Urea–N,N-dimethyl­acetamide (1/1)

Abstract

Urea forms a 1:1 solvate with N,N-dimethyl­acetamide (DMA) [systematic name: diamino­methanal–N,N-dimethyl­acetamide (1/1), C₄H₉NO·CH₄N₂O] with both mol­ecules positioned on a twofold axis, giving rise to rotational disorder of the DMA mol­ecule. The mol­ecules display a layered structure in which urea mol­ecules form hydrogen-bonded ribbons bounded by mol­ecules of solvent.

Related literature

For details on experimental methods used to obtain this crystalline compound, see: Florence et al. (2003 ▶). For crystal structures of urea, see: Fernandes et al. (2007 ▶); Vaughan & Donohue (1952 ▶), and references therein; Swaminathan et al. (1984 ▶); Pryor & Sanger (1970 ▶); Guth et al. (1980 ▶); Weber et al. (2002 ▶). For related literature, see: Etter (1990 ▶).

Experimental

Crystal data

• C₄H₉NO·CH₄N₂O

• M _r = 147.18

• Monoclinic,

• a = 7.2770 (3) Å

• b = 17.5394 (9) Å

• c = 7.3789 (4) Å

• β = 119.450 (3)°

• V = 820.11 (7) ų

• Z = 4

• Mo Kα radiation

• μ = 0.09 mm⁻¹

• T = 120 K

• 0.40 × 0.12 × 0.04 mm

Data collection

• Bruker–Nonius KappaCCD diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2007 ▶) T _min = 0.867, T _max = 1 (expected range = 0.864–0.996)

• 5338 measured reflections

• 941 independent reflections

• 552 reflections with I > 2.0σ(I)

• R _int = 0.048

Refinement

• R[F ² > 2σ(F ²)] = 0.050

• wR(F ²) = 0.150

• S = 0.89

• 939 reflections

• 63 parameters

• H atoms treated by a mixture of independent and constrained refinement

• Δρ_max = 0.31 e Å⁻³

• Δρ_min = −0.39 e Å⁻³

Data collection: COLLECT (Hooft, 1998 ▶); cell refinement: DENZO (Otwinowski & Minor, 1997 ▶) and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SIR92 (Altomare et al., 1994 ▶); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶) and Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: enCIFer (Allen et al., 2004 ▶) and publCIF (Westrip, 2008 ▶).

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N3—H31⋯O2i	0.87 (2)	2.06 (2)	2.930 (2)	180 (3)
N3—H32⋯O9ii	0.87 (2)	2.09 (2)	2.878 (3)	149.7 (19)

Symmetry codes: (i) ; (ii) .

supplementary crystallographic information

Comment

The crystal structure of urea has been widely studied (see for example, Vaughan and Donohue (1952) and references therein; Swaminathan et al. (1984), Pryor and Sanger (1970), Guth et al. (1980) and Weber et al. (2002)). This previously unreported crystalline solvate of urea was discovered during an investigation into the influence of different crystallization solvents on urea crystal morphology (see also Fernandes et al., 2007). The sample was obtained by slow evaporation from a saturated N,N-dimethylacetamide (DMA) solution at 298 K and identified by using multi-sample foil transmission X-ray powder diffraction analysis (Florence et al., 2003). Subsequent recrystallization produced a single-crystal suitable for X-ray diffraction at 120 K (Fig. 1).

Both molecules lie over a two fold rotation axis resulting in the DMA being disordered (see refinement section for details). Each urea molecule interacts with adjacent urea molecules via contact 1 (Fig. 2, entry 1, Table 1), forming a hydrogen bonded ribbon that runs in the direction [-1 0 1]. Molecules of DMA lie on the edge of the ribbons, connected through a second hydrogen bond (contact 2), (entry 2, Table 1).The DMA-bordered ribbons of urea pack side-by-side to form a two-dimensional sheet.

Experimental

The compound was sourced from Sigma-Aldrich and used as supplied. A single-crystal sample of the 1/1 solvate was recrystallized from a saturated N,N-dimethylacetamide solution by isothermal solvent evaporation at room temperature (298 K).

Refinement

The DMA moiety was found to be disordered over a 2-fold rotation axis, with atoms C7 and O9 sitting on this axis. The site occupancies of N4 and C8 were consequently fixed to 1/2, whilst that of C6 was fixed to 1.0 as this atom acts as a methyl carbon both attached to N4 and to C8 in the disordered model. All non-H-atoms were modelled with anisotropic displacement parameters. H-atoms attached to N3 were located in a difference Fourier map and their positions were freely refined. H-atoms attached to C6 and C7 were positioned geometrically, taking into account disorder and occupancy of the parents atoms, and their positions were fixed during refinement. U_iso(H) were assigned in the range 1.2–1.5 times U_eq of the parent atom.

Note that both the (1 1 0) and the (-2 0 2) reflections were excluded from the final refinement as they were significant outliers on the F_o versus Fc plot.

Figures

Fig. 1.

The molecular structure of the title compound showing 50% probablility displacement ellipsoids. Hydrogen atoms have been omitted for clarity. A twofold axis runs through C1, O2 of urea and O9, C7 of DMA, giving rise to the rotational disorder of the DMA molecule. Symmetry codes: (i) -x, y, 1/2 - z. (ii) -x, y, 3/2 - z.

Fig. 2.

Selected molecular packing, viewed down the a axis, of the title compound illustrating the hydrogen bonded network. Urea molecules (green) form an R22(8) motif (Etter, 1990) involving contact 1 (entry 1, Table 1) that propagates to form an infinite ribbon. DMA molecules (shown in blues with rotational disorder) are hydrogen bonded via N—H···O contacts 2 (entry 2, Table 1) at the edges of the ribbon. Hydrogen bonds are shown as dashed lines and hydrogen atoms have been omitted for clarity. Symmetry codes: (a) -x, 1 - y, 1 - z; (b) 1/2 - x, 1/2 - y, 1 - z.

Crystal data

C4H9NO·CH4N2O	F000 = 320
Mr = 147.18	Dx = 1.192 Mg m−3
Monoclinic, C2/c	Melting point: 406 K
Hall symbol: -C 2yc	Mo Kα radiation λ = 0.71073 Å
a = 7.2770 (3) Å	Cell parameters from 2218 reflections
b = 17.5394 (9) Å	θ = 3–27º
c = 7.3789 (4) Å	µ = 0.09 mm−1
β = 119.450 (3)º	T = 120 K
V = 820.11 (7) Å3	Lath, colourless
Z = 4	0.40 × 0.12 × 0.04 mm

Data collection

Bruker–Nonius KappaCCD diffractometer	941 independent reflections
Radiation source: Bruker-Nonius FR591 rotating anode	552 reflections with I > 2.0σ(I)
Monochromator: graphite	Rint = 0.048
Detector resolution: 9.091 pixels mm-1	θmax = 27.6º
T = 120(2) K	θmin = 3.4º
φ & ω scans	h = −9→9
Absorption correction: multi-scan(SADABS; Bruker, 2007)	k = −22→22
Tmin = 0.867, Tmax = 1	l = −9→9
5338 measured reflections

Refinement

Refinement on F2	Hydrogen site location: geom + difmap
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.050	Method = Modified Sheldrick w = 1/[σ2(F2) + ( 0.07P)2] ,where P = (max(Fo2,0) + 2Fc2)/3
wR(F2) = 0.150	(Δ/σ)max = 0.0001
S = 0.89	Δρmax = 0.31 e Å−3
939 reflections	Δρmin = −0.39 e Å−3
63 parameters	Extinction correction: none
Primary atom site location: structure-invariant direct methods

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
C1	0.0000	0.30587 (14)	0.2500	0.0293
O2	0.0000	0.23473 (9)	0.2500	0.0380
N3	0.1649 (2)	0.34642 (10)	0.3935 (3)	0.0360
N4	0.0668 (4)	0.37977 (18)	0.7962 (5)	0.0347	0.5000
C6	0.2835 (3)	0.40670 (13)	0.9670 (4)	0.0525
C7	0.0000	0.29897 (16)	0.7500	0.0508
C8	−0.0735 (5)	0.4351 (2)	0.6946 (6)	0.0347	0.5000
O9	0.0000	0.50307 (11)	0.7500	0.0628
H31	0.264 (3)	0.3224 (11)	0.499 (4)	0.0365*
H32	0.158 (3)	0.3959 (13)	0.393 (3)	0.0360*
H71	−0.1409	0.2969	0.6380	0.0608*	0.5000
H72	0.0074	0.2760	0.8696	0.0608*	0.5000
H73	0.0908	0.2732	0.7124	0.0608*	0.5000
H61	0.2880	0.4608	0.9665	0.0542*	0.5000
H62	0.3056	0.3894	1.0980	0.0542*	0.5000
H63	0.3889	0.3866	0.9409	0.0542*	0.5000
H64	0.2827	0.3526	0.9657	0.0542*	0.5000
H65	0.3108	0.4244	1.0994	0.0542*	0.5000
H66	0.3885	0.4250	0.9377	0.0542*	0.5000

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
C1	0.0239 (11)	0.0284 (14)	0.0251 (13)	0.0000	0.0038 (10)	0.0000
O2	0.0315 (9)	0.0245 (10)	0.0342 (11)	0.0000	−0.0022 (8)	0.0000
N3	0.0289 (8)	0.0261 (9)	0.0325 (10)	−0.0009 (6)	−0.0006 (7)	0.0011 (7)
N4	0.0290 (18)	0.0271 (17)	0.038 (2)	0.0003 (11)	0.0085 (16)	−0.0020 (14)
C6	0.0327 (10)	0.0554 (14)	0.0474 (14)	−0.0003 (9)	0.0026 (10)	0.0046 (11)
C7	0.0663 (19)	0.0236 (14)	0.059 (2)	0.0000	0.0286 (17)	0.0000
C8	0.0332 (19)	0.030 (2)	0.031 (2)	−0.0004 (14)	0.0084 (16)	0.0008 (16)
O9	0.0855 (16)	0.0210 (11)	0.0587 (16)	0.0000	0.0176 (13)	0.0000

Geometric parameters (Å, °)

O9—C8	1.288 (4)	C6—H63	0.9500
O9—C8i	1.288 (4)	C6—H64	0.9500
O2—C1	1.248 (3)	C6—H65	0.9500
N4—C6	1.531 (4)	C6—H61	0.9500
N4—C8	1.339 (5)	C6—H66	0.9500
N4—C7	1.483 (4)	C7—H72i	0.9500
N3—C1	1.348 (2)	C7—H73i	0.9500
N3—H32	0.87 (2)	C7—H71i	0.9500
N3—H31	0.87 (2)	C7—H71	0.9500
C6—C8i	1.488 (5)	C7—H72	0.9500
C6—H62	0.9500	C7—H73	0.9500
C6—N4—C7	124.9 (2)	C8i—C6—H61	72.00
C6—N4—C8	115.5 (3)	H62—C6—H63	110.00
C7—N4—C8	119.4 (3)	H62—C6—H64	72.00
C1—N3—H32	119.8 (14)	C8i—C6—H66	109.00
H31—N3—H32	120.7 (19)	N4—C7—H71i	75.00
C1—N3—H31	118.4 (14)	N4—C7—H72i	119.00
N4—C8—C6i	114.0 (3)	N4—C7—H73	109.00
O9—C8—N4	114.2 (3)	H71—C7—H72	110.00
O9—C8—C6i	131.8 (3)	H71—C7—H73	110.00
N4—C6—H61	109.00	N4—C7—H73i	126.00
N4—C6—H62	109.00	H71—C7—H71i	176.00
N4—C6—H63	109.00	H71—C7—H72i	68.00
N4—C6—H64	72.00	H71—C7—H73i	68.00
H61—C6—H63	110.00	H72—C7—H73	110.00
H61—C6—H64	178.00	N4i—C7—H72	119.00
H61—C6—H65	72.00	H71i—C7—H72	68.00
H61—C6—H66	68.00	N4i—C7—H71	75.00
N4—C6—H65	124.00	N4i—C7—H73	126.00
N4—C6—H66	122.00	H71i—C7—H73	68.00
H61—C6—H62	110.00	N4i—C7—H71i	109.00
H62—C6—H66	126.00	N4i—C7—H72i	109.00
C8i—C6—H62	121.00	N4i—C7—H73i	109.00
H63—C6—H64	68.00	H71i—C7—H72i	110.00
H63—C6—H65	123.00	H71i—C7—H73i	110.00
C8i—C6—H63	125.00	N4—C7—H71	109.00
H64—C6—H65	110.00	N4—C7—H72	109.00
H64—C6—H66	110.00	O2—C1—N3	121.84 (12)
C8i—C6—H64	109.00	O2—C1—N3ii	121.84 (12)
H65—C6—H66	110.00	N3—C1—N3ii	116.3 (2)
C8i—C6—H65	109.00

Symmetry codes: (i) −x, y, −z+3/2; (ii) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H31···O2iii	0.87 (2)	2.06 (2)	2.930 (2)	180 (3)
N3—H32···O9iv	0.87 (2)	2.09 (2)	2.878 (3)	149.7 (19)

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