Bulk Inclusions of Pyridazine‐Based Molecular Rotors in Tris(o‐phenylenedioxy)cyclotriphosphazene (TPP)

Abstract

A new class of rod‐shaped strongly dipolar molecular rotors for insertion into channels of hexagonal tris(o‐phenylenedioxy)cyclotriphosphazene (TPP) has been examined. Seven different 3,6‐disubstituted pyridazines and one singly 3‐substituted system have been prepared and studied by solid‐state nuclear magnetic resonance (NMR), X‐ray powder diffraction, and dielectric spectroscopy. NMR and X‐ray diffraction both show that all but one of these molecular rotors form hexagonal bulk inclusion compounds with TPP. In‐plane lattice parameters for the hexagonal phases increase with the size of the end group, which also controls the energy barriers for rotation of the pyridazine dipole. The barriers range from ≈4 kcal mol−1 for small or flexible end groups to less than 0.7 kcal mol−1 for 3‐methylbicyclo[1.1.1]pent‐1‐yl end groups after annealing to 235 °C, and an interpretation of these differences is offered. Computer modeling of the relaxed TPP channels followed by density functional calculation of the environment for one of the rotors provides quantitative agreement with the observed barrier. The systems with the lowest rotational barriers show signs of collective behavior, discussed in terms of antiferroelectric intrachannel and ferroelectric interchannel dipole–dipole interactions. A Curie temperature of 22 K is deduced for 3,6‐diadamant‐1′‐ylpyridazine, but no ordered dielectric phases are found. Conclusions have been drawn for improved rotor design.

Metal Complexes with Very Large Dipole Moments: the Anionic Carborane Nitriles 12-NC–CB11X11– (X = H, F, CH3) as Ligands on Pt(II) and Pd(II)

“…Combined ogranic phases were evaporated to dryness, and the solid residue was recrystallized from minimal amount of boiling HPLC water, giving a yellow solid product (520 mg, 82%). 1 H{ 11 Trimethylammonium 12-Cyano-1-carba-closo-dodecaborate-1-carboxylic acid (9). Cs + salt of 2 (200 mg, 0.66 mmol) was placed in a dry Schlenk flask.…”

Nonconjugated Hydrocarbons as Rigid‐Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry

“…Hexagonal tris( o ‐phenylenedioxy)cyclotriphosphazene (TPP) was employed as a host to investigate the behavior of dipolar rotor assemblies that acted as guests . A variety of different 3,6‐disubstituted pyridazines were synthesized including 3,6‐bis(3‐methylbicyclo[1.1.1]pent‐1‐yl)pyridazine 232 (Figure ).…”

“…Hexagonal tris(o-phenylenedioxy)cyclotriphosphazene (TPP) was employed as ah ostt oi nvestigate the behavior of dipolar rotor assembliest hat acted as guests. [286] Av ariety of different 3,6-disubstituted pyridazines were synthesized including 3,6bis(3-methylbicyclo[1.1.1]pent-1-yl)pyridazine 232 (Figure 36). It was seen that the BCP compound formed hexagonal bulk inclusion compounds with TPP and that the in-plane lattice parameters for the hexagonal phases increased with the size of the end group, which in turn controlled the energy barriers for rotation of the pyridazine dipole.O verall it was shown that through ac ombination of molecular design and optimal positioning of the rotor molecules in the host material, ad ramatic lowering of rotational barriers can be achieved.K ey steps in the synthesis of 232 included aG rubbs metastasis reaction to connect the two BCP moieties by ad ouble bond.…”

Structure of a monolayer of molecular rotors on aqueous subphase from grazing-incidence X-ray diffraction

“…According to approximate theory (48), the dipole-to-dipole distance of 8.3 Å and a dipole of ∼2.5 Debye (49) promise a Curie temperature T C = ∼120 K in the absence of defects. The use of a larger dipole would raise it further; for pyridazine (4) [μ = ∼4 Debye (50)] the expectation is T C = ∼300 K.…”