Di([5]trovacenyl)ethyne, Di([5]trovacenyl)butadiyne, and Di-1,4-([5]trovacenylethynyl)benzene: Electrocommunication and Magnetocommunication Mediated by -Cages/entities

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• 作者：Christoph Elschenbroich ; Jö ; rn Plackmeyer ; Mathias Nowotny ; Klaus Harms ; J&uuml ; rgen Pebler ; and Olaf Burghaus
• 刊名：Inorganic Chemistry
• 出版年：2005
• 出版时间：February 21, 2005
• 年：2005
• 卷：44
• 期：4
• 页码：955 - 963
• 全文大小：212K
• 年卷期：v.44,no.4(February 21, 2005)
• ISSN：1520-510X

文摘

The synthesis of dinuclear derivatives of trovacene (ages/gifchars/eta.gif" BORDER=0 >⁷-C₇H₇)V(ages/gifchars/eta.gif" BORDER=0 >⁵-C₅H₅) (1^{ages/entities/bull.gif">}) is reported, in which ethynyl (6^{ages/entities/bull.gif">ages/entities/bull.gif">}),butadiynyl (7^{ages/entities/bull.gif">ages/entities/bull.gif">}), and 1,4-di(ethynyl)phenyl (8^{ages/entities/bull.gif">ages/entities/bull.gif">}) groups serve as spacers between paramagnetic (S = ¹/₂) [5]trovacenylunits. The mononuclear precursors [5]trovacenylcarbaldehyde (2^{ages/entities/bull.gif">}) and [5]trovacenylacetylene (4^{ages/entities/bull.gif">}) are also described.Structural characterization by X-ray diffraction has been performed for 4^{ages/entities/bull.gif">}, 6^{ages/entities/bull.gif">ages/entities/bull.gif">}, 7^{ages/entities/bull.gif">ages/entities/bull.gif">}, and 8^{ages/entities/bull.gif">ages/entities/bull.gif">}. Electronic communicationas gleaned from cyclic voltammetry only manifests itself in the reduction processes where redox splitting ages/gifchars/delta.gif" BORDER=0 >E_1/2(0/1-, 1-/2-) is resolved for 6^{ages/entities/bull.gif">ages/entities/bull.gif">} (ages/gifchars/delta.gif" BORDER=0 >E_1/2 = 150 mV) and indicated for 7^{ages/entities/bull.gif">ages/entities/bull.gif">} (ages/gifchars/delta.gif" BORDER=0 >E_1/2 ages/entities/lsim.gif"> 80 mV). Magnetocommunicationleads to exchange coupling of the two electron spins which reside in vanadium centered orbitals. The valuesJ_EPR(6^{ages/entities/bull.gif">ages/entities/bull.gif">}) = (-)0.92, J_EPR(7^{ages/entities/bull.gif">ages/entities/bull.gif">}) = (-)0.56, and J_EPR(8^{ages/entities/bull.gif">ages/entities/bull.gif">}) = (-)0.005 cm^-1 are derived from the ⁵¹V hyperfine patterns.Accordingly, attenuation of exchange interaction by oligoalkyne spacers is weak, corresponding to a factor of 0.6only per added -Cages/entities/tbd1.gif">C- unit. In the determination of very weak long distance exchange interactions, EPR excelsbecause of the range 5 × 10^-4 ages/entities/lsim.gif"> J ages/entities/lsim.gif"> 1.5 cm^-1 accessible in the case of ⁵¹V as a reporting magnetic nucleus andbecause competing intermolecular exchange is quenched in dilute fluid solution. This is demonstrated by the valueJ_{ages/gifchars/chi.gif" BORDER=0 >}(7^{ages/entities/bull.gif">ages/entities/bull.gif">}) = -3.84 cm^-1 obtained from a magnetic susceptibility study, which exceeds J_EPR(7^{ages/entities/bull.gif">ages/entities/bull.gif">}) by a factor of 7. Thesmall magnitude of spin exchange interaction between trovacene units reflects the fact that the spin bearing V3d_z²orbital is virtually orthogonal to the ages/gifchars/pi.gif" BORDER=0 >-perimeter ligand orbitals and weakly overlapping only with the a_1g(ages/gifchars/sigma.gif" BORDER=0 >) ringorbitals, creating two bottlenecks for spin-exchange in the spacer-containing ditrovacenes.