Conformational analysis and potential anticancer activity of [Pt(phen)(L1-κS)2] studied by single crystal X-ray diffraction and variable temperature 1H and 195Pt NMR spectroscopy

Abstract

The mixed-ligand [Pt(phen)(L¹-κS)₂] complex, in which two N,N-diethyl-N′-1-naphthoylthioureato ligands (L¹)⁻ coordinate in an unusual κS-thio/amido mode, crystallises in two solvatomorphs, form I and form II, whose structures have been determined by single crystal X-ray diffraction. These crystals were obtained from tetrahydrofuran and methanol/water respectively showing interesting sandwich (form I) and half-sandwich (form II) intramolecular π-stacking arrangements between the naphthoyl moiety of the acylthioureato ligands and the 1,10-phenanthroline ligand that adopt an anti-conformation above and below the square planar coordination plane. Variable temperature ¹H and ¹⁹⁵Pt NMR spectroscopy showed that these π-stacking arrangements persist in methanol solution especially at lower temperatures, where significant chemical shift shielding and asymmetry are observed indicating at least 3 conformers at −50 °C. A preliminary study indicates that this new compound may have potential as a new anticancer agent since it is active against the A549 lung cancer cell-line with an IC₅₀ value of 6 ± 0.9 μM.