TETRANUCLEAR OSMIUM COMPLEXES OF TETRACYANOQUINODIMETHANE [TCNQ, ,5-DIENE-1,4-DIYLIDENE)BIS(PROPANE-1,3-DINITRILE)] AND 1,2,4,5-TETRACYANOBENZENE (TCNB) - SYNTHESIS, SPECTROELECTROCHEMISTRY AND MAGNETISM

The new complexes [(mu(4),eta(4)-TCNX) {Os(PR3)(2)(CO)(H)Cl)(4)], R = isopropyl, TCNX = tetracyanoquinodimethane [TCNQ, ,5-diene-1,4-diylide ne)bis(propane-1,3-dinitrile)] or 1,2,4,5-tetracyanobenzene (TCNB), we re studied by spectroelectrochemistry in the UV/VIS/NIR and IR regions and by EPR spectroscopy. Both compounds are reduced in two reversible steps and oxidized in a two-electron process (reversible for TCNQ, qu asi-reversible for TCNB). In all oxidation states studied (-, 0,2+) th e TCNQ complexes exhibited intense long-wavelength absorptions in the near IR region (lambda(max) >1000 nm). The EPR spectra of the monoanio nic forms exhibit hardly any g anisotropy and thus very little metal p articipation, suggesting an oxidation state formulation [(TCNX.-)(Os-I I)(4). The dication of the TCNQ system is formulated as [(TCNQ)(Os-2.5 )(4)] with an intervalence; transfer transition at lambda(max) = 1245 nm (epsilon = 50 000 M-1 cm(-1)). In the solid state, the neutral comp lexes show temperature dependent paramagnetism that could be fitted wi th a model implying two coupled S = 1/2 entities.