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ESR‐Spektren von CuN 4 ‐Chromophoren II : Komplexe mit Ammoniak, Äthylendiamin, Biguanid, N‐Trifluoracetimidoyl‐trifluoracetamidin, N‐Trichloracetimidoyl‐trichloracetamidin, Tetraaza‐undecan, Hexamethyl‐tetraaza‐cyclotetradecan und ‐cyclotetra decadien in Einkristallen
Author(s) -
Schneider W.,
Baccini P.
Publication year - 1969
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19690520720
Subject(s) - chemistry , crystallography , antibonding molecular orbital , delocalized electron , hyperfine structure , atomic orbital , atomic physics , electron , quantum mechanics , organic chemistry , physics
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 C URTIS . Ligands of the second group are biguanide, the CF 3 and CCl 3 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 CuN 4 , showing resolved hyperfine structure due to copper and nitrogen nuclear spins, are fitting a Spin‐Hamiltonian on the basis of virtual site symmetry D 4 h . The parameters g ∥, g ⟂, A ∥, and A ⟂ were used to derive delocalization coefficients in terms of the LCAO‐MO model introduced by M AKI and M C 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 A MMETER'S explanation of this phenomenon in terms of a virtual expansion of the d ‐shell in antibonding orbitals.