Search for: All records

Recent advances in understanding the electronic structure of metal ammonia complexes enable development of novel materials with diffuse electrons and catalytic applications. 

Positively charged metal–ammonia complexes are known to host peripheral, diffuse electrons around their molecular skeleton. The resulting neutral species form materials known as expanded or liquid metals. Alkali, alkaline earth, and transition metals have been investigated previously in experimental and theoretical studies of both the gas and condensed phase. This work is the first ab initio exploration of an f-block metal–ammonia complex. The ground and excited states are calculated for Th0–3+ complexes with ammonia, crown ethers, and aza-crown ethers. For Th3+ complexes, the one valence electron Th populates the metal’s 6d or 7f orbitals. For Th0–2+, the additional electrons prefer occupation of the outer s- and p-type orbitals of the complex, except Th(NH3)10, which uniquely places all four electrons in outer orbitals of the complex. Although thorium coordinates up to ten ammonia ligands, octa-coordinated complexes are more stable. Crown ether complexes have a similar electronic spectrum to ammonia complexes, but excitations of electrons in the outer orbitals of the complex are higher in energy. Aza-crown ethers disfavor the orbitals perpendicular to the crowns, attributed to the N-H bonds pointing along the plane of the crowns. 

Beryllium ammonia complexes Be(NH 3 ) 4 are known to bear two diffuse electrons in the periphery of a Be(NH 3 ) 4 2+ skeleton. The replacement of one ammonia with a methyl group forms CH 3 Be(NH 3 ) 3 with one peripheral electron, which is shown to maintain the hydrogenic-type shell model observed for Li(NH 3 ) 4 . Two CH 3 Be(NH 3 ) 3 monomers are together linked by aliphatic chains to form strongly bound beryllium ammonia complexes, (NH 3 ) 3 Be(CH 2 ) n Be(NH 3 ) 3 , n = 1–6, with one electron around each beryllium ammonia center. In the case of a linear carbon chain, this system can be seen as the analog of two hydrogen atoms approaching each other at specific distances (determined by n). We show that the two electrons occupy diffuse s-type orbitals and can couple exactly as in H 2 in either a triplet or singlet state. For long hydrocarbon chains, the singlet is an open-shell singlet nearly degenerate with the triplet spin state, which transforms to a closed-shell singlet for n = 1 imitating the σ-covalent bond of H 2 . The biradical character of the system is analyzed, and the singlet–triplet splitting is estimated as a function of n based on multi-reference calculations. Finally, we consider the case of bent hydrocarbon chains, which allows the closer proximity of the two diffuse electrons for larger chains and the formation of a direct covalent bond between the two diffuse electrons, which happens for two Li(NH 3 ) 4 complexes converting the open-shell to closed-shell singlets. The energy cost for bending the hydrocarbon chain is nearly compensated by the formation of the weak covalent bond rendering bent and linear structures nearly isoenergetic. 

Metal complexes with diffuse solvated electrons (solvated electron precursors) are proposed as alternative catalysts for the simultaneous CO 2 capture and utilization. Quantum chemical calculations were used to study the reaction of CO 2 with H 2 and C 2 H 4 to produce formic acid, methyldiol and δ-lactone. Mechanisms of a complete reaction pathway are found and activation barriers are reasonably low. The metal ligand complex readily reduces CO 2 and significantly stabilizes CO 2 ˙ − . Ligand identity minimally influences the reaction. Additional reactions and future strategies are proposed with the goal of inducing experimental interest. 

Background Early diagnosis is essential for effective stroke therapy. Strokes in hospitalized patients are associated with worse outcomes compared with strokes in the community. We derived and validated an algorithm to identify strokes by monitoring upper limb movements in hospitalized patients. Methods and Results A prospective case–control study in hospitalized patients evaluated bilateral arm accelerometry from patients with acute stroke with lateralized weakness and controls without stroke. We derived a stroke classifier algorithm from 123 controls and 77 acute stroke cases and then validated the performance in a separate cohort of 167 controls and 33 acute strokes, measuring false alarm rates in nonstroke controls and time to detection in stroke cases. Faster detection time was associated with more false alarms. With a median false alarm rate among nonstroke controls of 3.6 (interquartile range [IQR], 2.1–5.0) alarms per patient per day, the median time to detection was 15.0 (IQR, 8.0–73.5) minutes. A median false alarm rate of 1.1 (IQR. 0–2.2) per patient per day was associated with a median time to stroke detection of 29.0 (IQR, 11.0–58.0) minutes. There were no differences in algorithm performance for subgroups dichotomized by age, sex, race, handedness, nondominant hemisphere involvement, intensive care unit versus ward, or daytime versus nighttime. Conclusions Arm movement data can be used to detect asymmetry indicative of stroke in hospitalized patients with a low false alarm rate. Additional studies are needed to demonstrate clinical usefulness. 

Abstract Density functional theory and ab initio multi-reference calculations are performed to examine the stability and electronic structure of boron complexes that host diffuse electrons in their periphery. Such complexes (solvated electron precursors or SEPs) have been experimentally identified and studied theoretically for several s- and d-block metals. For the first time, we demonstrate that a p-block metalloid element can form a stable SEP when appropriate ligands are chosen. We show that three ammonia and one methyl ligands can displace two of the three boron valence electrons to a peripheral 1s-type orbital. The shell model for these outer electrons is identical to previous SEP systems (1s, 1p, 1d, 2s). Further, we preformed the first examination of a molecular system consisting of two SEPs bridged by a hydrocarbon chain. The electronic structure of these dimers is very similar to that of traditional diatomic molecules forming bonding and anti-bonding σ and π orbitals. Their ground state electronic structure resembles that of two He atoms, and our results indicate that the excitation energies are nearly independent of the chain length for four carbon atoms or longer. These findings pave the way for the development of novel materials similar to expanded metals and electrides. 

Teaming is a core part of engineering education, especially in the first and last years of engineering when project work is a prevalent focus. The literature on the effects of working in diverse teams is mixed. Negative findings include decreased affect, increased frustration, and sustained conflict in teams. Positive findings include increased productivity, production of high quality products, and divergent-thinking and idea generation. Given these mixed findings, it becomes important to not only understand the practical outputs of working in diverse teams, but also how the experience of working in diverse teams influences whether students see themselves as engineers and whether or not they feel they belong in engineering. Our project, Building Supports for Diversity through Engineering Teams, investigates how students’ attitudes towards diversity influence how students experience work in diverse teams through addressing two main research questions: 1) What changes occur in students’ diversity sensitivity, multicultural effectiveness, and engineering practices as a result of working in diverse teams? 2) How do students’ perceptions of diversity, affect, and engineering practices change because of working on diverse teams? Using a multi-method approach, we deployed survey instruments to determine changes in student’s attitudes about teaming, diversity sensitivity, and openness attitudes. We also observed students working in teams and interviewed these students about their perceptions of diversity and experiences in their teams. Preliminary results of the quantitative phase show that variance in students’ attitudes about diversity significantly increase over the semester, further reflecting the mixed results that have been seen previously in the literature. Additionally, Social Network Analysis was used to characterize the social structure practices of a multi-section, large-enrollment first-year engineering course. This reveals the underlying social structure of the environment, its inclusiveness, and how diverse students work with others on engineering. Initial results indicate that students are included in social networks regardless of gender and race. Preliminary results of the qualitative phase, using Interpretive Phenomenological Analysis, have yielded relationships between student’s definitions, valuation, and enactment of diversity in engineering spaces. Individual student’s incoming attitudes of diversity and previous experiences interact with practical needs in first-year engineering classrooms to create different microclimates within each team. These microclimates depict tensions between what instructors emphasize about diversity, stereotypes of engineering as focused on technical instead of social skills, and pragmatic forces of “getting the job done.” This knowledge can help explain some of the complexity behind the conflicting literature on diversity in teams. Ultimately, this research can help us understand how to build inclusive and diverse environments that guide students to learn how to understand their own complex relationship, understanding, and enactment of diversity in engineering. By understanding how students make sense of diversity in engineering spaces, educators and researchers can figure out how to introduce these concepts in relevant ways so that students can inclusively meet the grand challenges in engineering. This curriculum integration, in turn, can improve team interactions and the climate of engineering for underrepresented groups.