  The metal to insulator transition in the charge transfer NiS{2-x}Se{x}
compound has been investigated through infrared reflectivity. Measurements
performed by applying pressure to pure NiS2 (lattice contraction) and by
Se-alloying (lattice expansion) reveal that in both cases an anomalous metallic
state is obtained. We find that optical results are not compatible with the
linear Se-alloying vs Pressure scaling relation previously established through
transport, thus pointing out the substantially different microscopic origin of
the two transitions.
