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In the title compound, C5H14N3+·H2PO4-, the cation has a central guanidinium fragment with a planar geometry, as expected for a central Csp2 atom with a small charge delocalization along the three C-N bonds. The crystal packing is governed by hydrogen bonds so that the phosphate anions are linked head to tail, forming chains running parallel to the c direction. These chains in turn are interconnected by hydrogen bonds to intermediate tetra­methyl­guanidinium cations forming hydrogen-bonded molecular layers stacked parallel to the bc crystal planes.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100005187/na1466sup1.cif
Contains datablocks I, default

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100005187/na1466Isup2.hkl
Contains datablock I

CCDC reference: 147671

Comment top

Inorganic salts of phosphoric acids form compounds that exhibit a wealth of interesting physical properties such as ferroelectricity and optical non-linear phenomena like second harmonic generation, a classical example is potassium dihydrogen orthophosphate KDP (Rafhkovich, 1991). A general synthetic route to obtain organo-dihydrogen orthophosphate crystals has been detailed (Masse & Zyss, 1991). In all these compounds there is an inorganic subnetwork formed by the dihydrogen orthophosphate anions (H2PO4)n. When the organic species are strongly dipolar the anion sublattice is organized in a polar structure, examples are L-Argininium dihydrogen orthophosphate monohydrate (Aoki et al., 1971), 2-amino-5-nitropyridinium dihydrogen orthophosphate (Kotler et al., 1992) and sarcosine dihydrogen orthophosphate (Averbouch-Pouchot et al., 1988). In the case of a weakly dipolar organic species like glycine, the anion sublattice will organize in a nonpolar structure (Averbouch-Pouchot et al., 1988). As part of a project to study new compounds with potentially interesting optical and dielectric properties we have synthesized the title compound, (I). \sch

Similarly to aminoguanidinium dihydrogen orthophosphate (Adams, 1977), we report here its crystal structure, as determined by single-crystal X-ray diffraction. The compound crystallizes in a centrosymmetric space group, consequently no non-linear optical effects are observed.

Differential scanning calorimetry measurements performed from 93 to 673 K did not show any phase transition. The melting point occurs at about 493 K, followed by decomposition.

The geometry of the guanidinium group in (I) is planar, as expected for sp2 hybridization of the central C atom. The π delocalization along the three C–N bonds gives rise to C1–N2 [1.344 (1) Å] and C1–N3 [1.346 (1) Å] bond lengths larger than the value expected for a Csp2N bond [1.295 Å] and close to the expected value for a delocalized CN double bond [1.339 (5) Å]. The C1–N1 bond length [1.320 (1) Å] is somewhat shorter and compares well with the average value for the guanidinium cation [1.321 Å] (Allen et al., 1987). The larger value for the C1–N2 and C1–N3 bond lengths must be ascribed to the methyl substitution which makes the three bonds non-equivalent. Indeed, simple molecular orbital semiempirical calculations (extended Hückel) give different atomic charges on N1 (−0.376 e) and N2 and N3 (−0.590 e). As may be expected the two P–O distances for the OH groups are significantly longer than the other two P–O distances.

The basis of the molecular engineering in these salts is the obtention of structures with potential physical properties as a result of the hydrogen-bond crystal network which tends to reinforce the properties exhibited by the isolated molecule by arranging them as linear or layer molecular patterns.

In our case the hydrogen bonds also give rise to an interesting arrangement which is best understood with the aid of the diagram corresponding to the crystal structure viewed perpendicular to the a–b plane. On one hand, each phosphate ion is connected by two hydrogen bonds to each phosphate ion related to it by a c glide plane both with positive and negative fractional c translations. Given that the central P atoms lie at a very close distance to the glide planes (0.32 Å) it results in approximately linear phosphate chains parallel to the c direction.

On the other hand, each tetramethylguanidinium ion is hydrogen-bonded to two phosphate ions related to each other by an inversion centre and belonging to different chains giving rise to a framework of molecules connected by hydrogen bonds in the form of layers parallel to the b–c crystal planes and stacked according to the a lattice translation period. Besides, two C–H···O contacts interrelating molecules within the same layer and not depicted in the diagram have been detected.

Experimental top

The title compound was prepared by mixing equimolecular portions of two reagents: 1,1,3,3-tetramethylguanidine (99%) and phosphoric acid (85%) in a 1:1 solution of ethanol and water at room temperature. Good quality colourless single crystals of prism habit were grown from the solution by slow evaporation, one of them was selected and used for the X-ray analysis. The intensities were corrected for Lorentz-polarization effects and extinction factors were ignored. The space group was uniquely determined by the systematic absences in the reflection data set.

Refinement top

H-atom bond lengths and angles have been constrained in the refinement. Only the torsional angles of the CH3 and OH groups have been allowed to refine.

Computing details top

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: SET4 (de Boer & Duissenberg, 1984) and CELDIM (CAD4, Retting, 1989); data reduction: XRAY76 System (Stewart et al., 1976); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: PLATON (Spek, 1994); software used to prepare material for publication: PARST (Nardelli, 1995) and PARSTCIF (Nardelli, 1991).

Figures top
[Figure 1] Fig. 1. Structure of (I) showing 30% probability displacement ellipsoids. The hydrogen atoms are omitted for clarity.
[Figure 2] Fig. 2. The molecular packing, viewed along an axis perpendicular to the a–b plane showing the hydrogen bonding.
1,1,3,3-tetramethyl guanidinium phosphate top
Crystal data top
C5H14N3+·H2PO4Dx = 1.405 Mg m3
Dm = 1.40 Mg m3
Dm measured by flotation in bromobenzene and acetone
Mr = 213.18Melting point: 493 K
Monoclinic, P21/cMo Kα radiation, λ = 0.71069 Å
a = 11.225 (3) ÅCell parameters from 25 reflections
b = 10.951 (1) Åθ = 7–12°
c = 8.430 (2) ŵ = 0.26 mm1
β = 103.50 (1)°T = 293 K
V = 1007.6 (4) Å3Prism, colourless
Z = 40.80 × 0.50 × 0.40 mm
F(000) = 456
Data collection top
Enraf-Nonius CAD4
diffractometer
Rint = 0.000
Radiation source: fine-focus sealed tubeθmax = 33.0°, θmin = 2.6°
Graphite monochromatorh = 017
ω–2θ scansk = 016
3777 measured reflectionsl = 1212
3777 independent reflections3 standard reflections every 60 min min
3257 reflections with I > 2σ(I) intensity decay: none
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.034Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.105H-atom parameters constrained
S = 1.08Calculated w = 1/[σ2(Fo2) + (0.0639P)2 + 0.1114P]
where P = (Fo2 + 2Fc2)/3
3777 reflections(Δ/σ)max < 0.001
124 parametersΔρmax = 0.46 e Å3
0 restraintsΔρmin = 0.37 e Å3
Crystal data top
C5H14N3+·H2PO4V = 1007.6 (4) Å3
Mr = 213.18Z = 4
Monoclinic, P21/cMo Kα radiation
a = 11.225 (3) ŵ = 0.26 mm1
b = 10.951 (1) ÅT = 293 K
c = 8.430 (2) Å0.80 × 0.50 × 0.40 mm
β = 103.50 (1)°
Data collection top
Enraf-Nonius CAD4
diffractometer
Rint = 0.000
3777 measured reflections3 standard reflections every 60 min min
3777 independent reflections intensity decay: none
3257 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0340 restraints
wR(F2) = 0.105H-atom parameters constrained
S = 1.08Δρmax = 0.46 e Å3
3777 reflectionsΔρmin = 0.37 e Å3
124 parameters
Special details top

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 on F2 for ALL reflections except for 0 with very negative F2 or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The observed criterion of F2 > σ(F2) is used only for calculating R_factor_obs 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 (Å2) top
xyzUiso*/Ueq
P10.21200 (2)0.22099 (2)0.44607 (3)0.02297 (8)
O40.26662 (8)0.14310 (7)0.33544 (9)0.0318 (2)
O30.12944 (7)0.15363 (7)0.53532 (9)0.0296 (2)
O20.13625 (9)0.32927 (8)0.34687 (10)0.0384 (2)
H20.14210.32630.24940.058*
O10.31819 (7)0.28321 (8)0.57362 (10)0.0348 (2)
H10.29190.30670.65400.052*
N10.13166 (8)0.11300 (8)0.51765 (13)0.0358 (2)
H1A0.148400.035170.537200.043*
H1B0.055910.136200.474850.043*
N30.19506 (10)0.31397 (9)0.52252 (13)0.0386 (2)
N20.33639 (9)0.16108 (10)0.61799 (14)0.0415 (2)
C10.22015 (10)0.19494 (10)0.55254 (13)0.0309 (2)
C50.08049 (12)0.35246 (12)0.4126 (2)0.0459 (3)
H5A0.09240.43170.36450.069*
H5B0.01660.35970.47390.069*
H5C0.05560.29180.32570.069*
C20.36472 (13)0.04187 (13)0.6937 (2)0.0530 (4)
H2A0.44110.04690.77820.080*
H2B0.37420.01770.61080.080*
H2C0.29790.01620.74300.080*
C40.2563 (2)0.40878 (13)0.6335 (2)0.0626 (4)
H4A0.19680.44850.68510.094*
H4B0.29150.46950.57230.094*
H4C0.32160.37210.71770.094*
C30.43961 (13)0.2244 (2)0.5750 (2)0.0630 (5)
H3A0.49250.16460.53860.094*
H3B0.48670.26810.67070.094*
H3C0.408520.28280.48700.094*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
P10.02584 (12)0.02308 (12)0.02056 (11)0.00027 (7)0.00656 (8)0.00083 (7)
O40.0431 (4)0.0283 (3)0.0264 (3)0.0075 (3)0.0125 (3)0.0006 (3)
O30.0303 (3)0.0317 (3)0.0277 (3)0.0081 (3)0.0087 (3)0.0015 (3)
O20.0539 (5)0.0356 (4)0.0279 (3)0.0179 (4)0.0137 (3)0.0048 (3)
O10.0294 (3)0.0464 (5)0.0301 (3)0.0121 (3)0.0100 (3)0.0092 (3)
N10.0266 (4)0.0261 (4)0.0535 (6)0.0007 (3)0.0072 (4)0.0021 (4)
N30.0430 (5)0.0271 (4)0.0458 (5)0.0043 (4)0.0105 (4)0.0041 (4)
N20.0282 (4)0.0438 (5)0.0496 (6)0.0022 (4)0.0032 (4)0.0042 (4)
C10.0300 (4)0.0297 (4)0.0339 (5)0.0012 (3)0.0093 (4)0.0058 (4)
C50.0426 (6)0.0347 (6)0.0626 (8)0.0028 (5)0.0168 (6)0.0122 (5)
C20.0417 (6)0.0429 (7)0.0653 (9)0.0081 (5)0.0059 (6)0.0054 (6)
C40.0952 (13)0.0332 (6)0.0558 (8)0.0164 (7)0.0105 (8)0.0130 (6)
C30.0298 (6)0.0859 (13)0.0708 (10)0.0132 (7)0.0071 (6)0.0034 (9)
Geometric parameters (Å, º) top
P1—O41.4968 (7)N2—C21.455 (2)
P1—O31.5148 (7)C5—H5A0.98
P1—O11.5629 (8)C5—H5B0.98
P1—O21.5800 (8)C5—H5C0.98
O2—H20.84C2—H2A0.98
O1—H10.84C2—H2B0.98
N1—C11.3198 (13)C2—H2C0.98
N1—H1A0.88C4—H4A0.98
N1—H1B0.88C4—H4B0.98
N3—C11.3451 (14)C4—H4C0.98
N3—C51.461 (2)C3—H3A0.98
N3—C41.458 (2)C3—H3B0.98
N2—C11.3447 (15)C3—H3C0.98
N2—C31.466 (2)
O4—P1—O3114.78 (5)H5A—C5—H5B109.5
O4—P1—O1108.64 (5)N3—C5—H5C109.47
O3—P1—O1109.11 (4)H5A—C5—H5C109.5
O4—P1—O2110.24 (4)H5B—C5—H5C109.5
O3—P1—O2108.20 (5)N2—C2—H2A109.47
O1—P1—O2105.47 (5)N2—C2—H2B109.47
P1—O2—H2109.47H2A—C2—H2B109.5
P1—O1—H1109.47N2—C2—H2C109.47
C1—N1—H1A120.00H2A—C2—H2C109.5
C1—N1—H1B120.00H2B—C2—H2C109.5
H1A—N1—H1B120.0N3—C4—H4A109.47
C1—N3—C5120.91 (10)N3—C4—H4B109.47
C1—N3—C4121.53 (12)H4A—C4—H4B109.5
C5—N3—C4114.50 (12)N3—C4—H4C109.47
C1—N2—C3121.02 (12)H4A—C4—H4C109.5
C1—N2—C2121.27 (11)H4B—C4—H4C109.5
C3—N2—C2115.34 (12)N2—C3—H3A109.47
N1—C1—N2120.78 (11)N2—C3—H3B109.47
N1—C1—N3120.22 (10)H3A—C3—H3B109.5
N2—C1—N3119.01 (10)N2—C3—H3C109.47
N3—C5—H5A109.47H3A—C3—H3C109.5
N3—C5—H5B109.47H3B—C3—H3C109.5
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O30.882.082.924 (1)161
O2—H2···O3i0.841.792.616 (1)167
O1—H1···O4ii0.841.712.541 (1)169
N1—H1B···O3iii0.882.072.894 (1)155
C5—H5B···O2iii0.982.563.521 (2)167
C5—H5A···O2iv0.982.673.607 (2)159
Symmetry codes: (i) x, y1/2, z1/2; (ii) x, y1/2, z+1/2; (iii) x, y, z+1; (iv) x, y+1, z.

Experimental details

Crystal data
Chemical formulaC5H14N3+·H2PO4
Mr213.18
Crystal system, space groupMonoclinic, P21/c
Temperature (K)293
a, b, c (Å)11.225 (3), 10.951 (1), 8.430 (2)
β (°) 103.50 (1)
V3)1007.6 (4)
Z4
Radiation typeMo Kα
µ (mm1)0.26
Crystal size (mm)0.80 × 0.50 × 0.40
Data collection
DiffractometerEnraf-Nonius CAD4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
3777, 3777, 3257
Rint0.000
(sin θ/λ)max1)0.766
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.034, 0.105, 1.08
No. of reflections3777
No. of parameters124
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.46, 0.37

Computer programs: CAD-4 Software (Enraf-Nonius, 1989), SET4 (de Boer & Duissenberg, 1984) and CELDIM (CAD4, Retting, 1989), XRAY76 System (Stewart et al., 1976), SIR92 (Altomare et al., 1994), SHELXL93 (Sheldrick, 1993), PLATON (Spek, 1994), PARST (Nardelli, 1995) and PARSTCIF (Nardelli, 1991).

Selected geometric parameters (Å, º) top
P1—O41.4968 (7)N3—C51.461 (2)
P1—O31.5148 (7)N3—C41.458 (2)
P1—O11.5629 (8)N2—C11.3447 (15)
P1—O21.5800 (8)N2—C31.466 (2)
N1—C11.3198 (13)N2—C21.455 (2)
N3—C11.3451 (14)
O4—P1—O3114.78 (5)C5—N3—C4114.50 (12)
O4—P1—O1108.64 (5)C1—N2—C3121.02 (12)
O3—P1—O1109.11 (4)C1—N2—C2121.27 (11)
O4—P1—O2110.24 (4)C3—N2—C2115.34 (12)
O3—P1—O2108.20 (5)N1—C1—N2120.78 (11)
O1—P1—O2105.47 (5)N1—C1—N3120.22 (10)
C1—N3—C5120.91 (10)N2—C1—N3119.01 (10)
C1—N3—C4121.53 (12)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O30.882.082.924 (1)161
O2—H2···O3i0.841.792.616 (1)167
O1—H1···O4ii0.841.712.541 (1)169
N1—H1B···O3iii0.882.072.894 (1)155
C5—H5B···O2iii0.982.563.521 (2)167
C5—H5A···O2iv0.982.673.607 (2)159
Symmetry codes: (i) x, y1/2, z1/2; (ii) x, y1/2, z+1/2; (iii) x, y, z+1; (iv) x, y+1, z.
 

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