铀、钪族金属氮化碳配合物结构、成键和还原性质的密度泛函理论研究

Density Functional Theory Study of Structure,Bonding and Redox Property of Uranium and Scandium-Group Complexes Supported by Graphitic Carbon Nitride

石墨相氮化碳负载金属可制备高催化性能的单原子催化剂。本工作采用全电子相对论密度泛函理论研究了g-C_(3)N_(4)(CN)结构单元配位和稳定金属的行为;探索了形成配合物[M(CN)]^(z+)(M=Sc、Y、La、Ac和U;z=2和3)的结构、配体-金属相互作用和单电子还原性质。计算发现,配体通过六条M-N配位键配位中心离子,每条键强度为-0.79~-0.47 eV。对于Sc配合物,单电子还原主要发生在金属中心,而La和U配合物则是金属修饰的配体还原机制;Y配合物的配体和金属被均匀地还原;相比而言,Ac配合物的还原电子完全被配体捕获,金属几乎未参与。电子结构研究表明,[U(CN)]^(3+)具有3个U(5f)单电子高占据轨道,表明中心U为三价氧化态;而[U(CN)]^(2+)虽然具有4个U(5f)单电子占据轨道,但是配体的贡献是不可忽略的,即其U中心的氧化态介于二三价之间。

Graphitic carbon nitride(g-C_(3)N_(4))loaded by metal atom has been applied as an effective single atom catalyst.In the work,the complexation behaviors of g-C_(3)N_(4)(CN)with metal ions have been examined by relativistic density functional theory.The formed[M(CN)]^(z+)(M=Sc,Y,La,Ac and U;z=2 and 3)have been explored for their structures,metal-ligand interactions and redox properties.It is found that the metal ion has been rendered by six M-N dative bonds,each of which has the bonding strength ranging from-0.79 to-0.47 eV.Regarding Sc complexes,one-electron reduction mainly occurs around the metal center,while La and U complexes have metal-modified ligand reduction mechanism;both metal and ligand in Y complex are approximately equally reduced;in contrast,the ligand of Ac complex gets the reducing electron,and the metal is redox-innocent.This agrees with the fact that there are no experimental reports on Ac(Ⅱ)complexes.Electronic-structure analyses indicate that[U(CN)]^(3+)bears three high-lying single U(5f)occupied orbitals,suggesting the trivalent uranium center.However,despite having four single U(5f)occupied orbitals,[U(CN)]^(2+)still possesses considerable ligand contribution,leading to the uranium oxidation state mediating betweenⅡandⅢ.