The reaction of 4-hydroxyquinazoline (4HQZ) with aqueous solution of nitric acid afforded the corresponding quinazolinone-nitrate (4HQZN) complex in very good yield. The crystal structure of 4HQZN was determined and its structural and supramolecular structural aspects were analyzed. 4HQZN crystallized in the space group P21/c and monoclinic crystal system with one [4HQZ-H]+[NO3]− formula and Z = 4. Its supramolecular structure could be described as a 2D infinite layers in which the 4HQZN molecules are connected via N-H…O and C-H…O hydrogen bridges. Using DFT calculations, the relative stability of five suggested isomers of 4HQZN were predicted. It was found that the medium effects have strong impact not only on the isomers’ stability but also on the structure of the 4HQZN. It was found that the structure of 4HQZN in DMSO and methanol matched well with the reported X-ray structure which shed the light on the importance of the intermolecular interactions on the isomers’ stability. The structure of 4HQZN could be described as a proton transfer complex in which the nitrate anion acting as an e-donor whiles the protonated 4HQZ is an e-acceptor. In contrast, the structure of the isolated 4HQZN in gas phase and in cyclohexane could be described as a 4HQZ…HNO3 hydrogen bonded complex. Biological screening of the antioxidant, anticancer and antimicrobial activities of 4HQZ and 4HQZN was presented and compared. It was found that, 4HQZN has higher antioxidant activity (IC50 = 36.59 ± 1.23 µg/mL) than 4HQZ. Both of 4HQZ and 4HQZN showed cell growth inhibition against breast (MCF-7) and lung (A-549) carcinoma cell lines with different extents. The 4HQZ has better activity with IC50 of 178.08 ± 6.24 µg/mL and 119.84 ± 4.98 µg/mL, respectively. The corresponding values for 4HQZN are 249.87 ± 9.71 µg/mL and 237.02 ± 8.64 µg/mL, respectively. Also, the antibacterial and antifungal activities of 4HQZN are higher than 4HQZ against all studied microbes. The most promising result is for 4HQZN against A. fumigatus (MIC = 312.5 mg/mL).
Two 1D coordination polymers were synthesized by reaction of two ligands, 2-amino-4-picoline (2A4Pic) and quinoline-6-carboxylic acid (Qu-6-COOH) with two metal (II) nitrate (M = Cd and Cu) in the presence of azide as a linker. The synthesized metal complexes [Cd(2A4Pic)2(N3)2]n; (1) and [Cu(Qu-6-COO)(N3)(H2O)]n; (2) were isolated in single crystals and their X-ray structures revealed a 1D polymeric structure. Due to symmetry considerations, the asymmetric formula is half a [Cd(2A4Pic)2(N3)2] unit for 1 and one [Cu(Qu-6-COO)(N3)(H2O)] unit for 2. In complex 1, the Cd(II) is hexa-coordinated with two 2A4Pic molecules and four μ(1,1) azide units. Hence, the CdN6 coordination environment has a slightly distorted octahedral geometry. In 2, the Cu(II) is hexa-coordinated with three different ligands (Qu-6-COO¯, H2O and μ(1,1) N3¯) where all are connectors between the crystallographically related Cu(II) sites. Additionally, complex 2 distorted CuN2O4 octahedral geometry. In both complexes, the polymer arrays are connected by N…H hydrogen bonds and π–π stacking interactions. Based on Hirshfeld analysis, the percentages of N…H contacts are 43.1 and 27.4% for 1 and 2, respectively, while %C...C are 5.6 and 9.3%, respectively. Analysis of Cu-N, Cu-O, and Cd-N bonds using DFT calculations showed predominantly closed-shell coordination interactions with little covalent characters. Additionally, the negatively charged ligand groups were found to compensate the positive charge of the central metal ion to a larger extent than the electrically neutral ligands.
The two complexes, [Ni(DPPT)2](NO3)2*1.5H2O (1) and [Ni(DPPT)(NO3)Cl].EtOH (2), were synthesized using the self-assembly of (E)-2,4-di(piperidin-1-yl)-6-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)-1,3,5-triazine (DPPT) with Ni(NO3)2*6H2O in the absence and presence of NiCl2*6H2O, respectively. In both cases, the neutral tridentate DPPT ligand is found coordinated to the Ni(II) via three N-atoms from the hydrazone, pyridine and s-triazine rings. Hence, the homoleptic complex 1 has a NiN6 hexa-coordination environment while two NO3− are counter anions in addition to one-and-a-half crystallized hydration water molecules are found acting as an outer sphere. The heteroleptic complex 2 has a NiN3O2Cl coordination sphere where the coordination environment of the Ni(II) is completed by one bidentate nitrate and one chloride ion leading to a neutral inner sphere while the outer sphere contains one crystallized ethanol molecule. Both complexes have distorted octahedral coordination environments around the Ni(II) ion. Using Hirshfeld analysis, the intermolecular contacts H…H and O…H in 1 and the Cl…H, O…H, N…H, H…H, C…H and C…C in 2 are found to be the most important for crystal stability. The antimicrobial activity of complexes 1 and 2 was assessed against different bacterial and fungal strains, and the results were compared with the free ligand as well as the antibacterial (Gentamycin) and antifungal (Ketoconazole) positive controls. Both Ni(II) complexes are better antibacterial and antifungal agents than the free ligand. Interestingly, both Ni(II) complexes have similar antifungal activity against C. albicans compared to Ketoconazole.
The synthesis and crystal structures of three heteroleptic complexes of Zn(II) and Cd(II) with pyridine ligands (ethyl nicotinate (EtNic), N,N-diethylnicotinamide (DiEtNA), and 2-amino-5-picoline (2Ampic) are presented. The complex [Zn(EtNic)2Cl2] (1) showed a distorted tetrahedral coordination geometry with two EtNic ligand units and two chloride ions as monodentate ligands. Complexes [Zn(DiEtNA)(H2O)4(SO4)]·H2O (2) and [Cd(OAc)2(2Ampic)2] (3) had hexa-coordinated Zn(II) and Cd(II) centers. In the former, the Zn(II) was coordinated with three different monodentate ligands, which were DiEtNA, H2O, and SO42−. In 3, the Cd(II) ion was coordinated with two bidentate acetate ions and two monodentate 2Ampic ligand units. The supramolecular structures of the three complexes were elucidated using Hirshfeld analysis. In 1, the most important interactions that governed the molecular packing were O···H (15.5–15.6%), Cl···H (13.6–13.8%), Cl···C (6.3%), and C···H (10.3–10.6%) contacts. For complexes 2 and 3, the H···H, O···H, and C···H contacts dominated. Their percentages were 50.2%, 41.2%, and 7.1%, respectively, for 2 and 57.1%, 19.6%, and 15.2%, respectively, for 3. Only in complex 3, weak π-π stacking interactions between the stacked pyridines were found. The Zn(II) natural charges were calculated using the DFT method to be 0.8775, 1.0559, and 1.2193 for complexes 1–3, respectively. A predominant closed-shell character for the Zn–Cl, Zn–N, Zn–O, Cd–O, and Cd–N bonds was also concluded from an atoms in molecules (AIM) study.
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