research communications
and Hirshfeld-surface analysis of a monoclinic polymorph of 2-amino-5-chlorobenzophenone oxime at 90 K
aDepartment of Studies in Chemistry, University of Mysore, Manasagangotri, Mysuru-570 006, India, bDepartment of Chemistry, Government Science College, Hassan-573 201, India, cT. John Institute of Technology, Bengaluru-560 083, India, and dDepartment of Chemistry, University of Kentucky, Lexington, KY, 40506-0055, USA
*Correspondence e-mail: yathirajan@hotmail.com
The synthesis and 13H11ClN2O, are presented. The molecular conformation results from twisting of the phenyl and 2-amino-5-chloro benzene rings attached to the oxime group, which subtend a dihedral angle of 80.53 (4)°. In the crystal, centrosymmetric dimers are formed as a result of pairs of strong O—H⋯N hydrogen bonds. A comparison is made to a previously known triclinic polymorph, including differences in atom–atom contacts obtained via a Hirshfeld-surface analysis.
of a monoclinic polymorph of 2-amino-5-chlorobenzophenone oxime, CKeywords: crystal structure; benzophenone oxime; polymorph; Hirshfeld surface.
CCDC reference: 2265648
1. Chemical context
2-Amino-5-chlorobenzophenone is an ecologically friendly cross-linking agent. Benzophenone and related compounds have been reported to act as anti-allergic, anti-inflammatory, anti-asthmatic, and anti-anaphylactic agents (Evans et al., 1987; Wiesner et al., 2002; Sieron et al., 2004). Benzophenone derivatives are widely used in sunscreen lotions, offering UV-A and UV-B protection (Deleu et al., 1992). 2-Amino-5-chlorobenzophenone is used to produce intermediates for the synthesis of oxazolam drugs and intermediates for psychotherapeutic agents, such as chlorodiazepoxide and diazepam (Sternbach & Reeder, 1961a,b). 2-Aminobenzophenone and its derivatives have importance because of their applications in heterocyclic synthesis and medicines (Walsh, 1980) and are also used as anti-mitotic agents (Liou et al., 2002). The growth and characterization of 2-amino-5-chlorobenzophenone single crystals was reported by Mohamed et al. (2007). Synthesis, herbicidal evaluation and structure–activity relationships of some benzophenone oxime ether derivatives was reported by Ma et al. (2015). The synthesis, physicochemical, and biological evaluation of 2-amino-5-chlorobenzophenone derivatives as potent skeletal muscle relaxants was reported by Singh et al. (2015). Details of synthetic methodologies and the pharmacological significance of 2-aminobenzophenones as versatile building blocks was published by Chaudhary et al. (2018). The reactivity of for diverse methodologies and synthetic applications was recently reported by Rykaczewski et al. (2022). In view of the general importance of benzophenone derivatives and those of 2-amino-5-chlorobenzophenone in particular, this paper reports the 90 K and Hirshfeld-surface studies of a monoclinic form of 2-amino-5-chlorobenzophenone oxime, C13H11ClN2O, mon-2A-5CBO. A triclinic polymorph was recently published as a CSD communication (refcode REZSIB) by Lanzilotto, Housecroft et al. (2018). Some comparisons between the two crystal structures are presented.
2. Structural commentary
The overall conformation of the mon-2A-5CBO molecule (Fig. 1) is determined by torsion angles about the C6—C7 and C7—C8 bonds that connect the chloroaniline and phenyl rings to the oxime carbon, C7. These are held in check by an intra-molecular hydrogen bond, N1—H1NA⋯O1 [dD⋯A = 2.8875 (19) Å, Table 1]. These torsion angles result in a dihedral angle between the two rings of 80.53 (4)°. The conformation defining torsion and dihedral angles are gathered in Table 2 along with those of the triclinic polymorph, REZSIB (Lanzilotto, Housecroft et al., 2018). The conformations of the 2A-5CBO molecules in the two polymorphs are quite similar, as shown by the overlay plot in Fig. 2. The r.m.s. deviation obtained from a weighted least-squares fit of all non-hydrogen atoms using OFIT in SHELXTL-XP (Sheldrick, 2008) is only 0.1315 Å, with the largest deviation being 0.267 Å for C12.
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3. Supramolecular features
The main supramolecular constructs in the mon-2A-5CBO are R22(6) centrosymmetric dimers that result from pairs (O1—H1O⋯N2inv and O1inv—H1Oinv⋯N2, inv = 1 − x, 1 − y, 1 − z) of strong hydrogen bonds [dD⋯A = 2.7411 (16) Å, Table 1]. These are shown as dashed lines in Fig. 3 along with a representation of the Hirshfeld surface, as generated by CrystalExplorer (Spackman et al., 2021), on which the hydrogen bonds are responsible for the prominent red spots. Similar dimer motifs are present in REZSIB. The most striking difference in packing between the two polymorphs is that REZSIB exhibits slip-stacked π–π overlap [interplanar separation = 3.340 (2) Å, centroid–centroid distance = 3.897 (2) Å] of inversion-related (1 − x, −y, 1 − z) chloroaniline rings, whereas mon-2A-5CBO does not. Hirshfeld surface 2D-fingerprint plots for mon-2A-5CBO are shown in Fig. 4 and the differences in contacts between the polymorphs are summarized in Table 3.
4. Database survey
A survey of the Cambridge Structural Database (CSD: v5.43 including all updates through November 2022; Groom et al., 2016) returned 5507 hits for a search fragment consisting of unsubstituted benzophenone. A search using benzophenone oxime as the probe, however, returned only 35 entries. Of these, ten have a nitrogen-bound at the ortho-position of one of the benzene rings, while six have `any halogen' attached at one of the meta-positions. In only two structures is this halogen a chlorine atom: YIFCIC (Lanzilotto, Prescimone et al., 2018), C15H11Cl2FN2O2, 2-chloro-N-{4-chloro-2-[(2-fluorophenyl)(hydroxyimino)methyl]phenyl}acetamide and REZSIB (Lanzilotto, Housecroft et al., 2018), the triclinic (P) polymorph of the monoclinic (P21/n) 2A-5CBO described herein.
Some other related crystal structures include 2-amino-5-chlorobenzophenone as monoclinic (NUVFAL; Vasco-Mendez et al., 1996) and triclinic (NUVFAL02; Javed et al., 2018) polymorphs, benzophenone oxime (XULKUK; Sharutin et al., 2002), and 2-benzoyloxy-5-methylbenzophenone (OCAMOV; Sieron et al., 2004).
5. Synthesis and crystallization
The synthesis of 2A-5CBO (Fig. 5) was by a modification of Beckmann's conversion of benzophenone to benzophenone oxime (Beckmann, 1886). In a 100 ml round-bottom flask fitted with a magnetic stirrer was placed a mixture of 100 mmol (23.2 g) of 2-amino-5-chlorobenzophenone, 120 mmol (7 g) of hydroxylamine hydrochloride in 10 ml of ethanol. To this stirred mixture, 0.5 g of sodium hydroxide pellets was added in small portions. When the reaction became vigorous, the flask was placed in an ice bath. A condenser was attached to the flask and the mixture was refluxed for 5 minutes on a steam bath. The solution was cooled and poured into a beaker containing 5 ml of hydrochloric acid and crushed ice. This was stirred until a precipitate formed. After filtering the precipitate with suction and washing with cold distilled water, the product was spread out on filter paper and air dried. The yield was 87%. X-ray quality crystals were obtained from methanol by slow evaporation (m.p.: 390–393 K).
6. Refinement
Crystal data, data collection and structure . All hydrogen atoms were found in difference-Fourier maps. Those bound to carbon were subsequently included in the using a riding model, with constrained distances fixed at 0.95 Å and Uiso(H) values set to 1.2Ueq of the attached atom. The amine and oxime hydrogen atoms were refined freely.
details are summarized in Table 4
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Supporting information
CCDC reference: 2265648
https://doi.org/10.1107/S2056989023004668/tx2069sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989023004668/tx2069Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989023004668/tx2069Isup3.cml
Data collection: APEX3 (Bruker, 2016); cell
APEX3 (Bruker, 2016); data reduction: APEX3 (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2019/2 (Sheldrick, 2015b); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELX (Sheldrick, 2008) and publCIF (Westrip, 2010)'.C13H11ClN2O | F(000) = 512 |
Mr = 246.69 | Dx = 1.405 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 12.8264 (3) Å | Cell parameters from 9975 reflections |
b = 5.5423 (1) Å | θ = 2.5–27.5° |
c = 17.4082 (4) Å | µ = 0.31 mm−1 |
β = 109.522 (1)° | T = 90 K |
V = 1166.37 (4) Å3 | Semi-regular block, pale yellow |
Z = 4 | 0.30 × 0.24 × 0.02 mm |
Bruker D8 Venture dual source diffractometer | 2680 independent reflections |
Radiation source: microsource | 2294 reflections with I > 2σ(I) |
Detector resolution: 7.41 pixels mm-1 | Rint = 0.042 |
φ and ω scans | θmax = 27.5°, θmin = 2.4° |
Absorption correction: multi-scan (SADABS; Krause et al., 2015) | h = −16→16 |
Tmin = 0.924, Tmax = 0.971 | k = −7→7 |
26003 measured reflections | l = −22→22 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.033 | Hydrogen site location: mixed |
wR(F2) = 0.083 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.05 | w = 1/[σ2(Fo2) + (0.0334P)2 + 0.6832P] where P = (Fo2 + 2Fc2)/3 |
2680 reflections | (Δ/σ)max = 0.001 |
166 parameters | Δρmax = 0.32 e Å−3 |
0 restraints | Δρmin = −0.27 e Å−3 |
Experimental. The crystal was mounted using polyisobutene oil on the tip of a fine glass fibre, which was fastened in a copper mounting pin with electrical solder. It was placed directly into the cold gas stream of a liquid-nitrogen based cryostat (Hope, 1994; Parkin & Hope, 1998). Diffraction data were collected with the crystal at 90K, which is standard practice in this laboratory for the majority of flash-cooled crystals. |
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 | ||
Cl1 | 0.63274 (3) | 0.54249 (7) | 0.94134 (2) | 0.03072 (12) | |
O1 | 0.58250 (8) | 0.6496 (2) | 0.57328 (6) | 0.0249 (2) | |
H1O | 0.5830 (17) | 0.572 (4) | 0.5245 (14) | 0.055 (6)* | |
N1 | 0.58120 (12) | 1.1196 (3) | 0.64451 (9) | 0.0292 (3) | |
H1NA | 0.5690 (15) | 1.042 (4) | 0.5962 (12) | 0.037 (5)* | |
H1NB | 0.6301 (17) | 1.238 (4) | 0.6523 (12) | 0.045 (6)* | |
N2 | 0.47023 (9) | 0.6201 (2) | 0.56650 (7) | 0.0198 (3) | |
C1 | 0.59550 (11) | 0.9785 (3) | 0.71326 (9) | 0.0203 (3) | |
C2 | 0.66473 (11) | 1.0555 (3) | 0.79012 (9) | 0.0235 (3) | |
H2 | 0.705557 | 1.200830 | 0.794290 | 0.028* | |
C3 | 0.67496 (11) | 0.9256 (3) | 0.85971 (9) | 0.0223 (3) | |
H3 | 0.720922 | 0.983038 | 0.911337 | 0.027* | |
C4 | 0.61783 (11) | 0.7109 (3) | 0.85389 (8) | 0.0197 (3) | |
C5 | 0.54751 (10) | 0.6311 (3) | 0.77926 (8) | 0.0172 (3) | |
H5 | 0.507391 | 0.485190 | 0.776017 | 0.021* | |
C6 | 0.53533 (10) | 0.7638 (3) | 0.70891 (8) | 0.0165 (3) | |
C7 | 0.45154 (10) | 0.6753 (2) | 0.63216 (8) | 0.0165 (3) | |
C8 | 0.33591 (10) | 0.6438 (2) | 0.63101 (7) | 0.0156 (3) | |
C9 | 0.29101 (11) | 0.8182 (3) | 0.66846 (8) | 0.0189 (3) | |
H9 | 0.335250 | 0.950014 | 0.695888 | 0.023* | |
C10 | 0.18202 (11) | 0.8003 (3) | 0.66587 (9) | 0.0226 (3) | |
H10 | 0.151395 | 0.920969 | 0.690712 | 0.027* | |
C11 | 0.11782 (11) | 0.6062 (3) | 0.62701 (9) | 0.0229 (3) | |
H11 | 0.043042 | 0.594435 | 0.624967 | 0.028* | |
C12 | 0.16249 (12) | 0.4292 (3) | 0.59117 (9) | 0.0226 (3) | |
H12 | 0.118668 | 0.294962 | 0.565375 | 0.027* | |
C13 | 0.27141 (11) | 0.4477 (3) | 0.59285 (8) | 0.0189 (3) | |
H13 | 0.301768 | 0.326585 | 0.567964 | 0.023* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Cl1 | 0.0381 (2) | 0.0335 (2) | 0.01636 (17) | −0.00308 (17) | 0.00354 (14) | 0.00155 (15) |
O1 | 0.0139 (5) | 0.0399 (7) | 0.0236 (5) | −0.0007 (4) | 0.0097 (4) | −0.0040 (5) |
N1 | 0.0323 (7) | 0.0244 (7) | 0.0325 (7) | −0.0064 (6) | 0.0128 (6) | 0.0057 (6) |
N2 | 0.0127 (5) | 0.0282 (7) | 0.0205 (6) | 0.0008 (5) | 0.0081 (4) | 0.0002 (5) |
C1 | 0.0172 (6) | 0.0191 (7) | 0.0269 (7) | 0.0009 (5) | 0.0105 (5) | 0.0007 (6) |
C2 | 0.0178 (6) | 0.0199 (7) | 0.0342 (8) | −0.0042 (6) | 0.0107 (6) | −0.0058 (6) |
C3 | 0.0149 (6) | 0.0262 (8) | 0.0247 (7) | −0.0012 (5) | 0.0051 (5) | −0.0081 (6) |
C4 | 0.0177 (6) | 0.0235 (7) | 0.0176 (6) | 0.0017 (5) | 0.0057 (5) | −0.0005 (5) |
C5 | 0.0142 (6) | 0.0178 (7) | 0.0200 (6) | −0.0010 (5) | 0.0063 (5) | −0.0023 (5) |
C6 | 0.0132 (6) | 0.0182 (7) | 0.0192 (6) | 0.0009 (5) | 0.0069 (5) | −0.0019 (5) |
C7 | 0.0158 (6) | 0.0167 (7) | 0.0172 (6) | 0.0018 (5) | 0.0060 (5) | 0.0020 (5) |
C8 | 0.0153 (6) | 0.0188 (7) | 0.0135 (6) | 0.0016 (5) | 0.0057 (5) | 0.0029 (5) |
C9 | 0.0194 (6) | 0.0191 (7) | 0.0191 (6) | −0.0007 (5) | 0.0077 (5) | −0.0010 (5) |
C10 | 0.0209 (7) | 0.0246 (8) | 0.0260 (7) | 0.0029 (6) | 0.0128 (6) | −0.0001 (6) |
C11 | 0.0158 (6) | 0.0295 (8) | 0.0248 (7) | −0.0003 (6) | 0.0086 (5) | 0.0053 (6) |
C12 | 0.0211 (7) | 0.0240 (8) | 0.0216 (7) | −0.0059 (6) | 0.0055 (5) | 0.0002 (6) |
C13 | 0.0207 (6) | 0.0197 (7) | 0.0171 (6) | 0.0003 (5) | 0.0073 (5) | 0.0001 (5) |
Cl1—C4 | 1.7409 (14) | C5—H5 | 0.9500 |
O1—N2 | 1.4145 (14) | C6—C7 | 1.4903 (18) |
O1—H1O | 0.95 (2) | C7—C8 | 1.4869 (17) |
N1—C1 | 1.3894 (19) | C8—C13 | 1.3927 (19) |
N1—H1NA | 0.91 (2) | C8—C9 | 1.3937 (19) |
N1—H1NB | 0.89 (2) | C9—C10 | 1.3871 (18) |
N2—C7 | 1.2809 (17) | C9—H9 | 0.9500 |
C1—C2 | 1.402 (2) | C10—C11 | 1.386 (2) |
C1—C6 | 1.4065 (19) | C10—H10 | 0.9500 |
C2—C3 | 1.377 (2) | C11—C12 | 1.385 (2) |
C2—H2 | 0.9500 | C11—H11 | 0.9500 |
C3—C4 | 1.383 (2) | C12—C13 | 1.3913 (19) |
C3—H3 | 0.9500 | C12—H12 | 0.9500 |
C4—C5 | 1.3834 (18) | C13—H13 | 0.9500 |
C5—C6 | 1.3920 (19) | ||
N2—O1—H1O | 100.5 (13) | C1—C6—C7 | 123.03 (12) |
C1—N1—H1NA | 117.7 (13) | N2—C7—C8 | 116.31 (12) |
C1—N1—H1NB | 113.8 (13) | N2—C7—C6 | 125.78 (12) |
H1NA—N1—H1NB | 112.5 (17) | C8—C7—C6 | 117.90 (11) |
C7—N2—O1 | 112.76 (11) | C13—C8—C9 | 119.48 (12) |
N1—C1—C2 | 120.65 (14) | C13—C8—C7 | 121.94 (12) |
N1—C1—C6 | 121.17 (13) | C9—C8—C7 | 118.58 (12) |
C2—C1—C6 | 118.03 (13) | C10—C9—C8 | 120.30 (13) |
C3—C2—C1 | 121.59 (13) | C10—C9—H9 | 119.9 |
C3—C2—H2 | 119.2 | C8—C9—H9 | 119.9 |
C1—C2—H2 | 119.2 | C11—C10—C9 | 119.97 (13) |
C2—C3—C4 | 119.53 (13) | C11—C10—H10 | 120.0 |
C2—C3—H3 | 120.2 | C9—C10—H10 | 120.0 |
C4—C3—H3 | 120.2 | C12—C11—C10 | 120.11 (13) |
C3—C4—C5 | 120.47 (13) | C12—C11—H11 | 119.9 |
C3—C4—Cl1 | 119.77 (11) | C10—C11—H11 | 119.9 |
C5—C4—Cl1 | 119.76 (11) | C11—C12—C13 | 120.14 (13) |
C4—C5—C6 | 120.23 (13) | C11—C12—H12 | 119.9 |
C4—C5—H5 | 119.9 | C13—C12—H12 | 119.9 |
C6—C5—H5 | 119.9 | C12—C13—C8 | 119.98 (13) |
C5—C6—C1 | 120.10 (12) | C12—C13—H13 | 120.0 |
C5—C6—C7 | 116.75 (12) | C8—C13—H13 | 120.0 |
N1—C1—C2—C3 | 176.07 (13) | C1—C6—C7—N2 | 60.8 (2) |
C6—C1—C2—C3 | 0.5 (2) | C5—C6—C7—C8 | 55.87 (17) |
C1—C2—C3—C4 | 1.5 (2) | C1—C6—C7—C8 | −120.15 (14) |
C2—C3—C4—C5 | −2.5 (2) | N2—C7—C8—C13 | 39.36 (18) |
C2—C3—C4—Cl1 | 178.60 (11) | C6—C7—C8—C13 | −139.76 (13) |
C3—C4—C5—C6 | 1.4 (2) | N2—C7—C8—C9 | −139.76 (13) |
Cl1—C4—C5—C6 | −179.73 (10) | C6—C7—C8—C9 | 41.12 (17) |
C4—C5—C6—C1 | 0.7 (2) | C13—C8—C9—C10 | −1.7 (2) |
C4—C5—C6—C7 | −175.41 (12) | C7—C8—C9—C10 | 177.41 (12) |
N1—C1—C6—C5 | −177.17 (13) | C8—C9—C10—C11 | 1.0 (2) |
C2—C1—C6—C5 | −1.63 (19) | C9—C10—C11—C12 | 0.4 (2) |
N1—C1—C6—C7 | −1.3 (2) | C10—C11—C12—C13 | −1.1 (2) |
C2—C1—C6—C7 | 174.25 (12) | C11—C12—C13—C8 | 0.3 (2) |
O1—N2—C7—C8 | −178.54 (11) | C9—C8—C13—C12 | 1.05 (19) |
O1—N2—C7—C6 | 0.5 (2) | C7—C8—C13—C12 | −178.07 (12) |
C5—C6—C7—N2 | −123.16 (15) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1NA···O1 | 0.91 (2) | 2.23 (2) | 2.8875 (19) | 128.7 (16) |
O1—H1O···N2i | 0.95 (2) | 1.84 (2) | 2.7411 (16) | 156.4 (19) |
Symmetry code: (i) −x+1, −y+1, −z+1. |
mon-2A-5CBO | REZSIBa,b | |
Torsion angle | ||
N1—C1—C6—C7 | -1.3 (2) | -5.6 |
C1—C6—C7—N2 | 60.8 (2) | 56.7 |
C6—C7—N2—O1 | 0.5 (2) | 7.8 |
Dihedral angle | ||
C1–C6/C8–C13 | 80.53 (4) | 75.82 |
Notes: (a) The numbering scheme in REZSIB is different from mon-2A-5CBO; (b) Values from Mercury (Macrae et al., 2020), therefore there are no SUs. |
Atom contactsa | mon-2A-5CBO | REZSIB |
H···H | 38.6 | 43.6 |
H···C | 27.1 | 17.6 |
H···Cl | 15.8 | 13.6 |
H···N | 7.8 | 8.8 |
H···O | 5.1 | 6.4 |
C···Cl | 4.4 | 6.0 |
C···C | 0.0 | 3.9 |
Note: (a) Includes reciprocal contacts. All other contact percentages are negligible. |
Acknowledgements
DG is grateful to DOS in Chemistry, University of Mysore for providing research facilities. HSY thanks UGC for a BSR Faculty fellowship for three years.
Funding information
Funding for this research was provided by: National Science Foundation, Directorate for Mathematical and Physical Sciences (award No. CHE-1625732 to SP).
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