Synthesis, structural characterization and antioxidant/anti-inflammatory activity of pentacoordinated bis(isoselenocyanato) and bis(isothiocyanato) CuII and NiII complexes with Me5dien: Crystal structure of [Cu(Me5dien)(NCSe)2]

Complexes of the general formula [M(Me5dien)X2] [where M = CuII and NiII, Me5dien = N,N,N′,N″,N″- pentamethyldiethylenetriamine and X = (SCN−) or (SeCN−)] have been synthesized and characterized by elemental analyses, infrared and electronic spectroscopy, magnetic moment and molar conductivity measurements and X-ray crystallography. The crystal structure of [Cu(Me5dien)(NCSe)2] revealed the tridentate coordination of Me5dien and the N-terminal coordination of two SeCN ligands to the CuII ion. The latter adopts a distorted square pyramidal geometry, with the basal positions occupied by the three nitrogen atoms of Me5dien and by the nitrogen atom of one isoselenocyanate ligand. The apical position is occupied by the nitrogen atom of the second isoselenocyanate ligand. Infrared spectra of the complexes confirmed the N-terminal coordination of the pseudohalides and the tridentate coordination of the triamine. Electronic spectra were all consistent with five-coordinate square pyramidal geometries. The complexes are monomeric, paramagnetic and non-electrolytes in MeOH, but 1:1 electrolytes in DMSO. The complexes were tested for antioxidant/anti-inflammatory activity. The presence of a isoselenocyanato (NCSe) group leads to higher reducing activity in comparison to the isothiocyanato (NCS) group. The nature of the metal plays also an important role to this activity. Complex [Ni(Me5dien)(NCSe)2] is more potent than the corresponding copper complex and offers 44.7% protection against the carrageenin-induced rat paw edema.