The structural origins of the selectivity of rubidium ion over other a
lkali metal ions by tribenzo-21-crown-7 is investigated from single-cr
ystal X-ray diffraction: data for Cs(tribenzo-21-crown-7)(NO3), monocl
inic, P2(1)/c, a = 9.598(2) Angstrom, b = 23.466(3) Angstrom, c = 23.9
73(5) Angstrom, beta = 93.31(1)degrees, V = 5390(2) Angstrom(3), Z = 8
; data for [Rb(4,4'-bis-tert-butylbenzo,benzo-21-crown-7) (dioxane)(1.
5)(H2O)(0.18)][Cl] . (dioxane)1.82(H2O), triclinic, P (1) over bar, a
= 11.687(3) Angstrom, b = 12.800(4) Angstrom, c = 17.680(3) Angstrom,
alpha = 75.31(2)degrees, beta = 80.01(2)degrees, gamma = 69.09(2)degre
es, V = 2379.8(10) Angstrom(3), Z = 2; data for Na(4,4'-bis-tert-butyl
benzo,benzo-21-crown-7) ReO4 . 0.5(i-PrOH), monoclinic, P2(1)/c, a = 2
4.300(5) Angstrom, b = 14.066(3) Angstrom, c = 22.676(5) Angstrom, bet
a = 108.06(3)degrees, V = 7369(3) Angstrom(3), Z = 8; data for and 4,4
'-bis-tert-butylbenzo,benzo-21-crown-7, monoclinic, P2(1)/n, a = 16.42
7(2) Angstrom, b = 11.3675(9) Angstrom, c = 33.137(3) Angstrom, beta =
94.469(8)degrees, V = 6169.0(10) Angstrom(3), Z = 8. The structures r
eported here are the first reported for a tribenzo-21-crown-7, and the
alkali metal ion complexes are the first reported structures of these
ions with any 21-crown-7 ether. Different crown conformations are obs
erved for each structure. Molecular mechanics calculations were perfor
med on all conformers, and the results are related to the observed ext
raction selectivity for rubidium.