δ and φ back-donation in AnIV metallacycles

Abstract

In all known examples of metal-ligand (M-L) δ and φ bonds, the metal orbitals are aligned to the ligand orbitals in a "head-to-head" or "side-to-head" fashion. Here, we report two fundamentally new types of M-L δ and φ interactions; "head-to-side" δ and "side-to-side" φ back-bonding, found in complexes of metallacyclopropenes and metallacyclocumulenes of actinides (Pa-Pu) that makes them distinct from their corresponding Group 4 analogues. In addition to the known Th and U complexes, our calculations include complexes of Pa, Np, and Pu. In contrast with conventional An-C bond decreasing, due to the actinide contraction, the An-C distance increases from Pa to Pu. We demonstrate that the direct L-An σ and π donations combined with the An-L δ or φ back-donations are crucial in explaining this nonclassical trend of the An-L bond lengths in both series, underscoring the significance of these δ/φ back-donation interactions, and their importance for complexes of Pa and U in particular.

Structural and Spectroscopic Comparison of Soft‐Se vs. Hard‐O Donor Bonding in Trivalent Americium/Neodymium Molecules

“…In opposition to this, when the donor was Te instead, the M–Te lengths increased gradually to reach a maximum at Am before a sharp drop at Cm. One way of interpreting this is to consider that the U–Te bond has a much larger covalent contribution than that of an Am‐Te bond and is thus much shorter than it would be if purely ionic [28] . Simultaneously, calculations predict larger deviation from formal f orbital population at the Am 3+ center than that of U 3+ in model 6‐coordinate [M{N(Se=PH 2 ) 2 } 3 ] and that a similar observation is seen for Eu 3+ in the Ln series [13c] .…”

Distinct electronic structures and bonding interactions in inverse-sandwich samarium and ytterbium biphenyl complexes

“…The d bonding interaction in these inverse sandwich samarium biphenyl complexes is reminiscent of recently identied inverse sandwich lanthanide-boron binary clusters 73,74 and actinide metallacycles. 75…”

Boron‐Made N2: Realization of a B≡B Triple Bond in the B2Al3− Cluster

“…It was previously found that AdNDP is basis-set and method independent. [53][54][55] It revealed three stype lone pairs on Al atoms with occupation numbers (ONs) of 1.96-1.67 |e|, two s-type lone pairs on two B atoms with ON=1.46 |e|, one 2c-2e B-B σ bond with ON=1.89 |e|, and two 5c-2e π bonds involving all B and Al atoms with ON=2.00|e|. The last two fully delocalized 5c-2e bonds could also be viewed as two direct B-B 2c-2e π bonds with somewhat lower ON values, i.e.…”