摘要:
By comparing the nephelauxetic ratios beta of a number of molecular Pr-III compounds, and the Stater parameters F-2 (or Racah parameters E-1) of molecular Nd-III and selected Sm-III compounds, presumably more covalent types of Eu-III compounds could be identified. Powdered [Eu{N(SiMe3)(2)](3)] (1), "[Eu{OC(tBu)(3)](3)]" ("3") and [Eu(eta(5)-C5H5)(3)(CNC6H11)] (5) were resynthesized following usual procedures. The absorption transitions F-7(0) -> 5 Do of an oriented single crystal of 1, a glassy frozen solution of I dissolved in a mixture of 2-MeTHF/THF (ratio 3:1) ([Eu{N(SiMe3)(2)](3)(THF)], (2)), of "3" dissolved in 2-MeTHF ([Eu{OC(tBu)(3))(3)(MeTHF)], (4)), and of 5 dissolved in a mixture of the inert solvents methylcyclohexane/toluene (ratio 1:1), were measured at room and low temperatures (90 K). The energy differences of this transition for compounds 1, 2, 4 and 5 are larger than those of [Eu(H2O)(9)](3+) or even gaseous Eu3+, indicating quasi "anti-nephelauxetic" effects. Crystal field calculations, however, reveal that lower Slater parameters F-2 (or Racah parameters E-1) have to be used than those of [Eu(H2O)(9)](3+) in order to reproduce the experimental energy differences between F-7(0) and D-5(0), thus indicating the expected nephelauxetic effects of more covalent Eu-III compounds. (c) 2005 Elsevier B.V. All rights reserved.