Hydrogen-bonded materials based on organic tautomeric molecules: Theoretical treatment

The crystalline Br, I and CH3 derivatives of 9-hydroxyphenalenone (5X–9HPO) and their deuteroxy analogues (5X–9DPO) are treated by application of the Ising model approaches. The molecular field parameter (J0) as well as the tunneling parameter (Ω) are evaluated for each material with the help of different quantum chemistry procedures. As our evaluations show both relations Ω(D)/J0 and Ω(H)/J0 are less than unity in the case of 5CH3–9(H/D)PO derivatives that leads to an appearance of the low-temperature ordered (anti-ferroelectric) phase. A relatively small Ω(D)/J0 (0.2–0.4) values derived in the case of 5Br– and 5I–9DPO imply the tendency to transition into the similar phase in these species. At the same time a rather large values of Ω(H)/J0 (0.9–1.7) derived in the case of their hydroxy analogues speak in favor of their quantum paraelectric behavior. The obtained theoretical estimations and conclusions are compared with the available experimental data.