Research & Projects

Research Overview

My research experience spans 15 years as a synthetic inorganic chemist. I have the most experience in main-group and metal complex synthesis, but also have worked on projects in materials chemistry, catalysis, photoluminescence, and magnetism. Below are projects I’ve worked on at Sandia National Lab on the HyMARC project, in Todd Hudnall’s lab at Texas State University, and in Mike Rose’s lab at the University of Texas at Austin.

The HyMARC project (Hydrogen Materials Advanced Research Consortium) combines national laboratory expertise to develop clean, low-cost materials-based hydrogen storage systems that exceed the capabilities of physical storage (700 bar pressurized gas and liquid hydrogen) and meet U.S. Department of Energy (DOE) targets for stationary and transportation applications. We investigate interstitial metal hydrides, high-entropy alloys, complex metal hydrides, and alane-infiltrated MOFs and COFs. HyMARC seeks to identify, develop, and optimize storage for hydrogen end uses with thus-far undefined technical targets, particularly for stationary applications. By employing a co-design strategy, systems modeling and techno-economic analysis are directly coupled to materials discovery, design, and optimization to meet the requirements of specific use cases. 

Research in the Hudnall lab currently focused on the design and synthesis of catalysts derived from main-group carbenes. We are interested especially in electrophilic carbenes that could have useful impacts stabilizing low valent metals and improving catalytic turnover. 

My research in the Rose lab at UT focused on the design, synthesis, and applications of 3d transition metal complexes supported by mono- and multi-dentate antimony ligands. As a heavy main group element, antimony has several interesting properties including its excellent Lewis acid ability and large spin-orbit-coupling constant. Although classically labeled as a poor ligand with weak σ-bonding character, we were able to synthesize a wide variety of both homoleptic and heteroleptic antimony ligands and demonstrated successful metalations with high valent late 3d transition metals, including cobalt, nickel, and copper. We have also discovered useful and diverse applications and properties for each of these sets of complexes. 

Complex Metal Hydride/Amide Hydrogen Storage System: Improving the Kinetics with Additives. 

The complex metal hydride 2LiH:1Mg(NH2)2 has emerged as a promising material for stationary hydrogen storage applications, such as seasonal storage or energy backup systems, due to its high volumetric and gravimetric capacities and robust reversibility. However, its widespread adoption is hindered by sluggish reaction rates, performance degradation upon cycling, and improper end use cases. To address these problems and better understand the desorption pathway, we used metal borohydrides (MBH4; M = Li – Cs) as chemical probes. A thorough analysis of the bulk behavior of all six materials, including hydrogen cycling experiments, X-ray absorption spectroscopy, FTIR, pXRD, solid-state NMR, and ab initio DFT simulations, shows that the borohydride additives lower the activation energy of hydrogen release by about 20 kJ/mol for MBH4@2:1 materials versus pristine. Furthermore, more surface-sensitive studies show that the amide-to-imide desorption pathway in these materials, while essentially complete in the bulk, is incomplete in the near-surface region, suggesting an “inverse core-shell” desorption mechanism for amide dehydrogenation to imide. The kinetic enhancements produced by MBH4 additives (M = K, Rb, and Cs) are attributed to destabilization of the amide N-H bond and interaction with the LiH/Mg(NH2)2 interface to promote H-H bond formation. An inverse core-shell mechanism is also operative in the dihydrogenation of 2LiH:1LiNH2 to Li3N, suggesting this may be a general feature of amides. Given the fast dehydrogenation rate and large gravimetric capacity, these materials satisfy the requirements for telecom backups and seasonal microgrid storage applications.

Alane Infiltration into a Covalent Triazine Framework for Easier Rehydrogenation of Alane 

Alane (AlH3) has a high gravimetric capacity with low ΔH, however, it is prohibitively difficult to rehydrogenate under standard conditions (GPa). To ameliorate that situation, we infiltrated alane into a covalent triazine framework to form N-Al bonds and induce hydrogenation at lower pressures (1000 bar). We saw good initial infiltration of alane into the framework, but inconsistent rehydrogenation via Sieverts desorption measurements, pXRD, FTIR, DSC, and TGA experiments. Future studies will be performed to determine the degree of infiltration of alane into the framework. 

Photocatalytic C-H Activation with Diamidocarbene

Diamidocarbene (DAC) has been known to carbene chemists for over two decades, but recently we showed this molecule performs photocatalytic C-H activation under UV light, even insertion into inactivated sp3 carbons and Büchner ring expansion, which are rare feats in carbene catalysis. This project continued to expand the scope of these reactions, with highlights including the dicyclopropanation of bromonapthalene and insertion into tetramethylsilane (left). Another interesting highlight is the crystal structure of DAC + cyclohexane (right). This was diffracted using state-of-the-art electron diffraction technology to solve a single-crystal dataset. (Chem. Sci., 2023, 14, 7867-7874; https://doi.org/10.1039/D2SC05122B)

Towards the Synthesis of Electrophilic Diborylcarbenes

We sought to synthesize the first diborylcarbene, which is theorized to display a singlet ground state with both electrons in the pπ orbital, greatly enhancing the electrophilicity of the carbene. We made significant progress towards synthesizing the first diborylcarbene, utilizing a bis-pinacolatoborane scaffold and performing carbene trapping reactions with several substrates. The most promising of these trapping reactions was the formation of the dimer species (top left), which we confirmed the identity via NMR and high-res mass spectrometry in collaboration with Prof. Dave Schilter at Texas State.

Nickel(II)-Antimony Complexes for Metal Deposition

Five new nickel(II) antimony complexes (general structure: [Ni(I)2(SbR3)2-3]) were synthesized, crystallized, and extensively characterized to determine their steric, electronic, and spectroscopic properties. The geometries of the nickel(II) complexes were highly dependent on the steric bulk of the antimony ligand, either adopting a square planar or trigonal bipyramidal shape. From an application standpoint, the complexes showed intriguing electroless deposition properties of a nickel-copper alloy (Ni0.77Cu0.23) on to a Cu|Si wafer when heated and in organic solvents. The purity of the overall deposition was correlated with the strength of the antimony ligand. The strongest antimony ligand (SbiPr3) was the best scavenger of I2 during the heating process, which allowed for a clean deposition of a NiCu alloy, while the heated decomposition of complexes with weaker antimony ligands (e.g. SbMe2Ph) afforded a surface that was contaminated with CuI. All surfaces were analyzed via SEM/EDX, and powder XRD. (Inorg. Chem., 2018, 57, 10364-10374; https://doi.org/10.1021/acs.inorgchem.8b01565).

Thermoluminescent Copper(I)-Antimony Complexes with Tunable Near-IR Emission Properties

We synthesized several Cu(I)-Sb cuboids with general structure Cu4(I)4(SbR3)4 that showed thermoluminescent properties—as the temperature is lowered, the intensity of emission greatly increases. This is due to the contracting of the Cu4 core at the center of these complexes, confirmed by DFT calculations. Compared to the phosphine and arsine analogues, these stibine cuboids exhibit much more red-shifted emissions by virtue of the heavy atom effect and the shorter Cu-Cu bonds. It was found that the wavelength of emission for these complexes is dictated by two factors: the average bond distance of the Cu-Cu bonds, and the overall symmetry of the complex (cubic = furthest NIR). In this sense, we can directly tune the emission wavelengths of these materials by slightly altering the steric bulk and asymmetry of the antimony ligands in the metalation. We have also shown that the cuprophilic nature of these complexes is a critical component for the emission intensities. Once the Cu-Cu contacts shrink below 2.80 Å—twice the van der Waals radius for copper—the emission intensity exponentially increases. This work has impactful applications for near-IR emitting luminescent materials and further widens the scope and significance of the field of thermoluminescent copper cuboids. (Inorg. Chem., 2016, 55, 3206-3208; https://doi.org/10.1021/acs.inorgchem.5b02933) (Inorg. Chem., 2019, 58, 16330-16345, ACS Editor’s Choice, Invited Cover Art for December 2019 Issue; https://doi.org/10.1021/acs.inorgchem.9b00229).

Antimony-Supported Co(II) Complexes: Spin-Orbit-Coupling versus Geometric Effects

One of the most appealing properties of antimony is its large spin-orbit-coupling constant—on par with 4d and 5d transition metals. In the field of molecular magnetism, imparting a large amount of spin-orbit coupling to a metal center through ligand design has been achieved previously, but never with antimony ligands. We synthesized a class of novel paramagnetic Co(II)-Sb complexes and investigated their variable-field and variable-temperature magnetic properties. The fitted magnetic susceptibility SQUID data for the tetrahedral complex Co(I)2(SbiPr2Ph)2, showed high zero-field-splitting, D (|24.96| cm-1), versus the phosphine analogue, Co(I)2(PPh3)2 (-8.97 cm-1), which was corroborated by extensive magnetometry calculations (CASSCF, NEVPT2, and HFEPR). However, electronic absorbance measurements and AILFT calculations revealed the two complexes had similar amounts of spin-orbit coupling (ζeff Sb = 479.2 cm-1, ζeff P = 480.2 cm-1). These later findings suggest that geometric effects derived from the heavy ligands may play a larger role in achieving high D values in molecular paramagnetic complexes rather than spin-orbit coupling on the metal center (Inorg. Chem., 2022, 61, 6733-6741; https://doi.org/10.1021/acs.inorgchem.1c03366).