Chemistry Reference
In-Depth Information
tAbLe 4.20
Distribution Ratios for sodium and strontium and selectivity sr/na in nPHe
5 10
−
4
M M(no
3
)
n
/1 M H(no
3
)
4 M nano
3
/1 M H(no
3
)
Ligands
22
na
85
sr
D
sr
/
D
na
85
sr
CA6
−
−
−
0.4
CA7
0.006
8.3
1.3
>8,300
CA8
0.13
0.5
<0.001
>130
CA9
20
5
<0.001
>20,000
CA12
<0.001
2.9
>2,900
1.8
CA13
6.5
2.2
<0.001
>6,500
CA14
30
0.34
<0.001
>30,000
CA15
0.80
1.09
<0.001
>800
CA16
24
3.8
<0.001
>24,000
DC18C6
0.006
0.28
>47
−
Note:
(
C
L
= 10
−2
M).
2.5
2PyOC4
2PyOC6
1.5
HCl/2PyOC4
HCl/2PyOC6
0.5
4PyOC4
4PyO4Q
-0.5
-1.5
0.01
0.1
1
10
Nitric (acid), M
FIGURe 4.5
Strontium distribution ratios of DC18C6 (1) (10
−1
M in NPHE) and CA16 (2)
(10
−2
M in NPHE) as a function of the nitric acid concentration.
bearing the amide groups, which explains the remarkable efficiency of the octam-
ers. Formation of dinuclear species with octamers was confirmed by ESI mass spec-
trometry and by competitive spectrophotometry with 1-(2-pyridylazo)-2-naphthol
(PAN).
With the aim of studying the origin of strontium over sodium selectivity observed
for calixarenes bearing amide groups, Parma University determined the crystal
structures of strontium complexes with CA4, CA6, and CA8.
134
The hexameric CA4
consists of one Sr
2+
cation coordinated by the ligand. On the contrary, octameric
CA6 and CA8 crystallized as dinuclear strontium complexes (Sr:L = 2:1), although
equimolar amounts of strontium salt and ligand were used. This indicates a strong
tendency of the first strontium ion to preorganize the chelating groups to host the
second cation. In spite of unfavorable Coulomb interactions between two cations, this
