‘Optimized route’ to synthesize isoelectronic and isostructural Au(iii)- and Pt(ii)-NHC complexes: synthesis, structure, spectral properties, electrochemistry, and molecular docking studies

Abstract

We report the synthesis, structures, luminescent properties, and electrochemistry of gold(III) and platinum(II)-N-heterocyclic carbene complexes. The proligand 1-methyl-2-(pyridylmethyl)imidazo[1,5-a]pyridin-4-ylium hexafluorophosphate, (1·HPF₆), and two novel isoelectronic and isostructural complexes, viz. [Au(1)₂][PF₆]₃ (2), [Pt(1)₂][PF₆]₂ (3), were synthesized and characterized by several spectroscopic studies. Finally, the single crystal X-ray diffraction studies established the square planar geometry of both complexes 2 and 3. The solid state structures of both the square planar complexes revealed two C_carbene and two N_pyridine present in trans fashion around the central metal ions. The complexes showed strong absorbance at ∼350 nm and DFT studies demonstrated the ILCT transition. Both complexes are luminescent at ∼400 nm. DFT and TDDFT studies were performed to gain insights into the experimental findings of solid-state structures and electronic properties. Electrochemical studies of Au(III)-NHC complex 2 showed two irreversible Au(III) → Au(I) and Au(I) →Au(0) reductions at −0.75 V and −1.28 V, whereas Pt(II)-NHC complex 3 revealed Pt(II/IV) two-electron reversible oxidation potential at 0.53 V. Molecular docking analysis revealed the highest free binding energy for complex 3 with human-DNA topoisomerase as compared to complex 2 and proligand 1·HPF₆. Pharmacokinetics studies revealed the scope of the complexes to be potent drugs.