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Unique superhalogen properties of Pt(CN)n complexes (n = 1-6) containing cyanide (CN) pseudohalogen moieties bound with platinum (Pt) atom have been investigated under the quantum chemical formalism. The study involves theoretical calculations for both neutral and anionic forms of Pt(CN)n using density functional theory (DFT) with the hybrid functional B3LYP. In order to improve the accuracy of calculations, 6-311+G(d) basis set was implemented for CN moieties, whereas, SDD basis set supplemented with Stuttgart/Dresden relativistic effective core potential was used for Pt atom. HOMO-LUMO energy band gaps, vibrational frequencies and dissociation energies of Pt(CN)n complexes have been calculated to investigate their relative stability as well as reactivity. Additionally, superhalogen properties and salt forming capability of Pt(CN)n complexes have also been analyzed. Focus of analysis is on the delocalization of charges over attached CN ligands in successive members of the Pt(CN)n species. Reliable low-cost investigations on superacidity properties of associated protonated species have also been carried out keeping their industrial applications in mind.

Favipiravir is an antiviral medication currently being trialed as a COVID-19 treatment. These results motivate us to develop new species (possibly drugs) from favipiravir, perform comparative molecular docking, and reexamine their biological and pharmacological activities. Detailed quantum chemical research on favipiravir and its newly designed derivatives has been carried out with the help of DFT/B3LYP/6-311 + + G (d, p). In the present work, the structure of favipiravir has been modified and 12 new species have been modeled (all species are inherently stable because no virtual frequency is found during the vibration analysis). Reactivity of all species using various descriptors (local) such as Fukui function, local softness, electrophilicity, and global, i.e., electronegativity, hardness, HOMO-LUMO gap, etc. of the same are calculated and discussed. In silico studies such as molecular docking of all species and complete quantum chemistry studies suggest that four of them may mitigate the effects of the COVID-19 protease.