The determination of the geometry of Cu(II) complexes - An EPR spectroscopy experiment

An instrumental experiment is presented in which eleven Cu(II) complexes are studied with electron paramagnetic resonance (EPR) spectroscopy. The EPR spectroscopy allows the characterization of the geometry and electronic structure of the copper complexes. Three common ligands, ethylenediamine (en), 1,10-phenanthroline (phen), and 2,2′-bipyridine (bpy), were used. Examination of the EPR spectra of the solid-state compounds demonstrates that [Cu(en)2(ClO4)2], [Cu(en)2(BF4)2], and [Cu(en)2(NO3)2] have a dx2-y2 ground state and an elongated octahedral geometry; that [Cu(phen)2(H2O)](NO3)2, [Cu(phen)2(H2O)](BF4)2, and [Cu(bpy)2Cl]ClO4 are characterized by a geometry intermediate between the square pyramid and the trigonal bipyramid and a ground state corresponding to the linear combination of the dx2-y2 and dz2 orbitals; and that [Cu(phen)2Cl]ClO4, [Cu(phen)2Br]ClO4, [Cu(bpy)2Br]ClO4, [Cu(phen)2]ClO4, and [Cu(bpy)2I]ClO show a geometry close to the trigonal bipyramid and a ground state of dz2. A theoretical explanation of the results is presented.