Hydrogen-Bonded Organic⁻Inorganic Hybrid Based on Hexachloroplatinate and Nitrogen Heterocyclic Cations: Their Synthesis, Characterization, Crystal Structures, and Antitumor Activities In Vitro

Abstract

Three new crystal structures containing [PtCl₆]²⁻, pyridinium and benzimidazole groups have been prepared: [PtCl₆]·(H-bzm)₂·2(H₂O) (1), [PtCl₆]·(H-bipy)₂·2(H₂O) (2), [PtCl₆]·(H-dimethyl-bipy)₂·2(H₂O) (3) [H-bzm: benzimidazole cation, H-bipy: 2,2′-bipyridine cation, H-dimethyl-bipy: 4,4′-bimethyl-2,2′-bipyridine cation]. All compounds have been fully characterized by elemental analyses, single-crystal X-ray analyses, IR spectra, TG analyses, and fluorescence studies. Single-crystal X-ray diffraction analysis suggests that the primary synthon contains ⁺N⁻H···Cl⁻, including ionic bonding and hydrogen bonding interactions. The dimensions are enhanced further by secondary O⁻H ∙∙Cl and N⁻H ∙∙O hydrogen bonding interactions between donor and acceptor atoms located at the periphery of these synthons. Moreover, coulombic attractions between the ions play an important role in reinforcing the structures of these complexes. In addition, antitumor activity against human lung adenocarcinoma cell line (A549) and human nasopharyngeal carcinoma cell line (CNE-2) was performed. These complexes all showed inhibition to the two cell lines, while complex 3 exhibited higher efficiency than complexes 1⁻2.

Keywords: antitumor activities; hydrogen bonding; organic–inorganic hybrid complexes; structure.

Scheme 1

Organic cations to form the target complexes.

Scheme 2

Synthesis route for complexes 1–3.

Figure 1

View of the asymmetric unit of complex 1 with the numbering scheme. The thermal probability is drawn at 30%. Symmetry codes: i = x, −y, −z; ii = −x, −y, −z; iii = −x, y, −z.

Figure 2

Hydrogen-bonded motifs for complex 1. Hydrogen bonds are shown as dashed lines.

Figure 3

View of the asymmetric unit of complex 2 with the numbering scheme. The thermal probability is drawn at 30%. Symmetry code: i = −x, −y, −z.

Figure 4

Hydrogen-bonded motifs and the packing graphic for complex 2. Hydrogen bonds are shown as dashed lines.

Figure 5

View of the asymmetric unit of complex 3 with the numbering scheme. The thermal probability is drawn at 30%. Symmetry code: i = 2 − x, −y, −z.

Figure 6

Hydrogen-bonded motifs and the packing graphic for complex 3. Hydrogen bonds are shown as dashed lines.

Figure 7

TGA curves of complexes 1–3.

Figure 8

UV-vis spectra of complexes 1–3 in methanol.

Figure 9

Solid-state emission spectra for complexes 1–3.

Figure 10

Induction of apoptosis in tumor cells by complexes 1–3.

Figure 11

The cell cycles of A549 and CNE-2 treated with 24.6 μmol/L complex 3 for 48 h by FCM.