Synthesis, structure and Hirshfeld surface analysis of a coordination compound of cadmium acetate with 2-aminobenzoxazole

The molecular and crystal structures of a cadmium acetate coordination compound with 2-aminobenzoxazole were studied, and the Hirshfeld surfaces and fingerprint plots were generated to investigate various intermolecular interactions.

A first coordination compound of 2-aminobenzoxazole (2AB), namely, bis(2aminobenzoxazole-�N 3 )bis(acetato-� 2 O,O 0 )cadmium(II), [Cd(CH 3 COO) 2 (2AB) 2 ], has been synthesized from ethanol solutions of Cd(CH 3 (COO) 2 and 2AB.In the monoclinic crystals with the space group C2 1 /c, the cadmium ions coordinate two neutral 2AB molecules in a monodentate fashion through the oxazole N atom, while two acetate ligands are coordinated through the O atoms in a bidentate manner.The coordination polyhedron of the central ion is substantially distorted octahedral.There are two relatively strong intramolecular hydrogen bonds in the complex molecule.Additionally, two intermolecular hydrogen bonds associate complex molecules into columns running in the [110] and [110] directions.The Hirshfeld surface analysis shows that 45.7% of the intermolecular interactions are from H� � �H contacts, 24.7% are from O� � �H/H� � �O contacts and 18.8% are from C� � �H/H� � �C contacts, while other contributions are from N� � �H/H� � �N and O� � �O contacts.
An analysis of the Cambridge Structural Database (CSD, Version 5.43, update of March 2022; Groom et al., 2016) showed that there are no X-ray structures of 2AB and its metal complexes in the database.However, recently, we reported the structure and intermolecular interactions of a 2AB-fumaric acid organic salt in which the N atom of 2AB is protonated by a fumaric acid H atom (Razzoqova et al., 2022).Theoretically, metal complexes of 2AB may involve coordination through the N or O atoms of the oxazole ring and the N atom of the amino substituent.In order to define which way these possibilities will be realized, we have prepared a coordination complex of 2AB with cadmium and report here its molecular and crystal structure, as well as a Hirshfeld surface analysis.

Structural commentary
The structure of [Cd 2+ (CH 3 COO À ) 2 (2AB) 2 ] is shown in Fig. 1.The metal complex was obtained using the Cd(CH 3 COO) 2 salt for the synthesis.The Cd II ion coordinates two 2AB molecules through the oxazole N atom in a monodentate fashion.Furthermore, in order to compensate the positive charge of the central atom, two acetate ligands are coordinated in a bidentate manner through the O atoms.Despite the large ionic radius of the Cd atom, the coordination number of the central atom is six, in contrast to, for example, coordination numbers of four or eight in some mixed-ligand cadmium complexes (Kudiyarova et al., 2021;Ibragimov et al., 2017a).The two 2AB ligands and the two acetate ions are coordinated to the Cd centre in a cis arrangement.The bond lengths of the Cd ion are in the range 2.269 (2)-2.400(2) A ˚, while the bond angles vary from 53.35 (8) to 139.71 (8) � .Such a large difference in the valence distances and angles leads to a significant distortion of the octahedral coordination environment, caused by the acetate ligands acting as bidentate, with chelating angles of O3-Cd1-O4 = 53.57(8) � and O5-Cd1-O6 = 53.35(8) � of the cadmium polyhedron.The geometric parameters of the arene ring are similar to standard values and to those in other structures (Ibragimov et al., 2017b;Ruzmetov et al., 2022).In the 2AB molecules, all the atoms are located on a plane, with the greatest r.m.s.deviations from the main planes seen for the amino atoms N2 (0.017 A ˚) and N4 (0.026 A ˚).The dihedral angle between the mean planes of the 2AB molecules around the cadmium polyhedron is 65.59 � .The positions of the ligands allow the formation of two relatively strong intramolecular hydrogen bonds in the complex mol-research communications Acta Cryst. (2023).E79, 862-866 The molecular structure of the title complex with the atom-numbering scheme.Intramolecular hydrogen bonds are indicated by dashed lines.Displacement ellipsoids are plotted at the 30% probability level.

Figure 2
The formation of columns by hydrogen bonds in the crystal structure of the title complex.Generic atom labels without symmetry codes have been used.

Supramolecular features
There are two proton-donor hydrogen-bonding groups in the complex molecule, i.e.N2-H2 and N4-H4.Both of these groups realize their hydrogen-bonding capabilities by forming intramolecular N2-H2A� � �O5 and N4-H4A� � �O3 (first two hydrogen bonds in Table 1), and two intermolecular N2-H2B� � �O4 i and N4-H4B� � �O6 ii hydrogen bonds (the remaining two hydrogen bonds in Table 1).These intermolecular hydrogen bonds between the N atoms of the amino groups and the O atoms of the acetate carboxylate groups associate complex molecules into columns running in the [110] and [110] directions (Fig. 2).The interaction energies of the hydrogen-bond system were calculated within the molecules using the HF method (HF/3-21G) in the CrystalExplorer17 program (Fig. 3).The result shows the total energy (E tot ), which is the sum of the Coulombic (E ele ), polar (E pol ), dispersion (E dis ) and repulsive (E rep ) contributions.The four energy components were scaled in the total energy (E tot = 1.019E ele + 0651E pol + 0901E dis + 0.811E rep ).The interaction energies were investigated for a 3.8 A ˚cluster around the reference molecule.The calculation reveals two stronger interactions within the neighbouring molecules.The strongest interaction total energy (E tot ) is À 113.4 kJ mol À 1 (� À 27 kcal mol À 1 ), with the highest polar (À 32.5 kJ mol À 1 ), dispersion (À 51.3 kJ mol À 1 ) and repulsive (68.1 kJ mol À 1 ) energies (green-yellow).The second interaction among neighbouring molecules is similar to the first, with E tot = À 97.2 kJ mol À 1 .The main attractive interactions (Coulombic, dispersion and the sum total energy) show a stronger bonding effect along the crystallographic a direction (Fig. 3).

Hirshfeld surface analysis
To further investigate the intermolecular interactions present in the title compound, a Hirshfeld surface analysis was performed, and the two-dimensional (2D) fingerprint plots were generated with CrystalExplorer17 (Spackman et al., 2021).Fig. 4 shows the three-dimensional (3D) Hirshfeld surface of the complex with d norm (normalized contact Interaction energy calculations within the molecules was performed using the HF method (HF/3-21G) in the CrystalExplorer17 program.The thickness of the tube represents the value of the energy.The distribution of the interactions according to type shows strong interactions along the crystallographic a direction (the largest values are represented here).The total energy framework (in blue) and its two main components, dispersion (in green) and Coulombic energy (in red), are shown for a cluster around a reference molecule.also exhibit stronger interactions along the crystallographic a direction.

Figure 4
View of the three-dimensional Hirshfeld surface of the complex plotted over d norm in the range from À 0.6027 to 1.5939 a.u.

Synthesis and crystallization
Cd  title complex suitable for X-ray analysis were obtained by slow evaporation of the solution over a period of 10 d.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.The H atoms of the acetate methyl groups were placed in calculated positions and refined in the riding-model approximation, with U iso (H) = 1.5U eq (C) and C-H = 0.96 A ˚.The remaining H atoms were located experimentally and refined freely.(Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Bis(2-aminobenzoxazole-κN 3 )bis(acetato-κ 2 O,O′)cadmium(II)
Crystal data Extinction correction: SHELXL2016 (Sheldrick, 2015b), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.000082 (13) 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.

Figure 5
Figure 5The full 2D fingerprint plots for the title complex, showing all interactions and delineated into separate interactions.The d i and d e values are the closest internal and external distances (A ˚) from given points on the Hirshfeld surface contacts.

Table 2
Experimental details.