SOLVENT-SHARED RADICAL-ION PAIRS .CIRCLE-MINUS)NA(CIRCLE-PLUS)O(C2H5)(2)](INFINITY) - ESR EVIDENCE FOR 2 DIFFERENT AGGREGATES IN SOLUTION, ROOM-TEMPERATURE CRYSTALLIZATION, AND STRUCTURAL PROOF OF ANOTHER POLYMORPHIC MODIFICATION

The reduction of pyrene with sodium in aprotic diethyl ether allows to crystallize the extremely air-sensitive radical ion pair pyrene-sodiu m-diethylether. The single-crystal structure determination at 130 K sh ows that each sodium counter cation, solvated by one diethyl-ether mol ecule, is eta(3)- and eta(6)-coordinated to one of the short-axis six- membered rings of two pyrene radical anions. The resulting dibenzene-s odium sandwiches form a string, in which the hydrocarbon planes are ca nted to each other by 62 degrees. In the pyrene radical-anion skeleton , no distortion due to its negative charge can be detected relative to that of the neutral molecule. From the temperature-dependent signal m ultiplets of preceding ESR investigations, the solvent-separated pyren e radical anion as well as two different contact radical-ion pairs had been identified and their structures in solution approximated by pote ntial-energy estimates. Referring to the recently discovered long-axis Na+ contact ion pair polymorph, crystallized at lower temperatures, t he structure reported here represents the second and probably thermody namically more stable one. Both the ESR and the structural results pro vide some insight into the multidimensional networks of equilibria in aprotic solution, which are activated by alkali-metal reduction of uns aturated organic compounds.