Triarylazoimidazole-Zn II , Cd II , and Hg II Complexes: Structures, Photophysics, and Antibacterial Properties

: Novel triarylazoimidazoles containing strong electron donors ( p -NEt 2 ) or acceptors ( p -NO 2 ) by the azoaryl group, and their group 12 metal complexes were synthesized and fully characterized, including X-ray analysis for several complexes. Novel complexes exhibit red photo-luminescence emission ( Φ up to 0.21) in a solution. Moreover, the antibacterial activity of complexes was tested against Gram-positive microorganism S . aureus and Gram-negative microorganism E . coli .


Introduction
Imidazole function is an important group in biology, often playing a role as a supporting ligand in metal-containing systems [1][2][3]. This stimulates the synthesis and structural characterization of imidazole metal complexes to better understand the role of these ligands. Azoimidazoles constitute an important class of photoactive materials, which were intensively studied earlier [4][5][6][7][8][9]. In addition, they are interesting chelating ligands, which electronics could be easily modulated via facile structural tuning [6,8,10]. Recently we started exploring triarylazoimidazoles and their coordination compounds [2,11,12]. Surprisingly, triarylazoimidazoles received almost no attention in the literature. In our recent publication, we showed that coordination of some triarylazoimidazoles to Zn II , Cd II , and Hg II led to the formation of bright red emissive complexes (quantum yields up to 44%), which could be excited with a visible light [2]. Here, we report the synthesis and structural characterization of several novel triarylazoimidazoles and their emissive group 12 metal complexes (Φ up to 0.21). Introduction of the p-bromo substituent to the azoaryl substituent of the Zn-coordinated triarylazoimidazole shifts an emission maximum to 677 nm relatively to the unsubstituted triarylazoimidazole complex. In addition, we report antibacterial properties of novel complexes.

Materials and Methods
General remarks. Unless stated otherwise, all the reagents used in this study were obtained from the commercial sources (Aldrich (Schnelldorf, Germany), TCI-Europe (Zwi-jndrecht, Belgium), Strem (Bischheim, France), and ABCR (Karlsruhe, Germany)). NMR spectra were recorded on a Bruker Avance III (Karlsruhe, Germany) ( 1 H: 400 MHz); chemical shifts (δ) are given in ppm relative to TMS, coupling constants (J) in Hz. The solvent signals were used as references (CDCl 3 : δ C = 77.16 ppm; residual CHCl 3 in CDCl 3 : δ H = 7.26 ppm; CD 2 Cl 2 : δ C = 53.84 ppm; residual CHDCl 2 in CD 2 Cl 2 : δ H = 5.32 ppm); 1 H and 13 C assignments were established using NOESY, HSQC, and HMBC experiments; numbering schemes as shown in the inserts. C, H, and N elemental analyses were carried out on a Euro EA 3028HT CHNS/O analyzer (Pavia, Italy). Mass-spectra were obtained on a Bruker micrOTOF spectrometer equipped with the electrospray ionization (ESI) source (Bremen, Germany); MeOH, CH 2 Cl 2 , or MeOH/CH 2 Cl 2 mixture was used as a solvent. Solvents were purified by distillation over the indicated drying agents and were transferred under Ar: Et 2 O (Mg/anthracene), CH 2 Cl 2 (CaH 2 ), hexane (Na/K). Flash chromatography: Merck Geduran ® Si 60 (40-63 µm). Absorption spectra were measured in a 3.8 mL quartz cuvette using a UV-VIS spectrometer (UV-3600, Shimadzu, Kyoto, Japan) and photoluminescence emission and excitation spectra in the same cuvette, using a spectrofluorometer (RF-5031PC, Shimadzu). The luminescence quantum yield was determined using the slope method relative to the reference fluorophore, which the ethanol solution of Nile Blue dye (Φ = 0.27) excited at 590-625 nm, using a series of ethanol solutions of the sample with varying concentrations.

X-ray Diffraction Studies
XRD data for 9Hg'·2CH 3 OH, 8·solvate and 10Cd·1.75CH 3 OH·0.75H 2 O were collected using equipment of the Center for Molecular Studies of the Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences. The X-ray diffraction studies for 9Zn·CH 3 OH, 9Hg·CH 3 OH and 10 were performed at the Shared Equipment Center of the Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences. The X-ray measurements were performed using shared experimental facilities supported by INEOS RAS and IGIC RAS state assignment.
Single crystals of 9Zn·CH 3 OH, 9Hg·CH 3 OH, 9Hg'·2CH 3 OH, 8·solvate, 10 and 10Cd· 1.75CH 3 OH·0.75H 2 O were obtained from reaction mixtures. Intensities of the reflections for these crystals were collected with Bruker D8 Venture (9Zn·CH 3 OH, 9Hg·CH 3 OH, 10) and Bruker Quest (9Hg·2CH 3 OH, 8·solvate and 10Cd·1.75CH 3 OH·0.75H 2 O) diffractometers (Bruker AXS, Inc., Madison, WI, USA) at 100.0(2) K (MoKα-radiation, λ = 0.71073 Å). The structures were solved by the SHELXT method [13] and refined by full-matrix least squares against F 2 . Non-hydrogen atoms were refined anisotropically. H(N) and H(O) atoms were located on difference Fourier maps, and those of H(C) atoms were calculated. The unit cell of 8·solvate contains two solvent molecules (each occupies 186 Å 3 and has 50 counts of electrons), which were treated as a diffuse contribution to the overall scattering without specific atom positions by the SQUEEZE/PLATON procedure [14]. A similar procedure was applied to treat some of the highly disordered solvent molecules in 10Cd; two voids with volumes 624 and 199 Å 3 and 399 and 106 counts of electrons were found. All hydrogen atoms were included in a refinement by the riding model with U iso (H) = 1.5U eq (X) for methyl and hydroxy groups and 1.2U eq (X) for the other atoms. All calculations were made using the SHELXL2014 [15] and OLEX2 [16] program packages. Crystallographic parameters and refinement details for all complexes are listed in Table S1. CCDC 2166661-2166666 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/structures/ (accessed on 10 April 2022).

Computational Details
The DFT calculations based on the experimental X-ray geometries of 9Hg, 9Hg', 9Zn, and 10Cd were carried out with the help of the Gaussian-09 [17] program package. The topological analysis of the electron density distribution was performed by using the Multiwfn program (version 3.7) [18]. The Cartesian atomic coordinates for model supramolecular associates are presented in the attached xyz-files, Supplementary Materials.
Triarylazoimidazoles 7-11 appear as bright red solids, 7, 8, 10, and 11 [11] could be recrystallized from saturated MeOH solutions to produce crystals, suitable for analysis by single crystal X-ray crystallography ( Figure 1). In addition, we obtained single crystals of 8 ( Figure 1), which synthesis we reported earlier [2,12]. Data about molecular and crystal structures of pure triarylazoimidazoles are limited with those for 2-(p-bromophenyl)diazen-1-yl-containing imidazole 11 [11]. Herein we compare its geometry with that of p-methoxy-and p-nitrosubstituted analogs. The main geometrical parameters of these molecules are listed in Table 1. Bond distances are very close for these molecules ( Figure 1, Table 1). All molecules adopt a trans conformation with respect to the double N3=N4 bond. The azo double bond is elongated as compared with that in azobenzene, and the imidazole ring is nearly coplanar with the aryl group attached to the azo group ( Figure 1). This fact indicates a prominent electron delocalization within the molecule. The two other substituents at carbon atoms of the five-membered ring can freely rotate along single C-C bonds, visualized in Figure 1.
Subsequent addition of group 12 metal chlorides to 7-11 resulted in the formation of chelates 7Zn-11Zn, 7Cd-11Cd, and 7Hg-11Hg (Scheme 2), which precipitated from the reaction mixtures as dark purple microcrystalline solids. The crystals of complexes 9Zn, 9Hg, and 10Cd were suitable for analysis by single crystal X-ray crystallography. Data about molecular and crystal structures of pure triarylazoimidazoles are limited with those for 2-(p-bromophenyl)diazen-1-yl-containing imidazole 11 [11]. Herein we compare its geometry with that of p-methoxyand p-nitrosubstituted analogs. The main geometrical parameters of these molecules are listed in Table 1. Bond distances are very close for these molecules ( Figure 1, Table 1). All molecules adopt a trans conformation with respect to the double N3=N4 bond. The azo double bond is elongated as compared with that in azobenzene, and the imidazole ring is nearly coplanar with the aryl group attached to the azo group ( Figure 1). This fact indicates a prominent electron delocalization within the molecule. The two other substituents at carbon atoms of the five-membered ring can freely rotate along single C-C bonds, visualized in Figure 1. Subsequent addition of group 12 metal chlorides to 7-11 resulted in the formation of chelates 7Zn-11Zn, 7Cd-11Cd, and 7Hg-11Hg (Scheme 2), which precipitated from the reaction mixtures as dark purple microcrystalline solids. The crystals of complexes 9Zn, 9Hg, and 10Cd were suitable for analysis by single crystal X-ray crystallography. The structural investigations proved the formation of azoimidazole chelate complexes  Figure 2). The Cd complex 10Cd, which contained p-NO 2 substituent by the azoaryl group, contained two chelating azoimidazoles in contrast to 9Zn and 9Hg.  Metal atoms in 9Zn and 9Hg complexes coordinate one azaimidazole ligand in a bidentate-chelate mode, and two terminal chlorine atoms to form a distorted tetrahedral Scheme 2. Synthesis of triarylazoimidazole complexes 7Zn-11Zn, 7Cd-11Cd, and 7Hg-  Metal atoms in 9Zn and 9Hg complexes coordinate one azaimidazole ligand in a bidentate-chelate mode, and two terminal chlorine atoms to form a distorted tetrahedral Metal atoms in 9Zn and 9Hg complexes coordinate one azaimidazole ligand in a bidentate-chelate mode, and two terminal chlorine atoms to form a distorted tetrahedral MN 2 Cl 2 coordination polyhedron. Asymmetric unit of 10Cd contains two independent complexes. Their conformations are compared in Figure S2; they differ mainly in disposition of phenylmethoxy and nitrophenyl groups in respect to azoaimidazole fragments. In 10Cd, the large Cd 2+ atom binds two chelating aza ligands and two terminal bromine atoms to form an octahedral CdN 4 Br 2 coordination polyhedron with the nitrogen atoms of the azo group being in axial positions. Lengths of M-Cl, M-N1, and M-N4 bonds increase from Zn 2+ to Hg 2+ and to Cd 2+ and N-M-N chelate angles decrease in the same raw (Table 1). Delocalization within the imidazole ring at coordination becomes less pronounced as it follows from elongation of single and shortening of double bonds; however, coordination of the azoaryl moiety results in elongation of the N=N bond and shortening of the N4-Ar and C1-N3 bonds. For all three complexes, all azoimidazoles retain upon coordination the trans configuration at diazo groups, and nearly planar configuration of the azoimidazole moieties. However, the N4 atom of the azo bond is situated on the same side as the N2 atom of the imidazole ring in respect to the C1-N3 bond, while for neutral ligands, it is always situated on the same side as the N1(H) atom of the ring. Interestingly, the N atom of the diethylamino group is also almost planar with CNC plane being coplanar with the Crystals 2022, 12, 680 7 of 14 plane of the azoimidazole moiety, which indicates the significant electronic conjugation in the whole system.
Interestingly, the reaction of 9 with HgCl 2 resulted in the formation of a very small batch of crystals of 9Hg' (Figures 3 and S1) along with the main product 9Hg. Although we were not able to reproduce the synthesis of 9Hg', here we give a description of the crystal structure of 9Hg' since it is a remarkable one-dimensional coordination polymer. In this complex, chlorine atoms act as terminal ligands, and deprotonated azaimidazole 9 acts as a tridentate bridging and chelating ligand, which coordinates by both N atoms of the imidazole ring and the N4 atom of the azo group. Coordination bonds for the resulting tetrahedral HgN 2 Cl 2 coordination polyhedron are very close to the 9Hg, while delocalization within the five-membered ring becomes even more pronounced than in the neutral uncoordinated ligand (Table 1). Overall complex is a chain coordination polymer parallel with crystallographic axis c (Figure 3). ening of the N4-Ar and C1--N3 bonds. For all three complexes, all azoimidazoles retain upon coordination the trans configuration at diazo groups, and nearly planar configuration of the azoimidazole moieties. However, the N4 atom of the azo bond is situated on the same side as the N2 atom of the imidazole ring in respect to the C1-N3 bond, while for neutral ligands, it is always situated on the same side as the N1(H) atom of the ring. Interestingly, the N atom of the diethylamino group is also almost planar with CNC plane being coplanar with the plane of the azoimidazole moiety, which indicates the significant electronic conjugation in the whole system.
Interestingly, the reaction of 9 with HgCl2 resulted in the formation of a very small batch of crystals of 9Hg' (Figures 3 and S1) along with the main product 9Hg. Although we were not able to reproduce the synthesis of 9Hg', here we give a description of the crystal structure of 9Hg' since it is a remarkable one-dimensional coordination polymer. In this complex, chlorine atoms act as terminal ligands, and deprotonated azaimidazole 9 acts as a tridentate bridging and chelating ligand, which coordinates by both N atoms of the imidazole ring and the N4 atom of the azo group. Coordination bonds for the resulting tetrahedral HgN2Cl2 coordination polyhedron are very close to the 9Hg, while delocalization within the five-membered ring becomes even more pronounced than in the neutral uncoordinated ligand (Table 1). Overall complex is a chain coordination polymer parallel with crystallographic axis c (Figure 3). Presence of acidic hydrogen atoms in 8, 10, 9Zn, 9Hg, and 10Cd as well as a number of solvent water and MeOH molecules in solid 9Zn, 9Hg, 9Hg', and 10Cd allows for- Presence of acidic hydrogen atoms in 8, 10, 9Zn, 9Hg, and 10Cd as well as a number of solvent water and MeOH molecules in solid 9Zn, 9Hg, 9Hg', and 10Cd allows formation of strong H-bonds in these solids. Presence of some of these hydrogen bonds in metal complexes was confirmed using DFT calculations of isolate clusters followed by analysis of electron density distribution within the QTAIM approach (see Section 3.4) [28]. Herein we should note that in pure ligand 10 H-bonded dimers (see Figure S3 9Hg', and 10Cd. Planar configuration of the ligand also allows realization of hydrophobic C-H . . . π and stacking interactions in these compounds. Particularly, in H-bonded dimers in 9Zn and 9Hg the mean plains of ligands are situated parallel at distances 3.298(3) and 3.308(2) Å, respectively. Thus, geometry of these complexes allows realization of both hydrophilic and hydrophobic interactions in solids and ligand-receptor complexes.

Absorption and Emission Profiles
Ligands 7-10 exhibited a red color in the dichloromethane solution and the main absorption band with the absorption maximum close to 500 nm and additional absorption bands in the UV range ( Figure 4, Table 2). OHCl = 163.1-165.0°). In 9Hg', the amino group is absent, but methanol molecules are connected to the coordination polymer through O-H…O and O-H…Cl interactions (Figure S3; r(O…O) = 2.716(16) Å, OHO = 130.3°; r(O…Cl) = 3.124(10) Å, OHCl = 162.6°). In 10Cd, one of the amino groups interacts with a bromine atom of a neighboring complex, two others with methanol molecules, and the fourth one with a water molecule. Solvent molecules in 10Cd also take part in O-H…O and O-H…Br bonding. Besides a strong hydrogen bond, C-H…Hal and C-H…O interactions can be found in solid 9Zn, 9Hg, 9Hg', and 10Cd. Planar configuration of the ligand also allows realization of hydrophobic C-H…π and stacking interactions in these compounds. Particularly, in H-bonded dimers in 9Zn and 9Hg the mean plains of ligands are situated parallel at distances 3.298(3) and 3.308(2) Å, respectively. Thus, geometry of these complexes allows realization of both hydrophilic and hydrophobic interactions in solids and ligand-receptor complexes.

Absorption and Emission Profiles
Ligands 7-10 exhibited a red color in the dichloromethane solution and the main absorption band with the absorption maximum close to 500 nm and additional absorption bands in the UV range ( Figure 4, Table 2).  Arylazoimidazole compounds have the absorption maximum in the near UV range around 360 nm corresponding to intraligand π-π* charge transfer (ILCT) transitions [29,30], the bathochromic shift of this maximum to 480-510 nm in ligands 9-11 can be partly attributed to electron delocalization effect due to the presence of two additional aromatic rings. Position and intensity of the ILCT absorption band is also affected by  Arylazoimidazole compounds have the absorption maximum in the near UV range around 360 nm corresponding to intraligand π-π* charge transfer (ILCT) transitions [29,30], the bathochromic shift of this maximum to 480-510 nm in ligands 9-11 can be partly attributed to electron delocalization effect due to the presence of two additional aromatic rings. Position and intensity of the ILCT absorption band is also affected by electrondonating and electron-withdrawing groups at the para-position of the aryl rings. In ligands 7 and 9, the electron density shifts upon photoexcitation from the electron-donating OMe (Et 2 N) group to the imidazole ring (electron acceptor). Correspondingly, in agreement with the previous findings [31] a stronger electron donor in the R 1 position gives 9 a higher absorption maximum (493 vs. 441 nm) and a larger extinction coefficient (38,300 vs. 28,300 M −1 cm −1 ) compared to 7 [2]. Planar geometry of the arylazoimidazole fragment facilitates ILCT, thus producing large values of the extinction coefficients of 7 and 9. In 8 and 10-11, electron-donating methoxy groups at the R 2 position induce additional charge transfer from the aryl groups attached to the imidazole ring. This effect is further strengthened by the electron-withdrawing Br and NO 2 groups at the R 1 position, resulting in increase of absorption maximum from 466 (8) to 483 (11) and 512 nm (10). Lack of planarity between imidazole-attached aryl rings and imidazole hinders intraligand charge transfer and results in smaller values of extinction coefficients of the 8, 10, and 11 ligands compared with 7 and 9. Extinction coefficients of 9-11 ligands corresponded to 22-28,000 M −1 cm −1 values reported for similar arylazoimidazole and triarylazoimidazole compounds [2].
The ILCT absorption bands of the ligands 9 and 11 exhibited a bathochromic shift, which was especially strong in case of Zn and Cd complexes of 9 giving them inten-sive blue colors ( Figure 4, Table 2). The same coordination-induced spectral shift was previously discovered for the complexes of 7 and 8 [2]. This shift is attributed to the electron-withdrawing effect of metal ions coordinated to the azo group and imidazole ring and depends on the LUMO at the N1 and N4 nitrogen atoms. Thus, the strongest coordination-induced absorption shift was observed for complexes of 9 (from 493 to ca. 590 nm in 9Zn), where electron density in the excited state was localized at the imidazole ring as a result of charge transfer induced by the Et 2 N substituent. At the same time, in ligand 10, the nitro group itself exerted a strong electron-withdrawing effect via the aromatic ring and attracted electron density from the azo and imidazole groups; as a result the bathochromic shift of the absorption maximum induced by coordination was small (from 512 to 516 nm). The complexes of 11 with a weakly electron-withdrawing Br atom at the R 1 position exhibited an intermediate shift (from 483 to 527 nm). Coordination-induced bathochromic shift of the ILCT band also depended on the metal ion and followed the trend λ maxILCT (Hg) < λ maxILCT (Cd) < λ maxILCT (Zn) [2]. Additional absorption bands appeared in the UV-Vis spectra of complexes in the spectral region between 580 and 620 nm and is attributed to metal-to-ligand charge transfer (MLCT) transition. In case of complexes 9Zn and 9Cd, this coordination-induced MLCT band was even stronger than the ILCT band at 550-560 nm, for others it appeared as a shoulder on the absorption spectrum.
Whereas ligands 9-11 were nonluminescent, all complexes exhibited red photoluminescence emission in dichloromethane solutions with emission maximum between 650 and 680 nm ( Figure 4, Table 3), similar orange or red photoluminescence with emission maximum between 600 and 660 nm was previously observed for the metal complexes of 7 and 8 [2]. Table 3. UV-Vis absorption and photoluminescence characteristics of the complexes 9Zn-11Zn, 9Cd-11Cd, and 9Hg-11Hg in dichloromethane solution. which can be highly protonated at physiological pH. The resulting cation interacts with the anionic fragments of bacterial cell surface, which causes an osmotic imbalance, damages of the bacterial cell membrane, and leakage of the cell content into the external environment. The cascade of these unfavorable events for the bacterial cell inevitably leads to the death of the bacterium. The intracellular components of bacteria are characterized by strong absorption at 260 nm. This fact was used in previous studies to monitor the integrity of the bacterial cell membrane by spectrophotometry. We used this approach within the frames of the current work to study the effect of 7-11 on the integrity of the cell membranes of S. aureus and E. coli. We found that treatment of the bacterial suspension with 7-11 caused a dramatic increase in optical density from 0.5 to 0.9 in 6 min (9), 10 min (8, 10, 11), or 20 min (7). Thus, the tested organic compounds effectively damaged the bacterial cell membrane, but the effect of 9 most rapidly developed. The highest antibacterial effect of 9 can be explained by the presence of a larger number of N-atoms that can be protonated at a physiological pH value. The antibacterial activity of Zn(II), Cd(II), and Hg(II) complexes derived from 7-11 is substantially higher than that of the staring 7-11 (Table 1). Provided the same metal center, the complexes derived from 9 are characterized by the highest antibacterial effect, while the complexes derived from 7 are the least active. Moreover, provided the same ligand, the antibacterial activity of complexes increases in the rows Zn(II), Cd(II), Hg(II), and this corresponds to the previously reported data about antibacterial activity of Zn(II), Cd(II), and Hg(II) complexes with glibenclamide or 2,6-bis(benzimidazol-2-yl) pyridine ligands [32,33]. Thus, the most effective antibacterial complex proved to be 9Hg. The antibacterial activity of this complex is almost equal to that of the reference antibiotics ampicillin and gentamicin. N-H···Br in 9Hg, 9Hg', 9Zn, and 10Cd In order to confirm or disprove the hypothesis on the existence of various most interesting intermolecular hydrogen bonding interactions N-H···O, O-H···Cl, and N-H···Br in 9Hg, 9Hg', 9Zn, and 10Cd, and approximately quantify the strength of these supramolecular contacts from a theoretical viewpoint, the DFT calculations followed by the topological analysis of the electron density distribution within the QTAIM approach [28] were carried out at the ωB97XD/SDD level of theory for model supramolecular associates (see computational details and attached xyz-files in Supplementary Materials). Results of QTAIM analysis summarized in Table 5, the contour line diagrams of the Laplacian of electron density distribution ∇ 2 ρ(r), bond paths, and selected zero-flux surfaces, visualization of electron localization function (ELF), and reduced density gradient (RDG) analyses for the selected intermolecular hydrogen bonding interactions N-H···O, O-H···Cl, and N-H···Br in 9Hg and 10Cd are shown in Figure 5 for illustrative purposes. * r(A . . . D)-bond distance (Å); AHD-bond angle ( • ); ρ(r)-values of the density of all electrons, ∇ 2 ρ(r)-Laplacian of electron density, λ 2 -appropriate eigenvalues, H b -energy density, V(r)-potential energy density, G(r)-Lagrangian kinetic energy (a.u.) at the bond critical points (3, -1), corresponding to intermolecular hydrogen bonding interactions and strength for these contacts E int (kcal/mol) estimated as −V(r)/2 [34]. Symmetry codes to generate equivalent atoms in crystal structures: (i) 1-x, 1-y, 1-z. The QTAIM analysis of model supramolecular associates demonstrates the presence of intermolecular hydrogen bonding interactions N-H···O, O-H···Cl, and N-H···Br in 9Hg, 9Hg', 9Zn, and 10Cd ( Table 5). The low magnitude of the electron density (0.020-0.031 a.u.), positive values of the Laplacian of electron density (0.061-0.135 a.u.), and zero or very close to zero positive energy density (0.000-0.002 a.u.) in these bond critical points (3, -1) as well as the estimated strength of appropriate supramolecular contacts (4.7-9.4 kcal/mol) are typical for hydrogen bonds in such chemical systems The QTAIM analysis of model supramolecular associates demonstrates the presence of intermolecular hydrogen bonding interactions N-H···O, O-H···Cl, and N-H···Br in 9Hg, 9Hg', 9Zn, and 10Cd ( Table 5). The low magnitude of the electron density (0.020-0.031 a.u.), positive values of the Laplacian of electron density (0.061-0.135 a.u.), and zero or very close to zero positive energy density (0.000-0.002 a.u.) in these bond critical points (3, -1) as well as the estimated strength of appropriate supramolecular contacts (4.7-9.4 kcal/mol) are typical for hydrogen bonds in such chemical systems [23,[35][36][37]. The balance between the Lagrangian kinetic energy G(r) and potential energy density V(r) at the bond critical points (3, -1) reveals that a covalent contribution in all discussed intermolecular hydrogen bonding interactions N-H···O, O-H···Cl, and N-H···Br in 9Hg, 9Hg', 9Zn, and 10Cd is absent, and a sign of λ 2 indicates that these supramolecular contacts are attractive.

Conclusions
Overall, we reported the synthesis and characterization of novel triarylazoimidazoles and their group 12 metal complexes. Two triarylazoimidazoles (8 and 10) and four of their metal complexes (9Zn, 9Hg, 9Hg, 10Cd) were structurally characterized. Novel complexes exhibit red photoluminescence emission (Φ up to 0.21) in a solution. Moreover, the antibacterial activity of complexes was tested against Gram-positive microorganism S. aureus and Gram-negative microorganism E. coli.

Conflicts of Interest:
The authors declare no conflict of interest.