More Like this

1. PrB 7 − : A Praseodymium‐Doped Boron Cluster with a Pr II Center Coordinated by a Doubly Aromatic Planar η 7 ‐B 7 3− Ligand

   https://doi.org/10.1002/ange.201703111  

   Chen, Teng‐Teng ; Li, Wan‐Lu ; Jian, Tian ; Chen, Xin ; Li, Jun ; Wang, Lai‐Sheng ( May 2017 , Angewandte Chemie)

   The structure and bonding of a Pr‐doped boron cluster (PrB₇⁻) are investigated using photoelectron spectroscopy and quantum chemistry. The adiabatic electron detachment energy of PrB₇⁻is found to be low [1.47(8) eV]. A large energy gap is observed between the first and second detachment features, indicating a highly stable neutral PrB₇. Global minimum searches and comparison between experiment and theory show that PrB₇⁻has a half‐sandwich structure with C_6vsymmetry. Chemical bonding analyses show that PrB₇⁻can be viewed as a Pr^II[η⁷‐B₇³⁻] complex with three unpaired electrons, corresponding to a Pr (4f²6s¹) open‐shell configuration. Upon detachment of the 6s electron, the neutral PrB₇cluster is a highly stable Pr^III[η⁷‐B₇³⁻] complex with Pr in its favorite +3 oxidation state. The B₇³⁻ligand is found to be highly stable and doubly aromatic with six delocalized π and six delocalized σ electrons and should exist for a series of lanthanide M^III[η⁷‐B₇³⁻] complexes.

    

   more » « less
2. Origin of the 29 Si NMR chemical shift in R 3 Si–X and relationship to the formation of silylium (R 3 Si + ) ions

   https://doi.org/10.1039/D0DT02099K  

   Huynh, Winn ; Conley, Matthew P. ( November 2020 , Dalton Transactions)

   null (Ed.)

   The origin in deshielding of 29 Si NMR chemical shifts in R 3 Si–X, where X = H, OMe, Cl, OTf, [CH 6 B 11 X 6 ], toluene, and O X (O X = surface oxygen), as well as i Pr 3 Si + and Mes 3 Si + were studied using DFT methods. At the M06-L/6-31G(d,p) level of theory the geometry optimized structures agree well with those obtained experimentally. The trends in 29 Si NMR chemical shift also reproduce experimental trends; i Pr 3 Si–H has the most shielded 29 Si NMR chemical shift and free i Pr 3 Si + or isolable Mes 3 Si + have the most deshielded 29 Si NMR chemical shift. Natural localized molecular orbital (NLMO) analysis of the contributions to paramagnetic shielding ( σ p ) in these compounds shows that Si–R (R = alkyl, H) bonding orbitals are the major contributors to deshielding in this series. The Si–R bonding orbitals are coupled to the empty p-orbital in i Pr 3 Si + or Mes 3 Si + , or to the orbital in R 3 Si–X. This trend also applies to surface bound R 3 Si–O X . This model also explains chemical shift trends in recently isolated t Bu 2 SiH 2 + , t BuSiH 2 + , and SiH 3 + that show more shielded 29 Si NMR signals than R 3 Si + species. There is no correlation between isotropic 29 Si NMR chemical shift and charge at silicon. 

   more » « less
3. High‐Resolution Photoelectron Imaging of IrB 3 − : Observation of a π‐Aromatic B 3 + Ring Coordinated to a Transition Metal

   https://doi.org/10.1002/anie.201902406  

   Czekner, Joseph ; Cheung, Ling Fung ; Kocheril, G. Stephen ; Kulichenko, Maksim ; Boldyrev, Alexander I. ; Wang, Lai‐Sheng ( May 2019 , Angewandte Chemie International Edition)

   In a high‐resolution photoelectron imaging and theoretical study of the IrB₃⁻cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B₃ring coordinated with the Ir atom. The isomer with the higher EA consists of a B₃ring with a bridge‐bonded Ir atom (C_s,²A′), and the second isomer features a tetrahedral structure (C_3v,²A₁). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutralC_3visomer involves significant covalent Ir−B bonding and weak ionic bonding with charge transfer from B₃to Ir, and can be viewed as an Ir–(η³‐B₃⁺) complex. This study provides the first example of a boron‐to‐metal charge‐transfer complex and evidence of a π‐aromatic B₃⁺ring coordinated to a transition metal.

    

   more » « less
4. High‐Resolution Photoelectron Imaging of IrB 3 − : Observation of a π‐Aromatic B 3 + Ring Coordinated to a Transition Metal

   https://doi.org/10.1002/ange.201902406  

   Czekner, Joseph ; Cheung, Ling Fung ; Kocheril, G. Stephen ; Kulichenko, Maksim ; Boldyrev, Alexander I. ; Wang, Lai‐Sheng ( May 2019 , Angewandte Chemie)

   In a high‐resolution photoelectron imaging and theoretical study of the IrB₃⁻cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B₃ring coordinated with the Ir atom. The isomer with the higher EA consists of a B₃ring with a bridge‐bonded Ir atom (C_s,²A′), and the second isomer features a tetrahedral structure (C_3v,²A₁). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutralC_3visomer involves significant covalent Ir−B bonding and weak ionic bonding with charge transfer from B₃to Ir, and can be viewed as an Ir–(η³‐B₃⁺) complex. This study provides the first example of a boron‐to‐metal charge‐transfer complex and evidence of a π‐aromatic B₃⁺ring coordinated to a transition metal.

    

   more » « less
5. Electronic structure studies reveal 4f/5d mixing and its effect on bonding characteristics in Ce-imido and -oxo complexes

   https://doi.org/10.1039/D1SC06623D  

   Moreau, Liane M. ; Lapsheva, Ekaterina ; Amaro-Estrada, Jorge I. ; Gau, Michael R. ; Carroll, Patrick J. ; Manor, Brian C. ; Qiao, Yusen ; Yang, Qiaomu ; Lukens, Wayne W. ; Sokaras, Dimosthenis ; et al ( February 2022 , Chemical Science)

   This study presents the role of 5d orbitals in the bonding, and electronic and magnetic structure of Ce imido and oxo complexes synthesized with a tris(hydroxylaminato) [((2- t BuNO)C 6 H 4 CH 2 ) 3 N] 3− (TriNO x 3− ) ligand framework, including the reported synthesis and characterization of two new alkali metal-capped Ce oxo species. X-ray spectroscopy measurements reveal that the imido and oxo materials exhibit an intermediate valent ground state of the Ce, displaying hallmark features in the Ce L III absorption of partial f-orbital occupancy that are relatively constant for all measured compounds. These spectra feature a double peak consistent with other formal Ce( iv ) compounds. Magnetic susceptibility measurements reveal enhanced levels of temperature-independent paramagnetism (TIP). In contrast to systems with direct bonding to an aromatic ligand, no clear correlation between the level of TIP and f-orbital occupancy is observed. CASSCF calculations defy a conventional van Vleck explanation of the TIP, indicating a single-reference ground state with no low-lying triplet excited state, despite accurately predicting the measured values of f-orbital occupancy. The calculations do, however, predict strong 4f/5d hybridization. In fact, within these complexes, despite having similar f-orbital occupancies and therefore levels of 4f/5d hybridization, the d-state distributions vary depending on the bonding motif (CeO vs. CeN) of the complex, and can also be fine-tuned based on varying alkali metal cation capping species. This system therefore provides a platform for understanding the characteristic nature of Ce multiple bonds and potential impact that the associated d-state distribution may have on resulting reactivity. 

   more » « less