  The ground state of a two-dimensional, harmonically confined mesoscopic
assembly of up to thirty polar molecules is studied by computer simulations. As
the strength of the confining trap is increased, clusters evolve from
superfluid, to supersolid, to insulating crystals. For strong confinement, the
crystalline structure can be predicted based on classical energetics. However,
clusters of specific numbers of particles (i.e., N=12 and N=19) display a {\it
non-classical crystalline structure}, stabilized by quantum effects, in an
intermediate range of confinement strength. In these cases, coexistence of
quantum and classical crystalline configurations is observed at finite
temperature.
