| Popis: |
The cryptates [MAs4W40O140](28-n)-, (Mn+ = Na+, K+, Rb+, Cs+, NH4 + or Ba2+), have been investigated by 183W solution NMR. The six 183W lines have been assigned with the help of homonuclear 2JW-W coupling constants and by ID-COSY NMR. Depending on M, shielding of the resonance line of the W’s near the cryptant site is correlated with increasing stability of the M-cryptate. Slow M exchange (on the NMR time scale) for [MAs4W40O140](28_n)- contrasts with the rapid exchange observed for the parent cryptates [MAs4W42O142]20-n)-: this difference is discussed with respect to the geometry of the cavity. |
