supplementary materials


wm2748 scheme

Acta Cryst. (2013). E69, m395-m396    [ doi:10.1107/S160053681301622X ]

cis-Dichloridotetrakis(dimethyl sulfoxide-[kappa]O)chromium(III) chloride dimethyl sulfoxide monosolvate

N. A. Al-Najjar, A.-R. H. Al-Sudani, M. A. Shanshal, F. H. Mousa and B. M. Kariuki

Abstract top

The structure of the title compound, [CrCl2(C2H6OS)4]Cl·C2H6OS, consists of a CrIII ion coordinated by four O atoms of dimethyl sulfoxide (DMSO) ligands and two chloride ions in cis positions, forming a distorted CrCl2O4 octahedron. An isolated Cl- counter-anion and a positionally disordered DMSO molecule [occupancy ratio 0.654 (4):0.346 (4)] are also present. In the structure, the complex cations interact with the Cl- counter-anions and the DMSO solvent molecules via weak C-H...Cl and C-H...O interactions, forming a three-dimensional network.

Comment top

cis-Dichloridotetrakis(dimethyl sulfoxide-κO)chromium(III) chloride dimethyl sulfoxide monosolvate Metal adducts of aprotic volatile organic solvents have been extensively studied, but the potential of non-volatile aprotic solvent-metal adducts as precursors for useful metal complexes has not been systematically evaluated. The present results are part of a systematic study, including the preparation of anhydrous adducts formed between transition metals salts and non-volatile aprotic solvents (such as DMSO and DMF), their structure, bonding, solubility in common organic solvents, stability in air and the ease at which the coordinating non-volatile solvent molecules can be replaced by other organic molecules. DMSO is an aprotic, highly polar solvent. Its high dielectric constant makes it a good solvent for inorganic as well as organic compounds, and its electronic structure enables it to act as a donor molecule in the formation of coordination complexes with many metal salts. In addition, it can bind to the metal through either the oxygen or sulfur atoms. For examples, see: Boschmann & Wollaston (1982).

The molecular units of the title compound, [CrCl2(C2H6OS)4]Cl.C2H6OS, (I), are shown in Fig. 1. The complex cation consists of a chromium(III) ion coordinated by the oxygen atoms of four DMSO molecules with Cr—O distances in the range 1.978 (2)–1.996 (2) Å and two cis-positioned chloride ions with Cr—Cl distances of 2.3252 (10) and 2.3302 (9) Å to complete a distorted octahedral geometry. A third and isolated chloride ion balances the charge. An additional uncoordinating DMSO molecule occupies a location displaying disorder with two components with occupancies of 0.654 (4):0.346 (4). In the crystal, the methyl groups of the DMSO ligands interact with the chloride ions and solvent DMSO ligands via weak C—H···Cl and C—H···O interactions forming a three-dimensional network (Table 1, Fig. 2).

Related literature top

For details of the synthetic procedure, see: Pedersen (1970). For background to DMSO as a ligand, see: Boschmann & Wollaston (1982).

Experimental top

Complex (I) was prepared by the method described by Pedersen (1970), but on a smaller scale with excess DMSO and other volatile materials removed under dynamic vacuum at 373 K for 5h. The green solid obtained was crystallized by slow diffusion of methanol into a concentrated solution of the complex in DMSO to yield bright green crystals.

Refinement top

The methyl hydrogen atoms have been refined using a riding model with idealized geometry and displacement parameters 1.5 times those of the carbon atoms they are bonded to, and allowed for free rotation. The uncoordinating DMSO molecule is disordered over two sets of sites. Refinement of the disorder (occupancy ratio 0.654 (4):0.346 (4)) has been performed using PART 1, PART 2 and FVAR in SHELXL (Sheldrick, 2008). Atoms in close proximity have been refined with identical or similar displacement parameters using SIMU and ISOR instructions in SHELXL. The methyl hydrogen atoms for the disordered solvent have been refined using a riding model with staggered idealized geometry and displacement parameters 1.5 times those of the carbon atoms they are bonded to.

Computing details top

Data collection: COLLECT (Nonius, 2000); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and ACD/Chemsketch (Advanced Chemistry Development, 2008).

Figures top
[Figure 1] Fig. 1. The asymmetric unit of compound (I) with atom labels and displacement ellipsoids at the 50% probability level. Hydrogen atoms and the minor component of the disordered DMSO solvent molecules have been omitted for clarity.
[Figure 2] Fig. 2. Crystal packing in the structure of (I), with hydrogen atoms and the minor component of the disordered solvent omitted for clarity.
cis-Dichloridotetrakis(dimethyl sulfoxide-κO)chromium(III) chloride dimethyl sulfoxide monosolvate top
Crystal data top
[CrCl2(C2H6OS)4]Cl·C2H6OSZ = 2
Mr = 548.99F(000) = 570
Triclinic, P1Dx = 1.490 Mg m3
a = 9.4521 (2) ÅMo Kα radiation, λ = 0.71073 Å
b = 11.0048 (3) ÅCell parameters from 4673 reflections
c = 12.9761 (2) Åθ = 1.7–28.3°
α = 100.501 (2)°µ = 1.24 mm1
β = 109.007 (1)°T = 150 K
γ = 98.427 (1)°Irregular block, green
V = 1223.62 (5) Å30.20 × 0.20 × 0.20 mm
Data collection top
Nonius KappaCCD
diffractometer
5946 independent reflections
Radiation source: fine-focus sealed tube4673 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.028
ω and phi scansθmax = 28.3°, θmin = 1.7°
Absorption correction: multi-scan
(DENZO and SCALEPACK; Otwinowski & Minor, 1997)
h = 1012
Tmin = 0.790, Tmax = 0.790k = 1411
8105 measured reflectionsl = 1717
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.051H-atom parameters constrained
wR(F2) = 0.138 w = 1/[σ2(Fo2) + (0.0557P)2 + 2.3503P]
where P = (Fo2 + 2Fc2)/3
S = 1.11(Δ/σ)max = 0.001
5946 reflectionsΔρmax = 0.60 e Å3
263 parametersΔρmin = 0.78 e Å3
104 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.025 (2)
Crystal data top
[CrCl2(C2H6OS)4]Cl·C2H6OSγ = 98.427 (1)°
Mr = 548.99V = 1223.62 (5) Å3
Triclinic, P1Z = 2
a = 9.4521 (2) ÅMo Kα radiation
b = 11.0048 (3) ŵ = 1.24 mm1
c = 12.9761 (2) ÅT = 150 K
α = 100.501 (2)°0.20 × 0.20 × 0.20 mm
β = 109.007 (1)°
Data collection top
Nonius KappaCCD
diffractometer
5946 independent reflections
Absorption correction: multi-scan
(DENZO and SCALEPACK; Otwinowski & Minor, 1997)
4673 reflections with I > 2σ(I)
Tmin = 0.790, Tmax = 0.790Rint = 0.028
8105 measured reflectionsθmax = 28.3°
Refinement top
R[F2 > 2σ(F2)] = 0.051H-atom parameters constrained
wR(F2) = 0.138Δρmax = 0.60 e Å3
S = 1.11Δρmin = 0.78 e Å3
5946 reflectionsAbsolute structure: ?
263 parametersAbsolute structure parameter: ?
104 restraintsRogers parameter: ?
Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
C10.6408 (5)0.1645 (4)0.5124 (3)0.0366 (9)
H1A0.53590.12550.50310.055*
H1B0.71100.16600.58760.055*
H1C0.67120.11530.45550.055*
C20.5764 (5)0.3800 (4)0.6014 (3)0.0363 (9)
H2A0.57190.46880.60390.054*
H2B0.64410.37350.67470.054*
H2C0.47310.32960.58360.054*
C30.9311 (5)0.5941 (5)0.3820 (4)0.0614 (15)
H3A0.90160.65160.43450.092*
H3B1.01670.64060.36780.092*
H3C0.96270.52440.41460.092*
C40.7279 (4)0.6764 (4)0.2262 (3)0.0325 (8)
H4A0.63270.65860.16060.049*
H4B0.81170.72440.21110.049*
H4C0.71460.72630.29180.049*
C50.2475 (4)0.4740 (3)0.0385 (3)0.0305 (7)
H5A0.24890.54760.09450.046*
H5B0.16640.46780.03350.046*
H5C0.34690.48360.02910.046*
C60.0443 (4)0.3587 (4)0.1141 (3)0.0335 (8)
H6A0.01640.29570.15260.050*
H6B0.04070.34990.04340.050*
H6C0.06550.44400.16220.050*
C70.2549 (5)0.0618 (4)0.0167 (4)0.0436 (10)
H7A0.21690.00170.02700.065*
H7B0.18320.08810.05270.065*
H7C0.26340.13620.03350.065*
C80.4565 (5)0.1004 (4)0.2049 (4)0.0401 (9)
H8A0.55030.06840.27190.060*
H8B0.46200.18090.16110.060*
H8C0.36750.11360.22780.060*
Cr10.52927 (6)0.29891 (5)0.23597 (4)0.01952 (15)
O10.5147 (3)0.3118 (2)0.38722 (19)0.0249 (5)
O20.6420 (3)0.4782 (2)0.2902 (2)0.0311 (6)
O30.3352 (3)0.3613 (2)0.20325 (18)0.0244 (5)
O40.4037 (3)0.1239 (2)0.1927 (2)0.0307 (6)
S10.64885 (9)0.32182 (8)0.49640 (7)0.02458 (19)
S20.77235 (10)0.53209 (8)0.25343 (7)0.0274 (2)
S30.21164 (9)0.33420 (8)0.08474 (7)0.02458 (19)
S40.43771 (10)0.01195 (8)0.12109 (7)0.0277 (2)
Cl10.75712 (10)0.22914 (9)0.28666 (8)0.0336 (2)
Cl20.52160 (10)0.28710 (9)0.05303 (7)0.0309 (2)
C90.9921 (7)1.0231 (6)0.6406 (6)0.0398 (14)0.654 (4)
H9A0.98811.08830.59800.060*0.654 (4)
H9B1.06240.97100.62600.060*0.654 (4)
H9C1.02861.06370.72110.060*0.654 (4)
C100.8550 (7)0.8235 (7)0.6883 (6)0.0366 (14)0.654 (4)
H10A0.76330.76020.67710.055*0.654 (4)
H10B0.89800.87320.76670.055*0.654 (4)
H10C0.93140.78050.67120.055*0.654 (4)
O50.7674 (13)0.8501 (11)0.4809 (10)0.055 (3)0.654 (4)
S50.80493 (17)0.92523 (14)0.59820 (13)0.0339 (5)0.654 (4)
C9A0.875 (3)0.918 (2)0.6986 (15)0.091 (6)0.346 (4)
H9A10.90331.01020.71380.136*0.346 (4)
H9A20.95150.88820.75380.136*0.346 (4)
H9A30.77410.89270.70420.136*0.346 (4)
C10A0.812 (2)0.690 (2)0.5904 (18)0.113 (9)0.346 (4)
H10D0.74950.62730.52000.170*0.346 (4)
H10E0.75350.69910.64020.170*0.346 (4)
H10F0.90550.66220.62720.170*0.346 (4)
O5A0.723 (3)0.870 (3)0.482 (3)0.065 (6)0.346 (4)
S5A0.8659 (4)0.8479 (4)0.5591 (3)0.0520 (11)0.346 (4)
Cl30.90410 (10)0.28439 (9)0.80708 (8)0.0360 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.052 (2)0.0291 (18)0.0280 (18)0.0178 (17)0.0096 (17)0.0064 (14)
C20.050 (2)0.038 (2)0.0191 (16)0.0157 (17)0.0100 (16)0.0019 (14)
C30.034 (2)0.077 (4)0.058 (3)0.007 (2)0.008 (2)0.040 (3)
C40.0353 (19)0.0313 (18)0.0329 (18)0.0094 (15)0.0128 (16)0.0105 (15)
C50.0328 (18)0.0331 (19)0.0272 (17)0.0133 (15)0.0089 (15)0.0101 (14)
C60.0213 (17)0.041 (2)0.0347 (19)0.0072 (15)0.0056 (15)0.0091 (16)
C70.039 (2)0.042 (2)0.041 (2)0.0104 (18)0.0091 (18)0.0039 (18)
C80.056 (3)0.0290 (19)0.044 (2)0.0157 (18)0.025 (2)0.0116 (17)
Cr10.0207 (3)0.0202 (3)0.0191 (3)0.00655 (19)0.0082 (2)0.00480 (19)
O10.0209 (11)0.0345 (13)0.0215 (11)0.0094 (9)0.0081 (9)0.0091 (10)
O20.0325 (13)0.0257 (12)0.0369 (14)0.0002 (10)0.0213 (11)0.0009 (10)
O30.0249 (11)0.0309 (12)0.0170 (10)0.0115 (9)0.0058 (9)0.0043 (9)
O40.0356 (13)0.0204 (12)0.0403 (14)0.0031 (10)0.0244 (12)0.0002 (10)
S10.0223 (4)0.0267 (4)0.0205 (4)0.0047 (3)0.0031 (3)0.0046 (3)
S20.0247 (4)0.0260 (4)0.0330 (4)0.0046 (3)0.0126 (3)0.0084 (3)
S30.0244 (4)0.0258 (4)0.0198 (4)0.0079 (3)0.0037 (3)0.0025 (3)
S40.0324 (4)0.0221 (4)0.0309 (4)0.0047 (3)0.0181 (4)0.0015 (3)
Cl10.0277 (4)0.0448 (5)0.0360 (5)0.0190 (4)0.0145 (4)0.0146 (4)
Cl20.0394 (5)0.0377 (5)0.0229 (4)0.0171 (4)0.0162 (3)0.0092 (3)
C90.042 (3)0.025 (3)0.048 (4)0.003 (2)0.019 (3)0.004 (2)
C100.029 (3)0.046 (4)0.049 (4)0.014 (3)0.021 (3)0.028 (3)
O50.065 (7)0.053 (5)0.034 (4)0.008 (4)0.014 (5)0.004 (3)
S50.0329 (8)0.0317 (8)0.0407 (8)0.0098 (6)0.0140 (6)0.0144 (6)
C9A0.120 (16)0.108 (17)0.052 (10)0.057 (14)0.024 (10)0.029 (11)
C10A0.079 (14)0.19 (3)0.091 (15)0.059 (16)0.027 (12)0.058 (17)
O5A0.064 (12)0.068 (9)0.058 (9)0.032 (8)0.015 (8)0.007 (7)
S5A0.048 (2)0.056 (2)0.048 (2)0.0241 (16)0.0129 (17)0.0019 (15)
Cl30.0319 (5)0.0401 (5)0.0301 (4)0.0062 (4)0.0083 (4)0.0013 (4)
Geometric parameters (Å, º) top
C1—S11.774 (4)C8—H8B0.9800
C1—H1A0.9800C8—H8C0.9800
C1—H1B0.9800Cr1—O21.978 (2)
C1—H1C0.9800Cr1—O41.983 (2)
C2—S11.776 (4)Cr1—O11.993 (2)
C2—H2A0.9800Cr1—O31.996 (2)
C2—H2B0.9800Cr1—Cl12.3252 (10)
C2—H2C0.9800Cr1—Cl22.3302 (9)
C3—S21.777 (4)O1—S11.536 (2)
C3—H3A0.9800O2—S21.539 (3)
C3—H3B0.9800O3—S31.542 (2)
C3—H3C0.9800O4—S41.543 (2)
C4—S21.769 (4)C9—S51.784 (6)
C4—H4A0.9800C9—H9A0.9800
C4—H4B0.9800C9—H9B0.9800
C4—H4C0.9800C9—H9C0.9800
C5—S31.776 (4)C10—S51.766 (6)
C5—H5A0.9800C10—H10A0.9800
C5—H5B0.9800C10—H10B0.9800
C5—H5C0.9800C10—H10C0.9800
C6—S31.789 (4)O5—S51.494 (12)
C6—H6A0.9800C9A—S5A1.803 (18)
C6—H6B0.9800C9A—H9A10.9800
C6—H6C0.9800C9A—H9A20.9800
C7—S41.773 (4)C9A—H9A30.9800
C7—H7A0.9800C10A—S5A1.89 (2)
C7—H7B0.9800C10A—H10D0.9800
C7—H7C0.9800C10A—H10E0.9800
C8—S41.780 (4)C10A—H10F0.9800
C8—H8A0.9800O5A—S5A1.48 (2)
S1—C1—H1A109.5O4—Cr1—Cl192.15 (8)
S1—C1—H1B109.5O1—Cr1—Cl193.27 (7)
H1A—C1—H1B109.5O3—Cr1—Cl1176.17 (7)
S1—C1—H1C109.5O2—Cr1—Cl293.13 (8)
H1A—C1—H1C109.5O4—Cr1—Cl291.89 (8)
H1B—C1—H1C109.5O1—Cr1—Cl2174.31 (7)
S1—C2—H2A109.5O3—Cr1—Cl291.44 (7)
S1—C2—H2B109.5Cl1—Cr1—Cl292.34 (4)
H2A—C2—H2B109.5S1—O1—Cr1125.43 (14)
S1—C2—H2C109.5S2—O2—Cr1123.43 (15)
H2A—C2—H2C109.5S3—O3—Cr1123.90 (13)
H2B—C2—H2C109.5S4—O4—Cr1122.32 (14)
S2—C3—H3A109.5O1—S1—C1105.38 (16)
S2—C3—H3B109.5O1—S1—C2102.39 (16)
H3A—C3—H3B109.5C1—S1—C298.3 (2)
S2—C3—H3C109.5O2—S2—C4102.63 (17)
H3A—C3—H3C109.5O2—S2—C3103.7 (2)
H3B—C3—H3C109.5C4—S2—C398.8 (2)
S2—C4—H4A109.5O3—S3—C5104.49 (15)
S2—C4—H4B109.5O3—S3—C6102.73 (15)
H4A—C4—H4B109.5C5—S3—C697.85 (18)
S2—C4—H4C109.5O4—S4—C7102.81 (18)
H4A—C4—H4C109.5O4—S4—C8103.36 (17)
H4B—C4—H4C109.5C7—S4—C899.6 (2)
S3—C5—H5A109.5S5—C9—H9A109.5
S3—C5—H5B109.5S5—C9—H9B109.5
H5A—C5—H5B109.5H9A—C9—H9B109.5
S3—C5—H5C109.5S5—C9—H9C109.5
H5A—C5—H5C109.5H9A—C9—H9C109.5
H5B—C5—H5C109.5H9B—C9—H9C109.5
S3—C6—H6A109.5S5—C10—H10A109.5
S3—C6—H6B109.5S5—C10—H10B109.5
H6A—C6—H6B109.5H10A—C10—H10B109.5
S3—C6—H6C109.5S5—C10—H10C109.5
H6A—C6—H6C109.5H10A—C10—H10C109.5
H6B—C6—H6C109.5H10B—C10—H10C109.5
S4—C7—H7A109.5O5—S5—C10107.4 (5)
S4—C7—H7B109.5O5—S5—C9106.6 (5)
H7A—C7—H7B109.5C10—S5—C997.0 (3)
S4—C7—H7C109.5S5A—C9A—H9A1109.5
H7A—C7—H7C109.5S5A—C9A—H9A2109.5
H7B—C7—H7C109.5H9A1—C9A—H9A2109.5
S4—C8—H8A109.5S5A—C9A—H9A3109.5
S4—C8—H8B109.5H9A1—C9A—H9A3109.5
H8A—C8—H8B109.5H9A2—C9A—H9A3109.5
S4—C8—H8C109.5S5A—C10A—H10D109.5
H8A—C8—H8C109.5S5A—C10A—H10E109.5
H8B—C8—H8C109.5H10D—C10A—H10E109.5
O2—Cr1—O4173.67 (10)S5A—C10A—H10F109.5
O2—Cr1—O187.70 (10)H10D—C10A—H10F109.5
O4—Cr1—O186.93 (10)H10E—C10A—H10F109.5
O2—Cr1—O387.72 (10)O5A—S5A—C9A105.5 (13)
O4—Cr1—O388.30 (10)O5A—S5A—C10A106.5 (14)
O1—Cr1—O382.96 (9)C9A—S5A—C10A85.9 (8)
O2—Cr1—Cl191.50 (8)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1B···Cl30.982.783.682 (4)154
C2—H2C···O5i0.982.573.529 (14)165
C3—H3B···Cl3ii0.982.833.648 (5)142
C4—H4B···Cl3ii0.982.793.616 (4)143
C4—H4C···O50.982.433.377 (13)162
C8—H8C···Cl3iii0.982.803.641 (5)144
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+2, y+1, z+1; (iii) x+1, y, z+1.

Experimental details

Crystal data
Chemical formula[CrCl2(C2H6OS)4]Cl·C2H6OS
Mr548.99
Crystal system, space groupTriclinic, P1
Temperature (K)150
a, b, c (Å)9.4521 (2), 11.0048 (3), 12.9761 (2)
α, β, γ (°)100.501 (2), 109.007 (1), 98.427 (1)
V3)1223.62 (5)
Z2
Radiation typeMo Kα
µ (mm1)1.24
Crystal size (mm)0.20 × 0.20 × 0.20
Data collection
DiffractometerNonius KappaCCD
diffractometer
Absorption correctionMulti-scan
(DENZO and SCALEPACK; Otwinowski & Minor, 1997)
Tmin, Tmax0.790, 0.790
No. of measured, independent and
observed [I > 2σ(I)] reflections
8105, 5946, 4673
Rint0.028
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.051, 0.138, 1.11
No. of reflections5946
No. of parameters263
No. of restraints104
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.60, 0.78

Computer programs: COLLECT (Nonius, 2000), DENZO and SCALEPACK (Otwinowski & Minor, 1997), SIR92 (Altomare et al., 1993), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012), WinGX (Farrugia, 2012) and ACD/Chemsketch (Advanced Chemistry Development, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1B···Cl30.982.783.682 (4)154
C2—H2C···O5i0.982.573.529 (14)165
C3—H3B···Cl3ii0.982.833.648 (5)142
C4—H4B···Cl3ii0.982.793.616 (4)143
C4—H4C···O50.982.433.377 (13)162
C8—H8C···Cl3iii0.982.803.641 (5)144
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+2, y+1, z+1; (iii) x+1, y, z+1.
Acknowledgements top

The authors extend their appreciation to Cardiff University for supporting this research.

references
References top

Advanced Chemistry Development (2008). ACD/Chemsketch. Advanced Chemistry Development Inc., Toronto, Ontario, Canada.

Altomare, A., Cascarano, G., Giacovazzo, C. & Guagliardi, A. (1993). J. Appl. Cryst. 26, 343–350.

Boschmann, E. & Wollaston, G. (1982). J. Chem. Educ. 59, 57–58.

Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854.

Nonius (2000). COLLECT. Nonius BV, Delft, The Netherlands.

Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press.

Pedersen, E. (1970). Acta Chem. Scand. 24, 3362–3372.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.