The Preparation And Properties Of Molecular-Based Ferroic Materials

Molecular-based functional materials have always been a hot topic in the field of materials science,especially molecular-based ferroic materials?molecular-based magnetic materials and molecular-based ferroelectric materials?that have emerged in the past three decades.Compared with traditional inorganic materials,molecular-based ferroic materials are constructed from molecular units,which can be prepared through simple methods to achieve tunable structures,properties and multifuntions.These provide tremendous application prospects for molecular-based functional materials in the field of electronic,such as electronic information storage.Although molecular-based ferroic materials are favored by many scientific researchers,it is still challenging to develop new multifunctional materials.This thesis manily focuses on constructing magnetic,ferroelectric and multi-functional molecular-based ferroic materials.The main acheivements are as follows:?1?A variety of acidic imidazolium ionic liquids reacted with the transition metal ions?Zr^?,Zn^?,Mn^?,Cu^?,Fe^?,Fe^??and rare earth metal ions?Gd^??to synthesize ten metal organic complexes of?HMIM?₂Zr?SO₄?₃?DMSO?₂?1?,?HMIM?₂Zn?SO₄?₂?2?,?HMIM?₂Mn?SO₄?₂?3?,?MIM?₄Cu?HSO₄?₂?4?,Gd[?SO₄??NO₃??DMSO?₂]?5?,?HMIM?₄Fe₄O2?SO₄?₆?DMSO?₄?6?,?HEIM?₄Fe₄O2?SO₄?₆?DMSO?₄?7?,?HPIM?₄Fe₄O2?SO₄?₆?DMSO?₄?8?,?HBIM?₄Fe₄O2?SO₄?₆?DMSO?₄?9?and FeCl₂?DMSO?₄?EtSO₄?·DMSO?10??HMIM=1-methylimidazolium,HEIM=1-ethylimidazolium,HPIM=1-propylimidazolium,HBIM=1-buthylimidazolium?.Complex 1 and 10 exhibited mononuclear structures.Complex 2,3 and 5 had one-dimensional chain structures.Complex 4 was a three-dimensional supramolecular structure formed by hydrogen bonding.Complex 6–9 contained oxygen-bridged tetranuclear Fe₄^III clusters.Complex 3 revealed antiferromagnetic coupling.Complex 5exhibited antiferromagnetic coupling and magnetocaloric effect with-?S_m^max=28.8 J kg^-1 K^-1.Complexes 6–9 exhibited antiferromagnetic coupling.Complexes 10displayed weak antiferromagnetic interactions.?2?Five organic manganese halide complexes,namely C₄H₇N₂MnCl₃·H₂O?11?,?C₄H₇N₂?₂MnCl₄?12?,C₈H₉N₂MnCl₃·2H₂O?13?,CH₄N₂OMnCl₂?14?,(C₂H₁₂N₆)₃Mn₃Cl₁₂?15?were fabricated with Mn^II as the metal center.The effects of organic ligands and solvents on their structure,photoluminescence and magnetic properties were also studied.The perovskite-like structure complex 11 and the mononuclear structure complex 12 were prepared with 2-methylimidazole as the organic ligand in different solvent environments.Mn^II ions of complex 11 was six-coordinated with phosphorescence emission at 619 nm.Mn^II ions of complex 12 was four-coordinated with phosphorescence emission at 517 nm.Complex 11 exihibited reversible phosphorescence switching behavior between 619 nm and 517 nm under the effect of temperature and humidity.The phosphorescence emission of complex 12 red-shifted from 517 nm to 619 nm under the effect of humidity.Perovskite-like structured13 was prepared with 2-methylbenzimidazole as the ligand and its phosphorescence emission blue-shifted from 631 nm to 558 nm with vaired temperature.The phosphorescence emission of one-dimensional step-like chain structured compex 14constructed with urea as the ligand was at 619 nm.The phosphorescence emission was blue-shifted from 612 nm to 603 nm under mechanical pressure.The phosphorescence emission of trinuclear 15 prepared with guanidine carbonate as the ligand was at 635nm.Complexes 11–15 exhibited antiferromagnetic interactions.?3?The organic copper halide complexes BIXCuCl₄·H₂O?16?and BIXCuBr₄?17?were prepared with Cu^II as the metal center?BIX:1,4-bis[?1H-imidazol-1-yl?methyl]benzene?.BIX acted as a free cationic ligand in these crystal structures.Different from the centrosymmetric complex 17,complex 16 belong to noncentrosymmetric polar space group C_s.Complex 16 has room temperature ferroelectricity with saturation polarization value of P_s=2.02?C cm^-2 and antiferromagnetic coupling.The magnetic and ferroelectric properties of the complex16 changed after heating.Complex 16 was a potential multiferroic material.?4?The reversible mechanical flexibility of the near room temperature ferroelectrics supramolecular co-crystals Phz-H₂ca?18?and Phz-H₂ba?19?were firstly studied.The elastic bendable co-crystal 18 has been observed to display ferroelectricity.The co-crystal 18 and 19 had a relative large average elastic modulus and less hardness.The elastic mechanical properties of the co-crystal 18 are better than that of 19,which was attributed to halogen bond strength distinction.There are obvious Raman intensity variations depending on the bent regions of the tested samples.Both skeleton bonds stretching vibration intensities and some special band intensities related to the intermolecular interactions are obviously suppressed under bend stress.A proposal mechanistic model of the co-crystals was suggested that the crystal packing contain weak and dispersive interactions hydrogen-bond,halogen-bond and?···?stacking interactions in almost three orthogonal directions lead to the elastic flexibility of the co-crystals.