Coordinated scission of N–H or O–H bonds Ammonia and water both have well-explored acid-base chemistry at room temperature, revolving around proton exchange. In contrast, radical chemistry involving H-atom exchange is comparatively rare in these molecules in the absence of a high-energy stimulus. Bezdek et al. now show that coordination of ammonia or water to a molybdenum complex substantially weakens the N–H or O–H bonds, so much so that heating to 60°C liberates hydrogen (see the Perspective by Hoover). Theoretical and electrochemical analyses reveal the underpinnings of the bond-weakening phenomenon. Science , this issue p. 730 ; see also p. 707