Spectral, Molecular Modeling, and Biological Activity Studies on New Schiff's Base of Acenaphthaquinone Transition Metal Complexes

The newly synthesized Schiff's base derivative, N-allyl-2-(2-oxoacenaphthylen-1(2H)-ylidene)hydrazine-1-carbothioamide, has been characterized by different spectral techniques. Its reaction with Co(II), Ni(II), and Zn(II) acetate led to the formation of 1 : 1 (M:L) complexes. The IR and NMR spectral data revealed keto-thione form for the free ligand. On chelation with Co(II) and Ni(II), it behaved as mononegative and neutral tridentate via O, N1, and S donors, respectively, while it showed neutral bidentate mode via O and N1 atoms with Zn(II). The electronic spectra indicated that all the isolated complexes have an octahedral structure. The thermal gravimetric analyses confirmed the suggested formula and the presence of coordinated water molecules. The XRD pattern of the metal complexes showed that both Co(II) and Ni(II) have amorphous nature, while Zn(II) complex has monoclinic crystallinity with an average size of 9.10 nm. DFT modeling of the ligand and complexes supported the proposed structures. The calculated HOMO-LUMO energy gap, ΔEH-L, of the ligand complexes was 1.96–2.49 eV range where HAAT < Zn(II) < Ni(II) < Co(II). The antioxidant activity investigation showed that the ligand and Zn(II) complex have high activity than other complexes, 88.5 and 88.6%, respectively. Accordingly, the antitumor activity of isolated compounds was examined against the hepatocellular carcinoma cell line (HepG2), where both HAAT and Zn(II) complex exhibited very strong activity, IC50 6.45 ± 0.25 and 6.39 ± 0.18 μM, respectively.


Introduction
Schiff bases are a class of compounds that contain azomethine bond, -C�N-, which results from the condensation of active carbonyl compounds with a primary amine. e Schiff bases are very versatile where the most common Schiff bases have NO donor atoms, but in many cases, the oxygen atom may be replaced by sulfur atoms or added to the donor atoms, NS or NSO, respectively [1]. ey are widely applied in several fields such as drugs [2], agriculture [3], luminescent materials [4,5], and metal anticorrosion [6]. Moreover, in inorganic chemistry, Schiff bases are an interesting ligand due to their tendency to form stable complexes with most transition metal ions. e importance of Schiff base complexes has increased as they may serve as models for biologically important species [7,8].
iosemicarbazones, as a subclass of the Schiff bases, are formed by the reaction of ketone or aldehyde and thiosemicarbazide.
eir multidonor atoms enable chelation with metal ions to form neutral or charged stable and colored complexes. e remarkable biological activities and varied structural properties of thiosemicarbazone metal complexes promoted their application in the development of therapeutic agents [1,14,15]. Lately, two compounds exhibited antitumor activity against several human cell lines [16][17][18]. e thiosemicarbazone biological properties altered by metal ion coordination, e.g., the lipophilicity that controls the penetration rate into the cell, are changed and so reduce the side effects. Furthermore, the complexes may show new bioactivity which is not displayed by the free ligand [19,20].
Literature survey showed that acenaphthaquinone and its derivatives were widely used as starting and intermediate materials for the production of different compounds that have pharmaceutical importance [21,22], pesticides, dyes, drugs, and versatile fluorescent chemosensor [23][24][25][26]. However, a few reports on acenaphthaquinone thiosemicarbazone derivatives were observed. e cell proliferation inhibition activity on Friend erythroleukemia cells (FLCs) of acenaphthaquinone mono-thiosemicarbazone derivative and its Cu(II), Ni(II), Fe(III), and Zn(II) metal complexes was reported firstly where the ligand showed stronger inhibition than metal complexes but the Zn(II) complex was higher than other metal complexes. e X-ray single crystal of free ligand showed dimer-like structure in which intramolecular and intermolecular hydrogen bonds were formed. e Ni(II) complex crystal structure indicated that it has distorted octahedral geometry and the ligand behaved as in mononegative tridentate fashion via ONS donors [24]. Moreover, the bimetallic Hg(II) and Cd(II) complexes derived from the 4-phenyl acenaphthaquinone-4-phenyl thiosemicarbazone (APTH) spectral data indicated that the ligand coordinated to the metal ion in neutral tetradentate manner via nitrogen atoms of azomethine and N 2 H groups in addition to both oxygen and sulfur atoms. e APTH was employed as a chelating agent in cloud point extraction procedure of trace amounts of Hg(II) and Cd(II) ions from aqueous medium [27]. Furthermore, the acenaphthaquinone-3-(4-benzylpiperidyl)thiosemicarbazone metal complexes with Co(II), Ni(II), Cu(II), and Zn(II) ions were isolated, and their antibacterial activity against Gram negative and positive bacteria was studied where the complexes exhibited better activity than the ligand. e improved activity was explained by means of a drop in the polarity, which favors permeation of the complexes through the lipid layer of the bacterial cell membrane [28]. e acenaphthaquinone bis(thiosemicarbazone) precipitated onto multiwall carbon nanotubes (MWCNTs) and its Zn(II) and Hg(II) complexes were characterized by IR, TGA, XRD, SEM, and TEM techniques. e antibacterial studies of the functionalized MWCNTs against Gram positive and negative bacteria indicated that the MWCNT loaded with complexes exhibited more potent effect than that loaded with ligand only [29]. Finally, the 1 : 2 (M:L) acenaphthaquinone bis(4-allyl thiosemicarbazone) complexes of Ni(II), Cu(II), and Zn(II) were obtained via onepot synthetic method. e spectral and single crystal X-ray diffraction of the complexes indicated that ligand chelated to metal ion via the azomethine nitrogen and sulfur atom in mononegative bidentate fashion. e Zn(II) complex was found to be intrinsically fluorescent, so its uptake in IGROV and MCF-7 cancer cells was monitored by confocal fluorescence imaging in addition to comparable cytotoxicity to cisplatin against MCF-7 cell line [30]. erefore, herein, the synthesis, structure, and cytotoxic activity of a new Schiff base derivative of acenaphthaquinone, N-allyl-2-(2-oxoacenaphthylen-1(2H)-ylidene)hydrazine-1carbothioamide, and its metal complexes were reported.
e TG measurement was carried out using Shimadzu model 50 instrument under nitrogen flow (10 cm 3 /min) and 15°C/min heating rate. e mass spectra were recorded on a ermo-Scientific DSQ II spectrometer.
e powder X-ray diffraction spectra of the metal complexes were recorded on Bruker AXS D8 Advance diffractometer (Cu-Kα radiation of wavelength λ � 1.5406Å source). Magnetic moment measurements were carried out on a Sherwood Scientific magnetic balance. e complexes' molar conductance, 10 −3 mol/l in DMF, was recorded on Tacussel conductivity bridge CD6NG.

In Vitro Antitumor Activity.
e hepatocellular carcinoma cell line (HepG2) was used to investigate the anticancer activity by the well-known MTT assay established on the change in color from yellow to purple due to the conversion of tetrazolium bromide (MTT) to formazan derivative in viable cells, and the relative cell viability % was calculated [39,40]. e RPMI-1640 with 10% fetal bovine serum was utilized as a medium for the culture of the HepG2.

Results and Discussion
e reaction of HAAT with the Co(II), Ni(II), and Zn(II) acetate led to the formation of 1 : 1 (M:L) complexes (Table 1). All the isolated solid complexes have nonelectrolytic nature where their molar conductance was 9.8-10.3 Ω −1 ·cm 2 ·mol −1 [41]. All isolated solid complexes are soluble only in DMF and DMSO.
e new bands at 528 and 500 cm −1 were attributed to ](M-O) in addition to a band at 477 cm −1 which was assigned to ](M-N) [45,49]. Comparison with the ligand spectral data cleared that the bands due to ](C�O), ](C�N), and ](C�S) vibrations were shifted to lower wavenumber which indicated their participation in coordination with the metal ion. Hence, the ligand chelated with the metal ion as neutral tridentate via NOS atoms ( Figure 3).
Finally, the spectrum of [Zn(HAAT) (OAc) 2 ] complex presented ](N 4 H), ](N 2 H), and ](C�S) vibrational bands at 3323, 3264, and 935 cm −1 [43,45], respectively, which are almost at the same position exhibited in ligand spectrum and so endorsed that they are free (Table 2). Additionally, the spectrum showed two bands at 1677 and 1656 cm −1 ascribed to ](C�O) and ](C�N 1 ) [45,46] vibrations, respectively. e new bands at 1722 and 1568 cm −1 were assigned to ] as (OAc) and ] s (OAc) vibrations, respectively, of bidentate acetate ion (difference ≈ 154 cm −1 ) [45,48]. e new bands observed at 526 and 492 cm −1 were attributed to ](M-O) in addition to a band at 482 cm −1 which was assigned to ](M-N) [45,49]. Accordingly, the data revealed that ](C�O) and ](C�N 1 ) bands were shifted to lower or higher wavenumber, with respect to the ligand, which designated their participation in coordination with the metal ion as neutral bidentate via NO atoms ( Figure 4).

1 H NMR Spectral Data.
e ligand 1 H-NMR spectrum, in DMSO-d 6 , displayed singlet signals at 12.65 and 9.55 ppm due to N 4 H and N 2 H protons [27,44], respectively (Figure 1). As well, to confirm assignment, the addition of D 2 O solution led to the disappearance of these two signals ( Figure 5(a)). Furthermore, the spectrum displayed two doublet signals at 8.37 and 8.10 ppm in addition to two multiplet signals at 8.03 and 7.86 ppm assigned to the acenaphthaquinone protons at positions (d), (e), (f ), and (g) [27,44], respectively. In addition, three signals were observed at 5.96, 5.19, and 4.31 ppm and were attributed to (CH) allyl , (CH 2 ) allyl , and CH 2 protons [44,46], respectively. e spectrum of Zn(II) complex in d 6 -DMSO, compared to the ligand, displayed the singlet signals of both N 4 H and N 2 H at 12.65 and 9.55 ppm [27,44], the same positions shown in the ligand spectrum, which confirmed that they are free and the ligand existed in a thione form ( Figure 5(b)).    [27,44], respectively. e signals due to (CH) allyl , (CH 2 ) allyl , and CH 2 protons were observed at 5.95, 5.21, and 4.32 ppm [44,46], respectively.

Mass Spectra.
e HAAT mass spectrum confirmed the proposed molecular formula as it showed a molecular ion peak at m/z � 295 (22.95 %) that was coincided with its molecular weight (295.36) (Figure 6). e spectrum showed a weak peak at m/z � 280 (5.99%) which may be due to the loss of methyl radical from the allyl moiety, • CH 3 (Route I), or oxygen atom of the carbonyl group, • O (Route II), as shown in the fragmentation pattern (Scheme 1). Another peak observed at m/z � 254 and attributed to C 13 H 8 N 3 OS • and C 14 H 12 N 3 S • formulae in routes I and II, respectively, resulted from the loss of • C 2 H 2 moiety in both routes. e observed peak at m/z � 239 was ascribed to loss of • NH and • CH 3 radicals that led to the formation of C 13 H 7 N 2 OS • and C 13 H 9 N 3 S • moieties (F. Wt. 239.03 and 239.05) in routes I and II, respectively. Furthermore, the spectrum exhibited a base peak at m/z � 180 (100%) corresponding to the formula C 12 H 6 NO • (180.04) and C 12 H 8 N 2 •+ (180.07) in routes I and II, respectively (Scheme 1).
On the other hand, the Co(II), Ni(II), and Zn(II) complexes' mass spectra showed quite a lot of peaks where the most important one was the molecular ion peak that was observed at 458. 37

Electronic Spectra and Magnetic Moment Measurements.
e electronic spectrum of the ligand, in DMF, showed two bands at 35460 and 28570 cm −1 with a shoulder at 32890 cm −1 attributable to the π ⟶ π * transition of aromatic acenaphthaquinone moiety, carbonyl group, and both of azomethine and thione groups [44], respectively (Table 3). Moreover, the spectrum displayed a broad band at 21835 cm −1 with two shoulders at 22830 and 25000 cm −1 assigned to the n ⟶ π * transitions of thione, azomethine, and carbonyl groups [44,48], respectively ( Figure S7(a)).

ermal Analyses.
e thermogravimetric analyses of the ligand and isolated solid complexes confirmed the existence of H 2 O and/or EtOH molecules whichever outside or inside the chelation sphere. e thermal analysis curve of HAAT showed two decomposition steps at the 150-380 and 380-715°C range. e first step was attributed to the loss of the thione and allyl groups, C 4 H 6 NS (Found: 34.44%; Calcd.: 34.35%), while the second step corresponded to the complete decomposition of the ligand (Found: 61.35%; Calcd.: 61.63%) leading to a carbon ash residue (Found: 4.21%; Calcd.: 4.12%) ( Figure S8). e Co(II) and Zn(II) complexes' TG curves displayed only two successive decomposition stages over 125-445 and 445-610°C ranges. e first stage of the Co(II) complex was due to the loss of coordinated ethanol molecule and acetate anion (Found: 22.12%; Calcd.: 22.92%) while that of Zn(II) was due to the loss of the acetate anions (Found: 25.01%; Calcd.: 24.66%). e second stage in both complexes was attributed to complete decomposition of the ligand leading to a residue of metallic residue (Found: 12.95 and 13.80%; Calcd.: 12.86 and 13.65%, for Co(II) and Zn(II) complexes, respectively) ( Table 4). Finally, the curve of the Ni(II) complex showed that it has thermal stability up to 155°C at which the first decomposition step was observed and attributed to the loss of the coordinated water molecule and acetate anions (Found: 28.01%; Calcd.: 27.75%). e second step was observed over the 390-455°C range and corresponds to the loss of C 3 H 6 N moiety (Found: 11.78%; Calcd.: 11.44%). e third degradation step was extended from 455°C to 640°C and attributed to complete decomposition of the ligand (Found: 48.90%; Calcd.: 48.84%) leaving a metallic residue of nickel metal (Found: 11.31%; Calcd.: 11.97%) ( Figure S9).   (Figure 7). Powder XRD peaks were indexed into the face-centered monoclinic and P21/c (14) space group with a lattice constant; a � 8.405 ± 0.0003, b � 10.183 ± 0.0001, c � 13.731 ± 0.0002Å, α � 90°, β � 104.4°, and c � 90° [53]. e calculated interplanar spacing, d, together with relative intensities of the most intense peak was recorded and depicted in Table 5. Using the interplanar spacing (d) and miller indices (hkl), the lattice parameters of monoclinic (2) powder were evaluated from the peak position using the following relation [54,55]: e crystalline size of the Zn(II) complex, D, was evaluated using Debye-Scherrer's equation [56], D � 0.9 λ/βcosθ, where λ is the X-ray wavelength and β is the full width at half maximum intensity (FWHM). e obtained   e lattice strain was determined from the relation, ε � β/4tanθ [57,58], and was found to be 33.58 × 10 −3 , which denotes high lattice strain. Moreover, the dislocation density, δ, which refers to the crystal imperfection, was determined from Williamson and Smallman's relation, δ � 1/D 2 [59], and was found to be in the range from 3.76 to 56.95 × 10 −3 nm with an average value of 24.84 × 10 −3 nm which reflects the remarkable change of the grain size with values of 2θ of the complex.

Optical Band Gap.
Tauc's equation was applied to estimate the optical band gap (E g ) of the ligand and complexes from their absorption spectra, αh] � A (h] -E g ) r , where A and r are independent constants. e r value for the indirect transition was 1/2 while, for direct transition, it equals 2 [60,61]. e intercept with the x-axis, h], in the plot of (αh]) r against (h]) at different r values, established by linear portion extrapolating, represents the optical band gap (E g ). e plots of the ligand and complexes revealed that the transition mechanism that occurred is a direct one where at r � 2, the straight-line was obtained ( Figure 8). e data showed that the ligand has a higher E g value than complexes, 2.56 eV, while the Ni(II) complex has the lowest one, 2.18 eV (Table 6). erefore, it was concluded that the ligand and complexes have a semiconductive and efficient photovoltaic nature [62][63][64][65][66].

Molecular Modeling.
e HAAToptimized structure has a planar configuration as the dihedral angles data showed, for instance, that both the carbonyl oxygen and azomethine nitrogen atoms were coplanar with each other and the moiety, O-C nph-o -C nph-n -N 1 � -0.12° (Table S1). Likewise, the thiosemicarbazone moiety was planar and coplanar with acenaphthaquinone where N 1 -N 2 -CS-N 4 and N 2 -C S -N 4 -C allyl were 0.28 and 179.44°, respectively (Figure 9(a)). e ligand's bond lengths presented almost matched those obtained from single-crystal X-ray data of similar compounds [67], differences in 0.1 to 0.2Å range (Table S2). e azomethine bond angle, N 2 -N 1 -C nph-n , exhibited an ideal value for the sp 2 hybridization, 120.57°, while the carbonyl group suffered from small distortion from the standard value, 126.59°. e sp 3 hybrid NH groups showed more deviation from the standard value, 109.5°, where, e.g., C S -N 2 -N 1 and C allyl -N 4 -C S were 120.39 and 124.04°, respectively (Table S3).
On the other hand, the DFT optimized structure Co(II) complex revealed octahedral geometry around the metal atom in which the ligand has an angular configuration (Figure 9(b)). e dihedral angle data showed that both carbonyl oxygen and azomethine nitrogen were almost planar as O-C nph-o -C nph-n -N 1 � -8.73°while the thiocarbonyl carbon, C s , and N 2 H nitrogen atoms were tilted on the acenaphthaquinone plane by more than 110°as C S -N 2 -N 1 -C nph-n and C nph-o -C nph-n -N 1 -N 2 were -112.43 and 131.97°, respectively. e Co(II) atom slightly deviated from the acenaphthaquinone plane where C nph-n -C nph-o -O-Co and C nph-o -C nph-n -N 1 -Co angles were 19.27 and -8.08°, respectively. e bond angle data cleared that the complex has a small degree of distortion as, for example, the O-Co-N 1 , S-Co-N 1 , and O-M-S were 92.30, 86.94, and 97.02°, respectively, which are higher or lower than the ideal value (90°). Furthermore, another type of distortion was observed from the bond length data as the Co-S, 2.24Å, was longer than M-N 1 and M-O, 1.86 and 1.92Å, respectively, but compatible with the corresponding X-ray values [28,67] (Tables S1-S3).
As Co(II) complex, the Ni(II) complex exhibited less bond angle distortion from ideal values of the octahedral structure (Figure 9(c)); e.g., O-Ni-N 1 , S-Ni-N 1 , and O-Ni-S angles were 94.40, 88.31, and 176.93°, respectively. Moreover, the ligand has a less angular configuration, in comparison with the Co(II) complex, where the angle between the carbonyl oxygen and azomethine nitrogen, O-C nph-o -C nph-n -N 1 , was -5.80°while the thiocarbonyl carbon and N 2 H nitrogen atoms were tilted on the acenaphthaquinone plane as C S -N 2 -N 1 -C nph-n and C nph-o -C nph-n -N 1 -N 2 were -158.32 and 127.30°, respectively. e Ni(II) atom deviated from the acenaphthaquinone plane where the C nph-n -C nph-o -O-Ni and C nph-o -C nph-n -N 1 -Ni angles were 14.34 and -6.51°, respectively. Likewise, the bond lengths exhibited another type of distortion as the Ni-S bond was longer than M-N 1 and M-O bonds by ∼ 0.5Å but all were in accordance with the similar complexes reported previously [28,67] (Tables S1-S3).
Moreover, in Zn(II) complex, the dihedral angles indicated that the carbonyl oxygen, azomethine nitrogen, and N 2 H nitrogen atoms were coplanar to each other and the acenaphthaquinone moiety (Figure 9(d)), where O-C nph-o -C nph-n -N 1 � -0.70°and C nph-o -C nph-n -N 1 -N 2 � 177.88°. However, the thiocarbonyl carbon atom was tilted on the plane as C S -N 2 -N 1 -C nph-n � 154.41°. e Zn(II) atom slightly deviated from the acenaphthaquinone plane where the C nphn -C nph-o -O-Zn and C nph-o -C nph-n -N 1 -Zn angles were 0.15 and 0.82°, respectively. Likewise, the Zn(II) complex exhibited small bond length distortion as Zn-N 1 was longer than Zn-O bonds by 0.04-0.05Å and was in agreement with the X-ray reported values [28,67] (Tables S1-S3).
On the other hand, the energies of the frontier molecular orbitals, HOMO and LUMO, were determined where they act as electron donor and accepter, respectively. Figure 10 displayed the 3D plots of HOMO and LUMO orbitals of the investigated compounds. As shown in Table 6, the Co(II) complex has the lowest HOMO and LUMO energies (E H and E L ) while the Zn(II) complex exhibited the highest energies. e chemical stability and intramolecular charge transfer may be correlated with the HOMO-LUMO energy gap, ΔE H-L , where the ΔE H-L decrease results in more feasible charge transfer which is one of the significant factors affecting the molecule bioactivity [68][69][70]. e isolated compounds presented ΔE H-L gap ranging from 1.96 to 2.49 eV and may be ordered as HAAT > Zn(II) > Ni(II) > Co(II) ( Table 6). Moreover, it was observed that the ΔE H-L gap was lower than the optical band gap (Eg) by only 0.05-0.60 eV.
Finally, the obtained E H and E L values were employed to determine some chemical reactivity descriptors like electronegativity (χ), global hardness (η), softness (δ), and electrophilicity (ω) using the following equations [68] ( Table 6). e data indicated that the Co(II) complex has the highest Lewis acid character and charge transfer resistance, large χ, and η, respectively. e ligand has the highest electronic acceptability, softest, and electrophilicity that measure the energy reduction that originated from HOMO-LUMO electron flow, high δ, and ω, respectively.   hydrogen peroxide radicals, cause many life-threatening diseases. Human diseases, like cancer, diabetic mellitus, hypertension, and aging, may be initiated by the ROS capability to destruct DNA, proteins, and membrane functions. e ROS are a by-product of normal metabolism in different subcellular compartments, even under optimal circumstances [71][72][73]. e ligand and complexes were examined as an antioxidant by the ABTS method in which L-ascorbic acid was used as a standard material. e data showed that the ligand and Zn(II) complex have high activity than other complexes and close to the ascorbic acid, 88.5 and 88.6%, respectively (Table 7). e Ni(II) complex has comparable activity, 81.4%, while the Co(II) complex was the lowest one, 65.3% ( Figure 11). Comparison with previously reported allyl thiosemicarbazide compound, HADTsc [46], indicated that the HAAT and its complexes exhibited slightly higher antioxidant activity than HADTsc.
Finally, the L-ascorbic acid antioxidant activity may originate from its action as a reducing substance; i.e., it donates high-energy electrons to neutralize free radicals [74]. us, the activity of ligand may be attributed to its capability to serve as electron donors via heteroatom lone pair of electrons and its low HOMO energy. Moreover, the higher Zn(II) complex activity, in comparison with other complexes, may be attributed to the change in chelation environment around metal ion as all complexes have octahedral geometry but only the Zn(II) complex has higher electron donor ability due to the lone pair of electron of the free sulfur atom as well as lower HOMO energy.

In Vitro Antitumor Activity.
e thiosemicarbazones and its complexes presented well-established anticancer activity [75,76] which stimulated the study of HAAT and its metal complexes' cytotoxic activities against the hepatocellular carcinoma cell line (HepG2), the main type of liver cancer that is the second cause of cancer-related death [77] ( Table 7). Like the antioxidant activity, both HAAT and Zn(II) complex exhibited very strong activity, IC 50 6.45 ± 0.25 and 6.39 ± 0.18 μM, respectively, comparable to the doxorubicin standard, 4.50 ± 0.2 μM. e Ni(II) complex has moderate activity, IC 50 21.46 ± 0.72, while the Co(II) complex has weak cytotoxic activity, weak activity 67.31 ± 1.35 μM (Figure 11). In comparison with the data of allyl thiosemicarbazide compound, HADTsc [46] earlier reported, it was clear that the HAAT and its complexes displayed higher cytotoxic activity than HADTsc. Moreover, the average cells' relative viability percent at different concentrations of examined compounds indicated that ligand has a higher potent effect than the complexes at different concentrations while the Zn(II) complex was the most active complex (Figure 12). e selectivity index (SI) was calculated as the average of the IC 50 value in the normal cell line divided by the IC 50 value in the cancer cell line obtained, where the SI > 2 indicates high selectivity [78] (Table 7). Although both HAAT and Zn(II) complex exhibited very strong activity, their SI was 1.14 and 1.28, respectively, which indicated that they processed low selectivity toward the cancer cells. Also, the Co(II) and Ni(II) complexes exhibited lower SI in accordance with their high IC 50 values. Finally, the biological activity of metal complexes mainly depends on the coordination sphere around the central metal ion. According to Tweedy's chelation theory, the chelation process leads to a reduction of the metal atom polarity through partial sharing of its positive charge with donor groups and possible electron delocalization over the entire molecule which results in increasing the lipophilic character of the complex.
us, chelation enhances the penetration of the complexes through the cell membrane    and the deactivation of various cellular enzymes metalbinding sites in addition to denaturation of cellular proteins causing the normal cellular processes to be impaired [79][80][81]. Hence, from the structure point of view, the Zn(II) complex has an octahedral geometry, like other complexes, in which the ligand chelated via the carbonyl oxygen and azomethine nitrogen atoms while the sulfur atom is free in addition to two bidentate acetate ions. erefore, its activity may originate from (i) higher permeability through the cell membrane as it has more lipophilic character and (ii) the capability to form hydrogen bonds via the free sulfur atom with the active centers of different cellular constituents resulting in interference with normal cellular processes [79][80][81].

Conclusion
e spectral characterization of the new Schiff's base derivative, HAAT, N-allyl-2-(2-oxoacenaphthylen-1(2H)-ylidene)hydrazine-1-carbothioamide, revealed that it is in thione form. e HAAT formed 1 : 1 (M:L) octahedral complexes with Co(II), Ni(II), and Zn(II) acetates. e ligand chelated with Co(II), Ni(II), and Zn(II) ions as ONS donor in mononegative and neutral tridentate in Co(II) and Ni(II) complexes, respectively, while in Zn(II) complex, it acts as neutral bidentate, via ON atoms. e DFT calculations showed that the ligand has a planar structure while it has bent conformation reflecting its flexibility. e antioxidant activity investigation revealed that the ligand and Zn(II) complex have high activity almost equal to the standard material, ascorbic acid. Similarly, the MTT assay was utilized for the examination of the antitumor activity using the hepatocellular carcinoma cell line (HepG2). e data revealed that the ligand and Zn(II) complex presented very strong activity.
Data Availability e data that support the findings of this study are available in the supplementary material of this article.

Conflicts of Interest
e authors declare that they have no conflicts of interest. Figure S1: IR spectrum of HAAT in comparison with acenaphthaquinone. Figure S2: IR spectrum of Co(II) complex. Figure S3: IR spectrum of Ni(II) complex. Figure S4: e mass spectrum of the Co(II) complex. Figure S5: e mass spectrum of the Ni(II) complex. Figure S6: e mass spectrum of the Zn(II) complex. Figure S7: Electronic spectra of HAAT (a) and Co(II) complex (b). Figure S8: e TG curve of HAAT. Figure S9: e TG curve of Ni(II) complex. Figure S10: e powder XRD pattern of the Co(II) and Ni(II) complexes. Table S1: DFT calculated dihedral angles of the ligand and metal complexes (°). Table S2: DFT calculated bond length of the ligand and metal complexes (Å). Table S3: DFT calculated bond angles of the ligand and metal complexes (°). (Supplementary Materials)