MAGNETIC AND SPECTRAL PROPERTIES OF CHLOROAQUA[2,6-DIACETYLPYRIDINE BIS-(SEMICARBAZONE)]IRON(II) AND DIAQUA[2,6-DIACETYLPYRIDINE BIS-(SEMICARBAZONE)]NICKEL(II) - LIGAND FIELDS AND BONDING IN PENTAGONAL-BIPYRAMIDAL COMPLEXES

Principal crystal susceptibilities throughout the temperature range 10-300 K have been measured for the complexes [Ni(DAPSC)(H2O)2]2+(NO3-)2 H2O and [Fe(DAPSC)Cl,H2O]+Cl--2H2O, where DAPSC is 2, 6-diacetylpyridine bis-(semicarbazone). The unpolarized, single-crystal transmission spectra have been recorded in the UV, visible, and near-IR regions. The complete crystal magnetic properties and spectral features of the nickel complex have been reproduced simultaneously within the angular overlap model (aom) the parameters of which reflect the longer Ni-O(keto) bond lengths observed relative to Co-O in the analogous cobalt complex. The magnetism of the iron system is quantitatively reproduced by a similar model and reflects the similarity of the Fe-O(keto) bond lengths with respect to those in the cobalt complex. A detailed discussion of the equivalent orbital diagrams established by the ligand field analyses of the iron(II), cobalt(II), and nickel(II) complexes is presented, from which a rationale of the first-coordination-shell bond lengths in these and the analogous copper(II) molecules emerges. © 1979, American Chemical Society. All rights reserved.