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Solid-state interconversions: unique 100?% reversible transformations between the ground and metastable states in single-crystals of a series of nickel(II) nitro complexes.

ABSTRACT: The solid-state, low-temperature linkage isomerism in a series of five square planar group?10 phosphino nitro complexes have been investigated by a combination of photocrystallographic experiments, Raman spectroscopy and computer modelling. The factors influencing the reversible solid-state interconversion between the nitro and nitrito structural isomers have also been investigated, providing insight into the dynamics of this process. The cis-[Ni(dcpe)(NO2)2] (1) and cis-[Ni(dppe)(NO2)2] (2) complexes show reversible 100?% interconversion between the ?(1)-NO2 nitro isomer and the ?(1)-ONO nitrito form when single-crystals are irradiated with 400?nm light at 100?K. Variable temperature photocrystallographic studies for these complexes established that the metastable nitrito isomer reverted to the ground-state nitro isomer at temperatures above 180?K. By comparison, the related trans complex [Ni(PCy3)2(NO2)2] (3) showed 82?% conversion under the same experimental conditions at 100?K. The level of conversion to the metastable nitrito isomers is further reduced when the nickel centre is replaced by palladium or platinum. Prolonged irradiation of the trans-[Pd(PCy3)2(NO2)2] (4) and trans-[Pt(PCy3)2(NO2)2] (5) with 400?nm light gives reversible conversions of 44 and 27?%, respectively, consistent with the slower kinetics associated with the heavier members of group?10. The mechanism of the interconversion has been investigated by theoretical calculations based on the model complex [Ni(dmpe)Cl(NO2)].

SUBMITTER: Warren MR

PROVIDER: S-EPMC4164279 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Solid-state interconversions: unique 100 % reversible transformations between the ground and metastable states in single-crystals of a series of nickel(II) nitro complexes.

Warren Mark R MR Easun Timothy L TL Brayshaw Simon K SK Deeth Robert J RJ George Michael W MW Johnson Andrew L AL Schiffers Stefanie S Teat Simon J SJ Warren Anna J AJ Warren John E JE Wilson Chick C CC Woodall Christopher H CH Raithby Paul R PR

Chemistry (Weinheim an der Bergstrasse, Germany) 20140318 18

The solid-state, low-temperature linkage isomerism in a series of five square planar group 10 phosphino nitro complexes have been investigated by a combination of photocrystallographic experiments, Raman spectroscopy and computer modelling. The factors influencing the reversible solid-state interconversion between the nitro and nitrito structural isomers have also been investigated, providing insight into the dynamics of this process. The cis-[Ni(dcpe)(NO2)2] (1) and cis-[Ni(dppe)(NO2)2] (2) com ...[more]

PMID: 24644042

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Project description:Nanocomposite thin films comprised of metastable metal carbides in a carbon matrix have a wide variety of applications ranging from hard coatings to magnetics and energy storage and conversion. While their deposition using nonequilibrium techniques is established, the understanding of the dynamic evolution of such metastable nanocomposites under thermal equilibrium conditions at elevated temperatures during processing and during device operation remains limited. Here, we investigate sputter-deposited nanocomposites of metastable nickel carbide (Ni3C) nanocrystals in an amorphous carbon (a-C) matrix during thermal postdeposition processing via complementary in situ X-ray diffractometry, in situ Raman spectroscopy, and in situ X-ray photoelectron spectroscopy. At low annealing temperatures (300 °C) we observe isothermal Ni3C decomposition into face-centered-cubic Ni and amorphous carbon, however, without changes to the initial finely structured nanocomposite morphology. Only for higher temperatures (400-800 °C) Ni-catalyzed isothermal graphitization of the amorphous carbon matrix sets in, which we link to bulk-diffusion-mediated phase separation of the nanocomposite into coarser Ni and graphite grains. Upon natural cooling, only minimal precipitation of additional carbon from the Ni is observed, showing that even for highly carbon saturated systems precipitation upon cooling can be kinetically quenched. Our findings demonstrate that phase transformations of the filler and morphology modifications of the nanocomposite can be decoupled, which is advantageous from a manufacturing perspective. Our in situ study also identifies the high carbon content of the Ni filler crystallites at all stages of processing as the key hallmark feature of such metal-carbon nanocomposites that governs their entire thermal evolution. In a wider context, we also discuss our findings with regard to the much debated potential role of metastable Ni3C as a catalyst phase in graphene and carbon nanotube growth.

Dataset Information

Solid-state interconversions: unique 100?% reversible transformations between the ground and metastable states in single-crystals of a series of nickel(II) nitro complexes.

Publications

Solid-state interconversions: unique 100 % reversible transformations between the ground and metastable states in single-crystals of a series of nickel(II) nitro complexes.

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