Copper(II) complexes with neutral bis(pyrazolyl)methane ligands: The influence of steric hindrance on their structures and properties

By using the neutral bidentate nitrogen-containing ligands; bis(3,5-dimethyl-1-pyrazolyl)methane (L0″), bis(3,5-diisopropyl-1-pyrazolyl)methane (L1″), bis(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)methane (L3″), and bis(3,5-ditertiary-butyl-1-pyrazolyl)methane (L4″), the copper(II) nitrato complexes [Cu(L0″)2(NO3)]NO3 (1NO3), [Cu(L0″)(NO3)2] (2), [Cu(L1″)(NO3)2] (3), [Cu(L3″)(NO3)2] (4), and [Cu(L4″)(NO3)2] (5), chloro complexes [Cu(L0″)2Cl]2(CuCl4) (6CuCl4), [Cu(L0″)2Cl]2(Cu2Cl6) (6Cu2Cl6), [Cu(L1″)Cl2] (7), and [Cu(L3″)Cl2] (8), nitrito complexes [Cu(L0″)(ONO)2] (9) and [Cu(L1″)(ONO)2] (10), and the complexes with perchlorate ions [Cu(L0″)2(CH3OH)](ClO4)2 (11ClO4) and [Cu(L1″)2(H2O)](ClO4)2 (12ClO4) were systematically synthesized and fully characterized by X-ray crystallography and by IR, far-IR, UV–Vis absorption, and ESR spectroscopy. In comparison with the obtained complexes with four bis(pyrazolyl)methanes having different bulkiness at pyrazolyl rings, the second coordination sphere effects on the ligands are discussed in detail. Moreover, the structures and physicochemical properties of these obtained complexes are compared with those of the related complexes with the neutral tridentate tris(pyrazolyl)methane ligand.

New mononuclear copper(II) complexes using the bidentate nitrogen-containing ligands bis(3,5-dimethyl-1-pyrazolyl)methane (L0″), bis(3,5-diisopropyl-1-pyrazolyl)methane (L1″), bis(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)methane (L3″), and bis(3,5-ditertiary-butyl-1-pyrazolyl)methane (L4″) were synthesized and structurally characterized. Structural and physicochemical studies of these complexes demonstrate the critical differences in the properties depending on the second coordination sphere of the coligands.Figure optionsDownload as PowerPoint slide