Installing Quaternary Germanium Centers in Sila-Diamondoid Cores via Skeletal Isomerization.

This manuscript describes skeletal isomerization strategies to install one to four quaternary germanium atoms in the sila-adamantane core, in a cluster analogy to precision germanium doping in silicon-germanium alloys. The first strategy embodies an inorganic variant of single-atom skeletal editing, where we use a sila-Wagner-Meerwein bond shift cascade to exchange a peripheral Ge atom with a core Si atom. We can install up to four Ge atoms at the quaternary diamondoid centers based on controlling the SixGey stoichiometry of our precursor. We find that bridgehead Ge centers can be selectively functionalized over bridgehead Si centers in SiGe adamantanes; we use this chemistry in conjunction with scanning tunneling microscopy break-junction (STM-BJ) measurements to show that Si8Ge2 adamantane wires give a 60% increase in single-molecule conductance compared with Si10 adamantanes. These studies describe the first quantum transport measurements in sila-diamondoid structures, and demonstrate how main-chain Ge doping can be used to increase electronic transmission in sila-diamondoid-based molecular wires.

Site-Selective Functionalization of Sila-Adamantane and Its Ensuing Optical Effects.

The first syntheses of functionalized sila-adamantanes via site-selective reactions are described. Mechanistic inquiry into the isomerization of sila-adamantane revealed new approaches for installing halides at the 2-position of the cluster. Meanwhile, isomerization via Lewis acid catalysts with non-nucleophilic counteranions provided access to sila-adamantane on the gram-scale, enabling us to discover strategies for substituting its 1-, 3-, 5-, and 7-positions with identical or distinct functional groups. Optical absorbance and density functional theory studies show that σ-withdrawing substituents at the 1-position strongly perturb optical absorbance in sila-adamantane, whereas substituents at the exocyclic and 2-position are optically inert. As silicon diamondoids are atomically precise models for silicon nanocrystals, our findings suggest that passivation at tertiary surface sites carries an outsized impact on the optical properties of surface-functionalized Si nanocrystals.

Single-cluster electronics.

This article reviews the scope of inorganic cluster compounds interrogated in single-molecule break-junction measurements. This body of work lies at the intersection between the fields of inorganic cluster chemistry and single-molecule electronics, where discrete inorganic cluster molecules are used as the active components in molecular electronic circuitry. We explore the breadth of transition metal and main group cluster compounds that have been studied in single-cluster junctions, largely within the context of scanning tunnelling microscopy break-junction (STM-BJ) measurements. Our discussion centers on how the structure and bonding of inorganic cluster compounds give rise to desirable quantum transport effects such as room-temperature current blockade, sequential tunneling, voltage-gated conductance switching, destructive quantum interference, and high thermoelectric currents.