Isolated Linear Alkanes in Aromatic Nanochannels

Abstract

Novel channel-like inclusion compounds were formed by tris(o-phenylenedioxy)spirocyclotriphosphazene (TPP) with linear hydrocarbons. The molecular characterization was performed by 13 C and 31 P solid-state NMR under magic angle spinning conditions. The hexagonal symmetry of the host was verified in the 31 P and 13 C MAS spectra and by X-ray powder diffraction patterns. The new inclusion compounds present congruent meltings, and the temperatures increase with chain length. These compounds provide the opportunity to observe hydrocarbons confined as isolated chains in the solid state at temperatures 200 K above their melting points. Furthermore, the aliphatic chains are in the unusual state of being surrounded by aromatic rings displaced parallel to the channel. This geometry was proved by a through-space 1.4 ppm upfield shift on the 13 C resonances of the guests, due to the aromatic ring current. The mobility at the chain ends and the propagation of the conformational defects within the guest molecules is discussed and a comparison made with alkanes in different inclusion compounds and bulk alkanes in the high-temperature modification. The formation of the inclusion compounds was also highlighted by throughspace transferring of magnetization from the hydrogens of the host matrix to the chain carbons of a deuterated guest under Hartmann-Hahn conditions.

Arrays of Dipolar Molecular Rotors in Tris(o-phenylenedioxy)cyclotriphosphazene

“…A monoclinic modification of TPP [50,53] that does not form inclusion compounds is also known and below~150 C it is actually more stable than the empty hexagonal form. However, it is less stable than the hexagonal form, up to at least 350 C, if the latter is filled with a nonvolatile guest [52]. Hexagonal TPP offers considerable advantages as a host crystal for molecular rotors, but also has some shortcomings.…”

Inclusion Compound Based Approach to Forming Arrays of Artificial Dipolar Molecular Rotors: A Search for Optimal Rotor Structures

“…The lattice constant is 11.5–12 Å, depending on the guest. The internal channel diameter is 4.5–5 Å, permitting easy entry of linear alkanes, benzene, etc 35–44. The crystal consists of layers ≈5 Å thick.…”

“…TPP also has a monoclinic modification,36, 39 which does not form inclusion compounds and has a very distinct solid‐state NMR spectrum and X‐ray diffraction pattern. It actually is more stable than the empty hexagonal form, but when hexagonal TPP is filled with a nonvolatile guest, it is stabilized against transformation into the monoclinic form, up to at least 250 °C 38…”

A Family of Supramolecular Frameworks of Polyconjugated Molecules Hosted in Aromatic Nanochannels

“…TPP was synthesized according to a reported procedure 6c. Compounds 1 – 10 were prepared either by crystallization from o ‐xylene solutions of TPP (0.01 mole L −1 ) and guest molecules or by heating intimately mixed guest and TPP powders above the melting point of the guests (host–guest weight ratio of about 6:1); o ‐xylene was previously purified by n ‐nonane impurities by using molecular sieves and TPP itself as entrapment agent of linear alkanes.…”