Molecular and electronic structures of bis(dipicolylamine)copper(II) perchlorate and bis[2-(2-pyridylethyl)picolylamine]copper(II) perchlorate

The geometric isomers of bis(dipicolylamine)copper(II) perchlorate, [Cu(dipica)₂](ClO₄)₂, and bis[2-(2-pyridylethyl)picolylamine]copper(II) perchlorate, [Cu(pepica)₂](ClO₄)₂, have been prepared and their molecular structures determined by X-ray diffraction methods. The copper atom of cis-fac-[Cu(dipica)₂](ClO₄)₂, is six coordinate with an amine nitrogen and a pyridyl group of each facial dipica ligand forming a cis coordination plane, and the remaining pyridyl nuclei on the axial sites completing a distorted octahedral structure. The mixed trans-fac- & square-pyramidal-[Cu(dipica)₂](ClO₄)₂ comprises discrete hexacoordinate and pentacoordinate cations. The distorted trans-facial octahedral cation has two picolyl chelates in the equatorial plane and two slightly longer axial pyridyl groups. In the square-pyramidal cation, the basal plane is formed by a meridional tridentate dipicia and a pyridyl of another bidentate dipica ligand, of which the amine group is bound at the apex. The copper ion of trans-fac-[Cu(pepica)₂](ClO₄)₂ is bound by two picolyl chelates in the equatorial plane and two elongated axial pyridyl groups. The electronic structures of these complexes are deduced based on their electronic and e.p.r. spectra. The bonding properties and the formation of the geometric isomers are elucidated.