Periodic TableTalks: A Continuing Resource for Communicating Inorganic Chemistry in the Post-Pandemic Era

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To share the excellent contributions of our 2022–2023 Periodic TableTalks speakers, we present this Virtual Issue in which we have collected some of their work. In this Editorial, we provide a summary of the research programs of the speakers and the specific articles.

Jon Owen and his group at Columbia University study the kinetics and reaction mechanisms associated with the synthesis of metallic and semiconducting nanoparticles. His group has been a leader in understanding the roles of organic ligands in both synthesis and leveraging toward applications. In a recent publication, Owen reported a detailed study of the synthesis of ZnS nanocrystals using a series of disubstituted and trisubstituted thioureas, as well as trisubstituted phosphanecarbothioamides as sulfur sources (Chem. Mater., DOI: 10.1021/acs.chemmater.1c03432). The ligand sterics of the sulfur precursors were correlated with the size of the ZnS nanocrystal products, and the materials were characterized using a range of techniques, including pair distribution function analysis that defined the optical properties of the colloids. In another recent collaborative effort, Owen and co-workers reported a detailed mechanistic study outlining a multistep photon upconversion process with CdSe quantum dots functionalized with 10-R-anthracene-1,8-diphosphoric acid ligands (Chem. Mater., DOI: 10.1021/acs.chemmater.9b04294). Compared to monodentate ligands, bidentate ligands have high binding affinity and facilitate efficient triplet transfer processes. Such processes define energy storage and conversion relating to photocatalysis and thus have important implications for ongoing efforts in this field. His group has also been at the forefront of experimental design in colloidal nanosynthesis. This includes a recent article in which his group fine-tuned the kinetics of InP nanocrystal formation using aminophosphine precursors with different functional groups (Chem. Mater., DOI: 10.1021/acs.chemmater.0c01561). The designer aminophosphine reagents were synthesized with varying degrees of steric groups, which tended to slow down the rate of InP nanoparticle formation. The proposed mechanism deviated from the classic LaMer model, offering a new perspective on a challenging but important nanoparticle synthesis.

Laurel Schafer and her research group at the University of British Columbia work at the interface of inorganic and organic chemistry, developing organometallic complexes for use in atom-economic syntheses of amines, small molecules, heterocycles, and polymers. Her group has a particular interest in the catalytic behavior of group IV and lanthanide metal centers. Schafer’s Periodic TableTalks presentation focused on the development of novel N,O-chelated organometallic complexes and their application in various bond-activation processes. A series of thematically related recent papers from the Schafer group have paired these unique structural motifs with group IV metal centers, observing effective hydroaminoalkylation across a wide substrate scope. The use of these ligand scaffolds promotes catalytic behavior, effectively replacing ubiquitous metallocene complexes used in stoichiometric bond formations. For example, the group systematically investigated the C–N bond formation process using an N,O ligand around a zirconium center, evaluating the stoichiometric reactivity of catalytic intermediates to elucidate mechanistic insights (Organometallics, DOI: 10.1021/acs.organomet.2c00606). The group has also demonstrated that titanium-based catalysts can drive similar hydroaminoalkylation reactions with high turnover frequencies (ACS Catal., DOI: 10.1021/acscatal.1c00014). Critically, these catalysts employ metals that have low toxicity and can be generated with commercially available titanium amido precursors using a urea-based proligand, while reliably producing bonds in a regioselective manner across an array of substrates. In addition to their efforts in catalyst development, the group has reported on important fundamental structural characterization and bonding present in organometallic complexes. Clarkson and Schafer investigated the binding behavior of several N,O-chelates around a tungsten(VI) center, uncovering critical steric and electronic features that impacted reactivity in otherwise closely related complexes (Inorg. Chem., DOI: 10.1021/acs.inorgchem.6b02959).

Mas Subramanian and his solid-state chemistry group at Oregon State University have research interests centered around the development of design rules and structure–property relationships in functional inorganic solids that span a wide range of applications, including electronics, energy storage, superconductivity, catalysis, magnetics, and thermoelectrics. His offering in the Periodic TableTalks series dealt with the group’s 2009 serendipitous discovery of a deep-blue pigment, YInMn. This color is used in Crayola crayons! Their discovery was the subject of considerable reporting in popular media and has subsequently led the group to a number of fundamental advances in the area of solid-state materials for use as brightly colored pigments. To date, Subramanian and team have thoroughly and systematically investigated their original blue material, the first new blue pigment developed in more than 200 years. The blue pigment (sometimes called “MasBlue” for Mas Subramanian) is a solid solution with composition YIn_1–xMn_xO₃, whose structure is based on hexagonal YInO₃. In a series of related publications, the group expanded on the original pigment findings, the interrelated magnetic and optical properties of the solid solution (Inorg. Chem., DOI: 10.1021/acs.inorgchem.5b01306). The presence of the paramagnetic Mn(III) dopant ion imparts both the blue color and unusual magnetic behavior that was studied through a multipronged electron paramagnetic resonance and classical theoretical approach. In 2017, the group determined the local environment of the Mn(III) and In(III) ions in the solid-solution pigment and the implications of the observed crystallographic distortions for the observed properties of the material (Chem. Mater., DOI: 10.1021/acs.chemmater.6b02827). In more recent work, the group has been interested in systematic alkaline-earth substitutions on a bismuth ruthenate pyrochlore structure. They found that the extent of Bi(II) off-centering due to a lone-pair distortion could be modulated by altering the composition of the alkaline-earth site (Inorg. Chem., DOI: 10.1021/acs.inorgchem.0c01901).

Clifford Kubiak and his research group at the University of California, San Diego, have a longstanding research program centered on designing, optimizing, and understanding new molecules and materials for the electrocatalytic reduction of H⁺ and CO₂. Significant recent work by his group has focused on attaching small-molecule CO₂ electrocatalysts to electrode surfaces (Acc. Chem. Res., DOI: 10.1021/acs.accounts.9b00001). For example, a rhenium(I) tricarbonyl complex containing an alkynyl functional group, [Re(ethynyl-bpy)(CO)₃Cl] where bpy = 2,2′-bipyridine, was evaluated for its electrocatalytic CO₂ reduction properties and then grafted onto a glassy carbon electrode via both electropolymerization and azide–alkyne “click” chemistry (Organometallics, DOI: 10.1021/acs.organomet.8b00547). The alkyne group on the bpy ligand led to substantial improvements compared to related rhenium(I) tricarbonyl complexes without this moiety. Specifically, [Re(ethynyl-bpy)(CO)₃Cl] more selectively yielded CO as a product with a Faradaic efficiency of 96%, a lower overpotential, and a higher catalytic rate compared to the compound with the unfunctionalized bpy ligand. Coupled with its ability to be attached to solid electrode surfaces, this compound is a promising candidate for further development. In addition, the Kubiak group explored the effects of immobilizing H⁺ reduction catalysts to mesoporous TiO₂ electrodes (Inorg. Chem., DOI: 10.1021/acs.inorgchem.0c01669). This study employed [Ni(P₂N₂)₂]²⁺ complexes, compounds with pendent amine groups that facilitate H⁺ transfer to the metal hydride intermediate to facilitate the hydrogen evolution reaction (as noted in Chem. Rev., DOI: 10.1021/acs.chemrev.1c01001). The group synthesized two new [Ni(P₂N₂)₂]²⁺ complexes, one with a TiO₂-binding phosphonate on a pendent amine of the ligand and another on the phosphine donor. After attaching both compounds to a TiO₂ electrode, Kubiak and his group used detailed electrocatalytic studies to show that the amine-anchored catalyst was slightly less active than the phosphine anchored one, but this effect was relatively small. Thus, for these particular materials, the team concluded that macroscopic mass transport effects are more important when designing such hybrid molecular solid-state catalysts.

Vickie DeRose and her team at the University of Oregon investigate the mechanisms of action of platinum-based drug candidates, as well as their interactions with nucleic acids (Inorg. Chim. Acta, DOI: 10.1016/j.ica.2019.118984). Canonically, platinum-based drugs such as cisplatin have been believed to kill cancer cells by forming covalent adducts with genomic DNA, which inhibit transcription (Metallomics, DOI: 10.1039/B907567D). In recent studies, the second-generation platinum drug oxaliplatin was found to trigger cell death via the inhibition of ribosome biogenesis, which causes nucleolar stress (Nat. Med., DOI: 10.1038/nm.4291). DeRose and her team have been comprehensively investigating this phenomenon to understand which structural features in platinum(II) coordination compounds favor one mechanism over the other. They synthesized a series of platinum(II) compounds with different ligand types and then assessed their ability to cause redistribution of nucleophosmin, a marker for nucleolar stress within cancer cells (J. Am. Chem. Soc., DOI: 10.1021/jacs.9b10319). From this compound library, DeRose and co-workers concluded that complexes with chelating diamine ligands with large steric profiles gave rise to nucleolar stress. In a subsequent study, the team investigated the rate and extent to which nucleolar stress was caused by these compounds (ACS Chem Biol., DOI: 10.1021/acschembio.2c00399). Remarkably, there were significant differences in the speed at which the biological effects were triggered by these compounds that correlated with their structural features, including chirality. Overall, this body of work is important because it has laid the groundwork for understanding structure–activity relationships for platinum anticancer agents that act via a novel mechanism of action.

Over the course of the 2022–2023 academic year, the diverse and exciting chemistry by these 12 excellent speakers has made Periodic TableTalks immensely successful once again. We sincerely thank everyone for presenting their research and the attendees for contributing to the fantastic resulting scientific discussions. As the first series of Periodic TableTalks postpandemic, this success indicates that this initiative will be an effective and valuable forum for delivering cutting-edge inorganic chemistry to a broad global audience for years to come. We end by thanking Ana de Bettencourt-Dias, Nora Radu, Andy Borovik, and the rest of the leadership of the DIC Executive Committee for their commitment toward this virtual seminar series. We hope to see everyone at next year’s Periodic TableTalks!