In the rst title salt, [ Cu( C12H8N2) (2)( C5H10N2Se)]( ClO4) (2), the Cu-II centre occupies a distorted trigonal - bipyramidal environment de ned by four N donors from two 1,10- phenanthroline ( phen) ligands and by the Se donor of a 1,3- dimethylimidazolidine-2-selone ligand, with the equatorial plane defined by the Se and by two N donors from different phen ligands and the axial sites occupied by the two remaining N donors, one from each phen ligand. The Cu - N distances span the range 1.980 ( 10) - 2.114 ( 11) angstrom and the Cu - Se distance is 2.491 ( 3) angstrom. Intermolecular pi-pi contacts between imidazolidine rings and the central rings of phen ligands generate chains of cations. In the second salt, [ Cu( C10H8N2)(2-)( C3H6N2S)]( ClO4) (2), the Cu-II centre occupies a similar distorted trigonal-bipyramidal environment comprising four N donors from two 2,20- bipyridyl ( bipy) ligands and an S donor from an imidazolidine- 2- thione ligand. The equatorial plane is de ned by the S donor and two N donors from different bipy ligands. The Cu - N distances span the range 1.984 ( 6)-2.069 ( 7) angstrom and the Cu - S distance is 2.366 ( 3) angstrom. Intermolecular pi-pi contacts between imidazolidine and pyridyl rings form chains of cations. A major difference between the two structures is due to the presence in the second complex of two N - H center dot center dot center dot O hydrogen bonds linking the imidazolidine N H hydrogen- bond donors to perchlorate O- atom acceptors.