Abstract
The solvatochromism of the well-sepd. long-wavelength charge-transfer bands of the title complexes was studied in 36 aprotic solvents and in dichloromethane solns. of durene and hexamethylbenzene. The obsd. effects cannot be described with one of the conventional solvent parameters that have been successfully used for other transition-metal carbonyl complexes; however, they may be interpreted consistently in terms of strong n- and p-donor contributions from the solvents. Within a three-component M-A-D approxn., the p-accepting TCNE (A) interacts strongly with the low-valent metal fragment (M) on one side and weakly with donor solvents (D) on the other side of the mol. plane. A solvent parameter Ect(p) is derived, which should describe the (n + p) donor capability of solvents toward an approx. planar p-electron-accepting entity. The differences between the Cr and W series reflect the dipolar contributions to the total solvent effect. on SciFinder(R)
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