Molecular-Metallic Binding Characteristics of the Intermetalloid f-/p-Block Cluster [(La@In2Bi11)2Bi2]6

Abstract

Main goals of contemporary research in chemistry are to create new materials with unique properties and to understand the chemical bonding in them, especially between metal atoms in larger structures. The isolation of a single lanthanide atom in a In/Bi cage offers a non-standard bonding situation, which deserves thorough exploration. In this study, the bonding behavior of La, In, and Bi atoms in the ternary cluster [(La@In₂Bi₁₁)₂Bi₂]^6- and the complex [La(C₅Me₄H)₃] used for its synthesis are characterized and compared by applying high energy resolution X-ray spectroscopy and computations. A clearly detectable covalent La(5d)─Bi(6p) interaction, induced in a highly electron-rich environment, is illustrated. The electronic structure of the La atom can be described as having the character of an ion being trapped and bonded in a heterometallic Bi/In cage. The advanced X-ray spectroscopic experimental tools applied here enable comparative studies of binding properties, focusing on different metals within the intermetalloid cluster. These tools can be employed iteratively to support the development of synthetic strategies that aim at tuning bond characteristics at the boundary of covalent and metallic bonding, thereby advancing the chemical and physical properties of novel multinary cluster compounds. The results were corroborated by GW and Bethe-Salpeter-equation (GW-BSE) calculations.

Keywords: Covalency of Ln‐based bonds; GW‐BSE calculations; Intermetallic clusters; La HR‐XANES; La VB‐RIXS.

Figure 1

a) Schematic representation of the synthetic approach of [(La@In₂Bi₁₁)₂Bi₂]⁶⁻ by reaction of the precursor complex [La(C₅Me₄H)₃] with the binary Zintl anion (InBi₃)^2– (for details, see text). b) Hypothetic fragmentation (semi‐transparent mode) of the cluster into two monomeric units of the formula “[(La@In₂Bi₁₁)]⁴⁻” (analogous to the reported [(U@Tl₂Bi₁₁)]^{4−[ 24 ]}) and two formerly bridging “Bi⁺” atoms, to illustrate the monomeric model compound studied computationally below; note that a real fragmentation would immediately consume “Bi⁺” in larger polybismuthide anions.

Figure 2

a) Normalized La L₃‐edge VB‐RIXS, b) HR‐XANES spectra, c) the electron transitions involved, and (d) the pre‐edge and main absorption peaks of the La L₃‐edge HR‐XANES spectra of [(La@In₂Bi₁₁)₂Bi₂]⁶⁻, [La(C₅Me₄H)₃], and La₂O₃.

Figure 3

Experimental La L₃‐edge VB‐RIXS and La L₃‐edge HR‐XANES spectra for a), b) [K(crypt‐222)]⁺ salt of [(La@In₂Bi₁₁)₂Bi₂]⁶⁻ and c), d) for [La(C₅Me₄H)₃], in comparison with the results of DFT and BSE calculations. La s, d, and f contributions to the DOS of the cluster [(La@In₂Bi₁₁)₂Bi₂]⁶⁻ (a) and the precursor [La(C₅Me₄H)₃] (c). Plotted is the natural orbital population versus the quasiparticle energy as obtained from a one‐component (a) or two‐component (c) fsCD‐evGW@PBE0/x2c‐TZVPPall‐2c computations. Shown are Gaussian line shapes with full width at half maximum of 1.00 eV. Simulated La L₃‐edge XANES spectra of the model compound “[La@In₂Bi₁₁]⁴⁻” (b) and [La(C₅Me₄H)₃] (d), as obtained from a two‐component evGW‐BSE@PBE0/x2c‐TZVPPall‐2c computation. Shown are Gaussian line shapes with a full width at half maximum of 0.25 eV. The pre‐edge region of the spectra obtained from electric dipole transition moments are shown as solid blue lines in the insets in (b) and (d). Those obtained from both dipole and quadrupole transition moments are shown as green lines. The calculated and experimental data are aligned relative to the Fermi energy at 0 eV, and the calculated intensities in (a) and (b) are scaled for better comparison.

Figure 4

Simulated La L₃‐edge XANES of the precursor [La(C₅Me₄H)₃] as obtained from two‐component evGW‐BSE@PBE0/x2c‐TZVPPall‐2c computations. Also shown are the unrelaxed particle densities for the peaks A through E. The unrelaxed particle densities are visualized at an isovalue of 0.00075 electrons/bohr.

Figure 5

Simulated La L₃‐edge XANES spectra of the model compound “[La@In₂Bi₁₁]⁴⁻” as obtained from two‐component evGW‐BSE@PBE0/x2c‐TZVPPall‐2c computations. Also shown are the unrelaxed particle densities for the peaks A through F. The unrelaxed particle densities are visualized at an isovalue of 0.00075 electrons/bohr.

Figure 6

Simulated In L₁‐edge XANES spectra of the model compound “[(La@In₂Bi₁₁)Bi₂]²⁻” as obtained from two‐component evGW‐BSE@PBE0/x2c‐TZVPPall‐2c computations. Also shown are the unrelaxed particle densities for peaks A through C. The unrelaxed particle densities are visualized at an isovalue of 0.00075 electrons/bohr³. Gaussian line shapes with a full width at half maximum of 2.50 eV are shown. Spectra obtained from electric dipole transition moments in the velocity representation are shown as solid red line. Those obtained from second‐order transition moments are shown as dashed blue line. For peaks A to C, the intervals [4245,4255], [4255,42581], and [42581,4262] eV were integrated, respectively.

Figure 7

Natural populations of La s, p, d, and f shells of the unrelaxed electron densities corresponding to peaks A–D of the calculated La L₃−edge HR‐XANES spectra for [La(C₅Me₄H)₃] a) and [La@In₂Bi₁₁]⁴⁻ b) (cf. Figures 4 and 5), obtained from two‐component evGW‐BSE@PBE0/x2c‐TZVPPall‐2c computations. c) Natural populations of La, Bi, and In from the unrelaxed electron densities corresponding to peaks A–C of the calculated In L₁‐edge XANES spectrum of [(La@In₂Bi₁₁)Bi₂]²−, obtained from two‐component evGW‐BSE@PBE0/x2c‐TZVPPall‐2c computations (cf. Figure 6). Note that the peak notations (from A to E) refer to each individual spectrum; there is no relationship between the peaks in the three spectra.

Figure 8

Two Pipek‐Mezey LMOs (one orbital in the left and one in the right cage) of the [(La@In₂Bi₁₁)₂Bi₂]⁶⁻ cluster showing La 5d–Bi 6p covalency through a La 5d population of 0.42 in the natural population analysis. At the PBE0/x2c‐TZVPPall‐1c level, the La s, p, d, and f populations in each of the orbitals are 0.03, 0.11, 0.42, and 0.01 electrons, respectively. The orbitals are visualized at an isovalue of 0.025 bohr^−3/2.

Figure 9

a) Bi L₃‐edge and b) In L₁‐edge XANES spectra of the [(La@In₂Bi₁₁)₂Bi₂]⁶⁻ cluster and the cluster exposed to air as well as Bi metal a) and In metal b). Comparison between the calculated with the FDMNES code and experimental Bi L₃‐edge c) and In L₃‐edge d) XANES spectra of the [(La@In₂Bi₁₁)₂Bi₂]⁶⁻ cluster. Comparison between the calculated with the FDMNES code La L₃‐edge XANES and experimental La L₃‐edge HR‐XANES spectra of [La(C₅Me₄H)₃] precursor e) and [(La@In₂Bi₁₁)₂Bi₂]⁶⁻ cluster f). All spectra are normalized to the post‐edge region.