research communications
The H-pyrazolo[3,4-b]quinoline
of 3-chloro-2-(4-methylphenyl)-2aPG Department of Chemistry, Jain University, 52 Bellary Road, Hebbal, Bangalore 560 024, India, bUniversity B.D.T. College of Engineering, (a Constituent College of VTU, Belgaum), Davanagere 577 004, India, cDepartment of Chemistry, Keene State College, 229 Main Street, Keene, NH 03435-2001, USA, dDepartment of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, India, and eSchool of Chemistry, University of St Andrews, St Andrews, Fife KY16 9ST, Scotland
*Correspondence e-mail: jjasinski@keene.edu
In the molecule of 3-chloro-2-(4-methylphenyl)-2H-pyrazolo[3,4-b]quinoline, C17H12ClN3, (I), the dihedral angle between the planes of the pyrazole ring and the methylated phenyl ring is 54.25 (9)°. The bond distances in the fused tricyclic system provide evidence for 10-π delocalization in the pyrazolopyridine portion of the molecule, with diene character in the fused carbocyclic ring. In the crystal, molecules of (I) are linked by two independent C—H⋯N hydrogen bonds, forming sheets containing centrosymmetric R22(16) and R64(28) rings, and these sheets are all linked together by π–π stacking interactions with a ring-centroid separation of 3.5891 (9) Å.
CCDC reference: 1012361
1. Chemical context
Quinoline exhibits antimalarial, anti-bacterial, antifungal, anthelmintic, cardiotonic, anticonvulsant, anti-inflammatory and analgesic activity (Marella et al., 2013). Quinoline and its fused heterocyclic derivatives constitute an important class of compounds for new drug development (Kumar et al., 2009), and the medicinal applications of pyrazolo[3,4-b]quinolines have been summarized, along with an efficient synthetic method (Afghan et al., 2009). Recently, we have reported the synthesis of a number of novel pyrazolo[3,4-b]quinoline derivatives, including that of the title compound (I), and molecular of their binding affinity to the active sites of human telomerase (Sowmya et al., 2014). In a continuation of that study, we now report the crystal and molecular structure of one such example, the title compound 3-chloro-2-p-tolyl-2H-pyrazolo[3,4-b]quinoline, (I).
2. Structural commentary
Within the molecule of compound (I) (Fig. 1), the pendent phenyl group is twisted out of the plane of the fused heterocyclic ring system, as indicated by the relevant torsional angles (Table 1): the dihedral angle between the mean planes of the pyrazole and the methylated phenyl rings is 54.25 (9)°. The molecules of (I) exhibit no internal symmetry and thus they are conformationally chiral: however, the centrosymmetric accommodates equal numbers of both of the conformational enantiomers. The non-planar character of the molecular skeleton may be plausibly ascribed to the combined effects of the intramolecular non-bonded repulsion between the Cl substituent and the nearest H atom of the methylated phenyl ring, and of the direction-specific intermolecular interactions, in particular the hydrogen bonds.
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The bond distances in compound (I) (Table 1) show some interesting features. Within the pyrazole ring, the bond distances N1—C9A and N2—C3 (Fig. 1) are identical within experimental uncertainty, although these two bonds are formally double and single bonds, respectively. In the fused carbocyclic ring, the bonds C5—C6 and C7—C8 are much shorted than any other C—C bonds in the molecule. However, in the central pyridine ring, within each of the pairs of corresponding bonds C3A—C4 and C4—C4A, C8A—N9 and N9—C9A, and C3A—C9A and C4A—C8A, the two distances are very similar. These observations taken together are fully consistent with a 10-π delocalized system in the pyrazolopyridine portion of the molecule, comparable to those found in naphthalene and azulene (Glidewell & Lloyd, 1984), while the fused carbocyclic ring has more the character of an isolated diene (cf. Glidewell & Lloyd, 1986).
3. Supramolecular features
The supramolecular assembly in compound (I) is determined by two independent C—H⋯N hydrogen bonds (Table 2) and a π–π stacking interaction, which together link the molecules into a three-dimensional framework structure. The formation of this framework is readily analysed in terms of three simpler sub-structures (Ferguson et al., 1998a,b; Gregson et al., 2000). In the simplest sub-structure, the C—H⋯N hydrogen bond having atom C23 as the donor links an inversion-related pair of molecules, forming a cyclic centrosymmetric dimer characterized by an R22(16) (Bernstein et al., 1995) motif (Fig. 2), and this dimeric unit can be regarded as the basic building block in the supramolecular assembly. The second C—H⋯N hydrogen bond, having atom C26 as the donor, directly links the reference dimer, which is centred at (0, ½, ½) to four symmetry-related dimers centred at (0, 0, 0), (0 1, 0), (0, 0, 1) and (0, 1, 1), thereby leading to the formation of a hydrogen-bonded sheet lying parallel to (100), in which centrosymmetric R22(16) rings alternate with R64(28) rings (Fig. 3).
Only one hydrogen-bonded sheet passes through each π–π stacking interaction which is associated with the extensive overlap between the tricyclic ring systems of inversion-related pairs of molecules in adjacent sheets (Fig. 4). The pyridine rings of the molecules at (x, y, z) and (1 − x, 1 − y, 1 − z), which lie in adjacent sheets, are strictly parallel with an interplanar spacing of 3.3819 (6) Å. The ring-centroid separation is 3.5891 (9) Å, corresponding to a ring-centroid offset of ca 1.202 Å (Fig. 4). The effect of this interaction is to link all of the hydrogen-bonded sheets into a single three-dimensional array.
but the sheets are linked by theDespite the large number of aromatic C—H bonds in the molecule of compound (I), the only short C—H⋯π contact involves one of the C—H bonds of the methyl group. Not only are such bonds of low acidity but, perhaps more important, such a methyl group will be undergoing very rapid rotation about the adjacent C—C bond. When a group having local C3 symmetry, such as a methyl group, is directly bonded to another group having local C2 symmetry, such as a phenyl group, as in (I), the about the bond between them is very low, generally of the order of J mol−1 rather than the usual kJ mol−1 (Naylor & Wilson, 1957; Tannenbaum et al., 1956). Moreover, it has been shown that simple hydrocarbyl substituents undergo rapid rotation about C—C bonds in the solid state, even at reduced temperatures (Riddell & Rogerson, 1996, 1997). Therefore, while such a C—H⋯π intermolecular interaction may not be regarded as structurally significant, we report it here for completeness (Table 2).
4. Database survey
Structural information on un-reduced pyrazolo[3,4-b]quinolines carrying a substituent at the N2 position but not at N1, is sparse. In a series of pyrazolo[3,4-b]quinolin-5-ones, each carrying a substituent at N2, the central heterocyclic ring is in reduced form, carrying H atoms at positions 4 and 8 (Cannon et al., 2001a,b,c,d). By contrast, in a series of less highly reduced pyrazolo[3,4-b]quinolin-5-ones which each carry a substituent at N1 but not at N2, the central fused ring is fully aromatic (Mera et al., 2005; Cruz et al., 2006; Portilla et al., 2007). Similarly, in a series of benzo[f]pyrazolo[3,4-b]quinolines, in each of which there is a substituent at position 1, but not at position 2, the pyridine ring is fully aromatic (Portilla, Quiroga et al., 2005; Portilla, Serrano et al., 2005; Portilla et al., 2008).
5. Synthesis and crystallization
A sample of the title compound was prepared using the recently published procedure (Sowmya et al., 2014). Crystals suitable for single-crystal X-ray diffraction were obtained by slow evaporation, at ambient temperature and in the presence of air, of a solution in hexane–ethyl acetate (19:1, v/v).
6. Refinement
Crystal data, data collection and structure . All H atoms were located in difference maps, and then treated as riding atoms in geometrically idealized positions with C—H distances 0.95 Å (aromatic) or 0.98 Å (methyl) and with Uiso(H) = kUeq(C), where k = 1.5 for the methyl group, which was permitted to rotate but not to tilt, and 1.2 for all other H atoms.
details are summarized in Table 3
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Supporting information
CCDC reference: 1012361
https://doi.org/10.1107/S205698901500818X/sj5454sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S205698901500818X/sj5454Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S205698901500818X/sj5454Isup3.cml
Data collection: CrysAlis PRO (Agilent, 2012); cell
CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis RED (Agilent, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and PLATON (Spek, 2009).C17H12ClN3 | F(000) = 608 |
Mr = 293.75 | Dx = 1.390 Mg m−3 |
Monoclinic, P21/c | Cu Kα radiation, λ = 1.54184 Å |
a = 10.2194 (4) Å | Cell parameters from 2738 reflections |
b = 13.4661 (5) Å | θ = 4.4–72.6° |
c = 10.4600 (4) Å | µ = 2.36 mm−1 |
β = 102.780 (4)° | T = 173 K |
V = 1403.80 (10) Å3 | Block, yellow |
Z = 4 | 0.42 × 0.28 × 0.12 mm |
Agilent Eos Gemini diffractometer | 2479 reflections with I > 2σ(I) |
Radiation source: Enhance (Cu) X-ray Source | Rint = 0.032 |
ω scans | θmax = 72.6°, θmin = 4.4° |
Absorption correction: multi-scan (CrysAlis RED; Agilent, 2012) | h = −12→12 |
Tmin = 0.554, Tmax = 0.753 | k = −12→16 |
8443 measured reflections | l = −12→11 |
2738 independent reflections |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.040 | H-atom parameters constrained |
wR(F2) = 0.114 | w = 1/[σ2(Fo2) + (0.0702P)2 + 0.2814P] where P = (Fo2 + 2Fc2)/3 |
S = 1.05 | (Δ/σ)max < 0.001 |
2738 reflections | Δρmax = 0.36 e Å−3 |
191 parameters | Δρmin = −0.22 e Å−3 |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
N1 | 0.18699 (13) | 0.38247 (10) | 0.54035 (13) | 0.0290 (3) | |
N2 | 0.21652 (13) | 0.38697 (10) | 0.67397 (13) | 0.0269 (3) | |
C3 | 0.34907 (16) | 0.38742 (11) | 0.72750 (16) | 0.0271 (3) | |
Cl3 | 0.41552 (4) | 0.39736 (3) | 0.89093 (3) | 0.03435 (15) | |
C3A | 0.41587 (16) | 0.38246 (11) | 0.62459 (15) | 0.0257 (3) | |
C4 | 0.54815 (16) | 0.37944 (11) | 0.61183 (15) | 0.0280 (3) | |
H4 | 0.6210 | 0.3825 | 0.6860 | 0.034* | |
C4A | 0.56909 (16) | 0.37163 (11) | 0.48495 (16) | 0.0287 (3) | |
C5 | 0.70051 (17) | 0.36552 (13) | 0.45927 (18) | 0.0356 (4) | |
H5 | 0.7767 | 0.3680 | 0.5302 | 0.043* | |
C6 | 0.71795 (19) | 0.35618 (14) | 0.33496 (19) | 0.0401 (4) | |
H6 | 0.8060 | 0.3516 | 0.3197 | 0.048* | |
C7 | 0.60533 (19) | 0.35325 (13) | 0.22768 (18) | 0.0390 (4) | |
H7 | 0.6191 | 0.3472 | 0.1411 | 0.047* | |
C8 | 0.47823 (19) | 0.35900 (12) | 0.24644 (16) | 0.0352 (4) | |
H8 | 0.4045 | 0.3569 | 0.1730 | 0.042* | |
C8A | 0.45426 (17) | 0.36816 (11) | 0.37577 (15) | 0.0282 (3) | |
N9 | 0.32609 (13) | 0.37210 (10) | 0.38697 (13) | 0.0283 (3) | |
C9A | 0.30883 (16) | 0.37944 (11) | 0.51055 (15) | 0.0264 (3) | |
C21 | 0.10959 (16) | 0.39242 (12) | 0.74232 (16) | 0.0283 (3) | |
C22 | 0.01295 (16) | 0.46631 (12) | 0.70896 (16) | 0.0318 (3) | |
H22 | 0.0147 | 0.5109 | 0.6390 | 0.038* | |
C23 | −0.08594 (16) | 0.47332 (13) | 0.78014 (17) | 0.0356 (4) | |
H23 | −0.1520 | 0.5239 | 0.7588 | 0.043* | |
C24 | −0.09102 (16) | 0.40803 (14) | 0.88226 (17) | 0.0353 (4) | |
C25 | 0.00467 (17) | 0.33313 (14) | 0.90984 (18) | 0.0393 (4) | |
H25 | 0.0016 | 0.2870 | 0.9779 | 0.047* | |
C26 | 0.10438 (17) | 0.32453 (13) | 0.83996 (17) | 0.0360 (4) | |
H26 | 0.1685 | 0.2725 | 0.8590 | 0.043* | |
C27 | −0.19679 (19) | 0.41851 (18) | 0.9614 (2) | 0.0476 (5) | |
H27A | −0.1545 | 0.4387 | 1.0510 | 0.071* | |
H27B | −0.2424 | 0.3547 | 0.9636 | 0.071* | |
H27C | −0.2623 | 0.4689 | 0.9212 | 0.071* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0265 (7) | 0.0343 (7) | 0.0250 (7) | −0.0008 (5) | 0.0028 (5) | −0.0009 (5) |
N2 | 0.0244 (7) | 0.0303 (7) | 0.0251 (7) | 0.0004 (5) | 0.0035 (5) | −0.0002 (5) |
C3 | 0.0251 (8) | 0.0298 (8) | 0.0251 (8) | 0.0001 (6) | 0.0026 (6) | −0.0006 (6) |
Cl3 | 0.0305 (2) | 0.0482 (3) | 0.0228 (2) | 0.00019 (15) | 0.00256 (16) | −0.00138 (14) |
C3A | 0.0272 (8) | 0.0244 (7) | 0.0243 (8) | −0.0007 (5) | 0.0034 (6) | −0.0001 (6) |
C4 | 0.0261 (8) | 0.0288 (7) | 0.0278 (8) | −0.0013 (6) | 0.0033 (6) | −0.0009 (6) |
C4A | 0.0298 (8) | 0.0243 (7) | 0.0322 (8) | −0.0025 (6) | 0.0074 (7) | −0.0008 (6) |
C5 | 0.0304 (9) | 0.0361 (9) | 0.0411 (9) | −0.0026 (7) | 0.0093 (7) | −0.0028 (7) |
C6 | 0.0366 (9) | 0.0391 (9) | 0.0503 (11) | −0.0026 (7) | 0.0220 (8) | −0.0036 (8) |
C7 | 0.0500 (11) | 0.0363 (9) | 0.0359 (9) | −0.0041 (8) | 0.0204 (8) | −0.0028 (7) |
C8 | 0.0445 (10) | 0.0335 (9) | 0.0288 (8) | −0.0032 (7) | 0.0109 (7) | −0.0009 (7) |
C8A | 0.0336 (8) | 0.0226 (7) | 0.0287 (8) | −0.0014 (6) | 0.0078 (6) | 0.0003 (6) |
N9 | 0.0306 (7) | 0.0293 (7) | 0.0243 (7) | −0.0020 (5) | 0.0042 (5) | −0.0003 (5) |
C9A | 0.0270 (8) | 0.0246 (7) | 0.0267 (8) | −0.0008 (6) | 0.0038 (6) | −0.0002 (6) |
C21 | 0.0230 (7) | 0.0330 (8) | 0.0283 (8) | 0.0005 (6) | 0.0045 (6) | −0.0020 (6) |
C22 | 0.0266 (8) | 0.0352 (8) | 0.0305 (8) | 0.0015 (6) | −0.0003 (6) | 0.0016 (7) |
C23 | 0.0230 (8) | 0.0413 (9) | 0.0397 (9) | 0.0047 (6) | 0.0005 (7) | −0.0042 (7) |
C24 | 0.0236 (8) | 0.0463 (10) | 0.0355 (9) | −0.0018 (6) | 0.0053 (7) | −0.0075 (7) |
C25 | 0.0320 (9) | 0.0486 (10) | 0.0388 (9) | 0.0009 (7) | 0.0111 (7) | 0.0095 (8) |
C26 | 0.0300 (8) | 0.0378 (9) | 0.0418 (10) | 0.0067 (7) | 0.0114 (7) | 0.0084 (7) |
C27 | 0.0302 (9) | 0.0671 (13) | 0.0483 (11) | −0.0017 (8) | 0.0145 (8) | −0.0121 (10) |
N1—N2 | 1.3644 (18) | C7—H7 | 0.9500 |
N2—C3 | 1.346 (2) | C8—H8 | 0.9500 |
C3—C3A | 1.398 (2) | N2—C21 | 1.434 (2) |
C3A—C4 | 1.388 (2) | C3—Cl3 | 1.6993 (16) |
C4—C4A | 1.394 (2) | C21—C26 | 1.380 (2) |
C4A—C5 | 1.429 (2) | C21—C22 | 1.391 (2) |
C5—C6 | 1.357 (3) | C22—C23 | 1.385 (2) |
C6—C7 | 1.419 (3) | C22—H22 | 0.9500 |
C7—C8 | 1.358 (2) | C23—C24 | 1.393 (3) |
C8—C8A | 1.432 (2) | C23—H23 | 0.9500 |
C8A—N9 | 1.342 (2) | C24—C25 | 1.390 (3) |
N9—C9A | 1.346 (2) | C24—C27 | 1.507 (2) |
C9A—N1 | 1.349 (2) | C25—C26 | 1.384 (2) |
C3A—C9A | 1.430 (2) | C25—H25 | 0.9500 |
C4A—C8A | 1.446 (2) | C26—H26 | 0.9500 |
C4—H4 | 0.9500 | C27—H27A | 0.9800 |
C5—H5 | 0.9500 | C27—H27B | 0.9800 |
C6—H6 | 0.9500 | C27—H27C | 0.9800 |
C9A—N1—N2 | 103.40 (12) | C8—C8A—C4A | 118.05 (15) |
C3—N2—N1 | 113.60 (13) | C8A—N9—C9A | 115.12 (14) |
C3—N2—C21 | 126.87 (14) | N9—C9A—N1 | 123.20 (14) |
N1—N2—C21 | 119.52 (12) | N9—C9A—C3A | 124.38 (14) |
N2—C3—C3A | 107.30 (14) | N1—C9A—C3A | 112.41 (14) |
N2—C3—Cl3 | 124.06 (12) | C26—C21—C22 | 121.19 (15) |
C3A—C3—Cl3 | 128.59 (13) | C26—C21—N2 | 119.56 (14) |
C4—C3A—C3 | 136.66 (15) | C22—C21—N2 | 119.25 (14) |
C4—C3A—C9A | 120.04 (14) | C23—C22—C21 | 118.42 (16) |
C3—C3A—C9A | 103.30 (14) | C23—C22—H22 | 120.8 |
C3A—C4—C4A | 116.84 (15) | C21—C22—H22 | 120.8 |
C3A—C4—H4 | 121.6 | C22—C23—C24 | 121.64 (15) |
C4A—C4—H4 | 121.6 | C22—C23—H23 | 119.2 |
C4—C4A—C5 | 122.13 (16) | C24—C23—H23 | 119.2 |
C4—C4A—C8A | 119.06 (15) | C25—C24—C23 | 118.24 (15) |
C5—C4A—C8A | 118.81 (15) | C25—C24—C27 | 120.74 (17) |
C6—C5—C4A | 120.91 (17) | C23—C24—C27 | 121.02 (17) |
C6—C5—H5 | 119.5 | C26—C25—C24 | 121.16 (16) |
C4A—C5—H5 | 119.5 | C26—C25—H25 | 119.4 |
C5—C6—C7 | 120.32 (17) | C24—C25—H25 | 119.4 |
C5—C6—H6 | 119.8 | C21—C26—C25 | 119.26 (16) |
C7—C6—H6 | 119.8 | C21—C26—H26 | 120.4 |
C8—C7—C6 | 121.22 (16) | C25—C26—H26 | 120.4 |
C8—C7—H7 | 119.4 | C24—C27—H27A | 109.5 |
C6—C7—H7 | 119.4 | C24—C27—H27B | 109.5 |
C7—C8—C8A | 120.68 (17) | H27A—C27—H27B | 109.5 |
C7—C8—H8 | 119.7 | C24—C27—H27C | 109.5 |
C8A—C8—H8 | 119.7 | H27A—C27—H27C | 109.5 |
N9—C8A—C8 | 117.40 (15) | H27B—C27—H27C | 109.5 |
N9—C8A—C4A | 124.55 (14) | ||
C9A—N1—N2—C3 | 0.34 (16) | C8—C8A—N9—C9A | 179.20 (14) |
C9A—N1—N2—C21 | 179.24 (13) | C4A—C8A—N9—C9A | −0.2 (2) |
N1—N2—C3—C3A | −0.29 (17) | C8A—N9—C9A—N1 | −178.78 (14) |
C21—N2—C3—C3A | −179.08 (14) | C8A—N9—C9A—C3A | −0.4 (2) |
N1—N2—C3—Cl3 | 177.38 (11) | N2—N1—C9A—N9 | 178.30 (14) |
C21—N2—C3—Cl3 | −1.4 (2) | N2—N1—C9A—C3A | −0.27 (16) |
N2—C3—C3A—C4 | −179.33 (17) | C4—C3A—C9A—N9 | 1.1 (2) |
Cl3—C3—C3A—C4 | 3.1 (3) | C3—C3A—C9A—N9 | −178.44 (14) |
N2—C3—C3A—C9A | 0.10 (16) | C4—C3A—C9A—N1 | 179.66 (14) |
Cl3—C3—C3A—C9A | −177.43 (12) | C3—C3A—C9A—N1 | 0.11 (17) |
C3—C3A—C4—C4A | 178.21 (17) | N1—N2—C21—C22 | −53.7 (2) |
C9A—C3A—C4—C4A | −1.1 (2) | N1—N2—C21—C26 | 126.42 (16) |
C3A—C4—C4A—C5 | −178.51 (14) | C3—N2—C21—C22 | 125.08 (17) |
C3A—C4—C4A—C8A | 0.6 (2) | C3—N2—C21—C26 | −54.8 (2) |
C4—C4A—C5—C6 | 178.81 (16) | C26—C21—C22—C23 | 2.9 (2) |
C8A—C4A—C5—C6 | −0.3 (2) | N2—C21—C22—C23 | −177.01 (14) |
C4A—C5—C6—C7 | 0.6 (3) | C21—C22—C23—C24 | −0.6 (3) |
C5—C6—C7—C8 | −0.4 (3) | C22—C23—C24—C25 | −1.5 (3) |
C6—C7—C8—C8A | 0.0 (3) | C22—C23—C24—C27 | 178.15 (16) |
C7—C8—C8A—N9 | −179.12 (15) | C23—C24—C25—C26 | 1.4 (3) |
C7—C8—C8A—C4A | 0.3 (2) | C27—C24—C25—C26 | −178.25 (17) |
C4—C4A—C8A—N9 | 0.1 (2) | C22—C21—C26—C25 | −3.0 (3) |
C5—C4A—C8A—N9 | 179.25 (14) | N2—C21—C26—C25 | 176.89 (16) |
C4—C4A—C8A—C8 | −179.31 (14) | C24—C25—C26—C21 | 0.8 (3) |
C5—C4A—C8A—C8 | −0.2 (2) |
Cg1 represents the centroid of the C21–C26 ring. |
D—H···A | D—H | H···A | D···A | D—H···A |
C23—H23···N9i | 0.95 | 2.50 | 3.393 (2) | 157 |
C26—H26···N9ii | 0.95 | 2.50 | 3.449 (2) | 174 |
C27—H27A···Cg1iii | 0.98 | 2.84 | 3.653 (2) | 140 |
Symmetry codes: (i) −x, −y+1, −z+1; (ii) x, −y+1/2, z+1/2; (iii) −x, −y+1, −z+2. |
Acknowledgements
THSK thanks the authorities of Jain University for their support and encouragement. JPJ acknowledges the NSF–MRI program (grant No. 1039027) for funds to purchase the X-ray diffractometer.
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