EPR AND ENDOR STUDY OF TRIGONAL BIPYRAMIDAL COPPER-COMPLEXES WITH A NITROGEN DONOR TRIPODAL LIGAND

The characteristic features of the electronic structure of some trigon al bipyramidal (tbp) copper complexes of the quadridentate tripodal ni trogen donor ligands, tris(2-aminoethyl)amine (tren) and tris(2-dimeth ylaminoethyl)amine (trenMe(6)), with different ligands at the fifth co ordination position of tbp were studied in a powder form doped in diam agnetic zinc complexes by EPR and ENDOR. EPR shows that the copper com plexes of tren and trenMe(6) have a ground state with a d(z2) unpaired electron orbital, and that some of the complexes are distorted from a trigonal symmetry to rhombic, to the contrary to expectations from th e molecular formula. Ic is shown that a small structural or ligand-fie ld distortion would give a recognizable spectral deviation from trigon al symmetry. It should be noticed that the hyperfine couplings of all the coordinating nitrogen atoms in each complex were observed by ENDOR , and that they were useful for calrifying the characteristic features of the electronic structures of the tbp complexes. The ligand fields at the fifth coordination position of tbp affects all of the coordinat ion bonds as well as the spin distribution among the ligands. These li gand field effects on the electronic structures are discussed in refer ence to the ligand field parameters obtained by an EPR analysis. It is also shown that the ENDOR analysis well predicts the sp ratios of the coordinating orbitals of nitrogens, consistent with those obtained fr om the X-ray structural data on the complexes.