ON THE VARIATION OF BOND-LENGTH DURING LARGE-AMPLITUDE BENDING FROM ELECTRON-DIFFRACTION - THE CASE OF CACL2

All geometrical parameters, including bond lengths, are influenced by large-amplitude vibrations. The magnitude of this effect was examined for metal dihalides performing large-amplitude bending motions, using CaCl2 as an example. By using quantum chemical calculations it was sho wn that the effect of bending on the bond length is very sensitive to the choice of basis set. A dynamic electron diffraction analysis, augm ented with quantum chemical calculations, revealed that the effect of bending on the bond length is of moderate magnitude within experimenta l error. This fact contrasts with the consequences of other motions, i n particular stretching, that must always be accounted for in any mean ingful comparison of experimental and computed structures.