Artificial Investigations On The Biological Mn-Cluster For Photo Water-Splitting Reaction

Oxygen-evolving center?OEC?in photosystem ? of plants,algae and other photosynthetic organisms is a unique catalyst to perform the reaction of water splitting into oxygen,protons and electrons in a high efficiency and high safety in nature.Mimicking the structure of the OEC in PS? is essential for the development of cheap and efficient artificial catalysts for water splitting reaction,which is considered to be one ideal path to meet the requirement of the clean energy of our society.Therefore,artificial investigation of the OEC has been considered to be crucial for both basic scientific research and potential application in the world.Recently,crystallographic studies of the PS? have revealed that the core of the OEC is composed by[Mn₃CaO₄]?or[Mn₃SrO₄]?cubane lined with a fourth Mn ion through twom-O^2-bridge,forming an asymmetric[Mn₄CaO₅]?or[Mn₄SrO₅]?heterometallic cluster,which is coordinated by six carboxylate groups,one imidazole and four water molecules.This structure serves as a blueprint for the development of the artificial water-splitting catalyst.In this thesis,by combining the knowledge obtained from the previous studies of the biological OEC in PS? in our group,I have carried out a series of artificial studies to mimic the structure of the biological OEC:i)With the goal to mimic the[Mn₃CaO₄]or[Mn₃SrO₄]cubic structure as observed in the OEC,a new[Mn₃SrO₄]₂O complex has been synthesized through a two-step procedure by using the cheap chemical of Mn²⁺and Sr²⁺salts as starting materials,and MnO₄^-as oxidant.In this new complex,two[Mn₃SrO₄]cubane are connected by?-O^2-bridges,and three types of?-O^2-bridge(?₂-O^2-,?₃-O^2-,?₄-O^2-)are observed.It is the first time to have all types of?-O^2-bridges in one Mn-complex as these obtained in biological OEC.ii)Effect has been made to prepare MnCa-complex containing biological ligands?such as carboxylate group and water molecule,etc?.A series of[Mn₆Ca₂O₉]complexes mainly coordinated by carboxyl group and various number of water molecules have been synthesized.It has been found that water molecules in these complexes can be replaced by various small neutral molecules depending on the strength of hydrogen bond between water molecules and peripheral environments.This observation provides important chemical clue tounderstanding the physiological function of water molecules of coordinated to the OEC in PS?.iii)The precise mimicking of the OEC has been carried out.For the first time,we have reported the synthesis of artificial asymmetric Mn₄Ca-cluster as observed in OEC.Both the core structure and peripheral ligands in this cluster are very similar as those of the biological OEC.These complexes also model the physical and chemical characteristics of the biological OEC.The new complexes provide ideally chemical model to investigate the mechanism of water-splitting reaction in PS? in future,and may also promote to develop the cheap and efficient artificial catalysts for water splitting in laboratory.This work has been considered as a breakthrough of the field,and has been published on Science this year.