  We report the statistical properties of stars and brown dwarfs obtained from
three radiation hydrodynamical simulations of star cluster formation with
metallicities of 1, 1/10 and 1/100 of the solar value. The star-forming clouds
are subjected to cosmic microwave background radiation that is appropriate for
star formation at a redshift z=5. The results from the three calculations are
compared to each other, and to similar previously published calculations that
had levels of background radiation appropriate for present-day (z=0) star
formation. Each of the calculations treat dust and gas temperatures separately
and include a thermochemical model of the diffuse interstellar medium. We find
that whereas the stellar mass distribution is insensitive to the metallicity
for present-day star formation, at z=5 the characteristic stellar mass
increases with increasing metallicity and the mass distribution has a deficit
of brown dwarfs and low-mass stars at solar metallicity compared to the
Galactic initial mass function. We also find that the multiplicity of M-dwarfs
decreases with increasing metallicity at z=5. These effects are a result of
metal-rich gas being unable to cool to as low temperatures at z=5 compared to
at z=0 due to the hotter cosmic microwave background radiation, which inhibits
fragmentation at high densities.
