  We have studied complexes of gold atoms and imidazole (C$_3$N$_2$H$_4$,
abbreviated Im) produced in helium nanodroplets. Following the ionization of
the doped droplets we detect a broad range of different Au$_m$Im$_n^+$
complexes, however we find that for specific values of $m$ certain $n$ are
"magic" and thus particularly abundant. Our density functional theory
calculations indicate that these abundant clusters sizes are partially the
result of particularly stable complexes, e.g. AuIm$_2^+$, and partially due to
a transition in fragmentation patterns from the loss of neutral imidazole
molecules for large systems to the loss of neutral gold atoms for smaller
systems.
