Study On The Structures And Dielectric Properties Of A Series Of Hydrogen Bonded Organic Salts

Structural phase transitions in solid materials can lead to changes in physical and chemical properties,such as ferroelectricity and dielectric transition.These materials have applications in information storage,actuating,transducing,switching,and sensing.In recent years,organic molecule-based dielectric materials have attracted attention due to their rich structures,environmental friendness and multi-functionalities,which are expected to surpass or supplement existing dielectric materials.In this work,a series of small molecule-based hydrogen-bonded organic salts with one-dimensional to three-dimensional hydrogen-bonded networks were synthesized to expand the new dielectric response molecular materials,and their single crystal structures and dielectric transition properties were studied.PartⅠ:two compounds PTBBA（1）and（Im）（PTBBA）（Im=imidazole）（2）were obtained from p-tert-butylbenzoic acid（PTBB）,and their crystal structure,dielectric properties and thermal properties were studied.Among them,compound 1 undergoes reversible dielectric transition at low temperature,and the ordered disorder of tert-butyl is the source of dielectric transition.PartⅡ:ten compounds were synthesized from 3,4-Dihydroxy-3-cyclobutene-1,2-dione（SQA,Commonly known as squaric acid）,isophthalic acid（IPA）and organic amines:[（EA）（SQA）]₂（H₂O）（3）、[（TA）（SQA）]₂（H₂O）（4）、[（BA）（SQA）]₂（H₂O）（5）、[（PA）（SQA）]₂（H₂O）（6）、[（HA）（SQA）]₂（H₂O）（7）、（PZ）（SQA）（8）、[（SBA）（SQA）]₂（H₂O）（9）、（TMA）（IPA）（H₂O）（10）、（Im）（IPA）（H₂O）（11）、（SP）₂（IPA）（12）.The crystal structures,dielectric properties and thermal properties of 3-12 were studied.Compounds 3-7 show reversible structural phase tranistions and similar crystal structures.In the crystals,the square acid anions form planar hydrogen-bonded layers as templates.The cations locate between the layers in a tail-to-tail manner,forming a unique sandwich-like structure.The order-disorder transition of the cations is the source of the phase transitions.Compound 8 shows obvious dielectric anomalies in a low-temperature region.Through dielectric measurement,compounds 10 and 11 show reversible dielectric peaks at low temperatures.Crystal structure analysis reveals the dielectric change of 11 originates from the order-disorder transition of the trimethylamine cation.PartⅢ:two compounds,TCA（13）and（Im）（TCA）（14）,were obtained from4,4’4’’-tricarboxylic acid triphenylamine（TCA）and organic amine.Among them,Compound13 exhibits large reversible dielectric change at low temperature due to the solvent contained in the crystal.