I think will be some halogen
Cu can have ions Cu+, Cu++, Cu+++
with halogens
CuCl
CuCl2
CuCl3
I am not sure if the CuCl3 can exist as a compound
I saw some copper(III) oxide
with elements from the group of Oxygen will form
Cu2O
CuO
Cu2O3
doesn't fit with your experiment problem
and with nitrogen
Cu3N
Cu3N2
CuN
doesn't fit with your experiment either