Structure of Complexes in Solution Derived from X-Ray Diffraction

Structure of Complexes in Solution Derived from X-Ray Diffraction Measurements Georg Johansson... 

STRUCTURES OF COMPLEXES IN SOLUTION DERIVED FROM X-RAY DIFFRACTION MEASUREMENTS... 

Johansson G (1992) Structures of complexes in solution derived from X-ray diffraction measurements. Adv Inorg Chem 39 159-232... 

All ligands 3c through e-H2 form coordination compounds with titanium(IV) ions that possess dendrimer structures. Due to the non-polar Frechet-type dendritic substituents, the compounds are soluble only in solvents with low polarities (mixtures of methanol and chloroform). Consequently, the dimeric complexes are observed as the major species in solution. Fignre 2.6 shows the structural formula of L Lij (30)5X12 ] and the structure derived from x-ray diffraction of the anion of the GO dendrimer [Lij (30)5X12)] . Xhe central triple lithium-bridged part and the dendritic substituents decorating its periphery may be seen. 

Other types of complexes in aqueous as well as in nonaqueous solutions can also be successfully studied by means of X-ray diffraction and their structures can often be derived, completely or in part (7,12-15). Structural changes in the coordination sphere of a metal ion, caused by the stepwise replacement of solvent molecules on addition of a ligand, can be followed. Under favorable conditions structures can be derived for the whole series of complexes formed, from the solvated noncom-plexed metal ion to the complex in which all solvent molecules have been replaced. Structural changes beyond the first coordination sphere can sometimes be determined, making it possible to differentiate between inner- and outer-sphere complexes. Even when the information that can be obtained from X-ray diffraction measurements is not sufficient for an unambiguous determination of a structure, it may still give significant structural features, which, in combination with information from other sources, can lead to the complete structure. 

As in the molybdenum complexes derived from MgXg units some of the additional six ligands may be, for example, H2O molecules, and this is so in Ta6Cli4. 7 H2O, in which the structural unit is [Ta6Cli2(Cl2)(H20)4]. The basic structure of this unit had been deduced earlier from X-ray diffraction data obtained from a concentrated alcoholic solution of the compound. 

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