  The thermal and phase properties of a multifragmentation model which uses
clusters as degrees of freedom, are explored as a function of isospin. A good
qualitative agreement is found with the phase diagram of asymmetric nuclear
matter as established by different mean-field models. In particular, from the
convexity properties of the nuclear entropy, we show that uncharged finite
nuclei display first and second order liquid-gas-like phase transitions.
Different quantities are examined to connect the thermal properties of the
system to cluster observables. In particular we show that fractionation is only
a loose indication of phase coexistence. A simple analytical formula is
proposed and tested to evaluate the symmetry (free) energy from the widths of
isotopic distributions. Assuming that one may restore the isotopic composition
of break-up fragments, it is found that some selected isotopic observables can
allow to quantitatively access the freeze-out symmetry energy in
multifragmentation experiments.
