Tris trigonal twist angle

Fig. 5. The trigonal twist angle for a tris-bidentate complex.

Figure 29 Trigonal twist angle 9 in tris(bidentate) complexes with configurations (a) d, d", and d -d and (b) d -d, d , and d °.

The diethylammonium salt of the tris(tetraphenyldisiloxanediolato)zirconate(IV) anion (33) has been obtained in very low yield from the reaction of [Zr(NEt2)4] with diphenylsilanediol in THF. The ligand results, under the basic reaction conditions, from condensation of two Ph2Si(OH)2 molecules. Anion (33) has an octahedral tris-chelate structure with a twist angle (46.9°) that indicates some distortion towards trigonal prismatic geometry.466... 

Values of the normalized bite b and the twist angle 8 for these complexes are given in Table 14. In sharp contrast to other tris(chelate) complexes, it is very clear that 8 is not a simple function of b. In all cases 8 is lower than predicted, and in many cases the trigonal prism with 8 = 0° is observed. These dithiolate ligands are clearly different from other bidentate ligands, even other sulfur donors such as MeSCH=CHS, dithioacetylacetonate, dithiooxalate, dithiophosphates, dithiocarbamates and xanthates. 

Table 30 Comparison of the activation enthalpies for metal-centred inversion by the Bailor trigonal-twist mechanism with the bite (a), twist ( ), and pitch (y>) angles ofNN-disubstituted tris(dithiocarbamate) metal complexes...

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