ELECTRON-DEFORMATION DENSITY INVESTIGATIONS ON ORGANOMETALLIC COMPOUNDS: SUCCESS AND PITFALLS. C. Krüger, K. Angermund, J. Bruckmann, F. Lutz and C. Kopiske, Max-Planck-Institut fur Kohlenforschung D-45470 Mulheim a. d. Ruhr Strukturchemie

The detailed experimental determination of the Electron Deformation Densities of organometallic compounds and their ligands can reveal structural effects which are often overlooked in the course of a normal structural characterization of compounds. These minor effects include:

1. slight disorder problems within ligands,

2. heavy atom disorder,

3. general disorder on a molecular level,

4. co-crystallizing impurities (less than 3%).

Some of these effects, if not taken into account, cause molecular distortions larger than those introduced by erroneous space group assignment, etc.

Structural investigations of several phosphines, Nickel-phosphine as well as zirconium complexes will serve as examples. It is concluded that statistically more than 10% of all structural investigations published so far may suffer in their geometrical data from these effects.

A description of our standard low temperature data collection and data reduction procedure for EDD-measurements wil1 be given. Finally, EDD data obtained by scintillation counter techniques will be compared to CCD counter data using identical crystals as well as data reduction procedures.