Synthesis and spectral characterization of mono- and binuclear copper(II) complexes derived from 2-benzoylpyridine-N4-methyl-3-thiosemicarbazone: Crystal structure of a novel sulfur bridged copper(II) box-dimer

•Copper complexes of 2-benzoylpyridine-N4-methyl-3-thiosemicarbazone are prepared.•We report the molecular structure of sulfur bridged Cu(II) box-dimer.•The dimer is non-centrosymmetric.•EPR studies indicate dimeric nature of one of the complexes.•Thermogravimetric studies of some complexes are included.

Mononuclear and binuclear copper(II) complexes of 2-benzoylpyridine-N4-methyl thiosemicarbazone (HL) were prepared and characterized by a variety of spectroscopic techniques. Structural evidence for the novel sulfur bridged copper(II) iodo binuclear complex is obtained by single crystal X-ray diffraction analysis. The complex [Cu2L2I2], a non-centrosymmetric box dimer, crystallizes in monoclinic C2/c space group and it was found to have distorted square pyramidal geometry (Addison parameter, τ = 0.238) with the square basal plane occupied by the thiosemicarbazone moiety and iodine atom whereas the sulfur atom from the other coordinated thiosemicarbazone moiety occupies the apical position. This is the first crystallographically studied system having non-centrosymmetrical entities bridged via thiolate S atoms with Cu(II)I bond. The tridentate thiosemicarbazone coordinates in mono deprotonated thionic tautomeric form in all complexes except in sulfato complex, [Cu(HL)(SO4)]·H2O (1) where it binds to the metal centre in neutral form. The magnetic moment values and the EPR spectral studies reflect the binuclearity of some of the complexes. The spin Hamiltonian and bonding parameters are calculated based on EPR studies. In all the complexes g|| > g⊥ > 2.0023 and the g   values in frozen DMF are consistent with the dx2-y2dx2-y2 ground state. The thermal stabilities of some of the complexes were also determined.

Graphical abstractMono- and binuclear copper(II) complexes of 2-benzoylpyridine-N4-methyl-3-thiosemicarbazone (HL) have been synthesized and physico-chemically characterized. Crystal structure of a novel sulfur bridged copper(II)-iodo binuclear complex is obtained. It showed a distorted square pyramidal geometry with the square basal plane occupied by the thiosemicarbazone moiety and iodine atom whereas the sulfur atom from the other coordinated ligand occupies the apical position. The complex thus formed is non-centrosymmetric box-dimer.Figure optionsDownload full-size imageDownload as PowerPoint slide