Vertex‐Shared Linear Superatomic Molecules: Stepping Stones to Novel Materials Composed of Noble Metal Clusters

Extremely small metal clusters composed of noble metal atoms (M) have orbitals similar to those of atoms and therefore can be thought of as artificial atoms or superatoms. If these superatoms can be assembled into molecular analogs, it might be possible to create materials with new characteristics and properties that are different from those of existing substances. Therefore, the concept of superatomic molecules has attracted significant attention. The present review focuses on vertex‐shared linear M12n+1 superatomic molecules formed via the sharing of a single metal atom between M13 superatoms having icosahedral cores and summarizes the knowledge obtained to date in this regard. This summary discusses the most suitable ligand combinations for the synthesis of M12n+1 superatomic molecules along with the valence electron numbers, stability, optical absorption characteristics, and luminescence properties of the M12n+1 superatomic molecules fabricated to date. This information is expected to assist in the production of many M12n+1 superatomic molecules with novel structures and physicochemical properties in the future

Fully Electron-Transferred Donor/Acceptor Layered Frameworks with TCNQ^2–

In a series of two-dimensional layered frameworks constructed by two electron-donor (D) and one electron-acceptor (A) units (a D₂A framework), two-electron transferred systems with D⁺₂A^2– were first synthesized as [{Ru₂(R-PhCO₂)₄}₂(TCNQR_<i>x</i>)]·<i>n</i>(solv) (R = <i>o</i>-CF₃, R_<i>x</i> = H₂ (<b>1</b>), R = <i>o</i>-CF₃, R_<i>x</i> = Me₂ (<b>2</b>), R = <i>o</i>-CF₃, R_<i>x</i> = F₄ (<b>3</b>), R = <i>o</i>-Me, TCNQR_<i>x</i> = BTDA-TCNQ (<b>4</b>), R = <i>p</i>-Me, TCNQR_<i>x</i> = BTDA-TCNQ (<b>5</b>), where TCNQ is 7,7,8,8-tetracyano-<i>p</i>-quinodimethane and BTDA-TCNQ is bis­[1,2,5]­dithiazolotetracyanoquinodimethane). The D⁺₂A^2– system was synthesized by assembling D/A combinations of paddlewheel-type [Ru₂^II,II(R-PhCO₂)₄] complexes and TCNQR_<i>x</i> that possibly caused a large gap between the HOMO of D and the LUMO of A (Δ<i>E</i>_H–L(DA)). All compounds were paramagnetic because of quasi-isolated [Ru₂^II,III]⁺ units with weakly antiferromagnetically coupled <i>S</i> = 3/2 spins via diamagnetic TCNQR_<i>x</i>^2– and/or through the interlayer space. The ionic states of these compounds were determined using the HOMO/LUMO energies and redox potentials of the D and A components in the ionization diagram for Δ<i>E</i>_H–L(DA) vs Δ<i>E</i>_1/2(DA) (= <i>E</i>_1/2(D) – <i>E</i>_1/2(A); <i>E</i>_1/2 = first redox potential) as well as by previously reported data for the D₂A and DA series of [Ru₂]/TCNQ, DCNQI materials. The boundary between the one-electron and the two-electron transferred ionic regimes (1e–I and 2e–I, respectively) was not characterized. Therefore, another diagram for Δ<i>E</i>_H–L(DA) vs |²<i>E</i>_1/2(A) – ¹<i>E</i>_1/2(A)|, where ²<i>E</i>_1/2(A) and ¹<i>E</i>_1/2(A) are the second and first redox potentials of TCNQR_<i>x</i>, respectively, was used because the 2e–I regime is dependent on on-site Coulomb repulsion (<i>U</i> = |²<i>E</i>_1/2(A) – ¹<i>E</i>_1/2(A)|) of TCNQR_<i>x</i>. This explained the oxidation states of <b>1</b>–<b>5</b> and the relationship between Δ<i>E</i>_H–L(DA) and <i>U</i> and allowed us to determine whether the ionic regime was 1e–I or 2e–I. These diagrams confirm that a charge-oriented choice of building units is possible even when designing covalently bonded D₂A framework systems

Fully Electron-Transferred Donor/Acceptor Layered Frameworks with TCNQ^2–

In a series of two-dimensional layered frameworks constructed by two electron-donor (D) and one electron-acceptor (A) units (a D₂A framework), two-electron transferred systems with D⁺₂A^2– were first synthesized as [{Ru₂(R-PhCO₂)₄}₂(TCNQR_<i>x</i>)]·<i>n</i>(solv) (R = <i>o</i>-CF₃, R_<i>x</i> = H₂ (<b>1</b>), R = <i>o</i>-CF₃, R_<i>x</i> = Me₂ (<b>2</b>), R = <i>o</i>-CF₃, R_<i>x</i> = F₄ (<b>3</b>), R = <i>o</i>-Me, TCNQR_<i>x</i> = BTDA-TCNQ (<b>4</b>), R = <i>p</i>-Me, TCNQR_<i>x</i> = BTDA-TCNQ (<b>5</b>), where TCNQ is 7,7,8,8-tetracyano-<i>p</i>-quinodimethane and BTDA-TCNQ is bis­[1,2,5]­dithiazolotetracyanoquinodimethane). The D⁺₂A^2– system was synthesized by assembling D/A combinations of paddlewheel-type [Ru₂^II,II(R-PhCO₂)₄] complexes and TCNQR_<i>x</i> that possibly caused a large gap between the HOMO of D and the LUMO of A (Δ<i>E</i>_H–L(DA)). All compounds were paramagnetic because of quasi-isolated [Ru₂^II,III]⁺ units with weakly antiferromagnetically coupled <i>S</i> = 3/2 spins via diamagnetic TCNQR_<i>x</i>^2– and/or through the interlayer space. The ionic states of these compounds were determined using the HOMO/LUMO energies and redox potentials of the D and A components in the ionization diagram for Δ<i>E</i>_H–L(DA) vs Δ<i>E</i>_1/2(DA) (= <i>E</i>_1/2(D) – <i>E</i>_1/2(A); <i>E</i>_1/2 = first redox potential) as well as by previously reported data for the D₂A and DA series of [Ru₂]/TCNQ, DCNQI materials. The boundary between the one-electron and the two-electron transferred ionic regimes (1e–I and 2e–I, respectively) was not characterized. Therefore, another diagram for Δ<i>E</i>_H–L(DA) vs |²<i>E</i>_1/2(A) – ¹<i>E</i>_1/2(A)|, where ²<i>E</i>_1/2(A) and ¹<i>E</i>_1/2(A) are the second and first redox potentials of TCNQR_<i>x</i>, respectively, was used because the 2e–I regime is dependent on on-site Coulomb repulsion (<i>U</i> = |²<i>E</i>_1/2(A) – ¹<i>E</i>_1/2(A)|) of TCNQR_<i>x</i>. This explained the oxidation states of <b>1</b>–<b>5</b> and the relationship between Δ<i>E</i>_H–L(DA) and <i>U</i> and allowed us to determine whether the ionic regime was 1e–I or 2e–I. These diagrams confirm that a charge-oriented choice of building units is possible even when designing covalently bonded D₂A framework systems

Key factors for connecting silver-based icosahedral superatoms by vertex sharing

Metal nanoclusters composed of noble elements such as gold (Au) or silver (Ag) are regarded as superatoms. In recent years, the understanding of the materials composed of superatoms, which are often called superatomic molecules, has gradually progressed for Au-based materials. However, there is still little information on Ag-based superatomic molecules. In the present study, we synthesise two di-superatomic molecules with Ag as the main constituent element and reveal the three essential conditions for the formation and isolation of a superatomic molecule comprising two Ag13-xMx structures (M = Ag or other metal; x = number of M) connected by vertex sharing. The effects of the central atom and the type of bridging halogen on the electronic structure of the resulting superatomic molecule are also clarified in detail. These findings are expected to provide clear design guidelines for the creation of superatomic molecules with various properties and functions. Icosahedron-based M-13 nanoclusters are common building blocks to produce atomically precise superatomic molecules, but our understanding of the chemistry governing the connection between icosahedral M-13 units is limited. Here, the key factors influencing the vertex sharing connection between Ag13-xMx structures are studied, and the effects of different central metal atoms and the type of bridging halogen atom are clarified