Molecules with High Bond Orders and Ultrashort Bond Lengths: CrU, MoU, and WU

10-Valence-Electron C≡O and the 14-VE C≡Pt: Two Triple-Bonded Isoelectronic Families Differing by a dδ4 Ring

10-VE A≡A' Diatomics, such as N≡N, C≡O, etc., have a strong σ2π4 triple bond plus a lone pair at each end. In our studies on 14-VE A≡B systems, such as C≡Pt, we find a similar bonding system plus a (5dδ)4 ring. Here, the A atom belongs to groups 13-17 and the B atom to groups 7-11. Also the BB' combinations, triatomics, such as PtCO or DsCO or uranyl, and longer chains, such as AuCN and [NC-Au-CN]-, are discussed. The δ ring directly contributes to nuclear quadrupole coupling constants, and DFT calculations using the BH and H or mPW1K functionals reproduce the experimental trends of the NQCC.

Dative quadruple bonds between d10 transition metals and beryllium in BeM(PMe3 )2 and BeM(CO)2 (M = Ni, Pd, and Pt) complexes: Transition metal fragments as six-electron donor and two-electron acceptor

The structure, chemical bonding, and reactivity of neutral 16 valence electrons (VE) transition metal complexes of beryllium, BeM(PMe₃ )₂ (1M-Be) and BeM(CO)₂ (2M-Be, M = Ni, Pd, and Pt) were studied. The molecular orbital and EDA-NOCV analysis suggest dative quadruple bonds between the transition metal and beryllium, viz., one Be→M σ bond, one Be←M σ bond, and two Be←M π bonds. The strength of these bonding interactions varies based on the ligands coordinated to the transition metal. The Be←M σ bond is stronger than the Be→M σ bond when the ligand is PMe_3, whereas the reverse order is observed when the ligand is CO. This is attributed to the higher π acceptor strength of CO as compared to PMe₃ . Since these complexes have M-Be dative quadruple bonds, the beryllium center is susceptible to ambiphilic reactivity, as indicated by high proton and hydride affinity values.

Prediction of high bond-order metal-metal multiple-bonds in heterobimetallic 3d-4f/5f complexes [TM-M{N(o-[NCH2P(CH3)2]C6H4)3}] (TM = Cr, Mn, Fe; M = U, Np, Pu, and Nd)

Despite continuing and burgeoning interest in f-block complexes and their bonding chemistry in recent years, investigations of the electronic structures and oxidation states of heterobimetallic complexes, and their bonding features between transition-metals (TMs) and f-elements remain relatively less explored. Here, we report a quantum chemical computational study on the series of TM-actinide and -neodymium complexes [TMAn(L)] and [TMNd(L)] [An = U, Np, Pu; TM = Cr, Mn, Fe; L = {N(o-[NCH₂P(CH₃)₂]C₆H₄)₃}^3-] in order to explore periodic trend, generalities and differences in the electronic structure and metal-metal bonding between f-block and d-block elements. Based on the calculations, we find up to five-fold covalent multiple bonding between actinide and transition metal ions, which is in sharp contrast with a single bond between neodymium and transition metals. From a comparative study, a general trend of strength of the An-TM interaction emerges in accordance with the atomic number of the actinide metal, which relates to the nature, energy level, and spatial arrangement of their frontier orbitals. The trend presents a valuable insight for future experimental endeavour searching for isolable complexes with strong and multiple An-TM bonding interactions, especially for the experimentally challenging transuranic elements that require targeted research due to their radioactive nature.

Multiple Bonds in Uranium-Transition Metal Complexes

Novel heterobimetallic complexes featuring a uranium atom paired with a first-row transition metal have been computationally predicted and analyzed using density functional theory and multireference wave function based methods. The synthetically inspired metalloligands U{(ⁱPr₂PCH₂NAr)₃tacn} (1) and U(ⁱPr₂PCH₂NPh)₃ (2) are explored in this study. We report the presence of multiple bonds between uranium and chromium, uranium and manganese, and uranium and iron. The calculations predict a 5-fold bonding between uranium and manganese in the UMn(ⁱPr₂PCH₂NPh)₃ complex, which is unprecedented in the literature.

Preparation and Characterization of Uranium-Iron Triple-Bonded UFe(CO)3- and OUFe(CO)3- Complexes

We report the preparation of UFe(CO)₃^- and OUFe(CO)₃^- complexes using a laser-vaporization supersonic ion source in the gas phase. These compounds were mass-selected and characterized by infrared photodissociation spectroscopy and state-of-the-art quantum chemical studies. There are unprecedented triple bonds between U 6d/5f and Fe 3d orbitals, featuring one covalent σ bond and two Fe-to-U dative π bonds in both complexes. The uranium and iron elements are found to exist in unique formal U(I or III) and Fe(-II) oxidation states, respectively. These findings suggest that there may exist a whole family of stable df-d multiple-bonded f-element-transition-metal compounds that have not been fully recognized to date.