ESR SPECTRA OF CUN4 CHROMOPHORES .2. MONOCRYSTAL COMPLEXES WITH AMMONIA, ETHYLENEDIAMINE, BIGUANIDE, N-TRIFLUOROACETIMIDOYL-TRIFLUOROACETAMIDINE, N-TRICHLOROACETIMIDOYL-TRICHLOROACETAMIDINE, TETRAAZAUNDECANE, HEXAMETHYL TETRAAAZACYCLOTETRADECANE AND HEXAMETHYL TETRAAZACYCLOTETRA DECADIENE

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 PtII, NiII, or ZnII 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 D4h. The parameters g∥, g⟂, A∥, and A⟂ were used to derive delocalization coefficients in terms of the LCAO‐MO model introduced by MAKI and MCGARVEY. 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. Copyright © 1969 Verlag GmbH & Co. KGaA, Weinheim