RECENT INVESTIGATIONS ON THE (ME(6)L(18))(N-) UNIT BASED HALIDES AND OXYHALIDES (ME=NB, TA AND L=CL, BR, O) WITH RARE-EARTHS AS COUNTERCATIONS - ELECTRONIC AND STERIC EFFECTS

In this paper are reviewed a number of recently obtained (Me(6)L(18))( n-) based halides and oxyhalides with rare earths as countercations: M (x)REMe(6)X(18) (KLuNb6Cl18 type, R (3) over bar, and CsLuNb6Cl18 type , P (3) over bar 1c) and REMe(6)X(13)O(3) (ScNb6Cl13O3 type, 14(1)22). Their crystal structure data, obtained from isotypic compounds with j udiciously chosen M-RE-Me-X combinations, have allowed us to discuss r igorously the most important structural features appearing commonly in the Me(6) cluster chemistry: the systematic evolution of the Me-Me in tracluster and the Me-ligand distances, depending on both electronic a nd steric effects. The influence of countercation size on the (Me(6)L( 18))(n-) stacking is also considered. All these results form the basis of a consistent understanding of the (Me(6)L(18))(n-) based chemistry , when substitutions are performed on the various elements constitutin g these compounds.