Comparative Crystal Field Studies of some Ligands and the Lowest Singlet State of Paramagnetic Nickel(II) Complexes.

Abstract

Absorption spectra in the near infrared and visible regions were recorded for ethylenediamine tetraacetate (enta), glycinate (gly), acetyl acetonate (aca), 2,2'-bipyridine (bip), and o-phenanthroline (phen) complexes of Cr(III), Co(II), Ni(II), and Cu(II). The spectra were compared with those of aquo ions of the same elements and the results interpreted structurally. The place of aca complexes in the spectrochem. series was found. The max. absorption occurred at a slightly higher wave no. than for the aquo ion; e.g. Ni-(H2O)6++ 8500 cm.-1, Ni aca2 8800 cm.-1 Comparison of the spectra of the Ni and Cu complexes showed that the ratio of the band positions in cm.-1 of Cu to Ni is always >1 and varies from 1.1 to 1.7. This indicated tetragonality of the Cu complexes. The tris complexes of bip and phen of both Cu and Ni had spectra predicted by crystal-field theory for a cubic complex. The spectra for the Ni complexes, which are tabulated in detail, showed that the lowest singlet state, 1G3 (D), intermixes strongly with the triplet states and gives rise to double bands. The energy decrease of this state at increasing crystal-field strength was ascribed to interaction with some states of other electronic configurations. 58 references.