A theoretical probe for pentavalent bis-imido uranium complexes containing diverse axial substituents and equatorial donors: U[sbnd]N multiple bond and structural/electronic properties

Abstract

Pentavalent trans-bis(imido) uranium complexes, [UV(NR)2(THF)2(cis-I2)]− (2R), [UV(NR)2(THF)3(trans-I2)]− (3R) and [UV(NtBu)2(THF)3(cis-I2)]− (3tBu′), have been examined using relativistic density functional theory, where the R substituent is changed from CF3, Ph, H, Me, tBu to Cy. The calculated electron-spin density indicates the 5f1 configuration on the uranium center, which is mainly reflected by the HOMO with over 96% metal character. The UVN triple bond in these complexes is evidenced by computed bond length, bond order and electronic structure, although being weaker than UVIN in their hexavalent analogues and UVO in uranyl analogues. The UNH stretching vibrational frequencies of 2H and 3H are calculated between 698 and 745cm−1, while the UNC ones of other complexes are found in the range from 1043 to 1285cm−1. This shift is caused by the strong coupled interaction between sizable substituent and UN bond. The present study unravels that the changes of the R substituents as well as the number and the position of equatorial donors are capable of tuning structural and electronic properties of bis-imido complexes.