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The synthesis of potassium (η-4-allyl-2-methoxyphenol)trichloridoplatinate(II), K[PtCl(CHO)], (1), starting from Zeise's salt and Ocimum sanctum L. oil has been optimized. Starting from (1), three new platinum(II) complexes, namely (η-4-allyl-2-methoxyphenol)chlorido(2-methylquinolin-8-olato-κN,O)platinum(II), (2), (η-4-allyl-2-methoxyphenol)chlorido(5-nitroquinolin-8-olato-κN,O)platinum(II), (3), and (η-4-allyl-2-methoxyphenol)chlorido(5,7-dichloroquinolin-8-olato-κN,O)platinum(II), [Pt(CHClNO)Cl(CHO)], (4), containing eugenol and a quinolin-8-ol derivative (R-OQ), have been synthesized and characterized by elemental analyses, MS, IR, H NMR and NOESY spectra. For (1) and (4), single-crystal X-ray diffraction studies were also carried out. Complexes (2)-(4) show good inhibiting abilities on three human cancer cell lines, i.e. KB, Hep-G2 and LU, with IC values of 1.42-17.8 µM. Complex (3) gives an impressively high activity against KB, Hep-G2, LU and MCF-7, with IC values of 1.42-4.91 µM, which are much lower than those of cisplatin and some other platinum(II) complexes.

The crystal structures of cis-dichlorido(ethylamine-κN)(piperidine-κN)platinum(II), [PtCl2(C2H7N)(C5H11N)], (I), cis-dichlorido(3-methoxyaniline-κN)(piperidine-κN)platinum(II), [PtCl2(C5H11N)(C7H9NO)], (II), and cis-dichlorido(piperidine-κN)(quinoline-κN)platinum(II), [PtCl2(C5H11N)(C9H7N)], (III), have been determined at 100 K in order to verify the influence of the nonpiperidine ligand on the geometry and crystal packing. The crystal packing is characterized by N-H...Cl hydrogen bonding, resulting in the formation of chains of molecules connected in a head-to-tail fashion. Hydrogen-bonding interactions play a major role in the packing of (I), where the chains further aggregate into planes, but less so in the case of (II) and (III), where π-π stacking interactions are of greater importance.

Crystallization experiments with the dinuclear chelate ring complex di-μ-chlorido-bis[(η-2-allyl-4-methoxy-5-{[(propan-2-yloxy)carbonyl]methoxy}phenyl-κC)platinum(II)], [Pt(CHO)Cl], containing a derivative of the natural compound eugenol as ligand, have been performed. Using five different sets of crystallization conditions resulted in four different complexes which can be further used as starting compounds for the synthesis of Pt complexes with promising anticancer activities. In the case of vapour diffusion with the binary chloroform-diethyl ether or methylene chloride-diethyl ether systems, no change of the molecular structure was observed. Using evaporation from acetonitrile (at room temperature), dimethylformamide (DMF, at 313 K) or dimethyl sulfoxide (DMSO, at 313 K), however, resulted in the displacement of a chloride ligand by the solvent, giving, respectively, the mononuclear complexes (acetonitrile-κN)(η-2-allyl-4-methoxy-5-{[(propan-2-yloxy)carbonyl]methoxy}phenyl-κC)chloridoplatinum(II) monohydrate, [Pt(CHO)Cl(CHCN)]·HO, (η-2-allyl-4-methoxy-5-{[(propan-2-yloxy)carbonyl]methoxy}phenyl-κC)chlorido(dimethylformamide-κO)platinum(II), [Pt(CHO)Cl(CHNO)], and (η-2-allyl-4-methoxy-5-{[(propan-2-yloxy)carbonyl]methoxy}phenyl-κC)chlorido(dimethyl sulfoxide-κS)platinum(II), determined as the analogue {η-2-allyl-4-methoxy-5-[(ethoxycarbonyl)methoxy]phenyl-κC}chlorido(dimethyl sulfoxide-κS)platinum(II), [Pt(CHO)Cl(CHOS)]. The crystal structures confirm that acetonitrile interacts with the Pt atom via its N atom, while for DMSO, the S atom is the coordinating atom. For the replacement, the longest of the two Pt-Cl bonds is cleaved, leading to a cis position of the solvent ligand with respect to the allyl group. The crystal packing of the complexes is characterized by dimer formation via C-H...O and C-H...π interactions, but no π-π interactions are observed despite the presence of the aromatic ring.

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