Theoretical Study On Bonding Properties Of Unsupported Uranium-containing Heteronuclear Bimetallic Compounds

The rapid development of nuclear energy is inseparable from the study of actinide chemistry,which helps us understand the chemical behavior and change of actinides during the post-treatment of spent fuel.With the deep understanding of the unique electronic structure and nature of actinides,the study of actinide-heterobimetal complexes has become one of the hot issues in the field of organometallic chemistry and nuclear chemistry,of which are extremely challenging on synthesis and separation.In the past 30 years,the experimental study of actinide-heterobimetal complexes has greatly promoted the development of actinides on the chemical bonding theory.In this paper,the molecular structure,electronic structure and chemical bonding properties of unsupported heterobimetallic complexes with uranium-metal bond were systematically studied by means of relativistic density functional theory and chemical bonding analysis.Based on the first structurally authenticated L^ArU-FeCp（CO）₂(L^Ar=deprotonated p-terphenyl bis（aniline）ligand)complex bearing an unsupported U-Fe bond,we expanded the structures of complexes L^ArU-MCp（CO）₂（M=Fe,Ru,Os）and systematically investigated the U-M bonding nature by using scalar-relativistic quantum chemical calculations.Theoretical results reveal highly polarized U-M interactions in the three L^ArU-MCp（CO）₂ complexes.Moreover,the three U-M bonds are confirmed to show single bond feature.Topology of electron density reveals predominantly“closed shell”U-M interaction with obvious ionic interaction in the three L^ArU-MCp（CO）₂ complexes.In addition,the negative binding energy suggests that the three L^ArU-MCp（CO）₂ complexes are thermodynamically feasible.This work reveals the bonding nature of the three U-M bonds and expands our knowledge of the unsupported uranium-metal bonding in the heterobimetallic complexes.We built a series of potential complexes（CpSiMe₃）₃U-E（NCHMes）₂（E=Si,Ge,Sn,Pb）by constructing two neutral fragments[（CpSiMe₃）₃U]and[E（NCHMes）₂]and investigated their structures by using scalar-relativistic quantum chemical calculations.Theoretical results reveal that U-E bonds possess highly polarized U-E interactions and are also strong donor-acceptor interaction according to the analyses of MO（molecular orbital）,natural charge,QTAIM（quantum theory of atoms in molecules）and ELF（electron localization function）.Particularly,the four U-E bonds are mainly composed of U 6d orbitals and E ns orbital,which lead to the nature of donor-acceptor interaction for the U-E bonds.So the U-E bonds are significantly different from the general uranium-transition-metal and uranium-main-group bonds.Moreover,the U-E bonds strength in the（CpSiMe₃）₃U-E（NCHMes）₂ complexes follow the order of U-Si>U-Sn>U-Ge>U-Pb based on the analyses of bond orders and EDA（energy decomposed analysis）.In addition,the negative binding energies suggest that the four（CpSiMe₃）₃U-E（NCHMes）₂ complexes are thermodynamically feasible.This work reveals the divalent heavier group 14 complexes are promising donor ligands for building new unsupported uranium-metal bonds.