Supramolecular Architectures from Ammonium-Crown Ether Inclusion Complexes in Polyoxometalate Association: Synthesis, Structure, and Spectroscopy

Abstract

The tetrahedral (T d ) molecular cation ammonium ion (NH 4 þ ) gets incorporated with the smaller-cavity crown ethers through three N þ -H 3 3 3 O hydrogen bonding interactions, while the fourth N-H bond is projected outward from the crown ether cavity. A hydrogen bonding acceptor, such as a polyoxometalate anion, if placed in suitable position in the crystal lattice, can interact with the ammonium-crown ether supramolecular complex involving the fourth N-H bond donation. This article describes supramolecular association of ammonium-crown ether host-guest complexes with polyoxometalate anions in five crystalline solids, formulated as 5), where B18C6 = benzo-18-crown-6, DB18C6 = dibenzo-18-crown-6, DC18C6 = dicyclohexyl-18-crown-6, and DB30C10 = dibenzo-30-crown-10. Single crystal X-ray structural investigations on these solids confer P1 space symmetry (No. 2) for the compounds 1-2; C2/c space symmetry (No. 15) for the compound 3; P2 1 /n space symmetry (No. 14) for the compound 4, and C2/m (No. 12) space symmetry for the compound 5. Careful examination of the supramolecular interactions between the different molecular fragments show direct contact between the ammonium cation and the polyoxometalate anion (N þ -H 3 3 3 O) in the crystal structure of the compounds 1, 2, and 4. Lattice water molecules have taken the role of hydrogen bonding acceptor (N þ -H 3 3 3 O) in the crystal structure of compound 3, while the larger and flexible crown ether DB30C10 has wrapped around the ammonium cation in the case of compound 5. Thus, there is no direct supramolecular interaction between the ammonium cation and the polyoxometalate anion (N þ -H 3 3 3 O) in the crystal structures of compounds 3 and 5, where the ammonium-crown ether cations are associated with the polyoxometalate anions only via C-H 3 3 3 O hydrogen bonding interactions. Detailed spectroscopic (IR, 1 H NMR, and UV-visible) analyses have been included in comprehending the supramolecular association between the inclusion complexes and polyoxometalate anions. The X-ray powder diffraction analyses have been performed to scrutinize the phase purity of the solids.

Ceric Ammonium Nitrate and Ceric Ammonium Chloride as Precursors for Ceric Siloxides: Ammonia and Ammonium Inclusion

“…In the solid state, the cerium metal center in 3 is coordinated by five anionic ligands (three terminal siloxy and two bidentate nitrato, Figure ). Three tert ‐butoxy groups of three different siloxy ligands form a scaffold to accommodate the charge‐balancing ammonium cation which seems locked in place via hydrogen bonding with the tert ‐butoxy groups as well as a co‐crystallized acetonitrile solvent molecule . This distinct arrangement of the tert ‐butoxy groups in the solid‐state seems to be also observable in the ambient temperature 1 H NMR spectrum of 3 featuring two distinct environments in a 2:1 ratio (Figure S4).…”

Crown Ether Modulation Enables over 23% Efficient Formamidinium-Based Perovskite Solar Cells

“…Compared to the control films, two additional low- q signals (∼0.39 and ∼0.73 Å –1 ) appear in the treated films; the relative Bragg peak intensities decrease with increasing penetration depth (Figure e), implying that the new species are located predominantly at the surface of perovskite film, consistent with the species observed in the SEM image (Figure b). These species could be formed by the host–guest complexation of the crown ether with cations on the perovskite surface …”

“…These species could be formed by the host−guest complexation of the crown ether with cations on the perovskite surface. 22 The effects of crown ether treatment on the perovskite surface were further investigated by ATR-FTIR and XPS. The FTIR spectrum of pristine crown ether (DB24C8) powder reveals two characteristic peaks of the C−O stretching vibration at ∼1121 and ∼1219 cm −1 (Figure 1f), while the control perovskite film does not exhibit these peaks.…”

Supramolecular interactions mediated conformational modulation of flexible linker leading to the isolation of a metallo-macrocycle in a polyoxometalate matrix: Hirshfeld surfaces and 2D fingerprint plots

“…3 Spherical POMs, owing to the presence of negatively charged oxygen atoms on their surfaces, act as supramolecular synthons in crystal engineering. 4 Several cationic crown ethers, 5 porphyrins, 6 aza-macrocycles 7 and transition metal complexes 8 are reported with POM anions, and some of these hybrid materials have been used to isolate the toxic or radioactive metals from solutions. 9 The non-covalent interactions, in directing the selfassembly in coordination architectures through controlling the coordination geometry, 10a the coordination mode of the linkers, 10b etc.…”