Terence L. Schull

Tuning current rectification across molecular junctions

We demonstrate the ability to tune the current rectification in metal-molecule-metal junctions through control of the interaction strength of one of the two metal-molecule contacts. Current-voltage characteristics of thiolate bound molecular wires with a nitro or pyridine termination show that the extent of current rectification in a molecular junction correlates well with the extent of coupling between the chemical linker and metal electrode.

Oxygen Reduction Reaction on Platinum/Tantalum Oxide Electrocatalysts for PEM Fuel Cells

We investigate platinum supported on tantalum oxide as a possible catalyst for oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells. Three synthetic routes are evaluated to compare activities of tantalum-oxide-supported platinum fuel cell electrocatalysts: (i) deposition of platinum colloids on tantalum oxide followed by mechanical grinding with Vulcan carbon (VC); (ii) deposition of tantalum oxide on VC, followed by the deposition of platinum colloids; and (iii) deposition of Pt colloids on VC, followed by deposition of tantalum oxide. These are compared to a Pt/VC standard made with the same Pt colloids. The area-specific activities for the ORR at 0.9 V are a factor of 1.5 higher for catalysts synthesized via preparation route (ii) compared to a Pt/VC standard. The area-specific activities of the catalysts synthesized via routes (i) and (iii) are close to that of Pt/VC. The higher area-specific activity of the catalyst synthesized by route (ii) may be due to the preferential adsorption of OH groups to the oxide vs platinum surface.

Rhodium catalyzed allylic isomerization in water

Abstract A water-soluble rhodium bis-phosphine complex was used for the aqueous phase isomerization of three allylic alcohols. For the isomerization of cinnamyl alcohol, the catalyst was recycled with slight loss of activity and the optimum phosphine:rhodium ratio was found to be 6:1.

Use of Low‐Temperature Thermal Alkylation to Eliminate Ink Migration in Microcontact Printed Patterns

We demonstrate aqueous hydrogel-based microcontact printing of amine ligands into solvent-templated nanocavities of chloromethylphenyl-based siloxane or thin polymer films. Migration of pyridine ligands within films following printing, which can compromise pattern fidelity, is eliminated by heat treatment of the substrate. Gentle heating (e.g., 50 degrees C, 5 min) leads to the efficient alkylation of mobile pyridine adsorbate by the C-Cl bonds of the film, covalently tethering the adsorbate to the surface as a pyridinium salt. Subsequent binding of a Pd-based colloid to surface pyridinium (and remaining strongly bound and immobile pyridine ligand) sites permits selective electroless metal deposition and fabrication of patterned metal films.

The first examples of an aryl ring substituted by both phosphine and phosphonate moieties: synthesis and characterization of the new highly water-soluble phosphine ligand Na2[Ph2P(C6H4-p-PO3)]·1.5H2O and platinum(II) complexes

The highly water-soluble phosphine Na2[TPPMP]·1.5H2O (TPPMP =‘triphenylphosphine monophosphonate’) represents the first example of a compound containing an aryl ring which is substituted by both phosphine and anionic phosphonate moieties; the preparation and spectroscopic characterisation of the platinum(II) complexes (trans-and cis-Na4[PtCl2(TPPMP)2]·3H2O is described.

NEW CHIRAL PHOSPHINE-PHOSPHONITES DERIVED FROM (2R, 3R)-DIMETHYL TARTRATE,(S)-BINAPHTHOL AND (1R, 2S)-EPHEDRINE

Abstract The reaction of 2-lithiophenyldiphenylphosphine with phosphorus trichloride afforded the new unsymmetric phosphine, dichloro(2-diphenylphosphinophenyl)phosphine (4). Condensation of 4 with (a) (2R,3R)-dimethyl tartrate or (b) (S)-binaphthol in the presence of triethylamine gave new chiral phosphine-phosphonite ligands, (2R,3R)-[2-(2′-(diphenylphosphino)phenyl)-4,5-bis(carbomethoxy)-1,3,2-dioxaphospholane] ((2R,3R)-5) and (S)-[2-(diphenylphosphino)benzene][1,1′-binaphthalen-2,2′-diyl]phosphonite] ((S)-6). The analogous reaction of 4 with (1R,2S)-ephedrine using N-methylmorpholine as the base, gave [2-(2′-(diphenylphosphino)phenyl)-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine] (7) as a 95:5 mixture of diastereoisomers.

Synthesis of symmetrical triarylphosphines from aryl fluorides and red phosphorus: scope and limitations

Abstract The reaction of aryl fluorides with phosphide anion, generated in situ from the reduction of red phosphorus by lithium metal in liquid ammonia, gave symmetrical triarylphosphines in fair to good yields. Phosphonodiamide, sulfonamide, 2-oxazolyl, and nitrile groups were stable to the reaction conditions, while nitro and bromo substituents were not. para -Substituted aryl fluorides gave higher yields than meta -substituted aryl fluorides, and ortho -substituted aryl fluorides failed to react.

Rhodium-mediated delamination of layered copper and zinc vinylphosphonates

Zinc and copper vinylphosphonates were characterized by X-ray crystallography and IR, and have layered structures which undergo facile delamination on contact with aqueous solutions of rhodium trichloride.

Erratum: Electrochemical Observation of Ligand Effects on Oxygen Reduction at Ligand-Stabilized Pt Nanoparticle Electrocatalysts [ Electrochem. Solid-State Lett. , 11 , B161 (2008) ]

Erratum: Electrochemical Observation of Ligand Effects on Oxygen Reduction at Ligand-Stabilized Pt Nanoparticle Electrocatalysts [Electrochem. Solid-State Lett., 11, B161 (2008)] J. J. Pietron, Y. Garsany, O. Baturina, K. E. Swider-Lyons, R. M. Stroud, D. E. Ramaker, and T. L. Schull Naval Research Laboratory, Washington, District of Columbia 20375, USA Nova Research, Incorporated, Alexandria, Virginia 22308, USA Department of Chemistry, The George Washington University, Washington, District of Columbia 20052, USA

Chemical modification of surfaces utilizing noncovalent interactions

A critical requirement for using thin polymer films in many microelectronics applications is the ability to selectively immobilize materials on patterned polymer templates.1 Adaptation of standard covalent solution phase chemistries is the most direct approach, but suffers several drawbacks, including the following: (1) reduced reaction rates or yields due to surface steric effects, (2) distortion or dissolution of surface templates due to reagent/polymer incompatibilities, and (3) environmental and cost concerns arising from the use of nonaqueous solvents.