Tomasz K. Pietrzak

PREPARATION OF TRIPHYLITE-LIKE GLASSES AND NANOMATERIALS IN THE LiFePO4-V2O5 SYSTEM AND STUDY ON THEIR ELECTRICAL CONDUCTIVITY

Research on lithium iron phosphates is stimulated by their application as cathodes in Li-ion rechargeable batteries. The aim of this study was to enhance its initially poor electronic conductivity. A thermal nanocrystallization is applied to lithium-iron-phosphate and lithium-vanadium-iron-phosphates materials resulting in a significant increase of the electronic conductivity of the latter (almost 10-6 S/cm). The obtained nanomaterial exhibits very good thermal stability (up to 625°C), the activation energy 0.51 eV and moderate electronic conductivity at the room temperature, which is, however, a good starting point for further enhancement.

Unprecedented Variety of Outcomes in the Oxygenation of Dinuclear Alkylzinc Derivatives of an N,N‐Coupled Bis(β‐diketimine)

Reactions between O2 and organometallics with non-redox-active metal centers have received continuous interest for over 150 years, although significant uncertainties concerning the character and details of the actual mechanism of these reactions persist. Harnessing dinuclear three-coordinate alkylzinc derivatives of an N,N-coupled bis(β-diketimine) proligand (LH2 ) as a model system, we demonstrate for the first time that a slight modification of the reaction conditions might have a dramatic influence on the oxygenation reaction outcomes, leading to an unprecedented variety of products originating from a single reaction system, that is, partially and fully oxygenated zinc alkoxides, zinc alkylperoxides, and zinc hydroxide compounds. Our studies indicate that accessibility of the three-coordinate zinc center by the O2 molecule, coupled with the lower reactivity of Zn-Me vs. Zn-Et units towards dioxygen, are key factors in the oxygenation process, providing a novel tetranuclear methyl(methoxy)zinc {[L][ZnMe][Zn(μ-OMe]}2 and zinc ethoxide {[L][Zn(μ-OEt)]2 }2 . Remarkably, oxygenation of three-coordinate alkylzinc [L][ZnR]2 complexes at ambient temperature afforded a unique hydroxide {[L][Zn(μ-OH)]2 }2 . Oxygenation of the [L][ZnEt]2 complex in the presence of 4-methylpyridine (py-Me) at low temperature led to the isolation of a dinuclear zinc ethylperoxide [L][Zn(OOEt)(py-Me)]2 , which nicely substantiates the intermediacy of an unstable zinc alkylperoxide in the formation of the subsequent zinc alkoxide and hydroxide compounds. Finally, our investigations provide compelling evidence that a non-redox-active metal center plays a crucial role in the oxygenation process through assisting in single-electron transfer from an M-C bond to an O2 molecule. Although the oxygenation of zinc alkyls occurs by radical pathways, the reported results stand in clear contradiction to the widely accepted free-radical chain mechanism.

CCDC 1529392: Experimental Crystal Structure Determination

Related Article: Tomasz Pietrzak, Maciej Damian Korzynski, Iwona Justyniak, Karolina Zelga, Arkadiusz Kornowicz, Zbigniew Ochal and Janusz Lewinski|2017|Chem.-Eur.J.|23|7997|doi:10.1002/chem.201700503