Seven novel Copper(II) complexes, namely [Cu(Am4DHotaz)(HO)](ClO) (1), [Cu(Am4DHotaz)(NO)(MeOH)]·HO (2), [Cu(Am4Motaz)(HO)](ClO)·0.83HO (3), [Cu(Am4Motaz)(NO)]NO·MeOH (4), [Cu(Am4Eotaz)(NO)](NO)·2HO (5), [Cu(Am4Eotaz)(ClO)](ClO) (6) and [Cu(Am4Eotaz)(ClO)(HO)](ClO) (6a) (HAm4DHotaz = N'-(4-oxothiazolidin-2-ylidene)pyridine-2-carbohydrazonamide, Am4Motaz = N'-(3-methyl-4-oxothiazolidin-2-ylidene)pyridine-2-carbohydrazonamide and Am4Eotaz = N'-(3-ethyl-4-oxothiazolidin-2-ylidene)pyridine-2-carbohydrazonamide), have been successfully synthesized and characterized by several physicochemical techniques and, for 1-6 complexes, single crystal X-ray diffraction. Having the structural data as a base, complexes 1, 2 and 3 exhibited square pyramidal to square pyramidal slightly distorted geometry, whereas 4, 5 and 6 an intermediate between square pyramidal and trigonal bipyramidal. The ability of complexes 1-6 to cleave DNA was assayed with the aid of gel electrophoresis on supercoiled pUC18-DNA. Except for [Cu(Am4Motaz)(HO)](ClO)·0.83HO (3), the compounds were not able to perform DNA cleavage (data not shown). Since 3 has been shown to behave as a nuclease, its interaction with DNA was studied by means of thermal denaturation and viscosimetry measurements.