organic compounds
E)-1-{[(3,5-dimethylphenyl)imino]methyl}naphthalen-2-ol
of (aDepartment of Chemistry, Faculty of Science, Sohag University, 82524 Sohag, Egypt, and bDepartment of Physical and Analytical Chemistry, Faculty of Chemistry, Oviedo University-CINN, Oviedo 33006, Spain
*Correspondence e-mail: sgg@uniovi.es
The title compound, C19H17NO, has an E conformation about the N=C bond. The molecule is relatively planar, with the benzene ring and naphthalene ring plane being inclined to one another by 4.28 (10)°. There is an intramolecular O—H⋯N hydrogen bond generating an S(6) ring motif. In the crystal, molecules are linked via C—H⋯O hydrogen bonds, forming chains propagating along [100]. Within the chains there are π–π interactions involving the benzene ring and the naphthalene ring system of an adjacent molecule [inter-centroid distance = 3.6405 (14) Å].
Keywords: crystal structure; Schiff base; naphthalen-2-ol; imino; hydrogen bonding.
CCDC reference: 1406684
1. Related literature
For the diverse applications and biological activities of ); Dutta & Das (1988); Chandra & Sangeetika (2004); Cozzi (2004). For the biological activity and optical properties of derived from 2-hydroxynapthaldehyde, see: Abdel-Rahman et al. (2013a,b, 2014); Abu-Dief et al. (2013).
see: Schiff (18642. Experimental
2.1. Crystal data
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2.3. Refinement
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Data collection: CrysAlis CCD (Oxford Diffraction, 2010); cell CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2010); program(s) used to solve structure: SIR2011 (Burla et al., 2015); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 and PLATON (Spek, 2009).
Supporting information
CCDC reference: 1406684
10.1107/S2056989015011548/su5133sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S2056989015011548/su5133Isup2.hkl
Supporting information file. DOI: 10.1107/S2056989015011548/su5133Isup3.cml
Schiff bases, known as
or have recently received considerable attention due to their good performance in coordination chemistry, unique anti-bacterial, anti-cancer, and herbicidal applications (Schiff, 1864; Abdel-Rahman et al., 2013a,b,2014; Dutta & Das,1988). Studies showed that the presence of a lone pair of electrons in an sp2 hybridized orbital of the nitrogen atom of the azomethine group is of considerable chemical and biological importance (Chandra & Sangeetika, 2004; Cozzi, 2004). In continuation of our interest in the chemical, herbicidal and biological properties of we synthesized the title compound as a potential anti-bacterial agent.The title compound, has an E conformation about the N1═C11 bond, as illustrated in Fig. 1. The molecule is relatively planar with the benzene ring (C12—C17) and the naphthalene plane (C1—C10) being inclined to one another by 4.31 (10) °. There is an intramolecular O—H···N hydrogen bond generating an S(6) ring motif (Table 1 and Fig. 1).
In the crystal, molecules are linked via C—H···O hydrogen bonds (Table 1) forming chains propagating along [100], as shown in Fig. 2. Within the chains there are π-π interactions involving the naphthalene ring system and the benzene ring of an adjacent molecule [Cg1···Cg3i = 3.6405 (14) Å; Cg1 and Cg3 are the centroids of rings C1—C4/C9/C10 and C12—C17; symmetry code: (i) x - 1, y, z].
The title compound was prepared by treating 3,5-dimethylaniline (0.38 ml, 3 mmol) in 30 ml of dry ethanol with 2-hydroxynapthaldehyde (0.52 g, 3 mmol) with vigorous stirring at 343 K for 2 h. The reaction mixture was then left to stand at room temperature for 30 min. The yellow crystals were collected and washed several times in ethanol.
Crystal data, data collection and structure
details are summarized in Table 2. All the H atoms were positioned geometrically and refined using a riding model: O—H = 0.82 Å, C—H = 0.93 - 9.96 Å with Uiso(H) = 1.5Ueq(O,C) for hydroxyl and methyl H atoms and 1.2Ueq(C) for other H atoms. In the final cycles of in the absence of significant effects, 1185 Friedel pairs were merged and Δf ' set to zero.Data collection: CrysAlis CCD (Oxford Diffraction, 2010); cell
CrysAlis CCD (Oxford Diffraction, 2010); data reduction: CrysAlis RED (Oxford Diffraction, 2010); program(s) used to solve structure: SIR2011 (Burla et al., 2015); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and PLATON (Spek, 2009).C19H17NO | Dx = 1.240 Mg m−3 |
Mr = 275.33 | Cu Kα radiation, λ = 1.54184 Å |
Orthorhombic, P212121 | Cell parameters from 2417 reflections |
a = 6.2463 (2) Å | θ = 3.8–69.9° |
b = 10.2438 (3) Å | µ = 0.60 mm−1 |
c = 23.0533 (8) Å | T = 293 K |
V = 1475.08 (8) Å3 | Prism, colourless |
Z = 4 | 0.73 × 0.12 × 0.09 mm |
F(000) = 584 |
Oxford Diffraction Xcalibur (Ruby, Gemini) diffractometer | 2834 independent reflections |
Radiation source: Enhance (Cu) X-ray Source | 1422 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.032 |
Detector resolution: 10.2673 pixels mm-1 | θmax = 70.4°, θmin = 3.8° |
ω scans | h = −7→6 |
Absorption correction: analytical (CrysAlis PRO; Oxford Diffraction, 2010) | k = −12→12 |
Tmin = 0.915, Tmax = 0.94 | l = −27→28 |
8103 measured reflections |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.041 | H-atom parameters constrained |
wR(F2) = 0.121 | w = 1/[σ2(Fo2) + (0.0778P)2 + 0.0057P] where P = (Fo2 + 2Fc2)/3 |
S = 1.09 | (Δ/σ)max = 0.001 |
1649 reflections | Δρmax = 0.17 e Å−3 |
193 parameters | Δρmin = −0.14 e Å−3 |
C19H17NO | V = 1475.08 (8) Å3 |
Mr = 275.33 | Z = 4 |
Orthorhombic, P212121 | Cu Kα radiation |
a = 6.2463 (2) Å | µ = 0.60 mm−1 |
b = 10.2438 (3) Å | T = 293 K |
c = 23.0533 (8) Å | 0.73 × 0.12 × 0.09 mm |
Oxford Diffraction Xcalibur (Ruby, Gemini) diffractometer | 2834 independent reflections |
Absorption correction: analytical (CrysAlis PRO; Oxford Diffraction, 2010) | 1422 reflections with I > 2σ(I) |
Tmin = 0.915, Tmax = 0.94 | Rint = 0.032 |
8103 measured reflections |
R[F2 > 2σ(F2)] = 0.041 | 0 restraints |
wR(F2) = 0.121 | H-atom parameters constrained |
S = 1.09 | Δρmax = 0.17 e Å−3 |
1649 reflections | Δρmin = −0.14 e Å−3 |
193 parameters |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.6500 (4) | 0.7247 (2) | 0.05918 (10) | 0.0874 (7) | |
H1 | 0.7473 | 0.6710 | 0.0584 | 0.131* | |
N1 | 0.8802 (3) | 0.53539 (18) | 0.09101 (9) | 0.0551 (5) | |
C1 | 0.5709 (3) | 0.6003 (2) | 0.14386 (10) | 0.0511 (5) | |
C2 | 0.5267 (4) | 0.7006 (2) | 0.10264 (13) | 0.0641 (7) | |
C3 | 0.3348 (5) | 0.7757 (2) | 0.10869 (14) | 0.0740 (8) | |
H3 | 0.3038 | 0.8404 | 0.0817 | 0.089* | |
C4 | 0.1983 (4) | 0.7542 (3) | 0.15291 (13) | 0.0703 (7) | |
H4 | 0.0740 | 0.8040 | 0.1554 | 0.084* | |
C5 | 0.0928 (5) | 0.6360 (3) | 0.24126 (13) | 0.0712 (7) | |
H5 | −0.0293 | 0.6877 | 0.2437 | 0.085* | |
C6 | 0.1263 (5) | 0.5409 (3) | 0.28162 (13) | 0.0794 (8) | |
H6 | 0.0271 | 0.5275 | 0.3111 | 0.095* | |
C7 | 0.3088 (5) | 0.4643 (3) | 0.27857 (12) | 0.0728 (7) | |
H7 | 0.3322 | 0.3997 | 0.3062 | 0.087* | |
C8 | 0.4552 (4) | 0.4833 (3) | 0.23502 (11) | 0.0614 (6) | |
H8 | 0.5772 | 0.4314 | 0.2338 | 0.074* | |
C9 | 0.4256 (4) | 0.5796 (2) | 0.19192 (10) | 0.0524 (5) | |
C10 | 0.2386 (4) | 0.6573 (2) | 0.19625 (11) | 0.0577 (6) | |
C11 | 0.7513 (4) | 0.5198 (2) | 0.13492 (10) | 0.0508 (5) | |
H11 | 0.7791 | 0.4533 | 0.1613 | 0.061* | |
C12 | 1.0636 (4) | 0.4608 (2) | 0.07758 (10) | 0.0516 (5) | |
C13 | 1.1710 (4) | 0.4957 (2) | 0.02723 (11) | 0.0590 (6) | |
H13 | 1.1194 | 0.5640 | 0.0046 | 0.071* | |
C14 | 1.3542 (4) | 0.4297 (2) | 0.01026 (12) | 0.0639 (6) | |
C15 | 1.4288 (4) | 0.3287 (2) | 0.04512 (12) | 0.0644 (7) | |
H15 | 1.5511 | 0.2834 | 0.0340 | 0.077* | |
C16 | 1.3257 (4) | 0.2940 (2) | 0.09578 (12) | 0.0599 (6) | |
C17 | 1.1405 (4) | 0.3596 (2) | 0.11176 (11) | 0.0562 (6) | |
H17 | 1.0680 | 0.3359 | 0.1454 | 0.067* | |
C18 | 1.4130 (5) | 0.1868 (3) | 0.13355 (14) | 0.0790 (8) | |
H18A | 1.5003 | 0.1295 | 0.1106 | 0.119* | |
H18B | 1.2965 | 0.1383 | 0.1501 | 0.119* | |
H18C | 1.4979 | 0.2241 | 0.1640 | 0.119* | |
C19 | 1.4706 (6) | 0.4694 (3) | −0.04430 (15) | 0.0950 (11) | |
H19A | 1.4351 | 0.5581 | −0.0538 | 0.142* | |
H19B | 1.4286 | 0.4132 | −0.0756 | 0.142* | |
H19C | 1.6222 | 0.4622 | −0.0382 | 0.142* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0695 (12) | 0.0857 (13) | 0.1071 (15) | 0.0178 (11) | 0.0232 (13) | 0.0409 (12) |
N1 | 0.0420 (9) | 0.0567 (9) | 0.0667 (11) | 0.0027 (9) | 0.0022 (10) | 0.0052 (8) |
C1 | 0.0410 (10) | 0.0505 (10) | 0.0618 (13) | −0.0015 (9) | −0.0034 (11) | −0.0022 (9) |
C2 | 0.0518 (13) | 0.0585 (12) | 0.0819 (17) | 0.0050 (12) | 0.0038 (14) | 0.0120 (12) |
C3 | 0.0656 (15) | 0.0588 (13) | 0.098 (2) | 0.0161 (14) | 0.0032 (18) | 0.0149 (13) |
C4 | 0.0542 (13) | 0.0616 (13) | 0.095 (2) | 0.0151 (12) | 0.0018 (15) | −0.0004 (13) |
C5 | 0.0516 (13) | 0.0851 (17) | 0.0770 (17) | 0.0037 (13) | 0.0034 (14) | −0.0138 (14) |
C6 | 0.0640 (16) | 0.106 (2) | 0.0685 (17) | −0.0055 (18) | 0.0119 (15) | −0.0069 (16) |
C7 | 0.0659 (16) | 0.0889 (18) | 0.0638 (15) | −0.0074 (16) | 0.0016 (14) | 0.0051 (13) |
C8 | 0.0529 (13) | 0.0698 (13) | 0.0616 (14) | 0.0036 (12) | −0.0019 (12) | 0.0015 (11) |
C9 | 0.0438 (11) | 0.0546 (11) | 0.0587 (13) | −0.0040 (10) | −0.0046 (11) | −0.0066 (10) |
C10 | 0.0457 (11) | 0.0606 (12) | 0.0668 (15) | 0.0009 (11) | −0.0022 (12) | −0.0110 (11) |
C11 | 0.0428 (10) | 0.0513 (10) | 0.0583 (13) | −0.0011 (9) | −0.0034 (10) | 0.0025 (10) |
C12 | 0.0405 (10) | 0.0494 (10) | 0.0648 (14) | −0.0027 (10) | −0.0009 (10) | −0.0009 (9) |
C13 | 0.0590 (14) | 0.0536 (10) | 0.0645 (13) | 0.0000 (11) | 0.0065 (13) | 0.0035 (10) |
C14 | 0.0592 (14) | 0.0570 (12) | 0.0757 (16) | −0.0041 (12) | 0.0136 (14) | −0.0058 (11) |
C15 | 0.0512 (13) | 0.0542 (11) | 0.0877 (18) | 0.0019 (11) | 0.0070 (14) | −0.0090 (12) |
C16 | 0.0475 (12) | 0.0523 (11) | 0.0801 (16) | −0.0003 (11) | −0.0040 (14) | −0.0031 (11) |
C17 | 0.0474 (11) | 0.0554 (11) | 0.0658 (14) | −0.0006 (11) | −0.0007 (12) | 0.0042 (10) |
C18 | 0.0670 (16) | 0.0714 (15) | 0.099 (2) | 0.0149 (14) | −0.0076 (17) | 0.0115 (14) |
C19 | 0.096 (2) | 0.0869 (18) | 0.102 (2) | 0.0041 (19) | 0.046 (2) | 0.0044 (17) |
O1—C2 | 1.287 (3) | C8—H8 | 0.9300 |
O1—H1 | 0.8200 | C9—C10 | 1.417 (3) |
N1—C11 | 1.304 (3) | C11—H11 | 0.9300 |
N1—C12 | 1.411 (3) | C12—C13 | 1.387 (3) |
C1—C11 | 1.411 (3) | C12—C17 | 1.388 (3) |
C1—C2 | 1.427 (3) | C13—C14 | 1.385 (3) |
C1—C9 | 1.448 (3) | C13—H13 | 0.9300 |
C2—C3 | 1.431 (4) | C14—C15 | 1.391 (4) |
C3—C4 | 1.347 (4) | C14—C19 | 1.509 (4) |
C3—H3 | 0.9300 | C15—C16 | 1.380 (4) |
C4—C10 | 1.431 (4) | C15—H15 | 0.9300 |
C4—H4 | 0.9300 | C16—C17 | 1.388 (3) |
C5—C6 | 1.363 (4) | C16—C18 | 1.504 (3) |
C5—C10 | 1.398 (4) | C17—H17 | 0.9300 |
C5—H5 | 0.9300 | C18—H18A | 0.9600 |
C6—C7 | 1.386 (4) | C18—H18B | 0.9600 |
C6—H6 | 0.9300 | C18—H18C | 0.9600 |
C7—C8 | 1.372 (4) | C19—H19A | 0.9600 |
C7—H7 | 0.9300 | C19—H19B | 0.9600 |
C8—C9 | 1.412 (3) | C19—H19C | 0.9600 |
C2—O1—H1 | 109.5 | N1—C11—H11 | 118.8 |
C11—N1—C12 | 127.3 (2) | C1—C11—H11 | 118.8 |
C11—C1—C2 | 118.6 (2) | C13—C12—C17 | 120.0 (2) |
C11—C1—C9 | 121.8 (2) | C13—C12—N1 | 115.9 (2) |
C2—C1—C9 | 119.6 (2) | C17—C12—N1 | 124.1 (2) |
O1—C2—C1 | 122.7 (2) | C14—C13—C12 | 120.7 (2) |
O1—C2—C3 | 118.3 (2) | C14—C13—H13 | 119.7 |
C1—C2—C3 | 119.0 (2) | C12—C13—H13 | 119.7 |
C4—C3—C2 | 121.1 (2) | C13—C14—C15 | 118.5 (2) |
C4—C3—H3 | 119.5 | C13—C14—C19 | 120.1 (3) |
C2—C3—H3 | 119.5 | C15—C14—C19 | 121.4 (2) |
C3—C4—C10 | 122.0 (2) | C16—C15—C14 | 121.6 (2) |
C3—C4—H4 | 119.0 | C16—C15—H15 | 119.2 |
C10—C4—H4 | 119.0 | C14—C15—H15 | 119.2 |
C6—C5—C10 | 121.2 (3) | C15—C16—C17 | 119.2 (2) |
C6—C5—H5 | 119.4 | C15—C16—C18 | 120.6 (2) |
C10—C5—H5 | 119.4 | C17—C16—C18 | 120.2 (3) |
C5—C6—C7 | 119.8 (3) | C16—C17—C12 | 120.0 (2) |
C5—C6—H6 | 120.1 | C16—C17—H17 | 120.0 |
C7—C6—H6 | 120.1 | C12—C17—H17 | 120.0 |
C8—C7—C6 | 120.3 (3) | C16—C18—H18A | 109.5 |
C8—C7—H7 | 119.8 | C16—C18—H18B | 109.5 |
C6—C7—H7 | 119.8 | H18A—C18—H18B | 109.5 |
C7—C8—C9 | 121.8 (2) | C16—C18—H18C | 109.5 |
C7—C8—H8 | 119.1 | H18A—C18—H18C | 109.5 |
C9—C8—H8 | 119.1 | H18B—C18—H18C | 109.5 |
C8—C9—C10 | 116.8 (2) | C14—C19—H19A | 109.5 |
C8—C9—C1 | 124.0 (2) | C14—C19—H19B | 109.5 |
C10—C9—C1 | 119.2 (2) | H19A—C19—H19B | 109.5 |
C5—C10—C9 | 120.1 (2) | C14—C19—H19C | 109.5 |
C5—C10—C4 | 120.8 (2) | H19A—C19—H19C | 109.5 |
C9—C10—C4 | 119.1 (2) | H19B—C19—H19C | 109.5 |
N1—C11—C1 | 122.4 (2) | ||
C11—C1—C2—O1 | −3.3 (4) | C1—C9—C10—C4 | 0.0 (3) |
C9—C1—C2—O1 | 179.5 (2) | C3—C4—C10—C5 | −179.2 (3) |
C11—C1—C2—C3 | 174.9 (2) | C3—C4—C10—C9 | −1.3 (4) |
C9—C1—C2—C3 | −2.2 (4) | C12—N1—C11—C1 | −179.6 (2) |
O1—C2—C3—C4 | 179.3 (3) | C2—C1—C11—N1 | 1.2 (3) |
C1—C2—C3—C4 | 1.0 (4) | C9—C1—C11—N1 | 178.2 (2) |
C2—C3—C4—C10 | 0.8 (4) | C11—N1—C12—C13 | 178.5 (2) |
C10—C5—C6—C7 | 0.6 (4) | C11—N1—C12—C17 | −2.8 (4) |
C5—C6—C7—C8 | −0.3 (4) | C17—C12—C13—C14 | 0.6 (4) |
C6—C7—C8—C9 | −0.5 (4) | N1—C12—C13—C14 | 179.4 (2) |
C7—C8—C9—C10 | 0.9 (4) | C12—C13—C14—C15 | −0.6 (4) |
C7—C8—C9—C1 | −177.6 (2) | C12—C13—C14—C19 | −179.4 (3) |
C11—C1—C9—C8 | 3.1 (3) | C13—C14—C15—C16 | −0.4 (4) |
C2—C1—C9—C8 | −179.8 (2) | C19—C14—C15—C16 | 178.4 (3) |
C11—C1—C9—C10 | −175.3 (2) | C14—C15—C16—C17 | 1.4 (4) |
C2—C1—C9—C10 | 1.7 (3) | C14—C15—C16—C18 | −178.3 (3) |
C6—C5—C10—C9 | −0.1 (4) | C15—C16—C17—C12 | −1.4 (3) |
C6—C5—C10—C4 | 177.8 (3) | C18—C16—C17—C12 | 178.3 (2) |
C8—C9—C10—C5 | −0.6 (3) | C13—C12—C17—C16 | 0.4 (3) |
C1—C9—C10—C5 | 177.9 (2) | N1—C12—C17—C16 | −178.3 (2) |
C8—C9—C10—C4 | −178.5 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···N1 | 0.82 | 1.78 | 2.523 (3) | 149 |
C13—H13···O1i | 0.93 | 2.62 | 3.492 (3) | 156 |
Symmetry code: (i) x+1/2, −y+3/2, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···N1 | 0.82 | 1.78 | 2.523 (3) | 149 |
C13—H13···O1i | 0.93 | 2.62 | 3.492 (3) | 156 |
Symmetry code: (i) x+1/2, −y+3/2, −z. |
Footnotes
‡Present Address: Department of Physical and Analytical Chemistry, Faculty of Chemistry, Oviedo University-CINN, Oviedo 33006,. Spain.
Acknowledgements
We thank the Spanish Ministerio de Economía y Competitividad (MAT2013-40950-R and FPI grants: BES-2011-046948 to author MSMA) and the ERDF for financial support.
References
Abdel-Rahman, L. H., El-Khatib, R. M., Nassr, L. A. E. & Abu-Dief, A. M. (2013a). J. Mol. Struct. 1040, 9–18. CAS Google Scholar
Abdel-Rahman, L. H., El-Khatib, R. M., Nassr, L. A. E., Abu-Dief, A. M., Ismael, M. & Seleem, A. A. (2014). Spectrochim. Acta, 117, 366–378. CAS Google Scholar
Abdel-Rahman, L. H., El-Khatib, R. M., Nassr, L. A. E., Abu-Dief, A. M. & Lashin, F. E. (2013b). Spectrochim. Acta, 111, 266–276. CAS Google Scholar
Abu-Dief, A. M., Díaz-Torres, R., Sañudo, E. C., Abdel-Rahman, L. H. & Aliaga-Alcalde, N. (2013). Polyhedron, 64, 203–208. CAS Google Scholar
Burla, M. C., Caliandro, R., Carrozzini, B., Cascarano, G. L., Cuocci, C., Giacovazzo, C., Mallamo, M., Mazzone, A. & Polidori, G. (2015). J. Appl. Cryst. 48, 306–309. Web of Science CrossRef CAS IUCr Journals Google Scholar
Chandra, S. & Sangeetika, J. (2004). J. Indian Chem. Soc. 81, 203–206. CAS Google Scholar
Cozzi, P. G. (2004). Chem. Soc. Rev. 33, 410–421. Web of Science CrossRef PubMed CAS Google Scholar
Dutta, R. L. & Das, B. R. (1988). J. Sci. Ind. Res. 7, 547–555. Google Scholar
Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470. Web of Science CrossRef CAS IUCr Journals Google Scholar
Oxford Diffraction (2010). CrysAlis PRO, CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England. Google Scholar
Schiff, H. (1864). Chem. Pharm. Suppl. 3, 343. Google Scholar
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
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