Inorganic Chemistry

"Inorganic chemistry is concerned with the properties and behavior of inorganic compounds, which include metals, minerals, and organometallic compounds. "

American Chemical Society

Inorganic sessions have been scheduled for Monday Morning, Tuesday Morning, and Wednesday Afternoon.

If you find any errors in our listing please let us know at chemistrybuffalogss@gmail.com

Monday Morning

Session 1A - Room NSC 222 - Moderator: Abby Snyder

9:40 a.m. - 10:00 a.m.

Towards More Efficient Excited-State Charge Transfer in Heterostructures Consisting of Metal-Intercalated Vanadium Oxide Nanowires and Quantum Dots

Aaron Sheng, Junsang Cho, Nuwanthi Suwantaratne, Sarbajit Banerjee, David F. Watson

The State University of New York at Buffalo, Department of Chemistry

Nanostructured semiconductor heterostructures are a promising class of materials for light harvesting, charge transfer, and solar energy conversion. Efficient charge separation following photoexcitation is essential for harvesting solar energy for any type of heterostructure. Two key components of efficient charge separation are the energetic offsets between individual components of a heterostructure and the kinetics associated with the transfer of charges. Heterostructures of cadmium chalcogenide quantum dots (QDs) interfaced on metal-intercalated vanadium oxide nanowires (NWs) have shown to be a promising system for efficient charge separation. However, energetic offsets are not always ideal between the valence and conduction band edges, which in turn influences the kinetics of charge transfer. To address the issue, we are exploring more complex systems including ternary QDs, metal-doped QDs, and ternary heterostructures. This presentation will focus on our recent photoelectrochemical and steady-state and time-resolved spectroscopic characterization of excited-state charge transfer processes in these heterostructures. These fundamental studies are providing new insights into the influence of composition and energetics on kinetics and efficiencies of excited-state charge transfer.

10:00 a.m. - 10:20 a.m.

Synthesis and Characterization of Bio-inspired N, N, N ligand platform on Iron: A synthetic model for atypically coordinating non-heme iron enzymes

Parami Gunasekera, David C. Lacy

The State University of New York at Buffalo, Department of Chemistry

A ligand that mimic the atypically coordinating non heme iron facial triad (N, N, N type ligand) synthesized and characterized. The ligand 2,2’-(2-(1-ethylbenzimidazol-2yl) ethane-1,1-diyl) bis(1-methylbenzimidazole) (3-His), bears benzimidazole moieties that function as N donors so that it would coordinates facially to Fe (II) to produce mono nuclear metal complexes. The choice of benzimidazole as the N donor was based off of a pKa argument, where it is demonstrated that benzimidazole is chemically more related to the histidine moiety found in the as the nitrogen donor in the enzyme active sites. The coordination chemistry of 3-His on Fe (II) was studied with different iron salts to achieve mononuclear mono ligand complexes and the paramagnetic iron complexes where characterized by single crystal X-ray analysis, IR spectroscopy and NMR spectroscopy. The metal complexes are hypothesized to be structural and functional mimetic with relation to atypically coordinating nonheme iron centers. This was investigated through synthesis of model complexes with biorelevant substrates, 2-aminoethanethiol and cysteamine. The synthetic model complexes are expected to produce thiol dioxygenase like chemistry and be able to activate molecular oxygen.

10:20 a.m. - 10:40 a.m.

A New Family of Earth-Abundant Transition Metal Catalysts Featuring Redox-Active Bipyridyl-NHC Frameworks for the Electrochemical Reduction of CO₂

Kaitlin McCardle, Xiaojun Su, Lizhu Chen, Jonah W. Jurss, Julien A. Panetier

The State University of New York at Binghamton

An innovative family of nickel and cobalt catalysts featuring redox-active bipyridyl-N-heterocyclic carbene-based macrocycles has been developed for the electrocatalytic reduction of CO₂. The family features two sets of catalysts: one series of three nickel-based catalysts and one series of three analogous cobalt- based catalysts. The family of catalysts was developed with macrocyclic character in mind, such that as you move across the series, the ligand framework increases in rigidity. Here, the first member of each series features a non-macrocyclic framework, the second features a 16-membered macrocyclic scaffold, and the most rigid of the series features a 15-membered macrocyclic framework. DFT calculations reveal a delicate electronic balance between metal and ligand based redox chemistry that dictates selectivity for CO₂ reduction versus the competing proton reduction reaction. This critical interplay leads to a significant structure–activity relationship, where increasing the rigidity of the ligand scaffold increases the catalysts activity and selectivity for CO₂ reduction. Mechanistic studies reveal slight differences in the reduction pathways of the nickel and cobalt series, including changes in the role that the N-heterocyclic carbenes may play in stabilizing the M-CO₂ adduct. Notably, experimental results indicate that the most rigid cobalt catalyst is able to perform catalysis in aqueous conditions with a Faradaic yield for CO of 93%.

10:40 a.m. - 11:00 a.m.

Self-Assembled Cofacial Prisms for Small Molecule Activation

Matthew R. Crawley, Timothy R. Cook

The State University of New York at Buffalo, Department of Chemistry

Enzymatic O₂ reduction by cytochrome c oxidase occurs at a bimetallic dinuclear active site. Mechanistic understanding of such polynuclear catalysts has broad impact for energy-relevant small molecule activations. Through the use of tunable, dinuclear self-assembled cofacial architectures we aim to deepen a mechanistic understanding of O₂ reduction and other catalytic transformations at multi-nuclear catalysts. Coordination-driven self-assembly furnishes complex, tunable platforms in high yields without the synthetic complexity of analogous covalent systems. We have demonstrated this through the synthesis and characterization of a series of functionalized self-assembled prisms, along with reactivity studies thereof.

11:00 a.m. - 11:20 a.m.

Synthesis and characterization of manganese and iron tris(N-arylacetamide) metal complexes

Anthony F. Cannella, Samantha N. MacMillan, David C. Lacy

The State University of New York at Buffalo, Department of Chemistry

The activation of molecular oxygen in biological systems is typically accomplished by complex proteins with metal containing active sites. The primary and secondary coordination spheres around these metals dictates the reactivity of these proteins. Elucidating the mechanism of these reactions can be difficult in complex physiological systems. Therefore, metal complexes with ligands tuned to functionally mimic these active sites have been synthesized to study reaction mechanisms. The activation of molecular oxygen by non-heme transition metal complexes (e.g. Mn, Fe) is of interest to us. To further these efforts, we have previously investigated the reactivity of iron tris(N-arylacetamide) complexes and molecular oxygen. It is unknown whether the mechanism proceeds by an inner sphere or outer sphere electron transfer. Herein, we report the synthesis and characterization of new manganese and iron tris(N-arylacetamide) complexes with the goal of finding suitable redox partners for electron transfer studies.

Tuesday Morning

Session 4B - Room NSC 218 - Moderator: TBD

9:30 a.m. - 9:50 a.m.

Distance-Dependent Charge Transfer Study in CdSe Quantum Dot/β-Pb0.33V₂O₅ Nanowire Heterostructure Photocathodes

Nuwanthi Suwandaratne, David F. Watson

The State University of New York at Buffalo, Department of Chemistry

To enhance the efficiency of photoelectrochemical (PEC) water splitting, more attention has been focused on designing photocatalysts with new engineering strategies. We interfaced CdSe quantum dots (QDs) and β-Pb0.33V₂O₅ nanowires (NWs) together to form CdSe/β-Pb0.33V₂O₅ heterostructures as a promising candidate for PEC water-splitting. The resulting photocathodes have exhibited good stability and very high Faradaic efficiencies of (92 ± 5)%.

Intercalation of Pb²⁺ gives rise to midgap electronic states in the NWs, which are well-positioned to accept photogenerated holes from QDs, facilitating charge separation and redox photocatalysis. We previously revealed that photoexcitation of cadmium chalcogenide QDs, within heterostructures, is followed by the transfer of holes to midgap states of NWs on sub-picosecond time scales. However, there are suitable energetics for electron transfer as well from QDs to NW which is detrimental for effective charge separation.

In this study, we have demonstrated that electron transfer to NW can be slowed down by increasing the distance between NWs and QDs, which can potentially help in extracting electrons to reduce protons to generate hydrogen. These results are promising, in that we can improve the charge separation and enhance photocatalytic properties of CdSe/β-Pb0.33V₂O₅ heterostructure photocathode.

9:50 a.m. - 10:10 a.m.

Synthesis, Characterization and DFT Calculations of Heterocyclic-Substituted

Oligophosphazenes as Metal Chelators

Yuan (Mike) Xue, Wei-Yuan Chen, Carrie Salmon, Ryan Nash, Valentine Gogonea, Claire Tessier

The University of Akron

Polyphosphazenes with amino- or mixed amino- alkoxy- side groups have been applied as biodegradable materials. The objective of this project is to synthesize and characterize heterocyclic-substituted polyphosphazenes, which can use the lone electron pairs from substituents to chelate transition metals, and then release functional metal complexes by cleaving P-N or P-O side bonds for biomedical applications. Model studies have been done on oligomers to avoid consuming expensive polymers: cyclochlorophosphazene trimer and tetramer ([PCl₂N]₃ and [PCl₂N]₄) have been completely substituted with heterocyclic rings. The substituted oligomers have been treated with different metal precursors such as (dmso₂H)[trans-RuCl₄(dmso-S)₂]. The structure of substituted phosphazenes as well as metal complexes have been identified by a variety of instrumental analyses including ³¹P NMR, ¹H NMR, IR and UV-Vis, mass spectrometry and XRD. To have a better understanding of the metal-binding properties, DFT calculations have been run on the substituted phosphazene oligomers.

10:10 a.m. - 10:30 a.m.

Experimental and DFT Mechanistic Studies of Metal-Ligand Cooperative Catalytic Dehydrogenation

Paul Fanara, David C. Lacy

The State University of New York at Buffalo, Department of Chemistry

(De)hydrogenation of alcohols to aldehydes and esters and vice versa through a “green” pathway is an important tool in organic synthesis. In the past two decades, a number of catalysts have been developed that can perform (de)hydrogenations utilizing a hydrogen donor (2-propanol) or hydrogen gas. A subclass of these catalysts employs bifunctional ligand systems that participate in metal-ligand cooperativity (MLC). Specifically, Milstein’s catalyst uses an aromatization/dearomatization mechanism that removes the need for an H₂ acceptor/donor in (de)hydrogenation reactions. The possible mechanisms of (de)hydrogenation with Milstein’s catalyst have been studied extensively by computational methods. However, to date there have been no experimental studies performed to elucidate the mechanism of dehydrogenation with Milstein’s catalyst. Herein, we describe the results of our own DFT and experimental studies with Milstein’s catalyst (PyNP) and three novel catalysts (QNP, 1-P IsoQNP, 3-P IsoQNP). These novel catalysts systematically change key aspects of PyNP to uncover which components of the ligand are responsible for its activity. Understanding the key aspects of the ligand in these MLC-capable systems enables the design of new, more efficient catalysts.

10:30 a.m. - 10:50 a.m.

Mechanistic Study of Electrocatalytic CO₂ Reduction using a Series of Group VII Bipyridyl Tricarbonyl Complexes

Xiaohui Li, Siyoung Sung, Michael Nippe, Julien Panetier

The State University of New York at Binghamton

Carbon monoxide dehydrogenase enzymes, such as the nickel-carbon monoxide dehydrogenase II from Carboxydothermus hydrogenoformans, are able to extract energy from their environments in order to carry out the reversible conversion of CO to CO₂ at high rates and selectivity while operating near the thermodynamic potential. In order to mimic key structural features and functions of this enzyme, we have developed a series of group VII bipyridyl-tricarbonyl complexes for CO₂-to-CO conversion in the presence of water as proton source. One system of interest is [Mn{bpyMe(ImMe)](CO)₃Cl}]⁺, which features a charged imidazolium ligand in the secondary coordination sphere. In this work, we performed electronic structure calculations to understand the role of the imidazolium moiety in the second coordination sphere and show that the ligand does not only shift the reduction potentials positively due to electrostatic effects, but also facilitates the CO₂ addition step and stabilizes higher energy intermediates along the CO₂ reduction pathway through intramolecular hydrogen interactions between the ligand and the Mn-CO₂ adduct. Furthermore, our results indicate that the imidazolium moiety is also capable of facilitating the C-O bond cleavage by stabilizing the proton source nearby the carboxylic acid species.

10:50 a.m. - 11:10 a.m.

Phosphonate and Phosphinate Pendants in the Development of Macrocyclic Fe(III) Complexes

as T1 MRI Contrast Agents

Elizabeth Kras, Zuiru Lin, Joseph Spernyak, Janet R. Morrow

The State University of New York at Buffalo, Department of Chemistry

Phosphonate and phosphinate pendents introduce negatively charged donor groups to the coordination sphere of contrast agents and have been previously shown to increase relaxivity when present on Gd(III) and Mn(II) contrast agents. Here we present the synthesis and characterization of macrocyclic Fe(III) complexes with phosphorous-containing pendents towards studying T1 weighted MRI contrast, biodistribution and clearance in mice. Macrocyclic derivatives with either two or three phosphorous-containing pendents were prepared to study the effect of inner sphere and outer sphere water on T1 relaxivity of the complexes. The synthesis of phosphonate ligands is quite straightforward, but there are significant side products making it necessary to purify the ligands using recrystallization or chromatography. Preliminary T1 relaxivity values for the Fe(III) phosphinate complexes are promising with values ranging up to 2.89 mM^-1s^-1 without HSA and 3.48 mM^-1s^-1 with HSA. However, the solubility of the Fe(III) phosphinate complexes is less than that of the phosphonate complexes. Further functionalization of the phosphinate complexes may be needed as Fe(III) MRI contrast agents require high aqueous solubility (~100 mM). Work in progress includes additional T1 studies in MRI phantoms and new studies in mice.

11:10 a.m. - 11:30 a.m.

Manganese (I) complexes as hydrogenation catalysts using dihydrogen

Preshit Abhyankar, David C. Lacy

The State University of New York at Buffalo, Department of Chemistry

Hydrogenations using molecular dihydrogen are known to chemists and been exhaustively exploited in synthetic chemistry. However, they face the drawback of using rare earth metal (such as Pd, Pt, Ru, and Rh) based catalysts. With the recent move towards developing greener chemistry, it would be advantageous to develop base-metals centred catalysts with high efficiency and selectivity. Manganese-phosphine complexes have been known to chemists and have played a central role as ligands influencing the reactivity of catalysts. The recent reports of Mn(I) based catalysts lend credence to the hypothesis that Mn(I) based catalysts can be used for hydrogenations and transfer hydrogenations. These catalysts, however, employ complex ligands that require a multi-step synthesis. Our efforts centre around developing catalysts with Mn(I) centres capable of executing hydrogenations using molecular dihydrogen. We are tuning known systems (based on Ru) to incorporate Mn(I) as centres and are developing new Mn(I) systems that have non-complex yet tuneable ligands which can carry-out hydrogenations under mild conditions.

Wednesday Afternoon

Session 7A - Room NSC 222 - Moderator: Konstantinos Plakas

1:20 p.m. - 1:40 p.m.

Multi-Hole Transfer to Ferrocene Functionalized Self-Assemblies from Photo-Excited Quantum Dots

Austin Gilbert, David F. Watson, Timothy R. Cook

The State University of New York at Buffalo, Department of Chemistry

With an increasing demand for alternative energy sources, the study and development of photocatalysts for small-molecule activation has had a growing interest amongst researchers. These processes depend on the efficient transfer of multiple charge carriers to a substrate. Quantum dots have become an increasingly popular chromophore for photocatalytic systems due to their high oscillator strengths and size-tunable optical and electronic properties. We aim to investigate the hole transfer from photo-excited quantum dots to self-assemblies containing multiple redox-active sites. Coordination-driven self-assembly provides a modular synthetic strategy to designing appropriately functionalized metallacycles or metallacages which incorporate multiple ferrocene equivalents. Through proper tuning of the quantum dot surface chemistry these self-assemblies can be either coordinated or covalently tethered to the nanocrystalline surface. By tuning the size-dependent band-edge potentials of the quantum dots, the thermodynamic driving force for hole transfer to the ferrocene moieties of the self-assembly can be tuned. We aim to study dynamics and yields of excited-state charge transfer as function of the structure and composition of assemblies, interfacial electronic structure, and charge-transfer driving forces. From these experiments, we can gain a deeper fundamental understanding of multiple charge-transfer processes in order to develop better and more efficient photocatalysts for multi-electron redox processes.

1:40 p.m. - 2:00 p.m.

Photocatalytic hydrogen production using biomolecular catalysts

Saikat Chakraborty, Rebeckah Burke, Banu Kandemir, Todd D. Krauss, Kara L. Bren

University of Rochester, Department of Chemistry

H₂ produced from water in a light-driven reaction is a carbon-free alternative to fossil fuels. To this end, the Bren lab has developed biomolecular catalysts that benefit from water solubility, activity at moderate pH values, and the potential for engineering second-sphere interactions with the active site. With [Ru(bpy)₃]²⁺ as a photosensitizer and ascorbic acid as an electron donor, a cobalt-tripeptide (CoGGH) catalyst is shown to reduce protons from water at pH 7.1 with TONs (all TONs relative to catalyst) exceeding 1000. In a similar system, a cobalt-porphyrin peptide complex (CoMP11-Ac) produced H₂ from both pH 4.5 and 7.1 buffer solutions with TONs exceeding 1000 and 2200, respectively. Employing CdSe quantum dots with glutathione capping ligands for water-solubility as photosensitizer and ascorbic acid as electron donor, we found the system to be active at pH 4.5 with TONs for H₂ evolution exceeding 80,000. There is also significant H₂ production when the ligand capped nanocrystals are used with simple metallic salts such as cobalt chloride. We have found that cobalt complexes formed in situ with capping ligands dissociated from quantum dots are the active catalytic species in these systems, as confirmed by electrochemical analysis of cobalt-ligand complexes. Future work will focus on understanding the mechanistic pathways of the photocatalytic cycle.

2:00 p.m. - 2:20 p.m.

Phosphine-Phenol(ate) Manganese(I) Complexes; Synthesis, Coordination Chemistry, and Catalysis

Karthika J. Kadassery, Samantha N. MacMillan, David C. Lacy

The State University of New York at Buffalo, Department of Chemistry

The emergence of metal-ligand cooperativity in the field of non-precious metal catalysts led to an array of reports on Manganese(I) catalyzed (de)hydrogenation reactions. Majority of these reports focus on nitrogen-based ligand platforms such as PNN and PNP pincer ligands. Our efforts to develop diverse ligand platforms for Mn(I) catalysis led us to synthesize and explore phenol-based POP ligands. This new ligand platform revealed interesting coordination chemistry with manganese and yielded various mono and multi-nuclear complexes. The hemilabile phenolic OH group showed coordination induced OH bond weakening phenomenon and thus opened up avenues to hydrogen atom transfer (HAT) chemistry. The reactivity of these compounds towards acids and bases were investigated. Finally, the ability of these complexes in catalyzing various organic transformations was explored.

2:20 pm - 2:40 p.m.

Development of CoII and FeIII/II Macrocyclic Complexes with alcohol pendants as LipoCEST MRI Agents

Samira M. Abozeid, Didar Asik, Janet R. Morrow

The State University of New York at Buffalo, Department of Chemistry

High spin Co(II) complexes with exchangeable ligand protons have been reported as paraCEST or as water proton shift agents. The millimolar detection limit of small molecule paraCEST MRI agents, makes them less sensitive when used in animals. Sensitivity can be enhanced by designing supramolecular CEST agents. Currently, our laboratory is involved in the design of complexes with exchangeable water ligands for various types of CEST agents including supramolecular CEST agents, especially those with intra-liposomal water molecules. Paramagnetic Co(II), Fe(II) or Fe(III) complexes with alcohol pendants that lack an inner-sphere water ligand are effective water proton shift agents, attributed to hydrogen bonding of the complexes through second-sphere water interactions. When incorporated into liposomes, these complexes are promising as lipoCEST agents