  ESR studies at 9.27, 95.4, and 289.7 GHz have been performed on
(C$_5$H$_{12}$N)$_2$CuBr$_4$ down to 3.7 K. The 9.27 GHz data were acquired
with a single crystal and do not indicate the presence of any structural
transitions. The high frequency data were collected with a polycrystalline
sample and resolved two absorbances, consistent with two crystallographic
orientations of the magnetic sites and with earlier ESR studies performed at
300 K. Below $B_{C1}=6.6$ T, our data confirm the presence of a spin singlet
ground state.

Strongly Correlated Electrons