Interactions in flavanone and chalcone derivatives: Hirshfeld surface analysis, energy frameworks and global reactivity descriptors

Theoretical and Structural Chemistry Group, Department of Physical Chemistry, Faculty of Chemistry, University of Lodz, Pomorska 163/165, 90-236 Łódź, Poland, Department of Crystal Physics, Institute of Physics, University of Silesia, 75 Pułku Piechoty 1, 41-500 Chorzów, Poland, Department of Physical Chemistry, Faculty of Chemistry, University of Lodz, Pomorska 163/165, 90-236 Łódź, Poland, and Department of Inorganic and Analytical Chemistry, Faculty of Pharmacy, Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University in Toruń, Jurasza 2, 85-089 Bydgoszcz, Poland. *Correspondence e-mail: magdalena.malecka@chemia.uni.lodz.pl, lilianna.checinska@chemia.uni.lodz.pl


Introduction
The flavonoids, a group of polyphenolic compounds, constitute one of the most important families of natural products. As secondary metabolites of plants, they perform a range of functions, including pigmentation, a natural defence against pathogenic microorganisms and herbivores, and serve to protect the plant against UV-light exposure (Bonetti et al., 2017). Flavonoids are found in edible plants and in a large number of foods of plant origin. Among the flavonoids, the chalcone (CH) and flavanone (FL) classes have attracted much attention due to their wide-ranging antioxidant (Hsiao et al., 2007), antibacterial (Xu et al., 2019;Dan & Dai, 2020) and cancer-preventive potential (Szliszka et al., 2012), as well as their neuroprotective and hepatoprotective effects (Karimi-Sales et al., 2018;Mahapatra et al., 2015). Chalcones and their derivatives are incorporated in a wide range of synthetic applications and possess multitarget broad-spectrum biological activity (Zhuang et al., 2017). A vast number of naturally occurring flavanones and chalcones demonstrate polyhydroxylation in their aryl rings. New potentially bioactive chalcone-and flavanone-like molecules have been synthesized by the incorporation of different functionalities in both rings (Scheme 1) (Rosa et al., 2017). Table 1 Experimental details. Experiments were carried out at 100 K with Mo K radiation. Absorption was corrected for by multi-scan methods (CrysAlis PRO; Rigaku OD, 2015  Chalcones are key precursors in the biosynthesis of flavanones and other flavonoids. In plants, the synthesis of chalcone from malonyl-CoA (CoA is coenzyme A) and p-coumaroyl-CoA, catalysed by chalcone synthase, is followed by their intramolecular and stereospecific cyclization into (2S)-flavanone. Chalcone isomerases are specific for the formation of the six-membered heterocyclic ring characteristic of flavanones. Two such isomers, i.e. ortho-hydroxychalcone and flavanone, can undergo reversible isomerization in solution (Mai et al., 2013); this ortho-hydroxychalcone/flavanone pair is a good example of molecular switching, where molecules are capable of predictable and reversible conformational changes. Such compounds have become increasingly desirable targets for organic synthesis (Mai et al., 2013;Muller et al., 2016). Moreover, the physicochemical properties of chalcone and its derivatives, including their nonlinear optical and fluorescence properties, have received considerable attention owing to their associated delocalization of electronic charge distribution and overlapping -orbitals. Furthermore, the optical properties are related not only to the particular molecule, but are also heavily dependent on the crystal structure and intermolecular packing. It is therefore beneficial to determine the packing of the crystal structure by a detailed analysis of the intermolecular contacts. In addition, by introducing electron donor or acceptor groups to the aromatic rings of the chalcone scaffold, it is possible to modulate their optical properties and obtain chalcone derivatives with strong fluorescence, both in solution and in the solid state. The aim of this study is to provide comprehensive structural information for a series of 15 compounds, both flavanones and chalcones. Three aspects of these compounds are evaluated: (i) intermolecular interactions in the crystal lattice using the Hirshfeld surface approach (Spackman & Jayatilaka, 2009), (ii) lattice energy analysis (Turner et al., 2014), including energy framework visualization (Turner et al., 2015), and (iii) electronic molecular properties based on density functional theory (DFT) global reactivity descriptors. Seven compounds (five flavanones and two chalcones), namely, 7-methoxy-2-phenyl-3,4-dihydro-2H-1-benzopyran-4-one, FL1, 2-(4-methoxyphenyl)-3,4dihydro-2H-1-benzopyran-4-one, FL2, 2-(4-methoxyphenyl)-6methyl-3,4-dihydro-2H-1-benzopyran-4-one, FL3, 2-(4-chlorophenyl)-3,4-dihydro-2H-1-benzopyran-4-one, FL5, 8-bromo-6methyl-2-phenyl-3,4-dihydro-2H-1-benzopyran-4-one, FL8, (2E)-1-(2-hydroxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1one, CH2, and (2E)-1-(2-hydroxyphenyl)-3-(4-hydroxyphenyl)prop-2-en-1-one, CH4, were obtained as single crystals and their structures were solved and refined using X-ray diffraction data. As flavanones and chalcones are isomers of each other, it is possible to identify structural similarities and differences between them in terms of their weak intermolecular interactions in the crystal lattice and their energetics. To form an isomer pair with the self-solved structure, the appropriate compound was searched for in the Cambridge Structural Database (CSD, Version 5.39, 2018 release; Groom et al., 2016). Based on the results of the CSD search, two flavanone-chalcone pairs were added, thus increasing the total number of halogen-substituted compounds. Finally, the number of compounds was expanded to include the following: CH1 (Serdiuk et al., 2018;CSD refcode REPXIW), CH3 (Fun et al., 2011;URESOA), FL4 (Białoń ska et al., 2007;NUYRII01), CH5 (Fun et al., 2007;QEXLAH), FL6 (Cantrell et al., 1974;BRFLAY20), CH6A/B [two different polymorphs; Agilandeshwari et al. (2016) (Goud et al., 1995;YIVREA) and CH7 (Goud et al., 1995; YIVPUO) (Scheme 1). Unfortunately, in the case of flavanone FL8, the corresponding CIF is not present in the CSD.

X-ray diffraction
All H atoms were fixed geometrically at calculated positions using a riding model. The structures of FL3, FL8 and CH4 crystallize with two molecules in the asymmetric unit. In four refined structures, one or two C atoms of the heterocyclic ring were found to be disordered and were refined with two alternative positions, A and B (atom name, final site-occupancy factors for major component A), for FL1 [C2 atom, k A = 0.533 (6)], FL2 [C2 atom, k A = 0.526 (7)], FL3 [C2 and C3 atoms, k A = 0.549 (7); C52 and C53 atoms, k A = 0.932 (3)] and FL8 [C2 atom, k A = 0.928 (7); C52 atom, k A = 0.814 (7)]. Table 1 reports the results of the crystal structure determinations. mated in terms of four components, viz. electrostatic, polarization, dispersion and exchange-repulsion, with scale factors of 1.057, 0.740, 0.871 and 0.618, respectively. In the present study, the positional parameters of the major component (A) were chosen for the coordinates of the disordered atoms. According to CrystalExplorer procedures, the bond lengths to H atoms were normalized to standard neutron values. Crys-talExplorer17 (Turner et al., 2017;Mackenzie et al., 2017) was also used to generate the Hirshfeld surface (Spackman & Jayatilaka, 2009;McKinnon et al., 1998).

Calculation of lattice energies
The CE-B3LYP lattice energies were calculated according to Thomas et al. (2018) as half of the direct summation gained by the multiplication of E tot and N, where N is the number of molecule pairs in the cluster with that particular interaction energy for the nonpolar space group.
However, the polar space group (Pca2 1 for CH2 and P2 1 for CH4, CH6A and FL7) needs special consideration and the lattice energy is: In equation (2), the second term is a correction of the cell dipole, where p cell is a magnitude of the cell dipole moment, obtained as the sum of the vectors of the molecular dipole moments; V cell and Z cell represent the volume and number of unique molecules in the unit cell.

Calculations of global reactivity descriptors
The energies of frontier molecular orbitals, namely, the lowest unoccupied molecular orbital (E LUMO ) and the highest occupied molecular orbital (E HOMO ), were calculated based on the CIF files. First, each CIF was opened in CrystalExplorer and, after normalization of the C-H and O-H bond lengths to 1.083 and 0.983 Å , respectively, the input file for GAUS-SIAN09 was generated. The energies of the two orbitals were calculated using the B3LYP/6-31G(d,p) basis set. The HOMO and LUMO orbital energies were used to evaluate the following global reactivity descriptors: chemical potential [ = (E LUMO + E HOMO )/2], chemical hardness [ = (E LUMO À E HOMO )/2], softness ( = 1 À ) and electrophilicity (! = 2 /2). All computed values of the electron structure descriptors are summarized in Table S5 of the supporting information.

Structural commentary
The molecular structures of FL1, FL2, FL3, FL5, FL8, CH2 and CH4 are shown in Figs. 1-7. The main body of the flavanone structure consists of two fused rings, namely, a benzene ring and a pyran ring, with a phenyl ring substituted at atom C2 with different substituents at the para positions. The pyran rings adopt mainly envelope (E) or screw-boat (S) conformations with small asymmetry parameters (Duax & Norton, 1975) (Table 2); however, one molecule of FL8 displays a pyran ring demonstrating a conformation between boat and twist-boat. The appropriate puckering parameters (Cremer & Pople, 1975) are presented in Table 2. Although the geometric parameters for the chromanone skeleton do not differ signif-  Table 2 Ring puckering parameters with asymmetry parameters and the dihedral angle between the chromone skeleton (A/B rings) and ring C. icantly, the phenyl ring substituted at the C2 atom is usually inclined at an angle between 46.3 (2) and 89.2 (2) with respect to the main skeleton ( Fig. 8), as reflected in the dihedral angles between rings A/B and C ( Table 2). As expected, the main body of the chalcone structure consists of two nearly coplanar six-membered aromatic rings (A and B) connected by a threecarbon ,-unsaturated chain with a planar configuration along the double C C bond. The appropriate torsion angle for the CH2 molecule is C6-C7-C8-C9 of 178.5 (2) ; for  A view of the molecular structure of FL2, showing the atom-numbering scheme. Displacement parameters are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radius.

Figure 3
A view of the two independent molecules of the structure of FL3, showing the atom-numbering scheme. Displacement parameters are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radius.

Figure 4
A view of the molecular structure of FL5, showing the atom-numbering scheme. Displacement parameters are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radius.

Figure 5
A view the two independent molecules of the structure FL8, showing the atom-numbering scheme. Displacement parameters are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radius.

Figure 6
A view the two independent molecules of the structure of CH2, showing the atom-numbering scheme. Displacement parameters are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radius.

Figure 7
A view the two independent molecules of the structure of CH4, showing the atom-numbering scheme. Displacement parameters are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radius.

Figure 9
The crystal structure of FL1, with hydrogen bonds, showing chains along the [110] direction.
In the crystal structure of FL5, the only hydrogen bonds which are observed belong to the C-HÁ Á Á type (Table S2 in the supporting information). However, it seems that the
The crystal structure of chalcone CH2 is dominated by the presence of C5-H5Á Á ÁO1 i hydrogen bonds [symmetry code: (i) Àx + 3 2 , y, z À 1 2 ], which connect molecules into a C(5) chain propagating along the c axis ( Fig. 14) (Etter, 1990). It is worth mentioning that the close proximity between donor atoms O1 and C9 and acceptor atom O2 allows two intramolecular hydrogen bonds to be formed (Table 8). In addition, in the crystal lattice, a short distance is observed between the O2 atom and -electrons from ring A of the molecule related by the symmetry code (x, y À 1, z) ( Table S2 in the supporting information).
Compound CH4 crystallizes in the monoclinic space group P2 1 , with two independent molecules in an asymmetric unit.
Hirshfeld surface analysis was generated by Crystal-Explorer17 (Turner et al., 2017;Mackenzie et al., 2017) and comprised d norm surface plots and two-dimensional (2D) fingerprint plots. The fingerprint plots provide information about the nature and types of intermolecular interactions, and their quantitative contribution to the HS. The intermolecular interactions are visualized by colour coding, i.e. red for short and blue for long contacts. The differences between flavanones and chalcones are shown by 2D fingerprint plots based on crystallographic data. The full fingerprint plots and those decomposed into OÁ Á ÁH/HÁ Á ÁO, CÁ Á ÁC, CÁ Á ÁH/HÁ Á ÁC and HÁ Á ÁH are shown in Figs. S1 and S2 (see supporting information). All chalcones display the visible participation of  The formation of a zigzag chain along the b axis for the crystal structure of compound FL5.

Figure 13
A fragment of the molecular structure of FL8, with rings formed between two independent molecules.

Figure 14
A fragment of the molecular structure of CH2, with the chain propagating along the c axis.
CÁ Á ÁC contacts due tointeractions which appear in the central region of the fingerprint plots (Figs. S1 and S2 in the supporting information). The reciprocal OÁ Á ÁH interactions are present for FL4 and CH4 as long sharp symmetrical spikes, which can be attributed to the presence of the intermolecular interactions O3-H9Á Á ÁO2 in FL4 and O3-H31Á Á ÁO2 and O53-H531Á Á ÁO3 in CH4 ( Fig. S1 and Table S1 in the supporting information). In turn, the unusual shape of the 2D fingerprint plot for FL7 corresponds to the large number of HÁ Á ÁH contacts associated with the presence of two methyl substituents in the B ring (Scheme 1).
The relative percentage contributions of the four main molecular interactions are presented in Fig. 16.
The predominant type of interaction in the studied flavanone and chalcone crystals is that of HÁ Á ÁH close contacts. (Fig. 16d), which contribute between 29.3 and 48.5% of the HS, with comparable levels being observed between each pair of flavanone and chalcone isomers. A similar relationship between isomer pairs can also be observed for the contribution of OÁ Á ÁH interactions; flavanones FL1-FL4 and chalcones CH1-CH4 with hydroxy or methoxy substituents at positions R 3 and R 5 demonstrate a greater percentage contribution of OÁ Á ÁH interactions in the HS (19.4-21.8%) than FL5-FL7 and CH5-CH7, which contain a halogen atom. Figs. 16(b) and 16(c) show that, compared to other interactions, the greatest differences within each flavanone and chalcone isomer pair concern the contributions of CÁ Á ÁC and CÁ Á ÁH. However, in the case of FL1/CH1, FL3/CH3 and FL7/ CH7, the two isomers demonstrate similar percentages of CÁ Á ÁH interactions. This may be because of all the interactions in the crystal lattice of those compounds, C-HÁ Á Á andare the most energetically dominant, as indicated by the decomposition of the energy frameworks ( Fig. 17 and Table S4 in the supporting information). A number ofinteractions with relatively short Cg(I)Á Á ÁCg(J) distances for CH2, CH4, CH5, CH6A/B and CH7, ranging from 3.815 to 4.047 Å , are present, as reflected in the higher percentage contribution of CÁ Á ÁC contacts in the HS ( Fig. 16b and Table S3 in the supporting information). This is associated with the planar molecular structure of chalcones.

Energy framework analysis and lattice energy analysis
The relationship between the structural features of the compounds/isomers and their electronic descriptors/properties was enriched by the quantification of intermolecular interaction energies and the 3D topology of the interaction map. Firstly, the total interaction energy (E AB tot ) was calculated by the summation of the electrostatic, polarization, dispersion and exchange-repulsion energy components for each nearestneighbour molecular pair (McKinnon et al., 2007). Following this, the lattice energy (E CEÀB3LYP lat ) was estimated according to Thomas et al. (2018). The following trends may be observed: (i) For seven pairs of isomers, the value of E CEÀB3LYP lat is greater for the flavanones than for the chalcones. In addition, the E CEÀB3LYP lat (FL)/E CEÀB3LYP lat (CH) ratio ranges from 0.98 to 1.14 for the five pairs FL1/CH1, FL2/CH2, FL5/CH5 and FL6/ CH6A/B (two polymorphs).

Figure 15
A fragment of the molecular structure with a net of hydrogen bonds for CH4. On the left is the 'fir' formed by the hydrogen bonds and, on the right, two independent molecules (pink and green) are linked into the chain.
(ii) The opposite trend is observed in the case of pairs FL4/ CH4 and FL7/CH7, where the chalcones demonstrated a greater E CEÀB3LYP lat than the flavanones; this is probably due to the effect of the two independent chalcone molecules being present in an asymmetric unit, with an E CEÀB3LYP lat (FL)/ E CEÀB3LYP lat (CH) ratio of 0.70 for FL4/CH4 and 0.86 for FL7/ CH7. This is also observed in the FL3/CH3 pair of crystal structures, characterized by two independent molecules in the asymmetric unit; in this case, the E CEÀB3LYP lat (FL)/ E CEÀB3LYP lat (CH) ratio is 1.63, (iii) Two polymorphs of CH6 have two different energies, differing by 4%; of these, the CH6B polymorph is more stable.
(iv) Most of the interactions found in the analysed structures are of the types C-HÁ Á ÁO, C-HÁ Á Á and -. For these, the interaction energy ranges from À19.5 to À57.4 kJ mol À1 ; these values are comparable with the corresponding interaction energies for other structures published in (v) The highest interaction energy is À57.4 kJ mol À1 (for FL7); this may be due to the presence of onlyinteractions in the crystal lattice, which possesses an attractive dispersive nature with small repulsion and electrostatic contribution.

Energies of the frontier molecular orbitals and global reactivity descriptors
To compare the flavanone and chalcone series, the energies of the frontier molecular orbitals were calculated, and these values were used to evaluate various global reactivity descriptors, such as chemical hardness and softness, and electrophilicity index (Siram et al., 2013). The computed values of the electron structure descriptors are presented in Table S5 and a graphical representation of the electrondensity redistribution is given in Table S6 (see supporting information).
Flavanones demonstrate a higher energy gap (4.531-4.861 eV) than chalcones (3.695-3.957 eV) and hence exhibit greater chemical hardness and lower electrophilicity index values. Hence, flavanones have a greater capacity to receive electrons, while the chalcones demonstrate greater resistance to their electronic configuration changing. The presence of substituents possessing either electron-withdrawing or electron-donating characters can modulate the electrophilic power of compounds. In general, electron-withdrawing groups (EWG), such as Cl or Br, will decrease the energy of the LUMO orbital, while electron-donating groups (EDG), such as OH, CH 3 and OCH 3 , will increase its energy. The first four The relative contributions of selected intermolecular contacts to the Hirshfeld surface area in the pairs of flavanone-chalcone isomers. compounds in both series (flavanones and chalcones) contain only EDGs, compounds FL5/CH5 and FL6/CH6 contain EWGs, whereas compounds CH7, FL7 and FL8 possess both types of substituents. All flavanones and chalcones with halogen atoms, except CH7 (viz. FL5, CH5, FL6, CH6, FL7 and FL8), exhibit lower values of E LUMO than those with EDGs, and hence a higher electrophilicity index. The red colour on the electron-density redistribution plots (Table S6 in the supporting information) represents the donor parts of the molecule, i.e. where the electron originates, while the blue colour represents the direction in which the electrons are moving as a result of the excitation. The blue regions indicate the electrophilic sites of the molecules.
The redistribution of electron density for flavanones FL2, FL3 and FL4 show the same pattern represented by two distinct parts, the first with an electrophilic character (the whole of ring B with a carbonyl group in ring A) and the second with a nucleophilic character (the whole of ring C). In turn, for FL1, FL5, FL6, FL7 and FL8, the redistribution of electrons only occurs within rings A and B. The one feature  The energy frameworks for the pairs of crystals FL1/CH1, FL3/CH3 and FL7/CH7 (total energy is presented). Yellow and pink arrows indicate energetically dominant C-HÁ Á Á andinteractions, respectively. The cutoff value is selected individually to show only one/two highest energy, if it exists. common to all flavanones and chalcones is the presence of an electrophilic carbonyl group.
A comparison of the electronic properties of the analysed compounds and their intermolecular interactions, obtained using Hirshfeld surface analysis, revealed the presence of a number of relationships (Figs. S18 and S19 in the supporting information). A noticeable trend can be seen between the sum of the two most representative interactions (CÁ Á ÁH and HÁ Á ÁH) and the energy of the HOMO orbital or electrophilicity index. A more comprehensive analysis of the flavanone-chalcone pairs can be seen after calculating the differences between the global reactivity descriptors. Fig. 18 presents the differences in LUMO energy, HOMO energy and electrophilicity index within each pair. In the first three pairs, it can be seen that the shift of the methoxy group from the B ring in FL1/CH1 to the C ring in FL2/CH2, and then the further introduction of a methyl group (in FL3/CH3) results in a gradual decrease in the absolute differences in HOMO energy, together with an increase in LUMO energy and electrophilicity. A comparable relationship can be observed for the next three pairs, i.e. FL5/CH5, FL6/CH6 and FL7/CH7, which contain halogen atoms. Changing the Cl atom in FL5 and CH5 to a Br atom (FL6/CH6) causes a decrease in the LUMO energy and an increase in electrophilicity. In the FL7/ CH7 pair, the addition of two electron-donating groups (CH 3 ) increases the difference in E HOMO , but the electrophilicity is lower.

Conclusion
The investigation of the crystal structures of a series of flavanones and chalcones indicates that weak intermolecular interactions, such as C-HÁ Á ÁO, C-HÁ Á Á and -, contribute to the total crystal forces. The combination of Hirshfeld surface analysis, lattice energy calculations and HOMO-LUMO investigations confirm that the energetic parameters are substantially influenced by the molecular interactions resulting from the type and position of the substituents.
It appears that, in a general sense, E CEÀB3LYP lat is greater for flavanones than for chalcones in the case of compounds with one independent molecule in the asymmetric unit. The values of the global reactivity descriptors of flavanones and chalcones result from both the nature of the substituents in the molecule (EWG or EDG) and their position. As expected, chalcones appear to be stronger electrophiles than flavanones, most likely due to the presence of an ,-unsaturated link between the rings. However, an analysis of the electrophilicity changes within the isomers showed that as the number of substituents in the molecule increases the electrophilicity difference between the flavanone and chalcone components of the isomeric pair decreases.

7-Methoxy-2-phenyl-3,4-dihydro-2H-1-benzopyran-4-one (FL1)
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.40 e Å −3 Δρ min = −0.34 e Å −3 Special details 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. Refinement. Single-crystal X-ray data of five flavanone derivatives (FL1, FL2, FL3, FL5 and FL8) were collected on a micro-focus SuperNova diffractometer with an Atlas detector, whereas data collection of two chalcone derivatives (CH2 and CH4) was carried out on an Xcalibur diffractometer with a Sapphire3 detector; all using Mo Kα and ω scans at a low temperature of 100.0 (1) K. The X-ray data were corrected for absorption using CrysAlis PRO (Agilent, 2015). All structures were solved using SHELXT (Sheldrick, 2015a) and refined with SHELXL2014/7 (Sheldrick, 2015b). All non-H atoms were refined anisotropically.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.

2-(4-Chlorophenyl)-3,4-dihydro-2H-1-benzopyran-4-one (FL5)
Crystal data Special details 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. Refinement. Single-crystal X-ray data of five flavanone derivatives (FL1, FL2, FL3, FL5 and FL8) were collected on a micro-focus SuperNova diffractometer with an Atlas detector, whereas data collection of two chalcone derivatives (CH2 and CH4) was carried out on an Xcalibur diffractometer with a Sapphire3 detector; all using Mo Kα and ω scans at a low temperature of 100.0 (1) K. The X-ray data were corrected for absorption using CrysAlis PRO (Agilent, 2015). All structures were solved using SHELXT (Sheldrick, 2015a) and refined with SHELXL2014/7 (Sheldrick, 2015b). All non-H atoms were refined anisotropically.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Cl1  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.98 e Å −3 Δρ min = −0.61 e Å −3 Special details 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. Refinement. Single-crystal X-ray data of five flavanone derivatives (FL1, FL2, FL3, FL5 and FL8) were collected on a micro-focus SuperNova diffractometer with an Atlas detector, whereas data collection of two chalcone derivatives (CH2 and CH4) was carried out on an Xcalibur diffractometer with a Sapphire3 detector; all using Mo Kα and ω scans at a low temperature of 100.0 (1) K. The X-ray data were corrected for absorption using CrysAlis PRO (Agilent, 2015). All structures were solved using SHELXT (Sheldrick, 2015a) and refined with SHELXL2014/7 (Sheldrick, 2015b). All non-H atoms were refined anisotropically.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (

Special details
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. Refinement. Single-crystal X-ray data of five flavanone derivatives (FL1, FL2, FL3, FL5 and FL8) were collected on a micro-focus SuperNova diffractometer with an Atlas detector, whereas data collection of two chalcone derivatives (CH2 and CH4) was carried out on an Xcalibur diffractometer with a Sapphire3 detector; all using Mo Kα and ω scans at a low temperature of 100.0 (1) K. The X-ray data were corrected for absorption using CrysAlis PRO (Agilent, 2015). All structures were solved using SHELXT (Sheldrick, 2015a) and refined with SHELXL2014/7 (Sheldrick, 2015b). All non-H atoms were refined anisotropically.