Three　new　mononuclear　copper(ii)　complexes,　[Cu(L2)]　2+　(1),　[Cu(acac)(L)]+　(2),　and　[Cu(acac-Cl)(L)]　+　(3)　(L　=　2-(4-pyridine)oxazo[4,5-f]1,10-phenanthroline　(4-PDOP);　acac　=　acetylacetone;　acac-Cl　=　3-chloroacetylacetone),　have　been　synthesized　and　characterized　by　elemental　analysis,　high　resolution　mass　spectrometry　(Q-TOF),　and　IR　spectroscopy.　Two　of　the　complexes　were　structurally　characterized　by　single-crystal　X-ray　diffraction　techniques.　Their　interactions　with　DNA　were　studied　by　UV-vis　absorption　and　emission　spectra,　viscosity,　thermal　melting,　DNA　unwinding　assay　and　CD　spectroscopy.　The　nucleolytic　cleavage　activity　of　the　compounds　was　carried　out　on　double　stranded　pBR322　circular　plasmid　DNA　by　using　a　gel　electrophoresis　experiment　in　the　presence　and　absence　of　an　oxidant　(H2O2).　Active　oxygen　intermediates　such　as　hydroxyl　radicals　and　hydrogen　peroxide　generated　in　the　presence　of　L　and　complexes　1-3　may　act　as　active　species　for　the　DNA　scission.　The　cytotoxicity　of　the　complexes　against　HepG2　cancer　cells　was　also　studied.　©　2014　The　Royal　Society　of　Chemistry.