Poly-MTO, {(CH_3)_{0.92} Re O_3}_\infty, a Conducting Two-Dimensional Organometallic Oxide

Polymeric methyltrioxorhenium, {(CH_{3})_{0.92}ReO_{3}}_{\infty} (poly-MTO), is the first member of a new class of organometallic hybrids which adopts the structural pattern and physical properties of classical perovskites in two dimensions (2D). We demonstrate how the electronic structure of poly-MTO can be tailored by intercalation of organic donor molecules, such as tetrathiafulvalene (TTF) or bis-(ethylendithio)-tetrathiafulvalene (BEDT-TTF), and by the inorganic acceptor SbF$_3$. Integration of donor molecules leads to a more insulating behavior of poly-MTO, whereas SbF$_3$ insertion does not cause any significant change in the resistivity. The resistivity data of pure poly-MTO is remarkably well described by a two-dimensional electron system. Below 38 K an unusual resistivity behavior, similar to that found in doped cuprates, is observed: The resistivity initially increases approximately as $\rho \sim$ ln$(1/T$) before it changes into a $\sqrt{T}$ dependence below 2 K. As an explanation we suggest a crossover from purely two-dimensional charge-carrier diffusion within the \{ReO$_2$\}$_{\infty}$ planes at high temperatures to three-dimensional diffusion at low temperatures in a disorder-enhanced electron-electron interaction scenario (Altshuler-Aronov correction). Furthermore, a linear positive magnetoresistance was found in the insulating regime, which is caused by spatial localization of itinerant electrons at some of the Re atoms, which formally adopt a $5d^1$ electronic configuration. X-ray diffraction, IR- and ESR-studies, temperature dependent magnetization and specific heat measurements in various magnetic fields suggest that the electronic structure of poly-MTO can safely be approximated by a purely 2D conductor.Comment: 15 pages, 16 figures, 2 table

Strukturchemie von Organorhenium-, Organotechnetium- und Organoosmium-Komplexen

SIGLEAvailable from TIB Hannover: DW 6721 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Tuning Up an Electronic Structure of the Subphthalocyanine Derivatives toward Electron-Transfer Process in Noncovalent Complexes with C₆₀ and C₇₀ Fullerenes: Experimental and Theoretical Studies

Noncovalent π–π interactions between chloroboron subphthalocyanine (<b>1</b>), 2,3-subnaphthalocyanine (<b>3</b>), 1,4,8,11,15,18-(hexathiophenyl)­subphthalocyanine (<b>4</b>), or 4-<i>tert</i>-butylphenoxyboron subphthalocyanine (<b>2</b>) with C₆₀ and C₇₀ fullerenes were studied by UV–vis and steady-state fluorescence spectroscopy, as well as mass (APCI, ESI, and CSI) spectrometry. Mass spectrometry experiments were suggestive of relatively weak interaction energies between compounds <b>1</b>–<b>4</b> and fullerenes. The formation of a new weak charge-transfer band in the NIR region was observed in solution only for subphthalocyanine <b>4</b> when titrated with C₆₀ and C₇₀ fullerenes. Molecular structures of the subphthalocyanines <b>2</b> and <b>4</b> as well as cocrystallite of <b>4</b> with C₆₀ fullerene (<b>4···C</b>_<b>60</b>) were studied using X-ray crystallography. One of the C₆₀ fullerenes in the crystal structure of <b>4···C</b>_<b>60</b> was found in the concave region between two subphthalocyanine cores, while the other three fullerenes are aligned above individual isoindole fragments of the aromatic subphthalocyanine. The excited-state dynamics in noncovalent assemblies were studied by transient absorption spectroscopy. The time-resolved photophysics data suggest that only electron-rich subphthalocyanine <b>4</b> can facilitate an electron-transfer to C₆₀ or C₇₀ fullerenes, while no electron-transfer from the photoexcited receptors <b>1</b>–<b>3</b> to fullerenes was observed in UV–vis and transient spectroscopy experiments. DFT calculations using the CAM-B3LYP exchange-correlation functional and the 6-31+G­(d) basis set allowed an estimation of interaction energies for the noncovalent 1:1 and 1:2 (fullerene:subphthalocyanine) complexes. Theoretical data suggest that the weak (∼3.5–10.5 kcal/mol) van der Waals-type interaction energies tend to increase with an increase of the electron density at the subphthalocyanine core with compound <b>4</b> being the best platform for noncovalent interactions with fullerenes. DFT calculations also indicate that 1:2 (fullerene:subphthalocyanine) noncovalent complexes are more stable than the corresponding 1:1 assemblies

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