  Among the factors determining the quantum coherence of the spin in molecular
magnets is the presence and the nature of nuclear spins in the molecule. We
have explored modifying the nuclear spin environment in Cr$_7$Ni-based
molecular nanomagnets by replacing hydrogen atoms with deuterium or the halogen
atoms, fluorine or chlorine. We find that the spin coherence, studied at low
temperatures by pulsed electron spin resonance, is modified by a range of
factors, including nuclear spin and magnetic moment, changes in dynamics owing
to nuclear mass, and molecular morphology changes.
