 (3)	C2—N1	1.493 (4)
P1—O5	1.561 (3)	C2—C3	1.516 (5)
P1—O6	1.565 (3)	C3—C4	1.522 (5)
P2—O7	1.503 (3)	C4—C5	1.503 (5)
P2—O8	1.508 (2)	C5—N2	1.462 (5)
P2—O9	1.564 (3)	N2—C6	1.324 (5)
P2—O10	1.573 (3)	C6—N3	1.328 (5)
O1—C1	1.307 (5)	C6—N4	1.334 (5)
O2—C1	1.208 (5)
O3—P1—O4	113.96 (16)	O2—C1—C2	122.3 (3)
O3—P1—O5	111.15 (16)	O1—C1—C2	112.3 (3)
O4—P1—O5	109.07 (16)	N1—C2—C3	111.7 (3)
O3—P1—O6	112.29 (19)	N1—C2—C1	107.1 (3)
O4—P1—O6	103.45 (16)	C3—C2—C1	112.4 (3)
O5—P1—O6	106.40 (18)	C2—C3—C4	114.4 (3)
O7—P2—O8	115.60 (16)	C5—C4—C3	108.9 (3)
O7—P2—O9	107.17 (15)	N2—C5—C4	112.2 (3)
O8—P2—O9	110.52 (16)	C6—N2—C5	123.0 (3)
O7—P2—O10	108.84 (17)	N2—C6—N3	120.9 (3)
O8—P2—O10	110.55 (15)	N2—C6—N4	120.7 (3)
O9—P2—O10	103.42 (17)	N3—C6—N4	118.4 (3)
O2—C1—O1	125.4 (4)
O2—C1—C2—N1	−2.8 (5)	C2—C3—C4—C5	−171.2 (3)
O1—C1—C2—N1	178.7 (3)	C3—C4—C5—N2	−174.3 (3)
O2—C1—C2—C3	120.3 (4)	C4—C5—N2—C6	149.0 (4)
O1—C1—C2—C3	−58.2 (4)	C5—N2—C6—N3	8.5 (6)
N1—C2—C3—C4	−61.3 (4)	C5—N2—C6—N4	−170.2 (4)
C1—C2—C3—C4	178.4 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5···O8^i	0.79 (5)	1.85 (5)	2.637 (4)	172 (5)
O6—H6···O4^ii	0.91 (6)	1.69 (5)	2.564 (4)	159 (5)
O9—H9···O3^iii	1.18 (5)	1.39 (5)	2.518 (4)	157 (5)
O10—H10···O4^i	0.77 (7)	1.94 (8)	2.610 (4)	145 (7)
O1—H1···O7^iv	0.82	1.76	2.566 (4)	169
N1—H1A···O4^v	0.89	2.01	2.732 (4)	137
N1—H1B···O8^v	0.89	2.05	2.895 (4)	159
N1—H1C···O8^vi	0.89	2.04	2.911 (4)	165
N2—H2A···O10^iii	0.86	2.35	3.077 (5)	142
N3—H3C···O9^vii	0.86	2.16	2.981 (4)	158
N3—H3D···O7^viii	0.86	2.41	3.158 (5)	146
N3—H3D···O10^viii	0.86	2.47	3.237 (5)	150
N4—H4C···O3	0.86	2.13	2.914 (5)	152
N4—H4D···O7^viii	0.86	2.17	2.977 (5)	155

Symmetry codes: (i) x−1/2, −y+3/2, −z+1; (ii) x−1/2, −y+1/2, −z+1; (iii) x+1/2, −y+3/2, −z+1; (iv) x+3/2, −y+1/2, −z+1; (v) x+1/2, −y+1/2, −z+1; (vi) x+1, y−1, z; (vii) −x+5/2, −y+1, z+1/2; (viii) −x+3/2, −y+1, z+1/2.