Accurate high-resolution single-crystal diffraction data from a Pilatus3 X CdTe detector

Hybrid photon-counting detectors are widely established at third-generation synchrotron facilities and the specifications of the Pilatus3 X CdTe were quickly recognized as highly promising in charge-density investigations. This is mainly attributable to the detection efficiency in the high-energy X-ray regime, in combination with a dynamic range and noise level that should overcome the perpetual problem of detecting strong and weak data simultaneously. These benefits, however, come at the expense of a persistent problem for high diffracted beam flux, which is particularly problematic in single-crystal diffraction of materials with strong scattering power and sharp diffraction peaks. Here, an in-depth examination of data collected on an inorganic material, FeSb₂, and an organic semiconductor, rubrene, revealed systematic differences in strong intensities for different incoming beam fluxes, and the implemented detector intensity corrections were found to be inadequate. Only significant beam attenuation for the collection of strong reflections was able to circumvent this systematic error. All data were collected on a bending-magnet beamline at a third-generation synchrotron radiation facility, so undulator and wiggler beamlines and fourth-generation synchrotrons will be even more prone to this error. On the other hand, the low background now allows for an accurate measurement of very weak intensities, and it is shown that it is possible to extract structure factors of exceptional quality using standard crystallographic software for data processing (SAINT-Plus, SADABS and SORTAV), although special attention has to be paid to the estimation of the background. This study resulted in electron-density models of substantially higher accuracy and precision compared with a previous investigation, thus for the first time fulfilling the promise of photon-counting detectors for very accurate structure factor measurements.

Computing details

Program(s) used to refine structure: Volkov et al., (2006); molecular graphics: Volkov et al., (2006); software used to prepare material for publication: Volkov et al., (2006).

(I)

Crystal data

a = 26.7958 (18) Å	V = 2716.1 (3) Å^3
b = 7.1586 (5) Å	Z = 4
c = 14.1598 (11) Å	Cell parameters from 9573 reflections
α = 90°	θ = 2.2–20.1°
β = 90°	T = 20 K
γ = 90°

Data collection

Rint = 0.047	k = →
h = →	l = →

Refinement

Refinement on F^2	175 parameters
Least-squares matrix: full	0 restraints
R[F^2 > 2σ(F^2)] = 0.038	w2 = 1/[s^2(Fo^2)]
wR(F^2) = 0.025	(Δ/σ)max < 0.001
S = 1.03	Δρmax = 0.19 e Å^−3
26442 reflections	Δρmin = −0.17 e Å^−3

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

	x	y	z	Uiso*/Ueq
C1	0.527359 (2)	0	0.5	0.005
C2	0.553273 (1)	0.144732 (4)	0.549013 (2)	0.005
C3	0.526872 (1)	0.296485 (4)	0.587617 (2)	0.005
C4	0.552186 (1)	0.448163 (5)	0.634051 (3)	0.007
C5	0.526568 (1)	0.591265 (5)	0.675635 (3)	0.008
C6	0.607681 (1)	0.135037 (4)	0.572756 (2)	0.006
C7	0.623084 (1)	0.023845 (5)	0.648770 (3)	0.008
C8	0.672640 (2)	0.025107 (6)	0.679443 (3)	0.009
C9	0.707480 (2)	0.140262 (6)	0.634825 (3)	0.01
C10	0.692331 (1)	0.252881 (6)	0.559422 (3)	0.009
C11	0.642978 (1)	0.249454 (5)	0.528376 (3)	0.007
H4	0.59262	0.447716	0.636165	0.021
H5	0.546616	0.703353	0.710961	0.021
H7	0.595601	−0.062653	0.684369	0.021
H8	0.683479	−0.063187	0.738295	0.025
H9	0.745939	0.143322	0.658925	0.026
H10	0.719064	0.343899	0.524653	0.025
H11	0.631575	0.3367	0.469671	0.021

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.004675 (10)	0.004714 (10)	0.005698 (11)	0	0	−0.001007 (8)
C2	0.004862 (7)	0.004918 (7)	0.005903 (8)	−0.000187 (6)	−0.000163 (6)	−0.000931 (6)
C3	0.005485 (8)	0.004817 (7)	0.005858 (8)	−0.000225 (6)	0.000005 (6)	−0.001021 (6)
C4	0.006767 (9)	0.005983 (8)	0.007680 (9)	−0.000988 (7)	0.000324 (7)	−0.001989 (7)
C5	0.008343 (10)	0.005959 (8)	0.008402 (10)	−0.000730 (7)	0.000230 (7)	−0.002360 (7)
C6	0.005008 (7)	0.005938 (8)	0.005954 (8)	−0.000493 (6)	−0.000224 (6)	−0.000095 (6)
C7	0.006838 (9)	0.008906 (10)	0.006967 (9)	−0.000727 (7)	−0.000760 (7)	0.001564 (7)
C8	0.007731 (10)	0.011965 (12)	0.008345 (10)	0.000247 (8)	−0.002070 (8)	0.001426 (8)
C9	0.006031 (9)	0.012166 (12)	0.010684 (12)	−0.000279 (8)	−0.001450 (8)	−0.000472 (9)
C10	0.005667 (8)	0.009553 (10)	0.011155 (12)	−0.001240 (8)	0.000692 (8)	0.000280 (8)
C11	0.005938 (8)	0.007348 (9)	0.008293 (9)	−0.000747 (7)	0.000503 (7)	0.001046 (7)
H4	0.011643	0.023463	0.029214	−0.001721	−0.000462	−0.005032
H5	0.022369	0.016676	0.023444	−0.005915	−0.001862	−0.007394
H7	0.018133	0.024119	0.022188	−0.00509	0.001808	0.008126
H8	0.023501	0.030324	0.021075	0.00205	−0.006104	0.010101
H9	0.012279	0.035952	0.031059	−0.001945	−0.00685	0.002949
H10	0.017036	0.026697	0.030407	−0.007715	0.003191	0.006673
H11	0.021059	0.022156	0.020784	−0.00016	−0.001867	0.009474

Geometric parameters (Å, º)

C1—C1^i	1.4662	C6—C7	1.4009
C1—C1^ii	1.4662	C6—C11	1.4001
C1—C2	1.4273	C7—C8	1.3971
C1—C2^iii	1.4273	C7—H7	1.0862
C2—C3	1.4069	C8—C9	1.3965
C2—C6	1.4978	C8—H8	1.0855
C3—C3^ii	1.4401	C9—C10	1.3981
C3—C4	1.4392	C9—H9	1.0858
C4—C5	1.3665	C10—C11	1.3938
C4—H4	1.0839	C10—H10	1.0863
C5—C5^ii	1.4238	C11—H11	1.0837
C5—H5	1.0875
C1^iv—C1—C2	119.1102	C2—C6—C7	119.0503
C1^iv—C1—C2	119.1103	C2—C6—C11	121.9844
C1^iv—C1—C2	119.1102	C7—C6—C11	118.5693
C1^iv—C1—C2	119.1103	C6—C7—C8	121.0107
C2^iv—C1—C2	121.7795	C6—C7—H7	118.7326
C1—C2—C3	120.3167	C8—C7—H7	120.2519
C1—C2—C6	123.3016	C7—C8—C9	119.9037
C1—C2—C3	120.3167	C7—C8—H8	119.2871
C1—C2—C6	123.3016	C9—C8—H8	120.8075
C3—C2—C6	115.9772	C8—C9—C10	119.4572
C2—C3—C3	120.1874	C8—C9—H9	120.2786
C2—C3—C4	121.5367	C10—C9—H9	120.2615
C3—C3—C4	118.1188	C9—C10—C11	120.4101
C3—C4—C5	121.7128	C9—C10—H10	120.0337
C3—C4—H4	118.7840	C11—C10—H10	119.5561
C5—C4—H4	119.5025	C6—C11—C10	120.6420
C4—C5—C5	120.1551	C6—C11—H11	119.4032
C4—C5—H5	120.2102	C10—C11—H11	119.9533
C5—C5—H5	119.6028

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