Supervalence Bonding in Bi-icosahedral Cores of [M1Au37(SC2H4Ph)24]- (M = Pd and Pt): Fusion-Mediated Synthesis and Anion Photoelectron Spectroscopy

Au₃₈(PET)₂₄ (PET = SC₂H₄Ph) is known to have a bi-icosahedral Au₂₃ core consisting of two Au₁₃ icosahedrons by sharing three Au atoms. Previous theoretical studies based on a supervalence bond (SVB) model have demonstrated that the bonding scheme in the Au₂₃ core is similar to that in the F₂ molecule. The SVB model predicted that the electron configuration of the Au₂₃ core with 14 valence electrons is expressed as (1Σ)²(1Σ*)²(1Π)⁴(2Σ)²(1Π*)⁴ where each orbital is created by the bonding and antibonding interactions between the 1S and 1P superatomic orbitals of the icosahedral Au₁₃ units. Therefore, the bi-icosahedral Au₂₃ can be viewed as a di-superatomic molecule. To validate the SVB model, we herein conducted anion photoelectron spectroscopy (PES) on [M₁Au₃₇(PET)₂₄]^- (M = Pd and Pt), which are isoelectronic and isostructural with Au₃₈(PET)₂₄. To this end, the neutral precursors [M₁Au₃₇(PET)₂₄]⁰ were first synthesized by fusion reactions between hydride-doped clusters [HAu₉(PPh₃)₈]²⁺ and [M₁Au₂₄(PET)₁₈]^-. The formation of bi-icosahedral M₁Au₂₂ cores with open electronic structure in [M₁Au₃₇(PET)₂₄]⁰ was confirmed by single-crystal X-ray diffraction analysis and electron paramagnetic resonance measurement. Then, the target anions [M₁Au₃₇(PET)₂₄]^- were obtained by reducing [M₁Au₃₇(PET)₂₄]⁰ with NaBH₄, and isoelectronicity with [Au₃₈(PET)₂₄]⁰ was confirmed by optical spectroscopy and density functional theory calculations. Finally, anion PES on [M₁Au₃₇(PET)₂₄]^- observed two distinctive peaks as predicted by the SVB model: one from the nearly degenerate 1Π* orbitals and the other from the nearly degenarate 1Π and 2Σ orbitals.

A Charge-Transfer Salt Based on Ferrocene/Ferrocenium Pairs and Keggin-Type Polyoxometalates

A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of four ferrocenium (Fe^III) cations and one ferrocene (Fe^II) molecule per plenary Keggin anion in the crystal structure of [Fe^III (Cp)₂]₄[SiW₁₂O₄₀]·[Fe^II(Cp)₂]·2CH₃OH (1). Compound 1 thus constitutes the first example in the literature in which ferrocenium and ferrocene species coexist in the structure of a polyoxometalate-based salt. The two crystallographically independent ferrocenium species in the asymmetric unit of 1 exhibit different configurations: One displays an eclipsed conformation with ideal D_5h symmetry, whereas the conformation in the other one is staggered D_5d. The crystal packing of 1 can be best described as an organometallic sub-lattice of ferrocenium and ferrocene species linked by a network of π-π interactions that generates rectangular cavities of about 14 × 10 Å in which strings of Keggin anions and methanol molecules are hosted, further connected to each other via weak O_POM···C_MeOH-O_MeOH···O_POM type hydrogen bonds. The charge-transfer nature of the salt has been studied by solid-state diffuse reflectance UV-Vis spectroscopy and the presence of magnetically isolated Fe^III/Fe^II centres has been confirmed by Mössbauer spectroscopy. A topological study carried out on all of the pristine ferrocenyl species deposited in the Cambridge Structural Database (CSD) has allowed two main conclusions to be drawn: (1) these species tend to adopt extreme conformations (either eclipsed or staggered) with less than a 15% of examples showing intermediate states and (2) the oxidation state of the iron centres can be unequivocally assigned on the basis of a close inspection of the Fe···Cp distances, which allows ferrocene neutral molecules and ferrocenium cations to be easily distinguished.

Crystal Structure of Ca2Na2(CO3)3 (Shortite)

Ca2Na2(CO3)3 crystallizes in the orthorhombic unit cell a = 4.947(1) Å, b = 11.032(2) Å, and c = 7.108(1) Å at 25 °C with two formula weights in space-group Amm2. The structure has been redetermined, corrected, and refined to R w = 0.025, R = 0.020 using 684 "observed" x-ray reflections from a single crystal. Corrections were made for absorption and isotropic extinction. In the extinction refinements, r refined to 0.00017(1) cm. The structure consists of Ca2NaCO3 layers interleaved with Na(CO3)2 layers. The Ca ion is coordinated strongly to nine oxygens, including three CO3 edges, with Ca … O distances varying from 2.401(2) Å to 2.576(2) Å. One Na ion is coordinated strongly to eight oxygens, including two CO3 edges, with Na … O distances from 2.429(2) Å to 2.605(1) Å. The other Na ion is coordinated strongly to six oxygens, including one CO3 edge, at 2.296(1) Å to 2.414 Å, and weakly to a seventh at 3.050(3) Å. One CO3 group is coordinated to seven cations, the other is coordinated to eight. The CO3 groups have seemingly maximized their edge sharing with Ca ions rather than Na ions.

Dicationic 1-Germa and 1-Stannavinylidenes: Synthesis, Structure, and Reactivity

The synthesis of heteronuclear vinylidene analogues containing heavier group 14 elements (R2C=E:, E = Si, Ge, Sn) has been a challenging task due to their inherent instability. In this study, we report the synthesis of dicationic 1-germavinylidene (3Ge) and 1-stannavinylidene (3Sn) by using sym-bis(2-pyridyl)-tetraphenylcarbodiphosphorane (CDPPy2) as a donor ligand. Both 3Ge and 3Sn have been characterized by single-crystal X-ray diffraction analysis, NMR spectroscopy, and high-resolution mass spectrometry. The structural analysis, supported by the results of theoretical calculations, confirms that 3Ge and 3Sn feature a polarized C=E double bond and a lone pair of electrons located at the E atom (E = Ge and Sn). The reactions of 3Ge with IDippMCl (M = Cu, Ag, Au) give the M-Cl bond addition products. Mechanistic studies on the activation of the Au-Cl bond by 3Ge demonstrate its ambiphilicity. This work represents an example of the utilization of a carbone ligand as both an σ and π donor for the synthesis of heavier heteronuclear vinylidene analogues.