KINETICS OF COMPLEXATION OF LI+ AND NA+ WITH CYCLIC AND ACYCLIC POLYETHER LIGANDS IN NITROMETHANE

The kinetics of complexation of Li+ and Na+ in the low donor number so lvent nitromethane with the cyclic polyether dibenzo-24-crown-8 (DB24C 8), dibenzo-18-crown-6 (DB18C6), and the acyclic polyether tetraglyme have been investigated by ultrasonic relaxation techniques. The work w as done in the frequency range 1-600 MHz and at 35-degrees-C for the L i+ systems and at 25-degrees-C for the Na+ system (except for DB24C8 b ecause of low solubility of the ligand which necessitated working at 3 5-degrees-C). Working in excess Li+ with the ligand size mismatched, l igands DB24C8 and DB18C6 give some evidence of multimetal cation inter vention in the complexation affecting the reverse rate constants. Use of the open polyether tetraglyme with Li+ and Na+ permits the observat ion of two relaxation phenomena in the microsecond-to-nanosecond time range covered by the instrumentation. Evidence of anion interference i n the complexation mechanism at concentrations larger than approximate ly 0.1 M is also found, a result that is predictable from the low dono r number of nitromethane.