Recognition of Anion/Anion-Water Cluster by a Tripodal Amide Receptor
5.4 Conclusion
In summary, we have demonstrated we have shown the encapsulation of a planar cyclic tetrameric halide water cluster [X2(H2O)2]2− X = Cl−/Br− within the dimeric capsular assembly of a conformationally flexible tripodal amide receptor, where [X2(H2O)2]2− X = Cl− /Br− has acted as a template in the formation of the dimeric capsular complexes. The clusters are formed via strong halide (X = Cl− / Br−)–water interactions and possesses a planar cyclic tetrameric arrangement where each halide(X = Cl− / Br−) anion is hydrogen bonded with the two water molecules. Close inspections of the distance and angle measurement values of
91
these terameric water clusters confirmed that they are perfect parallelogram. However, in the case of higher homologous iodide anions the receptor changes its conformation and adopts noncapsular polymeric aggregation upon iodide coordination. Probably the larger size and lower charge density of the iodide ion is responsible for this conformational change in the receptor which indeed helps the formation of the 1D polymeric structure upon iodide coordination. The thermal stability of the halide–water cluster in complexes 3a and 3b has been studied by thermo-gravimetric analysis, which shows both the complexes are stable beyond 150 °C indicating strong hydrogen bonding between the anion–water cluster and the host molecules. The solution state receptor-hydrated halide (Cl− and Br−) interaction in complexes 3a and 3b has further been confirmed using 2D-NOESY NMR experiments. The NOESY spectra of both the complexes show significantly strong NOE coupling between the amide NH protons and water (H–O–H), suggesting encapsulation of hydrated halide anion(s) (Cl− or Br−) via hydrogen bonding interactions inside its tripodal cavity. Additionally, crystallization of the receptor in presence of HF in glass container gives SiF62-
complex. The formation of SiF62- instead of fluoride complex in presence of HF is presumably as a result of glass corrosion. Interestingly, depending on solvent of crystallization the receptor forms two different SiF62- complexes 3d and 3e. In 3d the SiF62- anion is encapsulated within dimeric capsular assembly of the protonated receptor, where in 3e SiF62- anion is located outside the tripodal cavity and stabilized mainly by N−H⋯F and C−H⋯F hydrogen bonding interactions with four receptor cations.
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Table 5.1 Crystallographic parameters and refinement details of halide complexes 3a, 3b and 3c.
Parameters 3a 3b 3c
Formula C45 H42Cl N7 O13 C45 H42 Br N7 O13 C45 H40 I N7 O12
Fw 924.31 968.76 997.74
Cry. system Triclinic Triclinic Monoclinic
Space group P-1 P-1 P 21/c
a/Å 9.3971(5) 9.4231(11) 8.0650(5)
b/Å 14.8204(7) 14.9240(12) 41.706(2)
c/Å 17.5829(9) 17.6464(15) 15.0999(8)
α/o 69.237(3) 68.839(8) 90.00
β/o 75.363(3) 74.960(9) 97.283(6)
γ/o 83.377(3) 83.360(8) 90.00
V/Å3 2214.51(19) 2234.3(4) 5038.0(5)
Z 2 2 4
Dc/g cm-3 1.386 1.440 1.315
μ (mm-1) 0.161 0.992 0.699
T/oK 298(2) 298(2) 298(2)
Total reflns 27999 18093 24379
Ind. reflns 10812 11412 12947
Obs. reflns 4793 4794 6479
Parameters 614 614 587
R1; wR2 (I > 2σ(I)) 0.0568, 0.1856 0.0830, 0.2748 0.1000, 0.3292
R(int) 0.0415 0.0770 0.0532
GOF (F2) 0.861 0.988 1.120
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Table 5.2 Crystallographic parameters and refinement details of hexafluorosilicate complexes 3d and 3e.
Parameters 3d 3e
Formula C90 H80 F6 N14 O24 Si C96 H102 F6 N16 O30 Si
Fw 1883.77 968.76
Cry. system Trigonal Triclinic
Space group R -3 P-1
a/Å 13.3641(7) 13.1197(5)
b/Å 13.3641(7) 13.1321(6)
c/Å 45.517(3) 15.7929(6)
α/o 90.00 108.655(2)
β/o 90.00 105.033(2)
γ/o 120.00 92.632(2)
V/Å3 7040.2(6) 2464.94(17)
Z 3 1
Dc/g cm-3 1.333 1.416
μ (mm-1) 0.118 0.125
T/oK 298(2) 298(2)
Total reflns 10351 30365
Ind. reflns 3736 11455
Obs. reflns 2030 9244
Parameters 206 708
R1; wR2 (I > 2σ(I)) 0.0987, 0.3140 0.0608, 0.1831
R(int) 0.0472 0.1291
GOF (F2) 1.057 0.830
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Table 5.3 Important hydrogen bonding contacts in complexes 3a, 3b and 3c.
Complexes D–H∙∙∙O d(H∙∙∙O)/Å d(D∙∙∙O)/Å ∠D–H∙∙∙O/o
3a N6H···Cl1 2.51 3.330(3) 162.9(3)
C11H···Cl1 2.76 3.544(4) 147.2(2) C35H···Cl1 2.88 3.567(3) 131.7(2) C41H···Cl1 2.81 3.684(3) 155.8(2) O13HA···Cl1 2.30 3.127(2) 162.3(1) O13HB···Cl1 2.32 3.177(2) 174.9(1) C20H···O13 2.57 3.374(3) 145.0(2) N4H···O13 2.07 2.92(1) 160.7(3) C26H···O13 2.40 3.252(4) 152.2(2) C12H···O13 2.71 3.551(4) 150.1(2)
3b N6H···Br1 2.66 3.481(4) 159.9(3)
C11H···Br1 2.76 3.638(7) 143.2(4) C35H···Br1 2.98 3.669(5) 131.3(3) C41H···Br1 2.88 3.789(5) 163.3(3) O13HA···Br1 2.42 3.250(5) 164.4(3) O13HB···Br1 2.48 3. 326 (4) 172.7(3) C20H···O13 2.57 3.374(6) 144.5(2) N4H···O13 2.23 3.058(6) 161.6(3) C26H···O13 2.42 3.227(7) 145.1(4) C12H···O13 2.81 3.634 (4) 148.0(4)
3c N2H···I1 3.08 3.795(5) 141.9(3)
N4H···I1 2.97 3.776(7) 155.2(4) N6H···I1 3.11 3.919(5) 156.2(3) C45H···I1 2.95 3.847(6) 161.9(3) C37H···I1 3.15 3.978(6) 147.7(4) N1H···O11 2.27 3.084(7) 148.0(3)
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Table 5.4 Important hydrogen bonding contacts in complexes 3d and 3e.
Complexes D–H∙∙∙O d(H∙∙∙O)/Å d(D∙∙∙O)/Å ∠D–H∙∙∙O/o
3d N2H···F1 2.07 2.847(6) 148.8(3)
C15H··· F1 2.41 3.210(8) 144.0(4) C15H··· F1 2.51 3.290(1) 140.9(0)
3e N4H···F1 2.08 2.820(4) 156.0(3)
C30HA···F1 2.65 3.511(4) 152.9(2) C30HA···F3 2.47 3.306(5) 148.8(2) C30HA···F2 2.66 3.424(4) 139.3(2) C31HA···F1 2.50 3.371(3) 149.1(2) C16HA···F2 2.25 3.057(4) 139.3(2) C16HA···F3 2.60 3. 364 (5) 135.3(2) O14H15O···F2 2.46 2.974(3) 114.0(4) O14H15O···F3 2.07 3.010(4) 171.0(5)
Figure 5.9 (a) Powder X-ray diffraction: simulated pattern from the single-crystal X-ray of complex 3a (bottom), experimental pattern from the crystalline solid 3a (top); (b) Powder X-ray diffraction:
simulated pattern from the single-crystal X-ray of complex 3b (bottom), experimental pattern from the crystalline solid of complex 3b (top).
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Figure 5.10 (a) Change in chemical shift of –NH resonances of L3H+.ClO4− with increasing concentration of standard fluoride solution in DMSO-d6 at 298
97
Figure 5.11 (a) Change in chemical shift of –NH resonances of L3H+.ClO4− with increasing concentration of standard chloride solution in DMSO-d6.
Figure 5.12 1H NMR titration curves of L3H+.ClO4−
with Cl− in DMSO-d6 at RT. Net changes in the chemical shifts of amidic –NH is shown against the increasing amount of chloride anion.
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