Electronic properties of unprecedented bridging organoimido-substituted hexamolybdate: new insights from density functional theory study.

The organoimido functionalization of polyoxometalates (POMs) has drawn tremendous attention due to particular merits in fabricating POM-based hybrid materials with finely tunable properties. The electronic properties, orbital and bonding characters of unprecedented bridging organoimido-substituted hexamolybdate are investigated using density functional theory methods. Among the organoimido-bridged hexamolybdates, Mo(6)O(16)(2,6-Me(2)-NC(6)H(3))(2)(mu(2)-2,6-Me(2)-NC(6)H(3)) (3-Ar-1), which features two terminal and one bridging organoimido ligand, is more favorable. The calculations confirm that the three-center (3c) pi bond originates from the coplanarity of bridging nitrogen atom with two Mo atoms and the hybridization of bridging nitrogen. The 3c bond stabilizes the organoimido-bridged anion 3-Ar-1. Compared with cis-bifunctionalized organoimido derivative Mo(6)O(17)(2,6-Me(2)-NC(6)H(3))(2) (2-Ar), the bonding interaction between terminal organoimido ligand and hexamolybdate cluster in 3-Ar-1 is strengthened by the bridging organoimido. The results are in good agreement with the analysis of the Wiberg bond index of the Mo-N bond. The organoimido segment modifies the occupied molecular orbitals of organoimido hexamolybdates. The unoccupied molecular orbitals in 3-Ar-1 are largely nonbonding O(p) and Mo(d) orbitals in character, which resemble those of 2-Ar.