Gated and Differently Functionalized (New) Porous Capsules Direct Encapsulates' Structures: Higher and Lower Density Water

Abstract

By the deliberate choice of the internal ligands of the porous nanocapsules [{(Mo)Mo(5)}(12){Mo(2)(ligand)}(30)](n-), the respective cavities' shells can be differently sized/functionalized. This allows one to trap the same large number of water molecules, that is, 100 in a capsule cavity with formate ligands having a larger space available, as well as in a cavity containing sulfates and hypophosphites, that is, with less space. Whereas the 100 molecules fill the space completely in the second case in which they are organized in three shells, a four-shell system with underoccupation and broken hydrogen bonds is observed in the other case. This is an unprecedented result in terms of the structurally well defined special forms of "higher and lower density" water molecule assemblies. Precisely, by replacing the larger ligands in the mentioned nanocapsule type by formates, voids in the capsule cavity of (HC(NH(2))(2))(22)[{(HC(NH(2))(2))(20)+(H(2)O)(100)} subset{(Mo)Mo(5)O(21)(H(2)O)(6)}(12){Mo(2)O(4)(HCO(2))}(30)]ca. 200 H(2)O are generated that get filled with water molecules concomitant with an expansion of the three to four shell {H(2)O}(100) cluster. The water shells in both capsules containing different ligands are organized in the form of dodecahedra (partly with underoccupation) and a strongly distorted rhombicosidodecahedron spanned by a {H(2)O}(60)={(H(2)O)(5)}(12) aggregate. The well-defined water shells only emerge if cations cannot enter into the capsules, which is achieved by closing the pores with plugs/guests such as formamidinium cations. The work is based on the syntheses of two new compounds, related single-crystal X-ray diffraction studies, and molecular dynamics simulations, which show remarkably that water molecule shell structuring occurs in the capsules due to the confined conditions even in the case of open pores and at room temperature if cation uptake is prevented.

Encapsulated Water Inside Mo132 Capsules: The Role of Long-Range Correlations of about 1 nm

“…In particular, we have studied the case that this ligand is either sulfate or the smaller formate, but both cases contain the same number (172) of water molecules trapped, according to the interpretation of the X-ray data for analogous systems as described in the Introduction. 50 Our analysis reveals that despite the similitude of the systems compared the behavior of the water confined is significantly different in both capsules. In particular, the slight increase in the accessible volume for the formate ligand capsule allows the confined water in this system to display a more bulky behavior in both the structure and the dynamics, of course, when disregarding the bound water in contact with the inner side of the cavity.…”

“…Experimentally the Mo 132 capsule with 30 SO 4 2− , due to its large negative charge (72 − ), contains some small NH 4 + ions inside the cavity after sealing it with larger formamidinium cations. 50 ). 50,54 In the following we will show the distinctive dynamic behavior of the confined water in the Mo 132 (HCO 2 ) and Mo 132 (SO 4 ) cavities.…”

“…50 ). 50,54 In the following we will show the distinctive dynamic behavior of the confined water in the Mo 132 (HCO 2 ) and Mo 132 (SO 4 ) cavities. Our results should stimulate further important studies of water under confined conditions, which are optimal in the case of the present capsules as their interior can be tuned widely from hydrophilic to hydrophobic.…”

“…Hence, the simulation results for this particular capsule are compared to the closer experimental system with similar characteristics of the inner medium, namely, the Mo 132 capsule with {20 H 2 PO 2 see ref50)). The simulations have revealed that the structure of the water inside the Mo 132 (SO 4 ) capsule is similar to that of the experimental Mo 132 (H 2 PO 2…”

Anions coordinating anions: analysis of the interaction between anionic Keplerate nanocapsules and their anionic ligands

“…[36][37][38][39][40][41][42][43][44][45] Some issues regarding Keplerate chemistry were addressed computationally using both classical and quantum methods. Our group demonstrated 46 that the layered structure of encapsulated water could be reproduced using molecular dynamics simulations, and studied its dynamic behaviour. 47,48 Other authors studied the assembly of Keplerates in sheet-like structures using Monte Carlo methods.…”