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Eight-coordinate tungsten (IV) and octahedral cobalt (III) coordination chelates and polymers

Emmanuelle Julia Darmon, University of Massachusetts Amherst


We have demonstrated our ability to synthesize and isolate dibromobis(bidentate)-tungsten(IV) complexes. Their presence has been confirmed by infrared spectra that contain the characteristic vibrations of the chelated ligands. The compounds are paramagnetic as expected. We used these compounds to form mixed-bidentate ligand eight-coordinated tungsten(IV) complexes and coordination polymers. In this study the syntheses of several diamagnetic mixed-ligand tungsten(IV) chelates are described. The magnetic susceptibility, infrared, ultraviolet-visible and nuclear magnetic resonance data point to this conclusion. The diamagnetic polymer obtained from the chelation of bis(8-hydroxy-5-quinolyl)methane bridging ligands to dibromobis(picolinato)tungsten(IV) has a degree of polymerization of at least ten based on proton nuclear magnetic resonance end group analysis. However, gel permeation chromatography in dimethylformamide of the less soluble fraction suggests the presence of a polymer of much higher molecular weight. We had more confidence in the condensation polymerization of the bis(5,7-dichloro-8-quinolinolato)bis (4-amino-3,5,6-trichloropicolinate)tungsten(IV). The synthesis of this compound proved difficult. Several cobalt(III)polyimine coordination polymers were also synthesized by the condensation of the diformylated trisacetylacetonatocobalt(III) with different diamines under different reaction conditions. The infrared data confirms the formation of imine bonds. Nuclear magnetic resonance spectra are difficult to interpret due to paramagnetism of the compound, but we do see the appearance of broad peaks around 8 ppm that can be assigned to CH=N protons. The m-phenylenediamine compound gives rise to a more soluble polymer than its para analog. The p-phenylene cobalt(III) polyimine was more extensively studied. It gives rise to a higher yield of a lower molecular weight polymer $\rm(\bar M\sb{n},\ 6400;\ \bar M\sb{w},$ 10,200 by gel permeation chromatography or $\rm\bar M\sb{w},$ 14,200 by viscometry). The polymers exhibit a high magnetic moment around 6 B.M. at room temperature that decreases with increasing temperature. No electron spin resonance spectrum can be observed even at low temperature. This compound is believed to be ferromagnetic through a coupling of the paramagnetic excited states of the cobalt centers. These polymers are thermally stable up to 150 to 200$\sp\circ$C.

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Recommended Citation

Darmon, Emmanuelle Julia, "Eight-coordinate tungsten (IV) and octahedral cobalt (III) coordination chelates and polymers" (1997). Doctoral Dissertations Available from Proquest. AAI9737516.