Studies On The Transformation Mechanism And Stability Reason Of Thermodynamical Metastable Matter By Structure Chemistry

Metastability is a stable state of a thermodynamic system other than the system’s state of lowest energy.In chemistry,metastable matter mainly includes two types:metastable molecules and metastable condensed matter.Because of its energy-containing thermodynamic properties,it differs greatly from the most stable thermodynamic materials in physical and chemical properties.In this thesis,the author mainly discusses metastable substances from three aspects:(1)Take Ag-S nanoscale clusters as an example to study metastable molecules.Firstly,the formation,growth and transformation mechanism of metastable clusters was studied.The structure of metastable clusters was determined by single crystal X-ray diffraction through time-resolved crystallization.Then,functionalized Ag-S nanoscale clusters with exact molecular formula and structure were used to develop cluster drug carriers,and a series of post-synthesis Ag-S semiconductor clusters were synthesized.A novel solution luminescence phenomenon was found in a special Ag-S cluster.Finally,metastable Ag-S nanoscale clusters were transformed into thermodynamically stable α-Ag2S nanospheres and/or microspheres with nearly monodisperse morphology and size.(2)Take IB group reduced nanoclusters as an example to study the stability of the electronic structure of metastable molecules.Based on the known structures reported by single crystal X-ray diffraction,a new theory for qualitative understanding of the stability of superatomic electronic structures is developed by using the decentralized orbitals splitting in point groups,atomic orbital patterns and one-dimensional potential box theory.(3)Take FAPbI3 organic-inorganic hybrid perovskite alloy as an example to study metastable condensed matter.Three new transition phases in the process of deactivation were successfully gained by the doping of bromine.The structure of each phase was determined by single crystal X-ray diffraction,and the significance of anion and cation doping on the phase stability of FAPbI3 perovskite was clarified by DFT calculation.