The Electronic Structure And Reaction Properties Of The Lanthanide Complex Of The Flexible Carbon-nitrogen Mixed Donor Were Calculated

The flexible small-cavity macrocycle,trans-calix[2]benzene[2]pyrrolide(H2L),h as been found experimentally and X-ray to complexate low-valent UⅢ and UⅣ w ith binding pockets(BP)of bis(arene)(Ar)and bis(pyrrolide)(PI),respectively.This switchable coordination of the uranium center has been explored using relati vistic density functional theory(DFT)in this thesis.Systematic calculations of[(BP-L)Anm(η-H)nBH4-n)]z+(BP = Ar and PI;An = Th,Pa,U,Np and Pu;m =Ⅲ and IV;n = 2 and 3;and z = 0 and 1;labeled as BP-Anm-nH),were carri ed out.Energetics and geometrical/electronic-structure analyses find that the size matching between actinide ion and binding pocket plays a significant role in det ermining the energetic ordering of isomers.The relatively large-size ThⅢ,PaⅢ,UⅢ and NpⅢ ions are selectively preferred by the large bis(arene)pocket.In contr ast,the small-size PuⅢ and AnⅣ(are held by the smaller bis(pyrrolide)to show energetically favored PI-An-3H isomer.Two δ(An-Ar2)bonding orbitals were fou nd for the former complexes;however,pure,core-like and isolated Pu(5f)charact er led to δ(An-Ar2)absent in the Ar-PuⅢ-2H complex,contributing to the more stable Pl-PuⅢ-3H isomer.Formation reactions of BP-Anm-nH demonstrate an e ndothermic process when using the H2L ligand reactant.Applying a more basic alkali ligand as reactant significantly reduces the reaction energy and presents the rmodynamic possibility to prepare the low-valent actinide complexes.This agrees with the experimental synthesis where K2L was utilized.Redox potentials(E0)f rom tri-to tetravalent actinides were calculated.The values of above actinide co mplexes decrease when An is crossed from Th to Pu,which agrees with the exp erimentally-measured results of E0(AnⅢ/Ⅳ).The highly reductive nature of the UⅠⅡ complex was manifested by the calculated E0 of over 1.1 V.