ESR-Spektren von CuN4-Chromophoren II: Komplexe mit Ammoniak, Äthylendiamin,Biguanid, N-Trifluoracetimidoyl-trifluoracetamidin,N-Trichloracetimidoyl-trichloracetamidin,Tetraaza-undecan,Hexamethyl-tetraaza-cyclotetradecan und -cyclotetra decadien in Einkristallen

The ESR spectra of eight copper complexes with two groups of nitrogen ligands have been measured in the solid state. The first group includes the σ-bonding ligands ammonia, ethylenediamine, 1,4,8,11-tetraaza-undecane, and the macrocyclic hexamethyl-1,4,8,11-tetraazacyclotetradecane of CURTIS . Ligands of the second group are biguanide, the CF₃ and CCl₃ derivatives of acetimidoyl-acetamidine, and hexamethyl-1, 4,8,11-tetraazacyclotetradecadiene. Single crystals of the parent Pt^II, Ni^II, or Zn^II compounds were used as host lattices and magnetic diluents. The spectra of the chromophores CuN₄, showing resolved hyperfine structure due to copper and nitrogen nuclear spins, are fitting a Spin-Hamiltonian on the basis of virtual site symmetry D_4h. The parameters g∥, g?, A∥, and A? were used to derive delocalization coefficients in terms of the LCAO-MO model introduced by MAKI and MC GARVEY . The comparative study clearly reveals that no reliable information on π-bonding is provided by application of this model. The results on σ-bonding ligands are particularly valuable in showing that the simple LCAO-MO model cannot account for the attenuation of spin orbit coupling due to σ-bonding in a physically meaningful way. Our results are qualitatively in agreement with AMMETER'S explanation of this phenomenon in terms of a virtual expansion of the d-shell in antibonding orbitals.