A 2ND MODIFICATION OF POTASSIUM FLUORENIDE AND THE STRUCTURE OF POTASSIUM 9-TERT-BUTYLFLUORENIDE - EFFECT OF CRYSTALLIZATION CONDITIONS AND SUBSTITUENTS ON SOLID-STATE CONTACT ION-PAIR INTERACTIONS

Crystallization of potassium fluorenide or 9-tert-butylfluorenide [formed from potassium metal and fluorene or 9-tert-butylfluorene in tetramethylethylenediamine (tmeda)] from a mixture of tmeda, tetrahydrofuran (THF) and diethyl ether yields [K(tmeda)2][Cl3H9] (1) or {[K(THF)2][mu-C13H8(tBu)][K(tmeda)][mu-C13H8(tBu)]}infinity (2). Compound 1 is a monomeric solvated ion pair with one eta5-coordinated fluorenyl and two chelating tmeda ligands and crystallizes in the monoclinic space group C2/c. Compound 1 is an example of polymorphism in organo-potassium compounds, as a polymeric structure of 1 obtained under slightly different crystallization conditions has been reported earlier, Compound 2 forms a polymeric chain with potassium coordinated to two anellated six-membered rings from two bridging 9-tert-butylfluorenyl systems and alternatingly solvated by one chelating tmeda or two THF. The crystal system for 2 is monoclinic, space group P2(1)/c. A comparative AM1 study on the fluorenyl and 9-tert-butylfluorenyl anion suggests a steric origin for the haptotropic potassium shift in 2. H-1- and C-13-NMR data for 1 and 2 as well as for 9-tert-butylfluorene are reported.