Crystal structure of propio­nitrile (CH₃CH₂CN) determined using synchrotron powder X-ray diffraction

The structure and thermal expansion of the astronomical molecule propio­nitrile have been determined from 100 to 150 K using synchrotron powder X-ray diffraction. This temperature range correlates with the conditions of Titan's lower stratosphere, and near surface, where propio­nitrile is thought to accumulate and condense into pure and mixed-nitrile phases. Propio­nitrile was determined to crystallize in space group, Pnma (No. 62), with unit cell a = 7.56183 (16) Å, b = 6.59134 (14) Å, c = 7.23629 (14), volume = 360.675 (13) ų at 100 K. The thermal expansion was found to be highly anisotropic with an eightfold increase in expansion between the c and b axes. These data will prove crucial in the computational modelling of propio­nitrile–ice systems in outer Solar System environments, allowing us to simulate and assign vibrational peaks in the infrared spectra for future use in planetary astronomy.

Computing details

(I)

Crystal data

C3H5N	V = 360.68 (1) Å^3
Mr = 55.08	Z = 4
Orthorhombic, PNMA	Synchrotron radiation
a = 7.56183 (16) Å	T = 100 K
b = 6.59134 (14) Å	colorless
c = 7.23629 (14) Å

Data collection

RPI diffractometer

2θmin = 3.000°, 2θmax = 83.000°, 2θstep = 0.004°

Refinement

Rp = 0.032	R(F) = 0.015
Rwp = 0.049

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

	x	y	z	Biso*/Beq
H1	0.0305 (12)	0.3779 (15)	0.3661 (15)	2.02 (4)
H2	0.3419 (13)	0.1230 (11)	0.4658 (14)	2.02 (4)
C1	0.1110 (3)	0.25	0.3522 (3)	2.02 (4)
C2	0.2684 (3)	0.25	0.4826 (3)	2.02 (4)
C3	0.2172 (2)	0.25	0.6802 (3)	2.02 (4)
N1	0.1711 (2)	0.25	0.8291 (2)	2.02 (4)
H3	0.149 (2)	0.25	0.212 (2)	2.02 (4)

Geometric parameters (Å, º)

H1—C1	1.0446 (1)	H1—H1^i	1.6860 (1)
H1—H3	1.6604 (1)
H3—H1—C1	37.925 (1)	H1^i—H1—C1	36.199 (1)
H1^i—H1—H3	59.489 (1)

Symmetry code: (i) x, −y+1/2, z.