Structure description of I
The title compound, I is crystalized in the triclinic crystal system with the Pī space group. A single molecule is present in the asymmetric unit of I. The ORTEP view of the asymmetric unit of I with an atom numbering scheme is illustrated in Fig. 1. The crystal data and crystallographic refinement statistics are summarized in Table 1. The two carbon and the oxygen atoms of the acetyl groups (atoms C7, C8, O3, and C9, C10, O4) are nearly co-planar with the central phenyl ring in I. This is witnessed by the dihedral angle between the central phenyl ring and each of the two mean planes of acetyl groups is 3.65 (5)ο and 8.36 (3)ο.
Table 1
The crystal data and refinement parameters for I
Parameters | I |
CCDC number | 2260315 |
Empirical formula | C10 H5 Br5 O4 |
Formula weight | 588.69 |
Wavelength (Ǻ) | 0.71073 |
Crystal system and Space group | Triclinic and Pī |
a (Ǻ) | 9.3626(2) |
b (Ǻ) | 30.7365(7) |
c (Ǻ) | 6.9825(1) |
α (°) | 85.495 (5) |
β (°) | 89.306(5) |
γ (°) | 68.859(4) |
V (Ǻ3) | 713.7(3) |
Z | 2 |
Calculated density (Mg/m3) | 1.394 |
Absorption (mm− 1) | 14.08 |
F(0 0 0) | 544 |
Crystal size (mm) | 0.247× 0.223 ×0.161 |
θ (°) | 1.8–30.1 |
Limiting indices, h | −10≤ h ≥ 10 |
k | −13 ≤ k ≥ 13 |
l | −15 ≤ l ≥ 15 |
Reflections collected/unique (Rint) | 148050/4127 |
(θ °) Completeness (%) | 25.42, 99.9 |
Refinement method | full-matrix least-squares on F2 |
Data/restraints/parameters | 4127/0/176 |
Goodness-of-fit (GOF) onF2 | 1.039 |
Final R indices [I > 2σ(I)] | R1 = 0.0400 |
| wR2 = 0.0944 |
R indices (all data) | R1 = 0.0629 |
| wR2 = 0.1031 |
Largest difference in peak and hole (e A− 3) | 1.232 and − 1.053 |
To compare the geometric parameters of I with related crystal structure reported in Cambridge Structural Database (CSD, Version 5.43, last update Mar 2022)(Groom et al. 2016), a search was made with the 4, 6-diacetylresorcinol skeleton in the CSD using Conquest module (Bruno et al. 2002). It gave 18 hits along with two polymorphic forms of 4, 6-diacetylresorcinol (CSD reference code: VOXPED and VOXPED01). Further, to understand the geometrical difference in the title compound I, the geometric parameters of two polymorphs (VOXPED and VOXPED01) are compared with I. There is a small deviation in geometric parameters seemed between I and two polymorphs (VOXPED and VOXPED01). Particularly, the Ccarbonyl–Cmethyl bond length (C7–C8:1.524 (6); C9–C10:1.523 (6) Å) is slightly longer in I when compared with two polymorphs and it falls at 1.461(VOXPED), 1.469 (VOXPED01)Å, respectively. On the other hand, the bond lengths of Caromatic–Ccarbonyl and C = O in acetyl groups in I and two polymorphs (VOXPED and VOXPED01) are comparable with each other. This slight bond length change in the Ccarbonyl–Cmethyl bond might be due to steric hindrance and the electronic effect of two substituted bromine atoms in the acetyl group. Furthermore, the structural optimization calculation was performed in the gas phase using the X-ray geometry as an initial model. The M06-2X/cc-pVTZ level of theory [40, 41] along with the incorporation of Grimme’s D3 dispersion correction [42] was used. Vibrational frequencies were computed for the optimized structures to confirm the proper convergence to energy minima on their respective potential energy surfaces. No imaginary frequency was observed for the optimized structure.
Table 2
Comparison of selected geometric parameters between X-ray and DFT calculation.
Atoms | Bond length, Å | Atoms | Bond angle, θ |
| X-ray | DFT | | X-ray | DFT |
Br1—C1 | 1.884(4) | 1.875 | C5—C9—C10 | 119.2 (3) | 118.2 |
Br2—C10 | 1.917(5) | 1.917 | C9—C10—Br2 | 118.8 (3) | 111.8 |
Br3—C10 | 1.933(5) | 1.944 | C9—C10—Br3 | 108.2 (3) | 107.0 |
Br4—C8 | 1.928(5) | 1.934 | Br2—C10—Br3 | 110.5 (2) | 112.2 |
Br5—C8 | 1.931(6) | 1.939 | Atoms | Torsion angle, θ |
O1—C6 | 1.335(5) | 1.318 | | X-ray | DFT |
O2—C2 | 1.334(6) | 1.319 | C6—C1—C2—O2 | -179.6 (3) | 179.8 |
O3—C7 | 1.231(6) | 1.221 | Br1—C1—C2—O2 | 1.7 (5) | -0.2 |
O4—C9 | 1.224(4) | 1.215 | C6—C1—C2—C3 | 0.6 (6) | -0.4 |
C1—C6 | 1.384(5) | 1.392 | Br1—C1—C2—C3 | -178.2 (3) | 179.7 |
C1—C2 | 1.377(6) | 1.393 | O2—C2—C3—C4 | 179.8 (3) | -179.8 |
C2—C3 | 1.434(6) | 1.426 | C1—C2—C3—C4 | -0.4 (5) | 0.4 |
C3—C4 | 1.396(6) | 1.387 | O2—C2—C3—C7 | -2.0 (5) | -0.4 |
C3—C7 | 1.455(5) | 1.460 | C1—C2—C3—C7 | 177.9 (3) | 179.8 |
C4—C5 | 1.384(5) | 1.384 | C2—C3—C4—C5 | -0.2 (5) | 0.5 |
C5—C6 | 1.432(6) | 1.427 | C7—C3—C4—C5 | -178.4 (3) | -178.9 |
C5—C9 | 1.456(6) | 1.467 | C4—C5—C6—C1 | -0.4 (5) | 1.3 |
C7—C8 | 1.524(6) | 1.530 | C9—C5—C6—C1 | -179.4 (3) | -177.9 |
C9—C10 | 1.523(6) | 1.532 | C4—C3—C7—O3 | 179.3 (4) | 179.6 |
Atoms | Bond angle, θ | C2—C3—C7—O3 | 1.2 (6) | 0.2 |
| X-ray | DFT | C4—C3—C7—C8 | 1.5 (6) | -0.5 |
C6—C1—C2 | 122.3 (4) | 121.0 | C2—C3—C7—C8 | -176.7 (4) | -179.9 |
C6—C1—Br1 | 118.9 (3) | 119.5 | O3—C7—C8—Br4 | 121.6 (3) | -116.9 |
C2—C1—Br1 | 118.8(4) | 119.5 | C3—C7—C8—Br4 | -60.4 (5) | -65.6 |
O2—C2—C1 | 118.7 (4) | 118.4 | C3—C7—C8—Br5 | 66.7 (4) | -65.6 |
O2—C2—C3 | 121.7 (4) | 122.0 | C3—C4—C5—C6 | 0.6 (5) | -1.4 |
C1—C2—C3 | 119.6 (4) | 119.7 | C3—C4—C5—C9 | 179.6 (3) | 177.9 |
C4—C3—C2 | 117.6 (4) | 118.6 | C2—C1—C6—O1 | -178.4 (3) | 179.8 |
C4—C3—C7 | 123.3 (4) | 122.6 | Br1—C1—C6—O1 | 0.4 (5) | -0.2 |
C2—C3—C7 | 119.0(4) | 118.8 | C2—C1—C6—C5 | -0.2 (5) | -0.4 |
C5—C4—C3 | 122.8 (4) | 122.5 | Br1—C1—C6—C5 | 178.6 (3) | 179.5 |
C4—C5—C6 | 118.7 (4) | 118.7 | C4—C5—C6—O1 | 177.7 (3) | -178.9 |
C4—C5—C9 | 122.6 (3) | 122.4 | C9—C5—C6—O1 | -1.3 (5) | 1.8 |
C6—C5—C9 | 118.7 (4) | 118.8 | C4—C5—C9—O4 | -171.4 (4) | 177.6 |
O1—C6—C1 | 118.8 (4) | 118.6 | C6—C5—C9—O4 | 7.5 (5) | -3.2 |
O1—C6—C5 | 122.1 (4) | 121.8 | C4—C5—C9—C10 | 7.5 (5) | -2.7 |
C1—C6—C5 | 119.1 (4) | 119.6 | C6—C5—C9—C10 | -171.8 (3) | 176.6 |
O3—C7—C3 | 122.3 (4) | 122.7 | O4—C9—C10—Br2 | 13.1 (5) | 24.38 |
O3—C7—C8 | 114.3 (4) | 114.5 | C5—C9—C10—Br2 | -167.6 (3) | -155.4 |
C3—C7—C8 | 123.3 (4) | 122.8 | O4—C9—C10—Br3 | -108.8 (4) | -98.8 |
C7—C8—Br4 | 113.7 (3) | 112.4 | C5—C9—C10—Br3 | -108.8 (4) | 81.5 |
C7—C8—Br5 | 110.7 (2) | 111.5 | C6—C1—C2—O2 | -179.6 (3) | 179.8 |
Br4—C8—Br5 | 112.1 (2) | 113.5 | Br1—C1—C2—O2 | 1.7 (5) | -0.2 |
O4—C9—C5 | 122.2 (4) | 122.4 | C6—C1—C2—C3 | 0.6 (6) | -0.4 |
O4—C9—C10 | 118.7(4) | 119.4 | | | |
As seen in Table 2, the bond lengths, bond angles, and torsion angles of experimental values and theoretical values are comparable with each other. The structural overlay diagram of the crystal structure and their optimized molecule is shown in Fig. 2. The atoms C1–C7, Br1, and C9 are used to overlay. Both structures are well overlaid with each other with a root mean square deviation (r.m.s.d) is 0.0177 Å except for bromine atoms in the acetyl group. The deviation around bromine atoms is witnessed by the largest deviations of bond lengths of C10–Br3 and C1–Br1 (0.01 Å) and bond angles of Br4–C8–Br5 (1.4°) and Br2–C10–Br3 (1.7°, Table 2). Similarly, the largest deviations of torsion angle ≈ 10–20° were observed around the bromine atoms in experimental and optimized molecules (Table 2). These deviations can be attributed to the fact that the theoretical calculations have been carried out with an isolated molecule in the gaseous phase and the experimental values correspond to the molecule in the crystalline state.
Crystal packing, Molecular dimers, Intermolecular interactions energy, and Lattice energy of I
The crystal packing of the title compound is shown in Fig. 3. As can be seen from Fig. 3, molecules are arranged in a column manner. The crystal packing of I is stabilized by the intramolecular O–H···O, C–H···Br interactions. Two intramolecular O–H···O (O2–H2···O3 and O1–H1···O4) interactions individually makes pesudo S(6) ring. The total lattice energy for the title compound is stabilized by −125.9 kcal mol−1.
Apart from intramolecular interaction, the four types of intermolecular interactions (C–H···Br, C–H···O, Cg···Cg, and Br···Br) play a vital role in the stabilization of crystal packing of I. The energetically significant five molecular dimers/pairs (M1-M5) were identified from the crystal packing of I with the aid of PIXEL analysis(Fig. 4.). These dimers are listed in Table 3 with the decreasing order of their stabilization energy (Etot). The Etot of these dimers falls in the range of Etot: -13.1 – -1.8 kcal mol-1.
Table 3
Geometrical parameters for intermolecular interactions exist in different molecular dimers in I and the intermolecular interaction energies in kcal mol-1.
Dimers | Important interactions | Geometry (Ȧ, °) | Symmetry operator | Distance (Å) | Ecoul | Epol | Edis | Erep | Etot | % Edis |
d(H···A) | d(D···A) | <D-H···A |
M1 | Cg1···Cg1 | | 3.933 | | -x + 2, -y, -z + 1 | 4.791 | -6.5 | -3.0 | -18.8 | 15.2 | -13.1 | 66 |
| C10-H10···Br1 | 3.04 | 3.605 | 119 | | | | | | | | |
M2 | Cg1···Cg1 | | 3.283 | | -x + 2, -y + 1, -z + 1 | 6.635 | -3.1 | -0.8 | -10.0 | 5.8 | -8.0 | 72 |
M3 | C10-H10···Br2 | 2.92 | 3.664 | 134 | -x + 2, -y, -z | 9.116 | -4.0 | -1.1 | -9.7 | 8.1 | -6.6 | 66 |
M4 | C8-H8···O4 = C9 | 2.26 | 3.207 | 164 | x-1, y + 1, z | 9.645 | -4.4 | -1.3 | -4.9 | 6.0 | -4.6 | 46 |
M5 | Br3···Br5 | | 3.671 | | x-1, y, z | 7.306 | -0.4 | -0.3 | -2.9 | 1.7 | -1.8 | 81 |
Total lattice energy | -61.3 | -19.1 | -173.5 | 128.1 | -125.9 | |
Among the five molecular pairs, the strongest molecular pair, M1 is stabilized (Etot: -13.1 kcal mol-1) by π ···π stacking interaction. Briefly, the two phenyl rings in M1 are arranged in a parallel-displaced manner(Venkatesan et al. 2018; Riwar et al. 2017) with the distance between both centroids of phenyl rings is 3.934 (3) Å (slippage: 1.984 Å, symmetry code: 2-x, -y, 1-z). The dihedral angle between both phenyl ring planes is 0° which indicates that both phenyl rings are in a parallel manner. This dimer, M1, is further stabilized by the C10-H10···Br1 interaction. The second strongest molecular dimer, M2 (Etot: -8.0 kcal mol-1) is also stabilized by another stacking interaction that formed between two pseudo rings with the distance between both centroids of two pseudo rings being 3.283 Å. Briefly, the intramolecular O2–H2···O3 interaction makes S(6) ring motif as mentioned earlier. In this S(6) ring motif stacked with another S(6) ring of the neighbouring molecule. Similar kinds of stacking interactions were observed in geminal amido-esters(Venkatesan et al. 2021b, 2021a) and other compounds(Blagojević and Zarić 2015). Apart from these two stacking pairs, the molecular pairs M3 (Etot: -6.6 kcal mol-1) and M4 (Etot: -4.6 kcal mol-1) are stabilized by C10–H10···Br2 and C8–H8···O4 = C9 interaction respectively. The C8–H8···O4 = C9 interaction in M4 links the neighbouring molecules into C8 motif and C10–H10···Br2 interaction in M3 links neigbhouring molecules into centrosymmetric dimeric structure with \({R}_{2}^{2}\left(6\right)\) motif. The combination of interactions in M3 and M4 dimers links neigbhouring molecules into the molecular layer which extends parallel to the 110 plane (Fig. 5).
In addition to C–H···Br/O and Cg···Cg interactions, a non-bonded Br5···Br3 contact in M5 with distance is 3.6706 (13) Å which additionally stabilized the crystal structure of I. The Etot for M5 is -1.8 kcal mol-1. It should be mentioned that the Br···Br contact is shorter (0.029 Å) than the sums of the van der Waals radii of two bromine atoms. The CSD search suggested that the 3232 hits were found for the Br···Br (Lieberman, Davey, and Newsham 2000) contacts. As can be seen from Table 2, the % dispersion contribution (% Edis=Edis/(EpolEdisp+Edis)) is higher in M5 (81%) and the least 46% is observed in M4. These results suggested that the Br5···Br3 contact is more dispersive in nature whereas the C8–H8···O4 = C9 interaction in M4 in the Coulombic (Ecou:56%) nature.
Hirshfeld Surface analysis
To understand the role of various intermolecular interactions in a qualitative manner, we employed Hirshfeld surface analysis(Spackman and Jayatilaka 2009; Spackman and McKinnon 2002; Turner et al. 2011; Wood et al. 2008; Spackman, McKinnon, and Jayatilaka 2008). The Hirshfeld surface analysis and two-dimensional fingerprint plots were generated from the CrystalExplorer17(Turner et al. 2017). The HS and 2D-FP were used to provide additional information and to quantify the intermolecular interactions in the title compound by using distinct colours and intensities to indicate short and long contacts, as well as the relative contribution of the different interactions in their solid-state (Venkatesan, Thamotharan, et al. 2016; Venkatesan, Rajakannan, et al. 2016; Venkatesan et al. 2015). The Hirshfeld surfaces (HS) mapped over the dnorm (-0.0155 to 1.0144 a.u.) and shape index are shown in Fig. 6.
The red spots on the HS map are visible for the C10–H10···Br2(M3), C8–H8···O4(M4), and Br5···Br3 (M5) interactions. The π stacking interaction between two phenyl rings is confirmed by the red and blue triangles on the surface of the shape-index diagram (Venkatesan et al. 2018). The two-dimensional fingerprint plot (2D-FP) and decomposed plots are shown in Fig. 7. The 2D-FP plots showed that the Br···Br (35.8%), Br···H (18.9%), O···H (10.5%) and Br···O (9.8%) contacts are first four most significant contacts in their crystal structure. The relative contribution of H···H contact is 1.9% which is lower than the C···C contact (2.8%) in the crystal structure of I. It indicates the steric hindrance of bromine atoms in the title compound I.
Quantitative molecular electrostatic potential map (MESP)
The molecular electrostatic potential map of I was generated at their crystal structure geometry from the corresponding wave functions using the WFA-SAS program(Bulat et al. 2010). The molecular electrostatic potential maps of I along with the location of the positive (Vsmax, black hemisphere, black coloured values) and negative potentials (Vsmin, blue hemisphere, red coloured value) are shown in Fig. 8.
From Fig. 8, the positive potentials are observed on the surface of bromine atoms and hydrogen atoms in phenolic and acetyl group (dibromide substituted terminal methyl group in the acetyl moiety). Interestingly, the distribution of electrostatic potential is found to be asymmetric in nature in all the five bromine atoms in the I. The highest Vsmax: 34.8 kcal mol-1 in one of the bromine (Br2) atom in the diacetyl group whereas, another bromine (Br1) atom attached in the phenyl ring has the lowest Vsmax: 13.1 kcal mol-1. The positive potentials on the surface of bromine atoms suggested that the interactions involved in the bromine atoms in I belong in the σ-hole interaction. The highest negative potential (Vsmin) is -13.8 kcal mol-1 and it is observed on the surface of oxygen O4 of the acetyl group. These molecular electrostatic differences witness the involvement of these atoms in the C8–H8···O4, C10–H10···Br2 interactions in the crystal packing.
Frontier Molecular Orbital Analysis
It is well known that frontier molecular orbital analysis is one of the potential tools for the study of molecular electronic charge mobility, the chemical reactivity, kinetic stability of molecules, and electronic transitions in the molecules. To understand the intramolecular charge transfer (ICT) process in I, frontier molecular orbital analysis is carried out. As seen from Fig. 9, the highest occupied molecular orbital (HOMO) is mainly localized in the central phenyl ring, hydroxy group, and bromine atom(Br1) which are attached in the phenyl ring whereas the lowest unoccupied molecular orbital (LUMO) is localized in the dibromoacetyl moiety of the title compound. The HOMO and LUMO diagram shows the existence of the intramolecular charge transfer in the title compound. The HOMO→LUMO energy(EH-L) gap was found to be 6.292 eV and the frontier molecular orbital energies, EHOMO and ELUMO, were − 8.357 eV and − 2.065 eV, respectively.
To understand the chemical reactivity and stability of I, the DFT global parameters are calculated. In the present investigation, the ionization potential (IP), electron affinity (EA), chemical hardness (Ƞ), chemical potential (µ), and electronegativity (χ) are computed. The calculated ionization potential (IP, Eq. 1) and electron affinity can be used to predict the electronic stability of I. The IP and EA values are obtained by Koopmans approximations, the negative of HOMO is taken as IP whilst the negative of LUMO is EA (Eq. 1–2). The calculated ionization potential (IP) and electron affinity (EA) values are 8.357 eV and 2.065 eV, respectively. The significant IP and EA values suggest its better electronic stability and it has a strong tendency to attract the valence electrons, and the least electropositive nature.
The global hardness (Ƞ, Eq. 3) is defined by the first and second-order partial derivatives of total energy (E) with respect to the number of electrons (N) at constant external potential v(r), e
The chemical hardness(η, Eq. 4 ) determines how resistant a cluster of nuclei and electrons is to variations in the distribution of its electrons, and the calculated chemical hardness (η) for I is 3.146 eV. The calculated chemical potential (µ, Eq. 5 ) value of I is − 5.211 eV and this smaller value suggests that the title compound has a soft nature and it has reactive toward incoming reagents.
The electrophilicity index (ω) value indicates the amount of energy lost as a result of the maximum amount of electron movement in the molecule. The calculated electrophilicity index (ω, Eq. 7) value of I is 4.316 eV and indicates that the compound has a good electron mobility nature.