Octacyanometallates K 4 [Mo(CN) 8 ] and K 4 [W(CN) 8 ] are completely protonated in superacidic mixtures of anhydrous hydrogen fluoride and antimony pentafluoride. The resulting hydrogen isocyanide complexes [Mo(CNH) 8 ] 4+ [SbF 6 ] - 4 and [W(CNH) 8 ] 4+ [SbF 6 ] - 4 are the first examples of eight-coordinate homoleptic metal complexes containing hydrogen isocyanide (CNH) ligands. The complexes were crystallographically characterized, revealing hydrogen-bonded networks with short N … H … F contacts. Low-temperature NMR measurements in HF confirmed rapid proton exchange even at -40 °C. Upon protonation, ṽ(C≡N) increases of about 50 cm -1 which is in agreement with DFT-calculations.