The interaction of 1,5-bis(3-methoxy-2-hydroxybenzaldehyde) thiocarbohydrazone (H4L) [1] with CuCl2·2H2O in methanol results in an unexpected complex [Cu2(H2Lcycl)(CH3OH)2Cl3]·CH3OH (1) with a novel asymmetrical ligand (H3Lcycl) containing a 1,3,4-thiadiazole ring. The cyclization of the parent H4L ligand with formation of 1,3,4thiadiazole ring occurs during complex formation . Complex 1 crystallizes in the tricliniic space group P-1, Z=2, a=8.2155(6), b=10.6699(7), c=16.7549(10) Å, α=89.414(5), β=81.290(6), γ=67.681(6)^o, V=1341.23(15) Å3. X-ray single-crystal structure analysis revealed that formation of 1,3,4-thiadiazole ring essentially changes the coordination mode of the ligand and sulfur atom does not participate in the coordination to metal. Complex 1 comprises two different copper(II) centers doubly bridged by a chloride anion and a phenoxido group of a tetradentate OONN ligand (Figure). The Cu1…Cu2 separation is 3.218 Å. One of the copper atom has square-pyramidal coordination environment and coordinates two N and one O atoms from the (H2Lcycl)- ligand and bridging chloride anion the basal plane. The apical position occupies another chlorido ligand. The atom Cu2 has distorted square-bipyramidal geometry. Two methanol molecules, bridging phenoxido atom O1, and monodentate chlorido ligand Cl3 form the basal plane, while Cl1 bridging anion and methoxy atom O2 reside the vertexes of bipyramid.