Transition metal complexes with thiosemicarbazide-based ligands. Part 56. Square-pyramidal complexes of copper(II) with 2-acetylpyridine S-methylisothiosemicarbazone

The article describes the synthesis and single-crystal X-ray analysis of two sulfato and one thiocyanato copper(II) complex with 2-acetylpyridine S-methylisothiosemicarbazone (HL) of the formulae [Cu(HL)SO4(H2O)]·H2O (1), [Cu2(HL)2(μ-SO4)2]·2H2O (2) and [Cu(HL)(NCS)(SCN)] (3), as well as the structure of the protonated ligand H2L+I−. Complexes 1 and 2 were obtained from the reaction of aqueous/methanolic CuSO4·5H2O and ethanolic/methanolic H2L+I− solutions, respectively. Complex 3 was synthesized by the reaction of methanolic solutions of Cu(ClO4)2·6H2O, the ligand and NH4SCN, with the addition of triethyl orthoformate. All three complexes have a slightly deformed square-pyramidal structure (τav = 0.15) with the tridentate NNN neutral ligand in the basal plane. In complexes 1 and 3 the apical position is occupied by the oxygen atom of the monodentate SO4 group, or the sulfur atom of the SCN group. Thanks to the hydrogen bonds, complex 3 may be thought of as having a pseudo-dimeric structure. In the authentic centrosymmetric dimer 2, the oxygen atoms of both SO4 groups occupy also the apical position of both coordination polyhedra, as well as an equatorial position. Complexes 1 and 3 have μeff values characteristic of magnetically isolated mononuclear Cu(II) complexes. In contrast to them, complex 2 has a μeff value of 1.57 BM, which is in agreement with its dinuclear structure. All the complexes, in addition to the X-ray analysis and magnetic measurements, were characterized by IR and UV–Vis spectroscopy and by thermal analysis.

The subject of this work is the synthesis and single-crystal X-ray analysis of two sulfato and one thiocyanato copper(II) complex with 2-acetylpyridine S-methylisothiosemicarbazone (HL) of the formulae: [Cu(HL)SO4(H2O)]·H2O (1), [Cu2(HL)2(μ-SO4)2]·2H2O (2) and [Cu(HL)(NCS)(SCN)] (3), as well as the structure of the protonated ligand H2L+I−. In contrast to complex 2, which is an authentic dimer, formed on account of the exo-bidentate coordination of both sulfato ligands, the structure of complex 3, thanks to hydrogen bonding, may be thought of as being a pseudo-dimer. All three complexes have slightly deformed square-pyramidal structures with the tridentate NNN neutral ligand in the basal plane. For complex 3, different modes of bonding of the ambidentate NCS group were discussed.Figure optionsDownload as PowerPoint slide