  We have studied the effect of Iridium doping (Rh$_{17-x}$Ir$_{x}$S$_{15}$) in
the Rhodium sites of the strongly correlated superconductor Rh$_{17}$S$_{15}$.
Even at low levels of doping (x = 1 and 2) we see a drastic change in the
superconducting properties as compared to those of the undoped system. We
deduce that there is a reduction in the density of states at the Fermi level
from reduced Pauli susceptibility and Sommerfeld coefficient in the doped
samples. Moreover, the second magnetization peak in the isothermal
magnetization scan (`fishtail') which was very prominent in the magnetization
data of the undoped crystal is suppressed in the doped samples. The temperature
dependence of resistivity of the doped crystals show a remarkably different
behavior from that of the undoped crystal with the appearance of a minima at
lower temperatures, the position of which is fairly constant at different
fields. Our data supports the notion that Iridium, which is a bigger atom than
Rhodium expands the lattice thereby, reduces the electron correlations that
existed due to the interaction between closer lying Rhodium atoms in the
undoped system.
