Reversible structural phase transition, ferroelectric and switchable dielectric properties of an adduct molecule of hexamethylenetetramine ferrocene carboxylic acid

Abstract

Metallo-organic molecules showing reversible structural phase transitions accompanied with ferroelectric and dielectric properties have seldom been reported. By making use of the "driving/controlling force" from the rotating motion of cyclopentadienyl rings for a reversible structural transition and then carrying out structural modifications on their local parts to create remnant polarization through this molecular system, we designed and constructed a new ferroelectric, which is the adduct of hexamethylenetetramine ferrocene carboxylic acid, (C 6 H 12 N 4 )[Fe(C 5 H 5 )(C 6 H 5 O 2 )] (1). Compound 1 undergoes a reversible structural phase transition at around 187 K, which is confirmed by remarkable dielectric and heat anomalies. The synergistic interactions of the twisting motions of the adduct molecules and the inner cyclopentadienyl rings lead to the reversible phase transition. A dipole moment from amine group to carboxylic acid at low temperature produces a net spontaneous polarization, which results in the ferroelectricity of 1-LTP. On further investigation, it is observed that compound 1 has a perfect ferroelectric hysteresis loop with a spontaneous polarization of 3.95 mC cm À2 .

Molecular Ferroelectric Piperidine‐4‐ylmethanaminium Perchlorate with Superior Switchable Dielectric Properties

“…Metal‐free three‐dimensional perovskite ferroelectrics has been reported . In addition, there are some molecular ferroelectrics with excellent switchable dielectric properties, such as (CHA) 2 CdCl 4 , hexamethylenetetramine ferrocene carboxylic acid, hexamethylene‐tetramine bisnopinic acid, dabco⋅p‐nitrophenol, and so on. Recently, a number of pyridyl‐based molecular ferroelectrics have been discovered, such as PyX (Py =pyridinium and X = ClO 4 , BF 4 , ReO 4 , IO 4 ), (4‐amino‐2‐bromopyridinium) (4‐amino‐2‐bromopyridine) tetrafluoroborate, pyridin‐4‐ylmethanaminium perchlorate, and so on.…”

Chiral to Chiral Phase Transition in a Novel Hydrogen Bond Type Molecular Ferroelectric

“…discovered that Rochelle salt derivatives, bis(imidazolium) l ‐tartrate is a new organic H‐bonded molecular ferroelectric material, where imidazole acts as a classical molecular rotator and l ‐tartaric acid as homochiral component . Moreover, by means of twist motion of two cyclopentadienyl rings in ferrocene for a reversible phase transition, our group also explored a new ferrocene derives, adduct of hexamethylenetetramine ferrocene carboxylic acid which displays ferroelectricity . These successful strategies show that some derivatives of molecule ferroelectrics such as the organic salts and neutral adducts are possibility of becoming new type of ferroelectrics.…”

Above Room Temperature Organic Dielectric Switchable Material: Diprotonated 1,4‐Diazabicyclo[2.2.2]octane Shifts between Two Pyruvic Acids

“…Generally speaking, the cocrystals fall into two categories; those made of inorganic‐organic components, and those made of pure organic components . They were all reported to possess switchable dielectrics , . Recently, an inorganic‐organic co‐crystal (Me 3 NH) 4 [Ni(NCS) 6 ] was studied by Jing‐Yan Liu et al, and it was reported that it undergoes an isostructural order‐disorder phase transition and it can function as a frequency‐tuned dielectric switch with highly adjustable switch temperature .…”

“…A well‐known case is the class of organic amine and organic acid cocrystals with the formula [A][B] or [A] 2 [B] (where, A = organic acid and B = organic amine, dabco, etc. ), where the ammonium cations in these structures make it very easy to achieve order‐disorder transitions around the phase transition temperature with obvious switchable dielectric anomalies . Horiuch i et al reported the ferroelectric organic solids, the cocrystals of 1:1 phenazine with chloranilic acid and bromanilic acid .…”

“…Enlightened by these discoveries, we attempted to synthesize an switchable dielectrics organic cocrystal with the formula [A] 2 [B], where the function of the hydrogen bonds was restricted within the trimeric unit region. Fortunately, we synthesized a cocrystal with distinctive architecture constructed from trimeric units, [H 2 dabco] · [PA] 2 ( 1 ), that underwent a dielectric phase transition above room temperature at 348 K. In the crystal of 1 , the strong hydrogen bond interactions are constrained within the trimeric unit.…”