Ammonium 4-methoxy­cinnamate

In the title compound, NH₄⁺·C₁₀H₉O₃^-, bimolecular layers of the anions are formed between layers of the cations. There are N-H...O hydrogen bonds between the ammonium ion and the carboxyl­ate groups of the anions. In the crystal structure, the C=C moiety of the cinnamate ion makes an angle of 117.1 (2)° with that of the nearest neighbour, indicating that a pedal rotation is required before [beta]-type [2+2]-photodimerization can take place, which is the predominant mode of the photochemistry of this compound.

S1. Comment

Organic solid-state reactions have the potential to control the stereoselectivity of chemical reactions. Ammonium salt formation is one way of designing the molecular arrangement of crystals (Ito et al., 1995; Ito & Olovsson, 1997; Ito, 1998). The photoreactivities of the ammonium and isopropylammonium salts of the fumaric acid dianion have been rationalized, based on their crystal structures (Hosomi et al., 1998). It is proposed that a small size or a planar structure of the amine is an important clue for converting photostable crystal packing into photodimerizable packing (Ito et al., 2003). In the present study, the structure of the ammonium salt of 4-methoxycinnamate, (I), has been determined in order to investigate the relationship between the crystal structure and its photoreactivity. The product in the solid-state photolysis of (I) is predominantly the β-type head-to-head dimer (Ito et al., 2003). \sch

Compound (I) consists of an ammonium cation and a p-methoxycinnamate anion (Fig. 1 and Table 1). The anions form bimolecular layers perpendicular to the a axis and the carboxylate groups are oriented on the outside, to form N—H···O hydrogen bonds with the ammonium cations (Fig. 2). This layer structure corresponds to the habit of the platelike crystals of (I) with a well developed (100) face. All the ammonium H atoms are connected to the carboxylate groups via hydrogen bonds (Table 2). Among them, atoms H4A and H4C are involved in bifurcated hydrogen bonds.

The close contact between the C6═C7 moieties in the crystal of (I) is C6···C6ⁱ or C6···C6ⁱⁱ of 3.984 (1) Å [symmetry codes: (i) x, 1/2 − y, 1/2 + z; (ii) x, 1/2 − y, z − 1/2]. However, the double bonds are not parallel to each other. Atoms C5 and C6 lie almost on the c-glide plane perpendicular to the b axis at y = 1/4, and the C5—C6═C7—C8 plane makes an angle of 75.9 (2)° with the glide plane (Fig. 3). Therefore, the C6═C7 bond axis makes an angle of 117.1 (2)° with the C6ⁱ═C7ⁱ axis, and the C7···C7ⁱ distance is 4.667 (3) Å. It seems that a pedal rotation of the cinnamate ion is required to achieve the parallel arrangement of the double bonds which is required before β-type [2 + 2]-photodimerization can take place. Pedal-like conformational changes and the dimerization of trans-cinnamamide in cocrystals with phthalic acid was previously reported by Ito et al. (2000) and was unambiguously proved by a partial single-crystal-to-single-crystal transformation (Ohba et al., 2001).

In the present study, the preliminary crystal structure of ammonium cinnamate, NH₄⁺·C₉H₇O₂⁻, (II), was also determined. Compound (II) was prepared by a similar method to (I) and colourless thin plate-like crystals were grown from a 2-propanol solution (m.p. 406–408 K). Crystal data for (II): monoclinic, space group P2₁/c, a = 20.033 (4) Å, b = 5.8741 (15) Å, c = 7.8681 (11) Å, β = 100.572 (14)°, V = 910.2 (3) ų, Z = 4, D_x = 1.205 Mg m⁻³, R(F) = 0.066 for 560 reflections with I>2σ(I). Compound (II) consists of an ammonium cation and a cinnamate anion, and the arrangements of the ions and the N—H···O hydrogen bonds are similar to those in (I). It seems that a pedal rotation is also required in (II) before β-type [2 + 2]-photodimerization can take place. Bryan et al. (1963) reported the crystal structure of ammonium hydrogen dicinnamate, (III), which was prepared by dissolving cinnamic acid and concentrated aqueous ammonia (molar ratio 2:1) in warm ethanol. In (III), the hydrogen dicinnamate anion is centrosymmetric. The two cinnamate moieties are connected by a short O—H···O hydrogen bond around the inversion centre and form N—H···O hydrogen bonds with the ammonium cations. The hydrophobic and hydrophilic layers are stacked alternately, similar to the molecular packing of (I) and (II).

S2. Experimental

The title compound, (I), was prepared by dissolving 4-methoxycinnamic acid and concentrated aqueous ammonia (molar ratio 1:1) in warm aqueous methanol (Ito et al., 2003). Crystals of (I) were grown from a methanol solution (m.p. 448–451 K). The crystal specimen was coated with adhesive to avoid efflorescence.

S3. Refinement

All H atoms were located from difference syntheses, and their positional parameters were recalculated geometrically and fixed, with C—H = N—H = 0.95 Å and U_iso(H) = 1.2U_eq(parent atom). Please check added text.

Computing details

Data collection: WinAFC Diffractometer Control Software (Rigaku, 1999); cell refinement: WinAFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 2001); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: TEXSAN.

Figures

	Fig. 1. The molecular structure of (I), with displacement ellipsoids plotted at the 50% probability level.
	Fig. 2. The projection of the crystal structure of (I) along b. Thin lines indicate hydrogen bonds.
	Fig. 3. The arrangement of ions in (I) generated by the c glide at y = 1/4. Primed atoms are at the symmetry position (x, 1/2 − y, 1/2 + z) and doubly primed atoms are at the symmetry position (x, 1/2 − y, z − 1/2 + z).

(I)

Crystal data

NH4^+·C10H9O3^−	F(000) = 416
Mr = 195.22	Dx = 1.248 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -P 2ybc	Cell parameters from 25 reflections
a = 22.077 (3) Å	θ = 10.2–13.6°
b = 5.9332 (9) Å	µ = 0.09 mm^−1
c = 7.9560 (8) Å	T = 298 K
β = 94.76 (1)°	Plate, colourless
V = 1038.5 (2) Å^3	0.5 × 0.5 × 0.1 mm
Z = 4

Data collection

Rigaku AFC-7R diffractometer	θmax = 27.5°, θmin = 2.8°
ω scans	h = −28→28
2973 measured reflections	k = 0→7
2383 independent reflections	l = −10→4
1203 reflections with I > 2σ(I)	3 standard reflections every 150 reflections
Rint = 0.012	intensity decay: 0.5%

Refinement

Refinement on F^2	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.047	w = 1/[σ^2(Fo^2) + (0.0635P)^2 + 0.0891P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.149	(Δ/σ)max < 0.001
S = 1.01	Δρmax = 0.18 e Å^−3
2383 reflections	Δρmin = −0.19 e Å^−3
127 parameters

Special details

Refinement. Refinement using reflections with F² > 0.0 σ(F²). The weighted R-factor (wR), goodness of fit (S) and R-factor (gt) are based on F, with F set to zero for negative F. The threshold expression of F² > 2.0 σ(F²) is used only for calculating R-factor (gt).

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

	x	y	z	Uiso*/Ueq
O1	0.07415 (7)	0.4052 (3)	0.3881 (2)	0.0642 (5)
O2	0.08615 (8)	0.0385 (3)	0.3536 (2)	0.0701 (5)
O3	0.43479 (7)	0.5709 (3)	0.0988 (2)	0.0644 (5)
N4	−0.04784 (8)	0.2175 (4)	0.3864 (2)	0.0568 (5)
C5	0.1042 (1)	0.2386 (4)	0.3474 (3)	0.0491 (5)
C6	0.1654 (1)	0.2690 (4)	0.2850 (3)	0.0550 (6)
C7	0.1962 (1)	0.4557 (4)	0.2913 (3)	0.0507 (5)
C8	0.25828 (9)	0.4886 (4)	0.2389 (3)	0.0473 (5)
C9	0.2871 (1)	0.3276 (4)	0.1451 (3)	0.0546 (6)
C10	0.3454 (1)	0.3592 (4)	0.0998 (3)	0.0558 (6)
C11	0.37689 (9)	0.5540 (4)	0.1498 (3)	0.0487 (5)
C12	0.3492 (1)	0.7146 (4)	0.2421 (3)	0.0564 (6)
C13	0.2904 (1)	0.6816 (4)	0.2843 (3)	0.0558 (6)
C14	0.4679 (1)	0.7694 (6)	0.1426 (4)	0.0807 (9)
H4A	−0.0717	0.3500	0.3686	0.0683*
H4B	−0.0612	0.1360	0.4792	0.0683*
H4C	−0.0064	0.2580	0.4098	0.0683*
H4D	−0.0521	0.1262	0.2880	0.0683*
H6	0.1834	0.1415	0.2368	0.0662*
H7	0.1769	0.5841	0.3340	0.0610*
H9	0.2660	0.1933	0.1118	0.0656*
H10	0.3640	0.2485	0.0349	0.0670*
H12	0.3706	0.8479	0.2768	0.0677*
H13	0.2715	0.7949	0.3463	0.0670*
H14A	0.4479	0.8953	0.0892	0.0971*
H14B	0.5077	0.7568	0.1064	0.0971*
H14C	0.4704	0.7891	0.2614	0.0971*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0567 (10)	0.066 (1)	0.072 (1)	0.0010 (9)	0.0197 (8)	−0.0014 (9)
O2	0.085 (1)	0.063 (1)	0.065 (1)	−0.0288 (10)	0.0213 (9)	−0.0022 (9)
O3	0.0415 (9)	0.076 (1)	0.077 (1)	−0.0068 (8)	0.0153 (8)	0.0018 (9)
N4	0.052 (1)	0.058 (1)	0.063 (1)	−0.0008 (10)	0.0135 (9)	0.008 (1)
C5	0.048 (1)	0.059 (2)	0.041 (1)	−0.015 (1)	0.0059 (9)	0.003 (1)
C6	0.054 (1)	0.051 (1)	0.060 (1)	−0.004 (1)	0.012 (1)	0.001 (1)
C7	0.051 (1)	0.052 (1)	0.049 (1)	−0.001 (1)	0.0086 (9)	0.002 (1)
C8	0.043 (1)	0.054 (1)	0.045 (1)	−0.004 (1)	0.0084 (9)	0.002 (1)
C9	0.052 (1)	0.051 (1)	0.061 (1)	−0.013 (1)	0.005 (1)	−0.001 (1)
C10	0.052 (1)	0.054 (1)	0.063 (1)	0.000 (1)	0.012 (1)	−0.003 (1)
C11	0.040 (1)	0.058 (1)	0.049 (1)	−0.004 (1)	0.0052 (9)	0.008 (1)
C12	0.051 (1)	0.060 (1)	0.060 (1)	−0.014 (1)	0.011 (1)	−0.008 (1)
C13	0.054 (1)	0.056 (2)	0.059 (1)	−0.006 (1)	0.016 (1)	−0.006 (1)
C14	0.054 (2)	0.092 (2)	0.098 (2)	−0.023 (2)	0.019 (1)	0.001 (2)

Geometric parameters (Å, º)

O1—C5	1.248 (3)	C8—C9	1.398 (3)
O2—C5	1.255 (3)	C8—C13	1.379 (3)
O3—C11	1.376 (3)	C9—C10	1.378 (3)
O3—C14	1.415 (4)	C9—H9	0.950
N4—H4A	0.951	C10—C11	1.389 (3)
N4—H4B	0.950	C10—H10	0.950
N4—H4C	0.950	C11—C12	1.376 (3)
N4—H4D	0.950	C12—C13	1.383 (4)
C5—C6	1.489 (3)	C12—H12	0.950
C6—C7	1.299 (3)	C13—H13	0.950
C6—H6	0.950	C14—H14A	0.950
C7—C8	1.478 (3)	C14—H14B	0.950
C7—H7	0.949	C14—H14C	0.950
C11—O3—C14	117.6 (2)	C8—C9—H9	119.2
H4A—N4—H4B	109.4	C10—C9—H9	119.2
H4A—N4—H4C	109.5	C9—C10—C11	119.6 (2)
H4A—N4—H4D	109.4	C9—C10—H10	120.2
H4B—N4—H4C	109.5	C11—C10—H10	120.2
H4B—N4—H4D	109.5	O3—C11—C10	115.5 (2)
H4C—N4—H4D	109.5	O3—C11—C12	124.8 (2)
O1—C5—O2	124.2 (2)	C10—C11—C12	119.7 (2)
O1—C5—C6	120.5 (2)	C11—C12—C13	119.9 (2)
O2—C5—C6	115.3 (2)	C11—C12—H12	120.0
C5—C6—C7	125.2 (2)	C13—C12—H12	120.0
C5—C6—H6	117.4	C8—C13—C12	121.8 (2)
C7—C6—H6	117.4	C8—C13—H13	119.1
C6—C7—C8	126.6 (2)	C12—C13—H13	119.2
C6—C7—H7	116.7	O3—C14—H14A	109.4
C8—C7—H7	116.7	O3—C14—H14B	109.4
C7—C8—C9	122.3 (2)	O3—C14—H14C	109.5
C7—C8—C13	120.3 (2)	H14A—C14—H14B	109.5
C9—C8—C13	117.4 (2)	H14A—C14—H14C	109.5
C8—C9—C10	121.5 (2)	H14B—C14—H14C	109.5
O1—C5—C6—C7	11.0 (3)	C8—C9—C10—C11	0.8 (4)
O2—C5—C6—C7	−169.5 (2)	C8—C13—C12—C11	1.1 (4)
O3—C11—C10—C9	−180.0 (2)	C9—C8—C13—C12	−1.1 (3)
O3—C11—C12—C13	179.0 (2)	C9—C10—C11—C12	−0.8 (3)
C5—C6—C7—C8	176.6 (2)	C10—C9—C8—C13	0.2 (3)
C6—C7—C8—C9	12.5 (4)	C10—C11—O3—C14	178.2 (2)
C6—C7—C8—C13	−166.4 (2)	C10—C11—C12—C13	−0.1 (3)
C7—C8—C9—C10	−178.8 (2)	C12—C11—O3—C14	−0.9 (3)
C7—C8—C13—C12	177.9 (2)	C12—C11—O3—C14	−0.9 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N4—H4A···O1^i	0.95	2.42	2.956 (3)	115
N4—H4A···O2^ii	0.95	2.09	2.779 (3)	128
N4—H4B···O2^iii	0.95	1.81	2.756 (3)	176
N4—H4C···O1	0.95	2.00	2.913 (2)	160
N4—H4C···O2	0.95	2.49	3.174 (3)	129
N4—H4D···O1^iv	0.95	1.95	2.887 (3)	168

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