COMMUNICATIONSCarbonyl addition reactions: To a solution of the cerium compound (1.5 mmol) in T H F ( 5 mL) cooled to -78'C, methyllithium (1.2 mmol, 0.75 mL of a 1 . 6~ solution in diethyl ether) was added. After 1 h the appropriate carbonyl derivative (2.0mmol) was added slowly and the mixture was stirred at -78°C for 30 min. Then, a saturated aqueous NH,CI solution (10 mL) was added, solid material war removed through a short pad of Celite, the Celite was rinsed with diethyl ether, and the ethereal solution was dried with MgSO,. The solvent was removed in vacuo and the residue purified by llash chromatography.

Reaction of various N-substituted diethanolamines H(2)L(3) (4) with calcium hydride and iron(III) chloride leads to the self-assembly of six-membered ferric wheels [Fe(6)X(6)(L(3))(6)] (5). Principally, all the iron coronands are isostructural; however, they differ fundamentally with respect to their crystal packing. Exemplarily, this is discussed for selected members of the space groups R, P, P2(1)/c, P2(1)/n, C2/c, and P. Depending on the nature of their sidearms, the ferric wheels create various substructures. For instance, the ferric wheels 5a-i of space group R or P are piled in parallel in cylindrical columns, which are surrounded by six parallel columns alternately dislocated by (1)/(3)c and (2)/(3)c against the central one. Pronounced van der Waals interactions give rise to compartmentation and incarceration of guest molecules as seen for 5e,g. However, in 5h strong pi-pi interactions create a three-dimensional scaffold. The most significant difference of the ferric wheels 5j-p of space groups P2(1)/c, P2(1)/n, and C2/c is that these ferric wheels are arranged in parallel in two orientations. They differ mainly only by the included angle of the two groups of parallel wheels. In the case of 5l, molecular chains are formed in the crystal due to pi-pi interactions. The ferric wheels 5q-y of space group P are packed in the crystal most simply, with all the ferric wheels piled in parallel.

It is like playing poker, if you play long enough you begin to make decisions based on probability, and if you are fortunate you may recognize how the cards are marked. Richard E.P. WinpennyMany of the higher nuclearity Werner-type clusters are fortuitous discoveries. This clearly suggests that the principles which control cluster formation are still poorly understood from the point of view of rational design. However, the predictable nature of coordination chemistry has been used successfully for the speci®c generation of the metalla-topomers of the well-known organic-based coronates and cryptates. Furthermore, it has been shown that the metal coordination geometry and the orientation of the interacting sites in a given ligand provide the instruction, or blueprint, for the rational design of high symmetry coordination clusters. Based on these principles, and the interplay with serendipity, directed syntheses for polynuclear metalla-coronates, sandwich complexes, manifold metalla-cryptates, and metalla-cylinders have been developed. Only recently, the combination of detailed symmetry considerations with the basic protocols of coordination chemistry have made the design of rational strategies for the construction of a variety of nanoscale systems with procured shape and size feasible. Highlights among these species are cube-like clusters and multicompartmental cylindrical nanostructures.

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