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The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (1-Pr(NP*)) with AgI at −35 °C. The Pr 4+ complex is characterized in solution via cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*).more »The identification of a tetravalent praseodymium complex in in situ UV-vis and EPR experiments is further validated by theoretical modeling of the redox chemistry and the UV-vis spectrum. The latter study was performed by extended multistate pair-density functional theory (XMS-PDFT) and implicates a multiconfigurational ground state for the tetravalent praseodymium complex.« less

Reaction of the complexes [Fe 2 (μ 2 -NP(pip) 3 ) 2 (NP(pip) 3 ) 2 ] ( 1-Fe ) and [Co 2 (μ 2 -NP(pip) 3 ) 2 (NP(pip) 3 ) 2 ] ( 1-Co ), where [NP(pip) 3 ] 1− is tris(piperidinyl)imidophosphorane, with nitrous oxide, S 8 , or Se 0 results in divergent reactivity. With nitrous oxide, 1-Fe forms [Fe 2 (μ 2 -O)(μ 2 -NP(pip) 3 ) 2 (NP(pip) 3 ) 2 ] ( 2-Fe ), with a very short Fe 3+ –Fe 3+ distance. Reactions of 1-Fe with S 8 or Se 0 result inmore »the bridging, side-on coordination (μ-κ 1 :κ 1 -E 2 2− ) of the heavy chalcogens in complexes [Fe 2 (μ-κ 1 :κ 1 -E 2 )(μ 2 -NP(pip) 3 ) 2 (NP(pip) 3 ) 2 ] (E = S, 3-Fe , or Se, 4-Fe ). In all cases, the complex 1-Co is inert.« less

Here we report measurements of the oxygen reduction reaction (ORR) at single Pt nanoparticles (NPs) through their collision with a Au microdisk electrode of lower electrocatalytic activity. Performing measurements at an elevated pressure (10-atm, pure O₂) raises the O₂concentration ∼50-fold over air-saturated measurements, allowing the ORR activity of smaller Pt NPs to be resolved and quantified, compared to measurements taken at atmospheric pressure. Single-NP ORR current vs potential measurements for 2.6, 16, and 24 nm radius citrate-capped Pt NPs, show the catalytic activity of the smallest Pt NPs to be roughly one order of magnitude greater than the activity ofmore »the larger NPs. The particle-by-particle nature of our measurement quantifies the distribution of electrocatalytic activities of individual particles, which we determine to be larger than can be explained by the distribution of particle sizes. Additionally, we report that some of the observed ORR current transients contain multiple sharp peaks per single-NP measurement, indicating multiple collisions of a single Pt NP at the electrode surface.

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