Bridging the gap - structure determination of the red polymorph of tetrahexylsexithiophene by Monte Carlo simulated annealing, first-principles DFT calculations and Rietveld refinement

The crystal structure of the red polymorph of tetrahexylsexithiophene (THST) is solved from X-ray powder diffraction data by a direct-space Monte Carlo simulated-annealing approach. First-principles density functional theory (DFT) calculations are used to distinguish between three nearly identical solutions in the space groups C2/m, C2 and P and to improve the overall accuracy of the crystal structure. The correct space group is found to be C2/m. In all space groups, the thiophene backbone is planar and the hexyl side chains assume an all-trans conformation except for two terminal methyl residues, which adopt a gauche orientation. The ability of first-principles DFT calculations to provide atomic coordinates of single-crystal quality is demonstrated by lattice-energy minimization of the known crystal structure of the yellow polymorph of THST. The combination of Monte Carlo simulated annealing, first-principles DFT calculations and Rietveld refinement presented in this paper is generally applicable. It provides a powerful alternative to standard approaches in cases where the information content of the powder diffraction pattern alone is insufficient to distinguish between different structure solutions. DFT calculations can also provide invaluable guidance in Rietveld refinement.

Computing details

Figures

(C2m_best_0k03shift)

Crystal data

?	β = 117.2444°
Mr = ?	V = ? Å^3
Monoclinic, C2/M	Z = ?
a = 24.9512 Å	? radiation, λ = ? Å
b = 7.5153 Å	× × mm
c = 13.8689 Å

Data collection

h = ?→?	l = ?→?
k = ?→?

Refinement

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

	x	y	z	Uiso*/Ueq
C1	−0.08856	0.00691	0.92701	0.00000*
H2	−0.16003	−0.11231	0.78473	0.00000*
C3	−0.04600	−0.00447	0.57910	0.00000*
C4	−0.46479	0.01074	0.30247	0.00000*
C5	−0.10866	−0.00395	0.54396	0.00000*
H6	−0.06622	−0.12427	0.76129	0.00000*
S7	−0.25669	0.00000	0.41614	0.00000*
H8	−0.15741	−0.06355	0.97291	0.00000*
H9	−0.16716	−0.12080	0.59950	0.00000*
H10	−0.42353	−0.11068	0.52283	0.00000*
H11	−0.36131	−0.06277	0.90081	0.00000*
C12	−0.36105	0.00265	0.47202	0.00000*
H13	−0.06448	0.11083	0.76004	0.00000*
H14	−0.05971	−0.08791	1.14326	0.00000*
H15	−0.31567	0.23772	0.90801	0.00000*
H16	−0.53947	0.01438	0.13524	0.00000*
S17	−0.43974	0.00516	0.14313	0.00000*
C18	−0.31917	0.00000	0.28804	0.00000*
C19	−0.13721	−0.00459	0.61819	0.00000*
H20	−0.21500	−0.00686	0.19846	0.00000*
H21	−0.33096	−0.00133	0.12283	0.00000*
H22	−0.10666	0.07388	1.15927	0.00000*
H23	−0.31667	0.10894	0.68397	0.00000*
H24	−0.26170	0.08578	0.99793	0.00000*
C25	−0.39276	0.00364	0.54340	0.00000*
H26	−0.06327	−0.11865	0.95249	0.00000*
H27	−0.33186	−0.11566	0.49303	0.00000*
C28	−0.29985	−0.00207	0.20894	0.00000*
C29	−0.49193	0.01123	0.19156	0.00000*
C30	−0.37771	−0.00869	0.73744	0.00000*
C31	−0.12943	0.00265	0.80522	0.00000*
S32	−0.09361	−0.00323	0.37108	0.00000*
C33	−0.02942	−0.00398	0.49672	0.00000*
C34	−0.14180	−0.00366	0.43097	0.00000*
C35	−0.20551	−0.00292	0.36261	0.00000*
C36	−0.23707	−0.00388	0.25000	0.00000*
C37	−0.37965	0.00307	0.27467	0.00000*
C38	−0.40096	0.00589	0.35165	0.00000*
C39	−0.09467	−0.00472	0.73930	0.00000*
C40	−0.12244	0.03888	0.99279	0.00000*
C41	−0.08155	0.04152	1.11442	0.00000*
C42	−0.34756	−0.00501	0.66359	0.00000*
C43	−0.33464	−0.03835	0.85744	0.00000*
C44	−0.29114	0.11446	0.91212	0.00000*
H45	−0.01305	−0.00606	0.66410	0.00000*
H46	−0.49014	0.01403	0.34822	0.00000*
H47	−0.16703	0.11186	0.60005	0.00000*
H48	−0.15834	0.12158	0.78150	0.00000*
H49	−0.05469	0.11229	0.94557	0.00000*
H50	−0.14677	0.16594	0.96765	0.00000*
H51	−0.04574	0.14102	1.13603	0.00000*
H52	−0.33003	0.11687	0.49534	0.00000*
H53	−0.42031	0.12447	0.52751	0.00000*
H54	−0.31965	−0.12508	0.67840	0.00000*
H55	−0.40255	0.11646	0.72770	0.00000*
H56	−0.41145	−0.11568	0.70980	0.00000*
H57	−0.30896	−0.16127	0.86614	0.00000*
H58	−0.26201	0.13990	0.87403	0.00000*

Bond lengths (Å)

C1—C31	1.522	C18—C28	1.386
C1—C40	1.520	C18—C37	1.434
C1—H49	1.099	C19—H47	1.101
C1—H26	1.100	C19—C39	1.522
H2—C31	1.101	H20—C36	1.084
C3—C5	1.409	H21—C28	1.086
C3—C33	1.382	H22—C41	1.093
C3—H45	1.086	H23—C42	1.099
C4—H46	1.082	H24—C44	1.096
C4—C29	1.368	C25—H53	1.099
C4—C38	1.417	C25—C42	1.528
C5—C19	1.496	C28—C36	1.401
C5—C34	1.397	C30—C43	1.529
H6—C39	1.098	C30—C42	1.524
S7—C35	1.747	C30—H55	1.100
S7—C18	1.747	C30—H56	1.099
H8—C40	1.100	C31—H48	1.100
H9—C19	1.100	C31—C39	1.522
H10—C25	1.099	S32—C34	1.746
H11—C43	1.098	S32—C33	1.745
C12—C38	1.502	C34—C35	1.430
C12—H27	1.101	C35—C36	1.390
C12—H52	1.101	C37—C38	1.394
C12—C25	1.524	C40—H50	1.099
H13—C39	1.098	C40—C41	1.520
H14—C41	1.097	C41—H51	1.096
H15—C44	1.097	C42—H54	1.100
H16—C29	1.081	C43—H57	1.099
S17—C37	1.753	C43—C44	1.523
S17—C29	1.717	C44—H58	1.093