Two Compartmentalized Inner Receptors for the Tetramethylammonium Guest within a Keplerate-Type Capsule.
The host-guest interactions between the spherical porous Keplerate anion, [Mo132O372(CH3CO2)30(H2O)72](42-) (abbreviated {Mo132}) and the tetramethylammonium cation have been investigated extensively by one- and two-dimensional (EXSY, ROESY, and DOSY) and variable-temperature NMR. Evidence of two inner receptor sites specific for a NMe4(+) guest appears consistent with a quite striking compartmentalization phenomenon. ROESY NMR analyses showed that both sites exhibit a close spatial proximity with the hanging inner acetate groups, while a quantitative EXSY study revealed that these two sites are differentiated by their exchange rates. These NMR data support the hypothesis that these two inner sites could be delimited by the hanging inner acetate groups forming triangular (S1) or pentagonal (S2) hydrophobic pockets on the inner side of the capsule wall. Furthermore, the stability constants associated with the trapping process of the NMe4(+) guest on both the S1 and S2 sites have been determined, showing that the stability constant of the S1 sites decreases significantly as the concentration of the capsule increases gradually, while that of the S2 sites remains nearly unaffected. Such an observation has been interpreted as a result of the plugging process of the {Mo9O9} pores by the counterions NH4(+), which causes unfavorable electrostatic interactions for the NMe4(+) coordination on the proximal S1 site. Finally, the thermodynamic parameters of the NMe4(+) transfer from the solvated situation to the interior of the capsule were estimated from variable-temperature NMR experiments that provide the split of the global process into two successive events corresponding to the plugging and transfer across the inorganic shell.
Institut Lavoisier de Versailles, UMR CNRS 8180, University of Versailles Saint Quentin en Yvelines, University Paris-Saclay , 45 avenue des Etats-Unis, 78035 Versailles, France.|Laboratoire de Chimie de Coordination Inorganique et Organométallique, Université Libanaise, Faculté des Sciences I , Hadath, Lebanon.
Nancy
N
Watfa
Institut Lavoisier de Versailles, UMR CNRS 8180, University of Versailles Saint Quentin en Yvelines, University Paris-Saclay , 45 avenue des Etats-Unis, 78035 Versailles, France.
Mohamed
M
Haouas
Institut Lavoisier de Versailles, UMR CNRS 8180, University of Versailles Saint Quentin en Yvelines, University Paris-Saclay , 45 avenue des Etats-Unis, 78035 Versailles, France.
Sébastien
S
Floquet
Laboratoire de Chimie de Coordination Inorganique et Organométallique, Université Libanaise, Faculté des Sciences I , Hadath, Lebanon.
Akram
A
Hijazi
Laboratoire de Chimie de Coordination Inorganique et Organométallique, Université Libanaise, Faculté des Sciences I , Hadath, Lebanon.
Daoud
D
Naoufal
Institut Lavoisier de Versailles, UMR CNRS 8180, University of Versailles Saint Quentin en Yvelines, University Paris-Saclay , 45 avenue des Etats-Unis, 78035 Versailles, France.
Francis
F
Taulelle
Institut Lavoisier de Versailles, UMR CNRS 8180, University of Versailles Saint Quentin en Yvelines, University Paris-Saclay , 45 avenue des Etats-Unis, 78035 Versailles, France.
Emmanuel
E
Cadot