X-ray structure, hirshfeld surfaces and interaction energy studies of 2,2-diphenyl-1-oxa-3-oxonia-2-boratanaphthalene.

Single crystal XRD structure of the title compound reveals that the molecule adopt non-planar structure. The molecule is puckered with the total puckering amplitude of (Q) = 0.368(3)Å. Crystals of the title molecules are interconnected by intermolecular O-H⋯O and C-H⋯O interactions to develop 1D chains extending infinitely along the crystallographic a-axis. The intermolecular interactions were explored by Hirshfeld surfaces and their associated fingerprint graphs are obtained which revealed that the H⋯H and H⋯C pairs of inter atomic contacts were pre-dominant in the crystal packing of title compound. The energy of intermolecular interactions are computed using the accurate energy density model of B3LYP/6-31 G(d,p).

Introduction

Boron fused tri- and tetra-coordinated molecules have found great importance for multifunctional applications such as OLEDs, bio-imaging etc. due to their wide window of electronic properties. Some of the tetra-coordinated boron chelated N, O structures have found to be highly emissive in solid state with colour tunability due to their rigid π-conjugated structures [1, 2]. Crystal structure and molecular packing play major role in the light emissive devices wherein weak π···π interactions greatly helps for enhanced emission [3]. Hence understanding the structural dynamics of the molecule is of great significance in this perspective. The literature study strongly reveals that, the organic compounds bearing hetero atoms possess significant biological activities such as anti-viral, anti-fungal, anti-cancer, etc. [4, 5, 6] Further, presence of inter-molecular interactions in the architecture of crystal packing and their co-operation with hydrogen bonding guides in the synthetic and catalytic utility. Owing to this, the intermolecular interactions present in the crystal were investigated by three dimensional Hirshfeld surfaces (3D-HS) and also their energies were evaluated using accurate energy density wavefunction of B3LYP/6-31G(d,p). With respect to all the above perspectives and in continuation of our ongoing work on structural studies, we now report the structural and Hirshfeld surface studies of the compound 2,2-diphenyl-1-oxa-3-oxonia-2-boratanaphthalene.

Procedures

Experimental

2,2-Diphenyl-1-oxa-3-oxonia-2-boratanaphthalene was synthesized according to the reported procedure [7]. 2-(diphenylboryl)ethanamine (100 mg, 0.96 mmol) was refluxed with 2-hydroxybenzaldehyde (100μL, 0.96 mmol) in 5 mL methanol for 4 h to obtain cream colour solid with 90% yield (Figure 1). Single crystals were grown in ethanol using slow evaporation method.

Figure 1

Schematic diagram of the compound 2,2-diphenyl-1-oxa-3-oxonia-2-boratanaphthalene.

Single crystal XRD

The structural and refinement details of the title compound are given in Table 1. A suitable size of block shaped single crystal was selected carefully for X-ray diffraction study. The diffraction data were collected on an Apex Bruker-II diffractometer equipped with MoKα radiation of wavelength 0.71073Å. Complete X-ray intensity data set was processed by SAINT software [8]. The crystal and molecular structure was solved by direct method using SHELXS and refined by full-matrix least squares based on F2 SHELXL [9, 10, 11]. All the non-hydrogen atoms were refined anisotropically while the hydrogen atoms were refined isotropically and placed at chemically ideal positions with isotropic displacement parameters as C–H = 0.93Å with Uiso(H) = 1.2Ueq(C) for aromatic rings and O–H = 0.82Å with Uiso(H) = 1.5Ueq(O). The molecular and packing diagram were generated using the MERCURY [12] while PLATON software was used to obtain geometric parameters viz., bond distances, inter-bond angles and torsional angles [13, 14]

Table 1

Crystal, structural and refinement statistics.

CCDC	2064704
Chemical formula	C21H19BNO2
Mr	328.18
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	290
a, b, c, β (Å,°)	9.1024(6), 17.8682(15), 10.9790(9), 96.933(2)
V (Å−3), Z	1772.6(2), 4
Radiation type	MoKα
μ (mm−1)	0.08
Crystal size (mm)	0.40 × 0.36 × 0.31
Diffractometer	APEX (Bruker, 2006)
No. of measured, independent and observed reflections	22044, 3649, 1990
Rint	0.05
(sin θ/λ)max (Å−1)	0.627
Goodness-of-Fit (S)	1.048
R[F2 > 2σ(F2)], wR(F2), S	0.0632, 0.2065, 1.048
No. of reflections	3649
No. of parameters	226
Data/Restraints/Parameters	3649/0/226
H-atom treatment	H-atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (eÅ−3)	0.55, -0.34
Index ranges	h = -11→10, k = -22→22, l = -13→13
Theta range (°)	Θmax = 25.2, θmin = 2.2

Computational studies

Three dimensional Hirshfeld surfaces (3D-HS) mapped on both dnorm and electrostatic potentials (ESP), and their associated two dimensional fingerprint graphs are carried out making use of Crystal Explorer 17.5 software and to compute three dimensional interaction energies [15, 16, 17, 18, 19, 20]

Results and discussions

Structural commentary

The molecular structure of the title compound consists of a ten-membered heterocyclic ring [O1–B1–N1–C1/C7] and two phenyl rings [C10/C15] and [C16/C21] which are interlinked such that to have a non-coplanar view, and an -ethoxy group as an extended conformation as given in thermal ellipsoids drawn at 50% probability (Figure 2). The ten-membered ring [O1–B1–N1–C1/C7] displayed a puckering environment at B1 with the total puckering amplitude (Q) of 0.368 (3)Å and displayed a half-chair conformation. The pseudorotation (θ) and the relative phase (φ) angles are 114.0(3)° and 136.6 (4)° respectively [21, 22]

Figure 2

Thermal ellipsoids of a title molecule at 50% of probability.

In the molecule, the mean planes of phenyl rings [(C10/C15) and (C16/C21)] are inclined with the dihedral angle of 77.05 (1)°. The central ten-membered ring (O1–B1–N1–C1/C7) makes the dihedral angle of 85.65(12)° and 87.55(1)° with the mean planes of phenyl rings (C10/C15) and (C16/C21) respectively, which reveals that the rings exhibits nearly an orthogonal relation to each other. The chain, N1–C8–C9–O2 adopts a -syn-clinal conformation with the torsional angle of -75.27°. The bond lengths and inter-bond angle values agree with the standard values [23, 24, 25, 26, 27, 28, 29].

Crystal packing

The crystal of the titled molecule are governed by an intermolecular O2–H2⋯O1 and C14–H14⋯O2 interactions (Table 2), to develop an independent 1D polymeric chains propagating indefinitely along crystallographic a-axis, as depicted in Figure 3. In addition to this, the titled molecule also comprise an intra-molecular C7–H7⋯O2 interaction, incorporating a self-assembly closed S(6) loop.

Table 2

Hydrogen bonding geometry (Å,°).

Interaction	D-H...A	d(H...A)	d(D...A)	Angle (D-H...A)	Symmetry code
Intra-molecular	C7–H7⋯O2	2.30	2.970(4)	129
Intermolecular	O2–H2⋯O1	2.08	2.900(3)	176	-1/2+x,1/2-y,1/2+z
	C14–H14⋯O2	2.52	3.363(4)	152	1+x,y,z

Figure 3

Packing of the title molecules when it is viewed along crystallographic a-axis.

Computational analysis

The volume of 3D-HS mapped on dnorm (Figure 4) and electrostatic potential (Figure 5) are 369.88Å2 and 435.97Å3 respectively, with the colour scales of [−0.5324 a.u (red) and +1.4509 a.u (blue)], and [−0.1112 a.u (red) and +0.1478 a.u (blue)] respectively. The surfaces are given in transparent mode to understand the position of all the elements and the functional groups available in the molecule. The dnorm furnishes both the donor and acceptor regions of hydrogen bonding interactions by forming red colour circular spots on its surface with equal brightness.

Figure 4

Front (a) and rear (b) views of Hirshfeld surface mapped on dnorm.

Figure 5

Front (a) and rear (b) views of HS mapped on electrostatic potentials.

For instance, the donor and acceptor regions of intermolecular O2–H2⋯O1 interaction can be viewed on the front and rear views of dnorm surfaces, given in Figures 4 a and b respectively. In Figure 4a the red spot surrounding O2–H2 and at the vicinity of O1 in Figure 4b are the indicators of donor and acceptor regions of O2–H2⋯O1 interaction (Table 2) [30, 31, 32, 33]. This is also substantiated by electrostatic potentials (Fig. 5a and b are front and rear views) by reflecting intense blue coloured patch around O2–H2, while the red coloured patch around O1 represents the electrostatic positive donor and negative acceptor potentials respectively. These electrostatic interactions serve as an important tool in the binding of protein targets [34].

The two-dimensional fingerprint graphs were generated in an expanded mode for all the major contacts, and it is delineated in Figure 6. Total contribution from all the pairs of inter atomic contacts is given in Figure 6(a). The highest contribution is represented by a pair of H⋯H inter atomic contacts with 60.9%, reflected as a pair of blue coloured spoke like pattern, merged almost in the middle of the graph at de + di = 1.1Å Figure 6(b). The 29.9% of contribution was made to the Hirshfeld surface from H⋯C pair of inter atomic contacts producing a pair of unique blue coloured wings between the region of 1.12Å<(de + di) < 1.72Å Figure 6(c). The pair of H⋯O inter atomic contacts represents only 7.9% of total contribution which is emerged as a characteristic sharp spikes over the region of 0.79 Å<(de + di) < 1.18Å Figure 6(d). Presence of H⋯O and H⋯C contacts correlates with the intermolecular interactions given in Table 2. Lastly, the C⋯C inter atomic contacts comprise only 2.2% to the crystal packing which is observed as an arrowhead pattern in the region of de + di ≈ 1.70Å pointing diagonally left downwards Figure 6(e). Overall study of fingerprint graphs reveals that the pair of H⋯H and H⋯C inter atomic contacts are the predominant ones. While H⋯O and C⋯C contacts are less significant in the formation of a three dimensional Hirshfeld surface.

Figure 6

Two dimensional fingerprints graphs for the title compound. The di and de along x and y represents the nearest adjacent nuclei internal and external from the three dimensional Hirshfeld surface. (a) Total contribution, (b) H⋯H (c) H⋯C (d) H⋯O and (e) C⋯C inter atomic contacts.

Three-dimensional interaction energies were computed for the title compound using the CrystalExplorer17.5 software [35, 36]. Interaction energy was calculated using an accurate energy density model of B3LYP/6-31G(d,p), during the calculation a cluster of seventeen molecules (comprising a total of 748 atoms) of various colour coding scheme from different Cartesian co-ordinates were surrounding the original one (showed by black coloured ball and stick model) within the default radius of 3.8Å. The total interaction energy (Etot) in the energy framework have been classified into classic electrostatic (Eele), polarization (Epol), dispersion (Edis) and exchange repulsion (Erep) energies [37].

Further, in the generation of electrostatic, dispersion and total energy frameworks, the tube size of 50 and threshold cut-off energy level of 10 kJ/mol were maintained. The Coloumbic (Eele) energy terms are represented by red coloured solid cylinders (Figure 7), and green coloured solid cylinders in the construction of dispersion energy (Etot) frameworks given in Figure 8. The total energy (Etot) terms are constructed by using the blue coloured solid cylinders (Figure 9). In each of the energy profile the difference in thickness of solid cylinders reveals the relative strength of interaction with the constituent members of a cluster [38, 39], and plays an important role in the integrity of a crystal packing. Also, the red- and orange-coloured dashed lines in all the energy profiles reveal the molecules involved in the hydrogen bonding interactions given in Table 2. The total interacting energies in the cluster of title compound are given in component form (Table 3). Accordingly, the highest total interaction energy (Etot = -67.6 kJ/mol from all the components) was noticed with a pair of symmetric pale-green coloured molecules interacting at the centroid distance of R = 7.76Å which correlates with the intermolecular O2–H2⋯O1 interaction. The total interaction energy (Etot = -18.2 kJ/mol) associated with an intermolecular C14–H14⋯O2 interaction confirms with the red coloured molecules at the centroid distance of R = 9.10Å. The least total interaction energy was observed as Etot = -1.8 kJ/mol associated with a couple of pink coloured molecules having the longest molecular centroid distance of R = 13.14Å. Further, the total energy from all the components in a cluster, the dispersion energy (Edis) terms were dominated over the other terms as observed in the reported compounds [40, 41, 42]. Further, the total interaction energies are varying with the molecular centroid distances obeying the laws of electrostatics.

Figure 7

Three-dimensional interaction energy profile for Coloumbic (Eele) terms generated with the tube size of 50 and cut-off energy of 10 kJ/mol for clarity purpose.

Figure 8

Three-dimensional interaction energy profile for dispersion (Edis) terms generated with the tube size of 50 and cut-off energy of 10 kJ/mol for clarity purpose.

Figure 9

Three-dimensional interaction energy profile for total energy (Etot) terms generated with the tube size of 50 and cut-off energy of 10 kJ/mol for clarity purpose.

Table 3

Three-dimensional interaction energies (kJ/mol) in component form for the title compound for electron density B3LYP/6-31G(d,p). Colour code: Colour coding scheme of molecules, N: Number of interacting molecules with the reference one, Symop: Rotational symmetry operator, R: Molecular centroid distance. Scale factor: E= kx E+ kx E+ kx E+ kx E Mackenzie et al. [43].

Conclusion

The title compound is crystallized in a monoclinic system with P21/n space group. The molecular structure of the compound was puckered at B1 and adopts half-chair conformation. The packing of molecules were governed by intra- and intermolecular C–H⋯O and O–H⋯O interactions and, they are explored by three dimensional Hirshfeld surfaces and fingerprint calculations, revealing that the H⋯H and H⋯C pairs of inter atomic contacts have made the significant contribution towards the formation of three dimensional Hirshfeld surfaces. The interaction energy calculations reveal -67.6 kJ/mol is the highest total interaction energy (from all the components) associated with an intermolecular O2–H2⋯O1 interaction. Further, in the energy frameworks, in each case the dispersion energy Edis term dominated over other components obeying laws of electrostatics.

Declarations

Author contribution statement

N. R. Sreenatha: Analyzed and interpreted the data; Wrote the paper.

D. P. Ganesha: Contributed reagents, materials, analysis tools or data.

A. S. Jeevan Chakravarthy, B. N. Lakshminarayana: Conceived and designed the experiments.

B Suchithra: Performed the experiments.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability statement

Data associated with this study has been deposited at CCDC under the accession number 2064704.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.

Specification Table

Subject area	X-ray crystallography
Compound	2,2-Diphenyl-1-oxa-3-oxonia-2-boratanaphthalene
Data category	Crystallographic data
Data acquisition format	CIF
Data type	Analysed
Procedure	Crystal structure determination, interpretation and computational analysis
Data accessibility	CCDC: 2064704