Creatininium di­hydrogenarsenate

The title compound, (C₄H₈N₃O)[H₂AsO₄], contains a network of creatininium cations and dihydrogenarsenate anions [mean As—O = 1.681 (2) Å]. The crystal packing involves anion-to-anion O—H⋯O, cation-to-anion N—H⋯O and cation-to-cation N—H⋯O hydrogen bonds, resulting in a chain structure.

Comment

The title compound, (I) (Fig. 1), was prepared as part of our ongoing structural studies of hydrogen-bonding inter­actions in protonated-amine (di)hydrogen arsenate mol­ecular salts (Wilkinson & Harrison, 2004; Todd & Harrison, 2005). The [H₂AsO₄]⁻ dihydrogenarsenate group in (I) shows a normal tetra­hedral geometry [mean As—O = 1.681 (2) Å], with the protonated As1—O3 and As1—O4 vertices showing their usual lengthening relative to the unprotonated As1—O1 and As1—O2 bonds, which have formal partial double-bond character (Table 1).

The creatininium cation is approximately planar [r.m.s. deviation for the non-H atoms = 0.031 Å; maximum deviation from the mean plane = 0.0597 (16) Å for N2]. The three C1—N bond distances (Table 1) are distinctly different, with C1—N1 much longer than the other two. This configuration perhaps indicates that the canonical form of the mol­ecule, with a formal double bond in the C1—N1 position and a formal positive charge on N1, is of less importance than the forms that place the double bond in the C1—N2 and C1—N3 positions and the positive charge on the respective N atoms. However, the rather short C2—N1 bond length suggests that some conjugation involving the C2=O5 group may also be significant. In the structure of creatininium dipicolinate monohydrate (Moghimi et al., 2004), the creatininium cation is constrained to be planar by mirror symmetry and an almost identical pattern of C—N bond lengths is observed.

As well as electrostatic attractions, the component species in (I) inter­act by means of a network of cation-to-anion N—H⋯O, anion-to-anion O—H⋯O and cation-to-cation N—H⋯O hydrogen bonds (Table 2). The [H₂AsO₄]⁻ units are linked into polymeric chains (Fig. 2) propagating along [100] by way of inversion-generated pairs of O3—H1⋯O2ⁱ and O4—H2⋯O1ⁱⁱ bonds (see Table 2 for symmetry codes). In graph-set notation (Bernstein et al., 1995), each inter-tetra­hedral linking motif corresponds to an R₂²(8) loop. The As1⋯As1ⁱ and As1⋯As1ⁱⁱ separations are 4.0608 (3) and 3.9286 (3) Å, respectively.

The organic species inter­acts with the dihydrogenarsenate chains by way of two N—H⋯O hydrogen bonds (Fig. 1), such that both sides of each [100] chain are decorated by the creatininium cations. The third creatininium N—H group is involved in a cation-to-cation N—H⋯O bond (Fig. 2) that appears to reinforce the chains. Overall, a chain structure along the a axis arises for (I), as shown in Fig. 3. Atoms O1 and O2 accept two hydrogen bonds each (bond angle sums about these atoms are 358.3 and 359.3°, respectively). A PLATON (Spek, 2003) analysis of (I) flagged the possible presence of two short C—H⋯O inter­actions (Table 2), although their structural significance is not clear.

PLATON also flagged a short C2⋯C2^v [symmetry code: (v) −x, 1 − y, −z] inter­molecular contact of 3.158 (3) Å, compared with a van der Waals radius sum of 3.40 Å (Bondi, 1964). This close contact might arise as part of a carbon­yl–carbon­yl inter­action, as described by Allen et al. (1998). In the notation of these workers, the situation in (I) corresponds to a `sheared antiparallel' or motif II inter­action (Fig. 4), generated by a centre of symmetry. Here, the O5=C2⋯O5^v and C2=O5⋯C2^v inter­action angles are 100.50 (14) and 79.50 (13)°, respectively, compared with the nominal values of 2 × 90° for a perfect rectangle of the four constituent atoms. This is slightly more distorted than the mean O=C⋯O and C=O⋯C angles of 96.5 (4) and 83.5 (4)° based on 553 contributors, as cited by Allen et al. (1998). The C2⋯O5^v separation of 3.147 (3) Å in (I) is slightly less than the C⋯O van der Waals separation of 3.22 Å.

The dihydrogenarsenate chain motif in (I) replicates that seen in t-butyl­ammonium dihydrogenarsenate (Wilkinson & Harrison, 2004). However, a different cation-to-anion hydrogen-bonding scheme leads to a layered structure in this phase. The intra­chain As⋯As separations of 4.2662 (3) and 4.3002 (4) Å in the t-butyl­ammonium compound are significantly larger than those seen in (I).

Figure 1 View of the asymmetric unit of (I), showing 50% probability displacement ellipsoids, with hydrogen bonds indicated by dashed lines.

Figure 2 Detail of a hydrogen-bonded chain in (I). Hydrogen bonds are indicated by dashed lines. [Symmetry codes as in Table 2; additionally, (vi) x − 1, y, z.]

Figure 3 Projection of the packing of (I) along the a axis. Hydrogen bonds are indicated by dashed lines.

Figure 4 Detail of (I), showing the possible carbon­yl–carbon­yl inter­action, with H atoms omitted for clarity. Hydrogen bonds are indicated by dashed lines. [Symmetry code: (v) −x, 1 − y, −z.]

Experimental

A 0.5 M aqueous creatine solution (10 ml) was added to a 0.5 M aqueous H₃AsO₄ solution (20 ml) to result in a clear solution. A mass of block-like crystals of (I) grew as the water evaporated over the course of a few days. The creatine transformed to creatinine under the low-pH conditions of the reaction.

Crystal data

• (C₄H₈N₃O)[H₂AsO₄]

• M_r = 255.07

• Monoclinic, P 2₁ /n

• a = 7.3576 (3) Å

• b = 10.4263 (5) Å

• c = 11.9471 (5) Å

• β = 102.908 (1)°

• V = 893.33 (7) ų

• Z = 4

• D_x = 1.897 Mg m⁻³

• Mo Kα radiation

• Cell parameters from 5020 reflections

• θ = 2.6–32.2°

• μ = 3.80 mm⁻¹

• T = 293 (2) K

• Chunk, colourless

• 0.49 × 0.33 × 0.24 mm

Data collection

• Bruker SMART 1000 CCD diffractometer

• ω scans

• Absorption correction: multi-scan(SADABS; Bruker, 1999)T_min = 0.223, T_max = 0.401

• 11192 measured reflections

• 3202 independent reflections

• 2403 reflections with I > 2σ(I)

• R_int = 0.029

• θ_max = 32.5°

• h = −11 → 11

• k = −15 → 15

• l = −17 → 18

Refinement

• Refinement on F²

• R[F² > 2σ(F²)] = 0.027

• wR(F²) = 0.069

• S = 1.00

• 3202 reflections

• 119 parameters

• H-atom parameters constrained

• w = 1/[σ²(F_o²) + (0.0381P)²] where P = (F_o² + 2F_c²)/3

• (Δ/σ)_max = 0.002

• Δρ_max = 0.59 e Å⁻³

• Δρ_min = −0.52 e Å⁻³

Table 1
Selected interatomic distances (Å)

As1—O1	1.6512 (13)
As1—O2	1.6563 (12)
As1—O4	1.7013 (15)
As1—O3	1.7134 (13)
C1—N2	1.305 (2)
C1—N3	1.321 (2)
C1—N1	1.374 (2)
C2—N1	1.367 (2)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H1⋯O2^i	0.85	1.77	2.618 (2)	177
O4—H2⋯O1^ii	0.82	1.79	2.598 (2)	169
N1—H3⋯O2	0.86	1.89	2.703 (2)	158
N2—H4⋯O5^iii	0.86	2.16	2.983 (2)	161
N2—H5⋯O1	0.86	1.89	2.747 (2)	172
C3—H6⋯O1^iv	0.97	2.46	3.334 (2)	149
C3—H7⋯O2^v	0.97	2.46	3.384 (2)	159
Symmetry codes: (i) -x, -y+2, -z; (ii) -x+1, -y+2, -z; (iii) x+1, y, z; (iv) ; (v) -x, -y+1, -z.

The hydr­oxy H atoms were found in difference maps and refined as riding on their carrier O atoms in their as-found relative positions. The H atoms bonded to C and N atoms were placed in idealized positions (C—H = 0.96–0.97 Å and N—H = 0.86 Å) and refined as riding, allowing for free rotation of the –CH₃ group. The constraint U_iso(H) = 1.2U_eq(carrier) or 1.5U_eq(meth­yl carrier) was applied.

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Supporting information

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Creatininium dihydrogenarsenate

Crystal data

(C4H8N3O)[H2AsO4]	F(000) = 512
Mr = 255.07	Dx = 1.897 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 5020 reflections
a = 7.3576 (3) Å	θ = 2.6–32.2°
b = 10.4263 (5) Å	µ = 3.80 mm^−1
c = 11.9471 (5) Å	T = 293 K
β = 102.908 (1)°	Chunk, colourless
V = 893.33 (7) Å^3	0.49 × 0.33 × 0.24 mm
Z = 4

Data collection

Bruker SMART 1000 CCD diffractometer	3202 independent reflections
Radiation source: fine-focus sealed tube	2403 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ω scans	θmax = 32.5°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −11→11
Tmin = 0.223, Tmax = 0.401	k = −15→15
11192 measured reflections	l = −17→18

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.027	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.069	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0381P)^2] where P = (Fo^2 + 2Fc^2)/3
3202 reflections	(Δ/σ)max = 0.002
119 parameters	Δρmax = 0.59 e Å^−3
0 restraints	Δρmin = −0.52 e Å^−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
As1	0.26213 (2)	0.928771 (15)	0.019997 (18)	0.03047 (7)
O1	0.46360 (18)	0.87172 (12)	0.09239 (13)	0.0373 (3)
O2	0.08787 (18)	0.82749 (11)	0.01759 (13)	0.0398 (3)
O3	0.2283 (2)	1.06885 (12)	0.08753 (15)	0.0438 (3)
H1	0.1274	1.1029	0.0514	0.053*
O4	0.2634 (2)	0.96492 (14)	−0.11868 (13)	0.0444 (3)
H2	0.3451	1.0179	−0.1198	0.053*
C1	0.3742 (2)	0.54747 (15)	0.13831 (17)	0.0311 (4)
C2	0.0711 (3)	0.51202 (17)	0.13441 (17)	0.0338 (4)
C3	0.1748 (3)	0.38752 (17)	0.16057 (18)	0.0355 (4)
H6	0.1640	0.3537	0.2344	0.043*
H7	0.1294	0.3240	0.1016	0.043*
C4	0.5201 (3)	0.33417 (18)	0.1848 (2)	0.0446 (5)
H8	0.4793	0.2528	0.1506	0.067*
H9	0.5636	0.3239	0.2662	0.067*
H10	0.6196	0.3664	0.1527	0.067*
N1	0.2003 (2)	0.60209 (13)	0.12221 (14)	0.0316 (3)
H3	0.1761	0.6817	0.1067	0.038*
N2	0.5212 (2)	0.61337 (15)	0.12952 (17)	0.0430 (4)
H4	0.6280	0.5763	0.1395	0.052*
H5	0.5112	0.6939	0.1138	0.052*
N3	0.3657 (2)	0.42406 (13)	0.16181 (15)	0.0345 (3)
O5	−0.0931 (2)	0.53087 (16)	0.12300 (15)	0.0489 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
As1	0.02924 (9)	0.01985 (8)	0.03993 (12)	−0.00035 (7)	0.00263 (7)	0.00260 (7)
O1	0.0290 (6)	0.0275 (6)	0.0517 (9)	0.0024 (5)	0.0011 (6)	0.0088 (6)
O2	0.0305 (6)	0.0231 (5)	0.0629 (10)	−0.0022 (5)	0.0042 (6)	0.0075 (6)
O3	0.0382 (7)	0.0294 (6)	0.0582 (10)	0.0038 (6)	−0.0012 (7)	−0.0102 (6)
O4	0.0428 (8)	0.0446 (7)	0.0421 (9)	−0.0107 (6)	0.0013 (7)	0.0051 (6)
C1	0.0325 (8)	0.0231 (7)	0.0364 (10)	0.0023 (6)	0.0051 (7)	0.0003 (6)
C2	0.0349 (9)	0.0316 (8)	0.0351 (10)	−0.0010 (7)	0.0085 (8)	−0.0012 (7)
C3	0.0384 (10)	0.0263 (7)	0.0418 (11)	−0.0038 (7)	0.0089 (8)	0.0015 (7)
C4	0.0440 (11)	0.0260 (8)	0.0602 (14)	0.0085 (8)	0.0039 (10)	0.0030 (8)
N1	0.0298 (7)	0.0230 (6)	0.0418 (9)	0.0031 (5)	0.0077 (6)	0.0028 (6)
N2	0.0282 (8)	0.0269 (7)	0.0722 (13)	0.0026 (6)	0.0077 (8)	0.0076 (8)
N3	0.0356 (8)	0.0216 (6)	0.0449 (10)	0.0017 (6)	0.0062 (7)	0.0021 (6)
O5	0.0340 (7)	0.0476 (8)	0.0678 (11)	0.0002 (7)	0.0176 (7)	0.0017 (8)

Geometric parameters (Å, º)

As1—O1	1.6512 (13)	C2—C3	1.503 (3)
As1—O2	1.6563 (12)	C3—N3	1.452 (2)
As1—O4	1.7013 (15)	C3—H6	0.9700
As1—O3	1.7134 (13)	C3—H7	0.9700
O3—H1	0.8488	C4—N3	1.451 (2)
O4—H2	0.8185	C4—H8	0.9600
C1—N2	1.305 (2)	C4—H9	0.9600
C1—N3	1.321 (2)	C4—H10	0.9600
C1—N1	1.374 (2)	N1—H3	0.8600
C2—O5	1.202 (2)	N2—H4	0.8600
C2—N1	1.367 (2)	N2—H5	0.8600
O1—As1—O2	112.36 (6)	C2—C3—H7	111.2
O1—As1—O4	112.96 (7)	H6—C3—H7	109.1
O2—As1—O4	107.28 (7)	N3—C4—H8	109.5
O1—As1—O3	105.56 (7)	N3—C4—H9	109.5
O2—As1—O3	111.00 (7)	H8—C4—H9	109.5
O4—As1—O3	107.62 (8)	N3—C4—H10	109.5
As1—O3—H1	108.6	H8—C4—H10	109.5
As1—O4—H2	109.2	H9—C4—H10	109.5
N2—C1—N3	127.51 (17)	C2—N1—C1	110.36 (14)
N2—C1—N1	122.20 (16)	C2—N1—H3	124.8
N3—C1—N1	110.29 (15)	C1—N1—H3	124.8
O5—C2—N1	125.52 (18)	C1—N2—H4	120.0
O5—C2—C3	128.01 (18)	C1—N2—H5	120.0
N1—C2—C3	106.45 (15)	H4—N2—H5	120.0
N3—C3—C2	102.73 (14)	C1—N3—C4	126.66 (16)
N3—C3—H6	111.2	C1—N3—C3	110.16 (15)
C2—C3—H6	111.2	C4—N3—C3	123.18 (15)
N3—C3—H7	111.2
O5—C2—C3—N3	179.0 (2)	N2—C1—N3—C4	0.9 (3)
N1—C2—C3—N3	0.8 (2)	N1—C1—N3—C4	−179.61 (18)
O5—C2—N1—C1	−178.5 (2)	N2—C1—N3—C3	−178.4 (2)
C3—C2—N1—C1	−0.2 (2)	N1—C1—N3—C3	1.0 (2)
N2—C1—N1—C2	179.00 (19)	C2—C3—N3—C1	−1.1 (2)
N3—C1—N1—C2	−0.5 (2)	C2—C3—N3—C4	179.53 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H1···O2^i	0.85	1.77	2.618 (2)	177
O4—H2···O1^ii	0.82	1.79	2.598 (2)	169
N1—H3···O2	0.86	1.89	2.703 (2)	158
N2—H4···O5^iii	0.86	2.16	2.983 (2)	161
N2—H5···O1	0.86	1.89	2.747 (2)	172
C3—H6···O1^iv	0.97	2.46	3.334 (2)	149
C3—H7···O2^v	0.97	2.46	3.384 (2)	159

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