Heather L. Buckley

Synthesis and Characterization of Thorium(IV) and Uranium(IV) Corrole Complexes

The first examples of actinide complexes incorporating corrole ligands are presented. Thorium(IV) and uranium(IV) macrocycles of Mes2(p-OMePh)corrole were synthesized via salt metathesis with the corresponding lithium corrole in remarkably high yields (93% and 83%, respectively). Characterization by single-crystal X-ray diffraction revealed both complexes to be dimeric, having two metal centers bridged via bis(μ-chlorido) linkages. In each case, the corrole ring showed a large distortion from planarity, with the Th(IV) and U(IV) ions residing unusually far (1.403 and 1.330 Å, respectively) from the N4 plane of the ligand. (1)H NMR spectroscopy of both the Th and U dimers revealed dynamic solution behavior. In the case of the diamagnetic thorium corrole, variable-temperature, DOSY (diffusion-ordered) and EXSY (exhange) (1)H NMR spectroscopy was employed and supported that this behavior was due to an intrinsic pseudorotational mode of the corrole ring about the M-M axis. Additionally, the electronic structure of the actinide corroles was assessed using UV-vis spectroscopy, cyclic voltammetry, and variable-temperature magnetic susceptibility. This novel class of macrocyclic complexes provides a rich platform in an underdeveloped area for the study of nonaqueous actinide bonding and reactivity.

Preparation and characterization of a tungsten(V) corrole dichloride complex

The first example of a tungsten(V) corrole complex, (Mes2(p-OMePh)corrole)WCl2, has been prepared through a metathesis reaction of a lithium corrole (Mes2(p-OMePh)corrole)Li3 ⋅ 6THF and WCl6. The product constitutes the first example of a tungsten(V) corrole complex synthesized under mild conditions and only the second example of a tungsten corrole complex.

Trace metal content of coal exacerbates air pollution-related health risks: the case of lignite coal in Kosovo

More than 6600 coal-fired power plants serve an estimated five billion people globally and contribute 46% of annual CO2 emissions. Gases and particulate matter from coal combustion are harmful to humans and often contain toxic trace metals. The decades-old Kosovo power stations, Europes largest point source of air pollution, generate 98% of Kosovos electricity and are due for replacement. Kosovo will rely on investment from external donors to replace these plants. Here, we examine non-CO2 emissions and health impacts by using inductively coupled plasma mass spectrometry (ICP-MS) to analyze trace metal content in lignite coal from Obilic, Kosovo. We find significant trace metal content normalized per kWh of final electricity delivered (As (22.3 ± 1.7), Cr (44.1 ± 3.5), Hg (0.08 ± 0.010), and Ni (19.7 ± 1.7) mg/kWhe). These metals pose health hazards that persist even with improved grid efficiency. We explore the air-pollution-related risk associated with several alternative energy development pathways. Our analysis estimates that Kosovo could avoid 2300 premature deaths by 2030 with investments in energy efficiency and solar PV backed up by natural gas. Energy policy decisions should account for all associated health risks, as should multilateral development banks before guaranteeing loans on new electricity projects.

Addressing technical barriers for reliable, safe removal of fluoride from drinking water using minimally processed bauxite ores

Throughout the developing world, over 200 million people drink groundwater containing fluoride concentrations surpassing the World Health Organizations maximum recommended contaminant level (WHO-MCL) of 1.5 mg F−/L, resulting in adverse health effects ranging from mottled tooth enamel to debilitating skeletal fluorosis. Existing technologies to remove fluoride from water, such as reverse osmosis and filtration with activated alumina, are expensive and are not accessible for low-income communities. Our group and others have demonstrated that minimally-processed bauxite ores can remove fluoride to safe levels at a fraction of the cost of activated alumina. We report results from testing for some technical challenges that may arise in field deployment of this technology at large scale, particularly in a sufficiently robust manner for application in development contexts. Anticipating possible modes of failure and addressing these challenges in advance in the laboratory is particularly important for technologies for vulnerable communities where the opportunity to re-launch pilot projects is limited and small failures can keep solutions from the people that need them most. This work addresses three potential technical barriers to reliable removal of fluoride from drinking water with bauxite ore from Visakhapatnam, Andhra Pradesh, India. We evaluate competition from co-occurring ions, adsorption reversibility, and potability of the product water with regards to leaching of undesirable ions during treatment with various adsorbent materials including raw and thermally activated bauxite, and synthetic gibbsite (a simple model system). Under the conditions tested, the presence of phosphate significantly impacts fluoride adsorption capacity on all adsorbents. Sulfate impacts fluoride adsorption on gibbsite, but not on either bauxite adsorbent. Nitrate and silicate (as silicic acid), tested only with gibbsite, do not affect fluoride adsorption capacity. Both thermally activated bauxite and gibbsite show non-reversible adsorption of fluoride at a pH of 6. Raw bauxite leached arsenic and manganese in a TCLP leaching test at levels indicating the need for ongoing monitoring of treated water, but not precluding safe deployment of bauxite as a fluoride remediation technology. Understanding these phenomena is crucial to ensure field deployment over large diverse geographical areas with aquifers varying in groundwater composition, and for ensuring that the appropriate engineering processes are designed for field implementation of this innovation.