Actinide Coordination Chemistry on Surfaces: Synthesis, Manipulation, and Properties of Thorium Bis(porphyrinato) Complexes

Abstract

Actinide-based metal−organic complexes and coordination architectures encompass intriguing properties and functionalities but are still largely unexplored on surfaces. We introduce the in situ synthesis of actinide tetrapyrrole complexes under ultrahighvacuum conditions, on both a metallic support and a 2D material. Specifically, exposure of a tetraphenylporphyrin (TPP) multilayer to an elemental beam of thorium followed by a temperatureprogrammed reaction and desorption of surplus molecules yields bis(porphyrinato)thorium (Th(TPP) 2 ) assemblies on Ag(111) and hexagonal boron nitride/Cu(111). A multimethod characterization including X-ray photoelectron spectroscopy, scanning tunneling microscopy, temperature-programmed desorption, and complementary density functional theory modeling provides insights into conformational and electronic properties. Supramolecular assemblies of Th(TPP) 2 as well as individual double-deckers are addressed with submolecular precision, e.g., demonstrating the reversible rotation of the top porphyrin in Th(TPP) 2 by molecular manipulation. Our findings thus demonstrate prospects for actinide-based functional nanoarchitectures.

Porphyrinoid actinide complexes

“…, Ag(111) and h -BN/Cu(111). 59 This in-situ synthesis consisted of three steps. First, a multilayer of the precursor H 2 TPP was grown on the substrate of choice.…”

“…In 2021, Rheinfrank and co-workers reported an alternative synthesis of Th(TPP) 2 (27), namely a solvent-free ultrahighvacuum method involving two different substrates (i.e., Ag(111) and h-BN/Cu(111). 59 This in-situ synthesis consisted of three steps. First, a multilayer of the precursor H 2 TPP was grown on the substrate of choice.…”

“…However, a greater apparent electronic gap was seen for the sample on h-BN/Cu(111) with a deviation from a perfect square antiprismatic coordination geometry around the Th centre being noted in the case of 27 produced on Ag(111). 59 An advantage of the h-BN supported product is that it allowed for thermal desorption of the intact sandwich complex, thereby permitting further studies, such as STS. Going forward, this synthetic method may permit the preparation of new complexes containing other actinide cations whose access is limited by traditional synthetic protocols.…”

Achieving High Photo/Thermocatalytic Product Selectivity and Conversion via Thorium Clusters with Switchable Functional Ligands

“…As relatively abundant actinides on earth, thorium and its derivatives have manifested critical applications in nuclear energy, medical, and industrial fields because of their radiation resistance, high temperature resistance, and high thermal conductivity. − However, the relatively low structural variability of these materials restricts their development to some extent in more potential applications. − The development of thorium-based coordination compounds provides more possibilities to overcome these restrictions, because more structural variations and functional modulations can be readily implemented through the diverse coordination numbers and intriguing coordination modes of thorium as well as coordination of different functional ligands . Particularly, thorium-based metal–organic frameworks (Th-MOFs) have been tuned for applications in gas adsorption, ion exchange, and radiation resistance through coordination modification with different organic ligands. − Nevertheless, the application of thorium-based functionalized materials (including thorium-based complexes) in the field of catalysis is still largely unexplored. − To date, a mere handful of Th-MOFs have been reported to be applied as heterogeneous catalysts for CO 2 cycloaddition and photocatalytic oxidation of 2-chloroethyl ethyl sulfide. − …”

High-Throughput Preparation of Supramolecular Nanostructures on Metal Surfaces

“…Supramolecular chemistry has been a subject of intense study for developing functional materials with various applications. , Molecular self-assembly at solid surfaces offers a promising strategy and unparalleled route for the large-scale construction of low-dimensional nanostructures, which have gained considerable attention in the past few decades. , The organized surface molecular nanostructures are driven by molecule–molecule and/or molecule–metal recognitions through dynamic noncovalent interactions including hydrogen and halogen bonding, van der Waals forces, and dipole–dipole and metal–organic coordinated interactions. − A spectrum of interesting, and in some cases peculiar, supramolecular nanostructures were successfully constructed on surfaces. ,− Another noteworthy factor to the popularity of surface-supported supramolecular chemistry lies in the expansion of the surface science community, particularly thanks to the advances of scanning probe microscopy (SPM), which enables the submolecular characterization of the surface-supported species. − …”