Osmium(IV) complexes with 1H- and 2H-indazoles: Tautomer identity versus spectroscopic properties and antiproliferative activity

► One-pot synthesis of osmium(IV) complexes with two different indazole tautomers. ► Spectroscopic behavior, solvatochromism. ► In vitro and in vivo cytotoxic activity of (H2ind)[OsCl5(1H-ind)] and (H2ind)[OsCl5(2H-ind)].