Hydrogen-bonds assisted by ionic interactions

The inner two CHD units form a tautomeric anion to which the outer two CHD molecules are connected in their enol form. The resulting [(CHD)4] anion interacts with one bis(7 -benzene)chromium cation via short C-H- - -OC hydrogen-bonds. Finally two such horse-shoe -shaped systems wrapped around the organometallic cation are related by a center of inversion. This results in an overall supramolecular 

Thus the main result of this experiment was the rational design of a self-assembled crystal structure based on the shape analogy between benzene and bis(t -benzene)chromium. Under similar reaction conditions bis(t7 -toluene)chromium reacts with CHD to afford [Cr( / -C6H5Me)2][(CHD)2], 102 [161b]. In the solid state 102 forms a C-H- -O hydrogen-bonded network in which the bis( 7 -toluene)-chromium cations alternate with clamps formed by the dimeric [(CHD)2] anions. 

Several related experiments have been shown to afford layered supramolecular Structures. For example, air-oxidation of bis( -benzene)chromium in a two-layer 

(a) Space-filling representation of 103 (b) spacefilling representation of the honeycomb framework formed by the [(HSQA)(H2SQA)]-anions in the supramolecular structure of 103 (Reproduced from ref. [162]). 

5 Supramolecular Self-Assembly by Hydrogen-Bond Interactions 

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