research communications
N,N′-dibenzyl-3,3′-dimethoxybenzidine
ofaDepartment of Chemistry (BK21 plus) and Research Institute of Natural Sciences, Gyeongsang National University, Jinju 52828, Republic of Korea
*Correspondence e-mail: thkim@gnu.ac.kr, jekim@gnu.ac.kr
The title compound, (systematic name: N,N′-dibenzyl-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine), C28H28N2O2, was synthesized by the reduction of a Schiff base prepared via a condensation reaction between o-dianisidine and benzaldehyde under acidic conditions. The molecule lies on a crystallographic inversion centre so that the contains one half-molecule. The biphenyl moiety compound is essentially planar. Two intramolecular N—H⋯O hydrogen bonds occur. The dihedral angle between the terminal phenyl and phenylene rings of a benzidine unit is 48.68 (6)°. The methylene C atom of the benzyl group is disordered over two sets of sites, with occupancy ratio 0.779 (18):0.221 (18). In the crystal, molecules are connected by hydrogen bonding between o-dianisidine O atoms and H atoms of the terminal benzyl groups, forming a one-dimensional ladder-like structure. In the data from DFT calculations, the central biphenyl showed a twisted conformation.
Keywords: crystal structure; hydrogen bond; one-dimensional ladder; o-dianisidine.
CCDC reference: 1820338
1. Chemical context
Benzidine derivatives have received increasing attention in recent years beacuse of their applications in a wide variety of domains, for instance as building blocks in the construction of functionalized organic/organometallic materials and as sensor materials (Hmadeh et al., 2008; Satapathi, 2015; Nagaraja et al., 2017). The chemical and physical properties of benzidine-based compounds have enabled their use in cell biology as staining reagents (Liu et al., 2004). Benzidine derivatives are also relevant examples of simple redox systems, which could find applications as OLEDs (Zhang et al., 2004) or electroactive organic polymeric compounds (D'Eramo et al., 1994). Recently, we have reported copper(I) coordination polymers based on pyromellitic diimide derivatives, and shown that emission peaks are shifted depending on the solvent (Kang et al., 2015). In an extension of previous research, we have synthesized a benzidine derivative as a diamine intermediate, in which a benzidine moiety was used instead of a pyromellitic diimide spacer unit, and report its here.
2. Structural commentary
The molecular structure of the title compound consists of a central dimethoxybenzidine unit and two terminal benzyl groups (Fig. 1). The molecule lies about a crystallographic inversion centre at the midpoint of the C4—C4(−x, −y, −z + 1) bond, thus the contains one half-molecule. The dihedral angle between the terminal phenyl and phenylene rings of a benzidine unit is 48.68 (6)°. Disorder was modelled for the methylene C atom of the benzyl group over two sets of sites with an occupancy ratio of 0.779 (18):0.221 (18). The biphenyl moiety is strictly planar [dihedral angle between rings = 0°; maximum deviation of 0.015 (2) Å for atom C3]. There is no pronounced anisotropy in the aryl anisotropic displacement parameters, indicating that there is no disorder or dynamic twisting process to accommodate the steric crowding of the ortho H atoms of the biphenyl moiety (El-Shafei et al., 2003). The molecular conformation is in part influenced by the formation of weak intramolecular N1—H1⋯O1 hydrogen bonds that enclose S(5) rings (Fig. 1, Table 1).
3. Supramolecular features
In the crystal, neighbouring molecules are linked by C10—H10⋯O1 hydrogen bonds (Table 1; yellow dashed lines in Fig. 2) that generate R22(24) rings. These contacts stack adjacent molecules, forming a one-dimensional ladder-like structure (Fig. 2). Neighbouring stacks of molecules in these ladders are not connected but lie parallel to the (01) plane (Fig. 3).
4. Database survey
The Cambridge Database (Version 5.27, last update February 2017; Groom et al., 2016) reveals polymorphs of related biphenyl derivatives that have both twisted and planar biphenyl conformations (Hoser et al., 2012). However, in the biphenyl compounds 4,4′-diamino-2,2′,6,6′-tetramethylbiphenyl (Batsanov et al., 2006), 2,2′-dichloro-5,5′-dipropoxybenzidine and 2,2′-dimethyl-5,5′-dipropoxybenzidine (El-Shafei et al., 2004), in which atoms other than hydrogen are substituted in the ortho positions of the biphenyl unit, adopt twisted biphenyl conformations due to steric repulsion between substituted atoms. Hybrid inorganic–organic complexes with benzidine dications display structures with either twisted or planar conformations for the benzidine unit and, in some case, even both conformations (Dobrzycki & Woźniak, 2009). Related structures with an essentially planar benzidine conformation include 3,3′-dipropoxybenzidine (El-Shafei et al., 2003), N,N-bis(diphenylphosphino)benzidine (Kayan et al., 2012) and N,N′-bis(4-chlorobenzylidene)-3,3′-dimethoxybiphenyl-4,4′-diamine (Subashini et al., 2011).
5. Theoretical calculations
DFT calculations have been performed to support the experimental values on the basis of the diffraction study using the GAUSSIAN09 software package (Frisch et al., 2009). Full geometry optimizations were performed using B3LYP levels of theory with a 6-311G* basis set. The bond lengths of the optimized parameter are in excellent agreement with the experimental crystallographic data (Table 2). Interestingly, however, while the central biphenyl conformation from the is found to be planar, that from the DFT calculations shows an angle of 37.67° between the two aromatic rings, Fig. 4. Furthermore, the dihedral angle between the terminal phenyl and phenylene rings of the title compound is 48.68 (6)° from the crystallographic data but 76.69° from the DFT calculation. Similarly, as a result of the twisted conformation found in the DFT calculations, the lengths of the intramolecular N—H⋯O hydrogen bonds from the X-ray and DFT calculation data are also slightly different, at 2.33 and 2.21 Å, respectively.
6. Synthesis and crystallization
A mixture of o-dianisidine (4.88 g, 20 mmol), benzaldehyde (4.71 g, 40 mmol) and acetic acid (2.47 g, 40 mmol) in 30 mL of toluene and 7 mL of ethanol was heated at refluxed for 6 h. Sodium borohydride (1.62 g, 40 mmol) was added and the mixture was refluxed for two h. After cooling to room temperature, water was added to the reaction mixture. The organic layer was collected and the water layer was extracted with dichloromethane. The combined organic layer was dried with anhydrous sodium sulfate then evaporated to give a solid. (silica gel, ethyl acetate/hexane = 30/70 (v/v) gave the pure product. Crystals suitable for X-ray were obtained by slow evaporation of an ethyl acetate/n-hexane solution (v/v = 30/70) of the title compound. 1H NMR (300 MHz, DMSO): δ = 8.31 (s, 2H, CHCO), 7.28 (m, 10H, phenyl), 6.64 (d, 2H, CCHC), 6.41 (d, 2H, CHCN), 5.52 (t, 2H, NH), 4.33 (d, 4H, CH2), 3.88 (s, 6H, CH3).
7. Refinement
Crystal data, data collection and structure . All H atoms were positioned geometrically and refined using a riding model: C—H = 0.95–0.99 Å with Uiso(H) = 1.2Ueq(C). The methylene C8 atom of the benzyl group is disordered over two sets of sites. Their occupancies refined to 0.779 (18) and 0.221 (18).
details are summarized in Table 3
|
Supporting information
CCDC reference: 1820338
https://doi.org/10.1107/S2056989018001688/sj5545sup1.cif
contains datablocks I, New_Global_Publ_Block. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989018001688/sj5545Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989018001688/sj5545Isup3.cml
Data collection: APEX2 (Bruker, 2014); cell
SAINT (Bruker, 2014); data reduction: SAINT (Bruker, 2014); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2010); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and publCIF (Westrip, 2010).C28H28N2O2 | Z = 1 |
Mr = 424.52 | F(000) = 226 |
Triclinic, P1 | Dx = 1.307 Mg m−3 |
a = 4.7089 (2) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 9.6760 (4) Å | Cell parameters from 5519 reflections |
c = 12.1952 (5) Å | θ = 2.6–28.0° |
α = 93.387 (3)° | µ = 0.08 mm−1 |
β = 92.165 (2)° | T = 173 K |
γ = 103.180 (2)° | Plate, yellow |
V = 539.32 (4) Å3 | 0.31 × 0.18 × 0.06 mm |
Bruker APEXII CCD diffractometer | 1683 reflections with I > 2σ(I) |
φ and ω scans | Rint = 0.019 |
Absorption correction: multi-scan (SADABS; Bruker, 2014) | θmax = 25.0°, θmin = 1.7° |
Tmin = 0.659, Tmax = 0.746 | h = −5→5 |
6528 measured reflections | k = −11→11 |
1888 independent reflections | l = −13→14 |
Refinement on F2 | 6 restraints |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.048 | H-atom parameters constrained |
wR(F2) = 0.145 | w = 1/[σ2(Fo2) + (0.0797P)2 + 0.2226P] where P = (Fo2 + 2Fc2)/3 |
S = 1.10 | (Δ/σ)max < 0.001 |
1888 reflections | Δρmax = 0.37 e Å−3 |
156 parameters | Δρmin = −0.60 e Å−3 |
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 | Occ. (<1) | |
O1 | 0.2453 (3) | 0.22554 (13) | 0.81729 (9) | 0.0350 (4) | |
N1 | 0.6872 (3) | 0.38961 (16) | 0.72486 (12) | 0.0367 (4) | |
H1 | 0.6890 | 0.3862 | 0.7968 | 0.044* | |
C1 | −0.0076 (4) | 0.15213 (19) | 0.86818 (14) | 0.0355 (4) | |
H1A | −0.1827 | 0.1701 | 0.8312 | 0.053* | |
H1B | 0.0024 | 0.1860 | 0.9459 | 0.053* | |
H1C | −0.0163 | 0.0498 | 0.8625 | 0.053* | |
C2 | 0.2594 (3) | 0.19646 (17) | 0.70622 (13) | 0.0275 (4) | |
C3 | 0.0682 (3) | 0.08840 (16) | 0.64431 (13) | 0.0270 (4) | |
H3 | −0.0911 | 0.0316 | 0.6786 | 0.032* | |
C4 | 0.1022 (3) | 0.06000 (16) | 0.53238 (13) | 0.0261 (4) | |
C5 | 0.3347 (4) | 0.14802 (18) | 0.48559 (14) | 0.0328 (4) | |
H5 | 0.3646 | 0.1318 | 0.4098 | 0.039* | |
C6 | 0.5243 (4) | 0.25895 (18) | 0.54660 (14) | 0.0329 (4) | |
H6 | 0.6790 | 0.3178 | 0.5114 | 0.039* | |
C7 | 0.4931 (3) | 0.28575 (17) | 0.65775 (14) | 0.0284 (4) | |
C8 | 0.8843 (16) | 0.5024 (3) | 0.6758 (5) | 0.0414 (13) | 0.779 (18) |
H8A | 0.7710 | 0.5531 | 0.6291 | 0.050* | 0.779 (18) |
H8B | 1.0144 | 0.4613 | 0.6282 | 0.050* | 0.779 (18) |
C8' | 0.791 (3) | 0.4999 (12) | 0.7085 (11) | 0.023 (3) | 0.221 (18) |
H8'1 | 0.6326 | 0.5513 | 0.7158 | 0.028* | 0.221 (18) |
H8'2 | 0.8268 | 0.4949 | 0.6291 | 0.028* | 0.221 (18) |
C9 | 1.0656 (4) | 0.60586 (18) | 0.76161 (15) | 0.0336 (4) | |
C10 | 1.1686 (4) | 0.56526 (18) | 0.86005 (15) | 0.0373 (5) | |
H10 | 1.1067 | 0.4695 | 0.8787 | 0.045* | |
C11 | 1.3596 (4) | 0.66246 (19) | 0.93095 (14) | 0.0368 (4) | |
H11 | 1.4302 | 0.6334 | 0.9978 | 0.044* | |
C12 | 1.4480 (4) | 0.80198 (18) | 0.90472 (15) | 0.0370 (4) | |
H12 | 1.5781 | 0.8693 | 0.9538 | 0.044* | |
C13 | 1.3474 (4) | 0.84355 (18) | 0.80734 (15) | 0.0357 (4) | |
H13 | 1.4098 | 0.9394 | 0.7889 | 0.043* | |
C14 | 1.1558 (4) | 0.74595 (18) | 0.73633 (14) | 0.0339 (4) | |
H14 | 1.0855 | 0.7754 | 0.6696 | 0.041* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0359 (7) | 0.0396 (7) | 0.0222 (6) | −0.0042 (5) | 0.0004 (5) | −0.0061 (5) |
N1 | 0.0347 (8) | 0.0398 (9) | 0.0262 (8) | −0.0081 (7) | 0.0009 (6) | −0.0086 (6) |
C1 | 0.0359 (9) | 0.0416 (10) | 0.0252 (9) | 0.0021 (7) | 0.0029 (7) | −0.0022 (7) |
C2 | 0.0303 (8) | 0.0285 (8) | 0.0224 (8) | 0.0056 (6) | −0.0033 (6) | −0.0015 (6) |
C3 | 0.0277 (8) | 0.0256 (8) | 0.0253 (8) | 0.0017 (6) | −0.0015 (6) | 0.0008 (6) |
C4 | 0.0270 (8) | 0.0258 (8) | 0.0244 (8) | 0.0050 (7) | −0.0047 (7) | −0.0001 (6) |
C5 | 0.0333 (9) | 0.0375 (9) | 0.0228 (8) | −0.0001 (7) | −0.0019 (7) | −0.0028 (7) |
C6 | 0.0307 (9) | 0.0339 (9) | 0.0286 (9) | −0.0033 (7) | 0.0007 (7) | 0.0001 (7) |
C7 | 0.0265 (8) | 0.0285 (8) | 0.0273 (9) | 0.0025 (6) | −0.0043 (6) | −0.0023 (6) |
C8 | 0.048 (2) | 0.0322 (14) | 0.037 (3) | −0.0026 (15) | −0.014 (2) | −0.0002 (13) |
C8' | 0.022 (4) | 0.029 (4) | 0.018 (4) | 0.005 (3) | 0.011 (3) | 0.003 (3) |
C9 | 0.0356 (9) | 0.0290 (9) | 0.0328 (9) | 0.0032 (7) | −0.0054 (7) | −0.0041 (7) |
C10 | 0.0454 (10) | 0.0255 (8) | 0.0366 (10) | 0.0003 (7) | −0.0055 (8) | 0.0017 (7) |
C11 | 0.0429 (10) | 0.0362 (10) | 0.0272 (9) | 0.0023 (8) | −0.0065 (8) | 0.0008 (7) |
C12 | 0.0346 (9) | 0.0331 (9) | 0.0367 (10) | −0.0027 (7) | −0.0055 (8) | −0.0056 (7) |
C13 | 0.0351 (9) | 0.0276 (9) | 0.0405 (10) | −0.0009 (7) | 0.0001 (8) | 0.0033 (7) |
C14 | 0.0368 (9) | 0.0337 (9) | 0.0298 (9) | 0.0055 (7) | −0.0010 (7) | 0.0033 (7) |
O1—C2 | 1.374 (2) | C6—H6 | 0.9500 |
O1—C1 | 1.425 (2) | C8—C9 | 1.498 (3) |
N1—C8' | 1.100 (12) | C8—H8A | 0.9900 |
N1—C7 | 1.394 (2) | C8—H8B | 0.9900 |
N1—C8 | 1.438 (7) | C8'—C9 | 1.549 (11) |
N1—H1 | 0.8800 | C8'—H8'1 | 0.9900 |
C1—H1A | 0.9800 | C8'—H8'2 | 0.9900 |
C1—H1B | 0.9800 | C9—C14 | 1.382 (2) |
C1—H1C | 0.9800 | C9—C10 | 1.389 (3) |
C2—C3 | 1.378 (2) | C10—C11 | 1.379 (2) |
C2—C7 | 1.408 (2) | C10—H10 | 0.9500 |
C3—C4 | 1.399 (2) | C11—C12 | 1.379 (2) |
C3—H3 | 0.9500 | C11—H11 | 0.9500 |
C4—C5 | 1.389 (2) | C12—C13 | 1.377 (3) |
C4—C4i | 1.491 (3) | C12—H12 | 0.9500 |
C5—C6 | 1.386 (2) | C13—C14 | 1.383 (2) |
C5—H5 | 0.9500 | C13—H13 | 0.9500 |
C6—C7 | 1.385 (2) | C14—H14 | 0.9500 |
C2—O1—C1 | 117.19 (12) | C9—C8—H8A | 109.3 |
C8'—N1—C7 | 129.4 (6) | N1—C8—H8B | 109.3 |
C7—N1—C8 | 119.6 (2) | C9—C8—H8B | 109.3 |
C7—N1—H1 | 120.2 | H8A—C8—H8B | 108.0 |
C8—N1—H1 | 120.2 | N1—C8'—C9 | 131.8 (9) |
O1—C1—H1A | 109.5 | N1—C8'—H8'1 | 104.3 |
O1—C1—H1B | 109.5 | C9—C8'—H8'1 | 104.3 |
H1A—C1—H1B | 109.5 | N1—C8'—H8'2 | 104.3 |
O1—C1—H1C | 109.5 | C9—C8'—H8'2 | 104.3 |
H1A—C1—H1C | 109.5 | H8'1—C8'—H8'2 | 105.6 |
H1B—C1—H1C | 109.5 | C14—C9—C10 | 118.83 (15) |
O1—C2—C3 | 124.56 (15) | C14—C9—C8 | 117.8 (2) |
O1—C2—C7 | 114.59 (14) | C10—C9—C8 | 123.1 (2) |
C3—C2—C7 | 120.84 (15) | C14—C9—C8' | 124.5 (4) |
C2—C3—C4 | 121.84 (15) | C10—C9—C8' | 114.0 (5) |
C2—C3—H3 | 119.1 | C11—C10—C9 | 120.71 (16) |
C4—C3—H3 | 119.1 | C11—C10—H10 | 119.6 |
C5—C4—C3 | 116.84 (15) | C9—C10—H10 | 119.6 |
C5—C4—C4i | 122.18 (18) | C10—C11—C12 | 119.89 (16) |
C3—C4—C4i | 120.98 (18) | C10—C11—H11 | 120.1 |
C6—C5—C4 | 121.75 (16) | C12—C11—H11 | 120.1 |
C6—C5—H5 | 119.1 | C13—C12—C11 | 119.95 (16) |
C4—C5—H5 | 119.1 | C13—C12—H12 | 120.0 |
C7—C6—C5 | 121.41 (16) | C11—C12—H12 | 120.0 |
C7—C6—H6 | 119.3 | C12—C13—C14 | 120.10 (16) |
C5—C6—H6 | 119.3 | C12—C13—H13 | 120.0 |
C6—C7—N1 | 124.04 (15) | C14—C13—H13 | 120.0 |
C6—C7—C2 | 117.31 (15) | C9—C14—C13 | 120.52 (16) |
N1—C7—C2 | 118.54 (15) | C9—C14—H14 | 119.7 |
N1—C8—C9 | 111.4 (4) | C13—C14—H14 | 119.7 |
N1—C8—H8A | 109.3 | ||
C1—O1—C2—C3 | −9.3 (2) | C3—C2—C7—N1 | −177.38 (14) |
C1—O1—C2—C7 | 171.68 (14) | C7—N1—C8—C9 | 177.7 (3) |
O1—C2—C3—C4 | −176.98 (14) | C7—N1—C8'—C9 | −160.1 (9) |
C7—C2—C3—C4 | 1.9 (2) | N1—C8—C9—C14 | −149.9 (3) |
C2—C3—C4—C5 | −1.4 (2) | N1—C8—C9—C10 | 36.3 (6) |
C2—C3—C4—C4i | 178.26 (16) | N1—C8'—C9—C14 | −175.1 (12) |
C3—C4—C5—C6 | −0.1 (3) | N1—C8'—C9—C10 | −13.8 (19) |
C4i—C4—C5—C6 | −179.73 (17) | C14—C9—C10—C11 | −0.6 (3) |
C4—C5—C6—C7 | 1.0 (3) | C8—C9—C10—C11 | 173.1 (4) |
C5—C6—C7—N1 | 175.71 (16) | C8'—C9—C10—C11 | −163.1 (6) |
C5—C6—C7—C2 | −0.5 (3) | C9—C10—C11—C12 | 0.6 (3) |
C8'—N1—C7—C6 | 43.5 (11) | C10—C11—C12—C13 | −0.6 (3) |
C8—N1—C7—C6 | 18.3 (4) | C11—C12—C13—C14 | 0.6 (3) |
C8'—N1—C7—C2 | −140.3 (11) | C10—C9—C14—C13 | 0.6 (3) |
C8—N1—C7—C2 | −165.6 (3) | C8—C9—C14—C13 | −173.5 (4) |
O1—C2—C7—C6 | 178.08 (14) | C8'—C9—C14—C13 | 161.1 (7) |
C3—C2—C7—C6 | −0.9 (2) | C12—C13—C14—C9 | −0.6 (3) |
O1—C2—C7—N1 | 1.6 (2) |
Symmetry code: (i) −x, −y, −z+1. |
D—H···A | D—H | H···A | D···A | D—H···A |
C10—H10···O1ii | 0.95 | 2.66 | 3.400 (2) | 135 |
N1—H1···O1 | 0.88 | 2.33 | 2.6464 (19) | 101 |
Symmetry code: (ii) x+1, y, z. |
Bond | X-ray | B3LYP (6-311G*) |
O1—C1 | 1.425 (2) | 1.4208 |
O1—C2 | 1.374 (3) | 1.3744 |
N1—C7 | 1.394 (2) | 1.3872 |
N1—C8 | 1.438 (5) | 1.4567 |
C2—C3 | 1.378 (2) | 1.3859 |
C3—C4 | 1.399 (2) | 1.4104 |
C4—C5 | 1.389 (2) | 1.3951 |
C5—C6 | 1.386 (2) | 1.3964 |
C6—C7 | 1.385 (2) | 1.3972 |
C2—C7 | 1.408 (2) | 1.4189 |
C8—C9 | 1.498 (6) | 1.5139 |
C9—C10 | 1.389 (3) | 1.400) |
C10—C11 | 1.379 (3) | 1.3921 |
C11—C12 | 1.380 (2) | 1.3966 |
C12—C13 | 1.377 (3) | 1.3923 |
C13—C14 | 1.383 (3) | 1.3965 |
C9—C14 | 1.382 (2) | 1.3976 |
C4—C4i | 1.491 (2) | 1.4823 |
Symmetry code: (i) -x, -y, -z + 1. |
Funding information
This research was supported by the Basic Science Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Nos. 2015R1D1A4A01020317 and 2017R1D1A3A03000534)
References
Batsanov, A. S., Low, P. J. & Paterson, M. A. J. (2006). Acta Cryst. E62, o2973–o2975. Web of Science CSD CrossRef IUCr Journals Google Scholar
Brandenburg, K. (2010). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Bruker (2014). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
D'Eramo, F., Arévalo, A. H., Silber, J. J. & Sereno, L. (1994). J. Braz. Chem. Soc. 5, 213–218. CAS Google Scholar
Dobrzycki, L. & Woźniak, K. (2009). J. Mol. Struct. 921, 18–33. Web of Science CSD CrossRef CAS Google Scholar
El-Shafei, A., Boyle, P. D., Hinks, D. & Freeman, H. S. (2003). Acta Cryst. C59, o71–o73. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
El-Shafei, A., Hinks, D., Boyle, P. D. & Freeman, H. S. (2004). Acta Cryst. C60, o569–o571. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E., Robb, M. A., Cheeseman, J. R., Scalmani, G., Barone, V., Mennucci, B., Petersson, G. A., Nakatsuji, H., Caricato, M., Li, X., Hratchian, H. P., Izmaylov, A. F., Bloino, J., Zheng, G., Sonnenberg, J. L., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Vreven, T., Montgomery, J. J. A., Peralta, J. E., Ogliaro, F., Bearpark, M., Heyd, J. J., Brothers, E., Kudin, K. N., Staroverov, V. N., Kobayashi, R., Normand, J., Raghavachari, K., Rendell, A., Burant, J. C., Iyengar, S. S., Tomasi, J., Cossi, M., Rega, N., Millam, J. M., Klene, M., Knox, J. E., Cross, J. B., Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Stratmann, R. E., Yazyev, O., Austin, A. J., Cammi, R., Pomelli, C., Ochterski, J. W., Martin, R. L., Morokuma, K., Zakrzewski, V. G., Voth, G. A., Salvador, P., Dannenberg, J. J., Dapprich, S., Daniels, A. D., Farkas, O., Foresman, J. B., Ortiz, J. V., Cioslowski, J. & Fox, D. J. (2009). Gaussian09. Gaussian Inc, Wallingford, Connecticut, USA. Google Scholar
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CSD CrossRef IUCr Journals Google Scholar
Hmadeh, M., Traboulsi, H., Elhabiri, M., Braunstein, P., Albrecht-Gary, A. & Siri, O. (2008). Tetrahedron, 64, 6522–6529. Web of Science CrossRef CAS Google Scholar
Hoser, A. A., Jarzembska, K. N., Dobrzycki, Ł., Łukasz, , Gutmann, M. J. & Woźniak, K. (2012). Cryst. Growth Des. 12, 3526–3539. Google Scholar
Kang, G., Jeon, Y., Lee, K. Y., Kim, J. & Kim, T. H. (2015). Cryst. Growth Des. 15, 5183–5187. Web of Science CSD CrossRef CAS Google Scholar
Kayan, C., Biricik, N., Aydemir, M. & Scopelliti, R. (2012). Inorg. Chim. Acta, 385, 164–169. Web of Science CSD CrossRef CAS Google Scholar
Liu, L. F., Yulan, Z. & Qian, X. H. (2004). Dyes Pigments, 60, 17–21. Web of Science CrossRef CAS Google Scholar
Nagaraja, V., Kumar, M. K. & Giddappa, N. (2017). Spectrochim. Acta A Mol. Biomol. Spectrosc. 173, 407–417. Web of Science CrossRef CAS PubMed Google Scholar
Satapathi, S. (2015). Inorg. Chem. Commun. 56, 22–34. Web of Science CrossRef CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Subashini, A., Ramamurthi, K. & Stoeckli-Evans, H. (2011). Acta Cryst. E67, o1296–o1297. Web of Science CSD CrossRef IUCr Journals Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Zhang, S. T., Wang, Z. J., Zhao, J. M., Zhan, Y. Q., Wu, Y., Zhou, Y. C., Ding, X. M. & Hou, X. Y. (2004). Appl. Phys. Lett. 84, 2916–2918. Web of Science CrossRef CAS Google Scholar
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