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Logo of actae2this articlesearchopen accesssubmitActa Crystallographica Section E: Crystallographic CommunicationsActa Crystallographica Section E: Crystallographic Communications
 
Acta Crystallogr E Crystallogr Commun. 2017 July 1; 73(Pt 7): 932–935.
Published online 2017 June 2. doi:  10.1107/S2056989017007812
PMCID: PMC5499262

Crystal structure of {N-[(6-bromo­pyridin-2-yl)(phen­yl)methyl­idene]-2,6-di­methyl­aniline-κ2 N,N′}di­chlorido­zinc di­chloro­methane hemisolvate

Abstract

The solvated title compound, [ZnCl2(C20H17BrN2)]·0.5CH2Cl2, comprises a bidentate imino­pyridine ligand and two Cl atoms bound to a zinc2+ cation in a distorted tetra­hedral arrangement. The chelate bond lengths are consistent with localized C=N double bonds and a C—C single bond, as expected for an unreduced ligand bound to a closed-shell transition metal cation. Apart from weak nonclassical C—H(...)Cl hydrogen bonds between the complex mol­ecules and the disordered solvent mol­ecules (occupancy = 0.5), no further significant inter­molecular inter­actions are observed.

Keywords: crystal structure, imino­pyridine, redox-active ligand, coordination compound, zinc(II), pyridyl halide

Chemical context  

Redox-active ligands bearing an α-imino­pyridine core have received much attention in the literature (Bianchini et al., 2007  ; Lu et al., 2008  ). While most α-iminopyridine ligands reported to date feature a methyl imine ‘backbone’, a small number of variants featuring more electron-withdrawing phenyl backbones have been reported (Archer et al., 2006  ; Tondreau et al., 2013  ; Yang et al., 2010  ). Single-crystal X-ray diffraction studies have been a critical component in the elucidation of the electronic structure of base metal complexes featuring these redox-active ligands (Bart et al., 2006  ; Lu et al., 2008  ; Tondreau et al., 2013  ). A comparison of the Nimine—Cimine, Cimine—Cipso, and Cipso—Npyridine bond lengths for reduced and unreduced ligands as free bases or closed-shell complexes facilitate conclusions about redox non-innocence for such ligand sets. To this end, the preparation of the titular zinc(II) complex featuring the unreduced ligand was undertaken. Inclusion of a bromine functionality in the remaining ortho position of the pyridine ring allows for the introduction of an additional donor arm that differs from the imine fragment (Zhang & Lu, 2016  ; He et al., 2016  ).

Structural commentary  

The mol­ecular structure of the titular compound is shown in Fig. 1  . In this complex, the Zn2+ cation adopts a distorted tetra­hedral arrangement (Table 1  ), being surrounded by two Cl atoms and two N atoms. The N atoms comprise the donor atoms for an α-imino­pyridine ligand, forming a five-membered ring when bound to the Zn2+ cation (Zn1—N2—C7—C8—N15). The Zn2+ cation lies 0.3855 (3) Å above the plane defined by the chelate (N2/C7/C8/N15), in a distorted tetra­hedral arrangement (τ4 parameter = 0.8999; Yang et al., 2007  ). Distortions to the geometry about the metal cation and the arrangement of the pyridine and phenyl rings [dihedral angle = 66.62 (13)°] may be attributed to the steric pressure exerted by the ligand substituents, and packing constraints within the unit cell.

Figure 1
The mol­ecular stucture of 3-ZnCl2, with displacement ellipsoids shown at the 30% probability level and a partial numbering scheme. H atoms have been omitted for clarity. Cocrystallized CH2Cl2 solvent (disordered) is present in the ratio 3-ZnCl ...
Table 1
Selected geometric parameters (Å, °)

Bond lengths and angles for the α-imino­pyridine fragment (N2/C7/C8/N15) of the ligand are consistent with the depiction as localized C=N double bonds, and as a C—C single bond. A comparison of the observed bond lengths with the average bond lengths for neutral and doubly-reduced α-imino­pyridine (α-IP; Lu et al., 2008  ) and pyridine di­imine (PDI; Bart et al., 2006  ) ligands is given in Table 2  .

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Object name is e-73-00932-scheme1.jpg

Table 2
Comparison of Nimine—Cimine, Cimine—Cipso, and Cipso—Npyridine bond lengths (Å)

Supra­molecular features  

One half of a disordered mol­ecule of di­chloro­methane is present in the asymmetric unit, close to a center of inversion. While no hydrogen bonding is observed between the complex mol­ecules in this crystal, several short contacts (less than the sum of the van der Waals radii) are observed between neighbouring mol­ecules. Notably, neither dimerization nor stoichiometric binding of solvent to the metal cation is observed for this complex, in contrast to some base metal complexes of similar ligands (Dai et al., 2016  ; Song et al., 2011  ). However, a weak C—H(...)Cl inter­action binds the disordered solvent molecule to the complex (Table 3  ). Fig. 2  depicts the packing within the unit cell, as viewed along the a axis.

Figure 2
Packing of 3-ZnCl2·0.5CH2Cl2, viewed along a.
Table 3
Hydrogen-bond geometry (Å, °)

Synthesis and crystallization  

The titular compound was prepared in good yield using the scheme described in Fig. 3  . Experimental details are described below for each stage of the synthesis.

Figure 3
Schematic representation of the preparation of ligand (3) and the corresponding zinc(II) complex (3-ZnCl2).

Preparation of (6-bromopyridin-2-yl)phenyl ketone, (2)  

Following the method of Kobayashi and co-workers (Ishikawa et al., 2005  ), to a solution of 2,6-di­bromo­pyridine (1, 10.0 g, 42.2 mmol) in diethyl ether (200 ml) at 195 K, was added n-BuLi (29 ml of a 1.6 M solution in diethyl ether, 46.4 mmol) dropwise over 5 min. The solution was stirred at 195 K for 1 h, after which benzo­nitrile (4.8 ml, 46.4 mmol) was added dropwise over 5 min. The resultant solution was allowed to warm to room temperature, at which point the yellow solution turned dark red. After 1 h, cold aqueous 3 M HCl (250 ml) was added to the solution causing the dark-red solution to turn yellow, and the organic phase was removed. To the aqueous layer, 3 M NaOH (250 ml) was added, and the mixture was extracted with diethyl ether (3 × 100 ml). The organic fractions were combined, dried over MgSO4, and concentrated under reduced pressure. The product (2) was recrystallized from ethanol, yielding a light-yellow crystalline solid (4.35 g, 16.6 mmol, 39%; m.p. 330–333 K).

Preparation of N-[(6-bromo­pyridin-2-yl)(phen­yl)methyl­idene]-2,6-di­methyl­aniline, (3)  

Following the method of Meneghetti et al. (1999  ), a round-bottomed flask containing 2 (3.00 g, 12.6 mmol), 2,6-di­methyl­aniline (3.15 ml, 25.2 mmol), ~30 mg of p-toluene­sulfonic acid catalyst, and toluene (300 ml) were fitted with a Dean–Stark apparatus, and brought to reflux for 6 d. The mixture was washed with a saturated aqueous solution of NaHCO3, dried over MgSO4, and concentrated under reduced pressure. The resultant brown (crude) product was purified by column chromatography (silica 50–70 ml) with a 4:1 (v/v) hexa­nes–ethyl acetate mixture as eluant (R F = 0.62) to yield 3 as a bright-yellow solid (2.85 g, 8.4 mmol, 67%; m.p. 361–366 K).

Preparation of {N-[(6-bromo­pyridin-2-yl)(phen­yl)meth­yl­idene]-2,6-di­methyl­aniline-κ2 N,N′}dichloridozinc di­chloro­methane hemisolvate, (3-ZnCl2)  

Anhydrous zinc(II) chloride (0.068 g, 0.50 mmol) and 3 (0.237 g, 0.65 mmol) solids were added to a Schlenk flask fitted with a magnetic stirrer bar, and the flask was flushed with argon. Anhydrous tetra­hydro­furan (10 ml) was added to the flask, and the solution was allowed to stir for 16 h. The solvent and other volatiles were removed in vacuo, and the residue was rinsed with dry pentane to yield 3-ZnCl2 as a yellow solid (0.251 g, 0.50 mmol, >99%). Single crystals suitable for X-ray diffraction were obtained by diffusion of diethyl ether into a saturated solution of 3-ZnCl2 in CH2Cl2. 1H NMR (CDCl3, 400 MHz; see also supporting information) δ 8.01 (d, J = 8.0 Hz, 1H, aryl m-CH), 7.95 (t, J = 8.0 Hz, 1H, aryl p-CH), 7.60 (d, J = 7.6 Hz, 1H, aryl m-CH), 7.49 (t, J = 7.2 Hz, 1H, phenyl p-CH), 7.39 (t, J = 7.2 Hz, 2H, phenyl m-CH), 7.21 (d, J = 7.6 Hz, 2H, phenyl o-CH), 7.01–6.92 (m, 3H, pyridine CH), 5.30 (s, 0.5 × 2H, CH2Cl2), 2.30 (s, 6H, CH3). 13C{1H} NMR (CDCl3, 100 MHz, see also supporting information): δ 169.2 (C=N), 150.3 (aryl ipso-C), 144.5, 142.4, 142.2 (aryl p-CH), 133.9 (aryl m-CH), 131.8 (phenyl p-CH), 130.4 (phenyl ipso-C), 128.9 (aryl o-C), 128.8 (phenyl m-CH), 128.6 (pyridine CH), 127.8 (phenyl o-CH), 127.0 (aryl m-CH and pyridine CH), 19.2 (CH3); m.p. 529–537 K. Analysis calculated (%) for C20.5H18N2BrCl3Zn: C 45.26, H 3.33, N 5.15; found: C 45.19, H 3.40, N 5.06.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 4  . H atoms were placed in calculated positions, and their positions were initially refined using distance and angle restraints. A disordered mol­ecule of di­chloro­methane was located close to a center of inversion. All atoms from the solvent mol­ecule were refined with a fixed occupancy of 0.5, and SAME and SIMU restraints were employed.

Table 4
Experimental details

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S2056989017007812/wm5393sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017007812/wm5393Isup2.hkl

CCDC reference: 1552501

Additional supporting information: crystallographic information; 3D view; checkCIF report

Acknowledgments

Funding for this work was provided by the Getty College of Arts and Sciences at Ohio Northern University, and Hamilton College. Katherine Manning (Hamilton College) conducted initial experiments to prepare the ligand. Anthony Chianese (Colgate University) assisted with the data collection and refinement of the titular compound.

supplementary crystallographic information

Crystal data

[ZnCl2(C20H17BrN2)]0.5CH2Cl2F(000) = 1084
Mr = 544.02Dx = 1.689 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.7107 Å
Hall symbol: -P 2ybcCell parameters from 12051 reflections
a = 13.7338 (3) Åθ = 3.8–29.4°
b = 11.25476 (16) ŵ = 3.40 mm1
c = 15.2274 (3) ÅT = 110 K
β = 114.654 (3)°Block, colourless
V = 2139.14 (14) Å30.55 × 0.40 × 0.32 mm
Z = 4.0

Data collection

Xcalibur, Ruby, Gemini ultra diffractometer5308 independent reflections
Radiation source: Enhance (Mo) X-ray Source4127 reflections with I > 2.0σ(I)
Graphite monochromatorRint = 0.036
Detector resolution: 10.3533 pixels mm-1θmax = 29.3°, θmin = 3.8°
ω scansh = −18→17
Absorption correction: analytical (CrysAlis PRO; Oxford Diffraction, 2007)k = −14→14
Tmin = 0.322, Tmax = 0.457l = −20→20
23484 measured reflections

Refinement

Refinement on F2Hydrogen site location: difference Fourier map
Least-squares matrix: fullH-atom parameters not refined
R[F2 > 2σ(F2)] = 0.031 Method = Modified Sheldrick w = 1/[σ2(F2) + ( 0.05P)2 + 0.0P] , where P = (max(Fo2,0) + 2Fc2)/3
wR(F2) = 0.080(Δ/σ)max = 0.021
S = 0.97Δρmax = 1.67 e Å3
5308 reflectionsΔρmin = −1.68 e Å3
263 parametersExtinction correction: Larson (1970), Equation 22
58 restraintsExtinction coefficient: 50 (10)
Primary atom site location: structure-invariant direct methods

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/UeqOcc. (<1)
Zn10.24497 (2)0.66355 (2)0.19030 (2)0.0137
N20.21816 (15)0.59443 (17)0.05484 (14)0.0135
C30.20764 (19)0.6512 (2)−0.02501 (18)0.0160
C40.1773 (2)0.5966 (2)−0.11413 (18)0.0208
C50.1573 (2)0.4766 (2)−0.11927 (18)0.0212
C60.1680 (2)0.4147 (2)−0.03669 (18)0.0174
C70.19888 (18)0.4754 (2)0.04920 (17)0.0131
C80.22025 (19)0.4160 (2)0.14363 (17)0.0125
C90.20005 (19)0.2860 (2)0.14404 (17)0.0142
C100.0955 (2)0.2442 (2)0.09284 (18)0.0183
C110.0740 (2)0.1235 (2)0.09313 (19)0.0213
C120.1553 (2)0.0442 (2)0.14188 (19)0.0223
C130.2597 (2)0.0854 (2)0.19275 (19)0.0209
C140.2819 (2)0.2055 (2)0.19430 (18)0.0168
N150.25598 (15)0.48235 (17)0.21897 (14)0.0123
C160.29039 (19)0.4345 (2)0.31477 (17)0.0129
C170.2158 (2)0.4167 (2)0.35422 (17)0.0149
C180.2548 (2)0.3766 (2)0.44935 (19)0.0194
C190.3632 (2)0.3522 (2)0.50168 (18)0.0224
C200.4345 (2)0.3712 (2)0.46047 (18)0.0211
C210.40003 (19)0.4153 (2)0.36666 (17)0.0161
C220.4773 (2)0.4419 (2)0.32364 (18)0.0209
C230.0983 (2)0.4407 (2)0.2971 (2)0.0217
Cl240.38192 (5)0.76686 (6)0.28643 (5)0.0258
Cl250.08112 (5)0.72624 (5)0.16364 (5)0.0192
Br260.23574 (2)0.81580 (2)−0.013723 (19)0.0209
C270.4520 (5)0.0542 (4)0.4947 (5)0.09800.5000
Cl280.5144 (3)0.0784 (2)0.4268 (2)0.11550.5000
Cl290.4668 (2)−0.0462 (2)0.5761 (2)0.06530.5000
H410.16900.6395−0.17030.0212*
H510.13810.4360−0.17550.0243*
H610.15470.3338−0.04170.0201*
H1410.35140.23330.22780.0201*
H1310.31190.03320.22400.0264*
H1210.1414−0.03570.14180.0274*
H1110.00350.09630.05920.0263*
H1010.04080.29630.05960.0203*
H2310.06100.42950.33610.0276*
H2320.08360.51960.27170.0276*
H2330.06840.38650.24320.0276*
H1810.20470.36840.47600.0250*
H1910.38820.32360.56520.0242*
H2010.50760.35580.49520.0231*
H2210.54910.42500.36920.0243*
H2230.47090.52440.30450.0243*
H2220.46120.39420.26620.0243*
H2710.38070.04340.44610.0989*0.5000
H2720.47800.12540.53600.0989*0.5000

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
Zn10.01653 (16)0.01006 (14)0.01384 (15)−0.00110 (11)0.00568 (12)−0.00071 (11)
N20.0140 (10)0.0133 (10)0.0141 (10)0.0004 (8)0.0066 (8)0.0013 (8)
C30.0145 (12)0.0143 (12)0.0191 (13)0.0003 (9)0.0070 (10)0.0031 (10)
C40.0238 (14)0.0236 (13)0.0143 (12)−0.0008 (11)0.0073 (11)0.0049 (11)
C50.0285 (15)0.0218 (13)0.0115 (12)−0.0015 (11)0.0068 (11)−0.0007 (10)
C60.0186 (13)0.0163 (12)0.0171 (13)0.0000 (10)0.0072 (10)0.0002 (10)
C70.0121 (12)0.0133 (11)0.0148 (12)0.0011 (9)0.0064 (9)0.0008 (9)
C80.0106 (11)0.0141 (11)0.0135 (12)0.0015 (9)0.0057 (9)0.0005 (9)
C90.0202 (13)0.0126 (11)0.0124 (12)−0.0012 (10)0.0094 (10)−0.0013 (9)
C100.0218 (13)0.0160 (12)0.0185 (13)−0.0023 (10)0.0097 (11)−0.0019 (10)
C110.0249 (14)0.0207 (13)0.0208 (14)−0.0071 (11)0.0119 (11)−0.0047 (11)
C120.0410 (17)0.0109 (12)0.0219 (14)−0.0064 (11)0.0201 (12)−0.0026 (10)
C130.0327 (16)0.0158 (12)0.0168 (13)0.0062 (11)0.0128 (12)0.0029 (10)
C140.0201 (13)0.0171 (12)0.0130 (12)0.0004 (10)0.0067 (10)−0.0012 (10)
N150.0120 (10)0.0132 (10)0.0129 (10)0.0007 (8)0.0062 (8)0.0010 (8)
C160.0194 (13)0.0086 (11)0.0115 (11)−0.0007 (9)0.0072 (10)−0.0010 (9)
C170.0212 (13)0.0094 (11)0.0170 (12)−0.0026 (9)0.0110 (10)−0.0027 (9)
C180.0293 (15)0.0152 (12)0.0206 (13)−0.0055 (11)0.0171 (12)−0.0021 (11)
C190.0336 (16)0.0184 (13)0.0125 (12)−0.0038 (11)0.0069 (11)0.0030 (10)
C200.0205 (14)0.0210 (13)0.0163 (13)−0.0005 (11)0.0023 (11)0.0004 (11)
C210.0188 (13)0.0144 (12)0.0145 (12)−0.0023 (10)0.0064 (10)−0.0024 (10)
C220.0164 (13)0.0271 (14)0.0187 (13)−0.0003 (11)0.0069 (11)0.0009 (11)
C230.0193 (14)0.0225 (14)0.0283 (15)−0.0021 (11)0.0149 (11)0.0013 (11)
Cl240.0251 (4)0.0216 (3)0.0236 (3)−0.0094 (3)0.0032 (3)−0.0017 (3)
Cl250.0188 (3)0.0157 (3)0.0221 (3)0.0015 (2)0.0076 (3)−0.0023 (2)
Br260.02633 (16)0.01324 (14)0.02203 (15)−0.00216 (10)0.00906 (12)0.00460 (10)
C270.058 (3)0.062 (3)0.133 (3)0.017 (2)0.000 (2)−0.027 (3)
Cl280.065 (2)0.0416 (13)0.160 (3)0.0215 (12)−0.0322 (17)−0.0336 (16)
Cl290.0343 (12)0.0717 (18)0.0902 (17)−0.0027 (12)0.0261 (12)−0.0279 (14)

Geometric parameters (Å, º)

Zn1—N22.088 (2)C14—H1410.929
Zn1—N152.0778 (19)N15—C161.438 (3)
Zn1—Cl242.1761 (7)C16—C171.401 (3)
Zn1—Cl252.2281 (7)C16—C211.395 (3)
N2—C31.327 (3)C17—C181.393 (3)
N2—C71.361 (3)C17—C231.504 (4)
C3—C41.386 (4)C18—C191.391 (4)
C3—Br261.885 (2)C18—H1810.938
C4—C51.374 (4)C19—C201.382 (4)
C4—H410.947C19—H1910.939
C5—C61.391 (3)C20—C211.395 (3)
C5—H510.907C20—H2010.936
C6—C71.376 (3)C21—C221.492 (4)
C6—H610.926C22—H2210.959
C7—C81.500 (3)C22—H2230.966
C8—C91.490 (3)C22—H2220.970
C8—N151.283 (3)C23—H2310.941
C9—C101.399 (4)C23—H2320.956
C9—C141.397 (3)C23—H2330.966
C10—C111.390 (4)C27—Cl29i1.849 (2)
C10—H1010.921C27—Cl28i1.846 (2)
C11—C121.380 (4)C27—C27i1.753 (2)
C11—H1110.938C27—Cl281.618 (2)
C12—C131.394 (4)C27—Cl291.626 (2)
C12—H1210.919C27—H2710.958
C13—C141.384 (3)C27—H2720.989
C13—H1310.894
N2—Zn1—N1579.01 (8)C16—C17—C18117.3 (2)
N2—Zn1—Cl24127.60 (6)C16—C17—C23121.8 (2)
N15—Zn1—Cl24114.61 (6)C18—C17—C23120.9 (2)
N2—Zn1—Cl25100.92 (6)C17—C18—C19121.0 (2)
N15—Zn1—Cl25109.18 (6)C17—C18—H181116.6
Cl24—Zn1—Cl25118.50 (3)C19—C18—H181122.3
Zn1—N2—C3129.22 (17)C18—C19—C20120.0 (2)
Zn1—N2—C7112.23 (15)C18—C19—H191120.2
C3—N2—C7118.2 (2)C20—C19—H191119.8
N2—C3—C4123.8 (2)C19—C20—C21121.2 (2)
N2—C3—Br26116.74 (18)C19—C20—H201120.7
C4—C3—Br26119.45 (19)C21—C20—H201118.1
C3—C4—C5117.6 (2)C20—C21—C16117.4 (2)
C3—C4—H41122.2C20—C21—C22121.4 (2)
C5—C4—H41120.2C16—C21—C22121.2 (2)
C4—C5—C6119.8 (2)C21—C22—H221110.4
C4—C5—H51121.5C21—C22—H223109.5
C6—C5—H51118.7H221—C22—H223110.2
C5—C6—C7119.0 (2)C21—C22—H222110.4
C5—C6—H61118.4H221—C22—H222108.8
C7—C6—H61122.6H223—C22—H222107.5
C6—C7—N2121.5 (2)C17—C23—H231110.3
C6—C7—C8123.3 (2)C17—C23—H232113.3
N2—C7—C8115.0 (2)H231—C23—H232107.6
C7—C8—C9118.7 (2)C17—C23—H233110.6
C7—C8—N15116.5 (2)H231—C23—H233107.6
C9—C8—N15124.8 (2)H232—C23—H233107.4
C8—C9—C10118.5 (2)Cl29i—C27—Cl28i106.86 (4)
C8—C9—C14122.0 (2)Cl29i—C27—C27i53.59 (5)
C10—C9—C14119.4 (2)Cl28i—C27—C27i53.36 (5)
C9—C10—C11119.8 (2)Cl29i—C27—Cl2813.11 (5)
C9—C10—H101120.3Cl28i—C27—Cl28119.62 (4)
C11—C10—H101119.9C27i—C27—Cl2866.26 (4)
C10—C11—C12120.5 (2)Cl29i—C27—Cl29119.83 (4)
C10—C11—H111119.3Cl28i—C27—Cl2913.31 (5)
C12—C11—H111120.2C27i—C27—Cl2966.24 (4)
C11—C12—C13119.9 (2)Cl28—C27—Cl29132.35 (5)
C11—C12—H121120.7Cl29i—C27—H271102.3
C13—C12—H121119.4Cl28i—C27—H271107.3
C12—C13—C14120.1 (2)C27i—C27—H271118.0
C12—C13—H131119.2Cl28—C27—H27199.8
C14—C13—H131120.7Cl29—C27—H271105.3
C9—C14—C13120.2 (2)Cl29i—C27—H272105.3
C9—C14—H141119.3Cl28i—C27—H272108.5
C13—C14—H141120.5C27i—C27—H272116.6
Zn1—N15—C8114.62 (16)Cl28—C27—H27297.1
Zn1—N15—C16123.06 (15)Cl29—C27—H272100.4
C8—N15—C16122.0 (2)H271—C27—H272125.2
N15—C16—C17119.9 (2)C27i—Cl28—C2760.38 (4)
N15—C16—C21116.9 (2)C27i—Cl29—C2760.17 (4)
C17—C16—C21123.0 (2)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···AD—HH···AD···AD—H···A
C4—H41···Cl25ii0.952.753.666 (3)162

Symmetry code: (ii) x, −y+3/2, z−1/2.

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Articles from Acta Crystallographica Section E: Crystallographic Communications are provided here courtesy of International Union of Crystallography