Magnetic susceptibility, electron spin resonance, and C-13 nuclear-mag
netic-resonance data on NH3K3C60 reveal that NH3K3C60 is a narrow-band
metal with a transition to an insulating ground state at 40 K. This t
ransition suppresses the superconductivity that is expected to occur a
t around 30 K according to a simple empirical relation between T-c and
the cell volume in alkali-metal-doped C-60 superconductors.