Tetranuclear osmium complexes of tetracyanoquinodimethane TCNQ, 2,2'-(cyclohexa-2,5-diene-1,4-diylidene)bis(propane-1,3-dinitrile) and 1,2,4,5-tetracyanobenzene (TCNB). Synthesis, spectroelectrochemistry and magnetism

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Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry, (1997)


Tetranuclear complexes (m4,h4-TCNX)Os(PPri3)2(CO)(H)Cl4 TCNX = tetracyanoquinodimethane (TCNQ, 2,2'-(cyclohexa-2,5-diene-1,4-diylidene)bis(propane-1,3-dinitrile)) or 1,2,4,5-tetracyanobenzene (TCNB), were prepd. and studied by spectroelectrochem. in the UV/visible/NIR and IR regions and by EPR spectroscopy. Both compds. are reduced in two reversible steps and oxidized in a two-electron process (reversible for TCNQ, quasi-reversible for TCNB). In all oxidn. states studied (-, 0, 2+) the TCNQ complexes exhibited intense long-wavelength absorptions in the near IR region (lmax \textgreater 1000 nm). The EPR spectra of the monoanionic forms exhibit hardly any g anisotropy and thus very little metal participation, suggesting an oxidn. state formulation (TCNX.bul.-)(OsII)4. The dication of the TCNQ system is formulated as (TCNQ)(Os2.5)4 with an intervalence transfer transition at lmax = 1245 nm (e = 50,000 M-1 cm-1). In the solid state, the neutral complexes show temp. dependent paramagnetism that could be fitted with a model implying two coupled S = 1/2 entities. on SciFinder(R)



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