Cu(II) complexes of the tridentate thiosemicarbazone ligands diacetyl monooxime thiosemicarbazone (dmoTSCH 2 ) and diacetyl monooxime (4-phenyl)thiosemicarbazone (dmoPhTSCH 2 ) have been synthesized. X-ray crystal structures of dmoPhTSCH 2 and [Cu(dmoTSCH)Cl] 2 ·H 2 O (1·H 2 O) are also reported. The Cu(II) compound 1·H 2 O is a dinuclear complex, where the Cu(II) centers have a square pyramidal geometry and are bridged by two thiolato ligands. A C 2 axis passes through the middle of Cu 2 S 2 rectangle. Variable temperature susceptibility measurement for 1·H 2 O shows that this compound exhibits a very weak antiferromagnetic behavior (in the solid state) with J 1 =−2.97cm −1 , using the Heisenberg isotropic spin Hamiltonian (H=−J 1 S 1 ·S 2 ). DFT calculations show that the intramolecular magnetic interaction should be ferromagnetic, and the net antiferromagnetic behavior is due to competition with antiferromagnetic intermolecular interactions through hydrogen bonds.