Part I. 3,4-diazabenzvalene, the azoalkane precursor to tetrahedrane. Part II. Magnetic properties of polaronic polymers

by Kaisaki, David A.

Abstract (Summary)
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The synthesis and reactivity of 3,4-diazabenzvalene (9) are described. This strained diazene thermally decomposes to yield cyclobutadiene dimer with a unimolecular rate at constant -60°C of 5.24 x 10(-4) sec(-1). This corresponds to a half-life for 9 of 22 min. at -60°C. The high thermal reactivity of 9 is postulated to be due to a six-electron, concerted [...] + [...] + [...] N2 extrusion mechanism as opposed to the one-bond diazenyl biradical mechanism observed in the similar molecule, 48. Low temperature (-100 to -150°C) 1H NMR spectroscopy of -196°C photolysis products of 9 in a variety of solvents showed the formation of cyclobutadiene dimer and pyridazine. Attempts at the 10 K FT-IR matrix isolation photolysis studies on 9 failed due to our inability to sublime the cooled, unstable diazene onto the matrix window. No evidence of tetrahedrane formation upon photolysis or thermolysis at any temperature was observed. The magnetic behavior of AsF5- and I2-doped poly(metaphenyleneoctatetraene) (PMPOT) derivatives is also investigated. A synthetic scheme for O-alkyl substituted PMPOT derivatives is developed using the Wittig reaction as the polymerization method. O-alkyl substitution provides an increase in solubility and degree of polymerization relative to the unsubstituted, intractable, parent polymer PMPOT. The O-octadecyl-substituted PMPOT derivative, PMPOT-18, is completely soluble in chloroform or toluene and has a degree of polymerization of 22. Oxidative doping of PMPOT-18 and PMPOT-6 (O-hexyl-substituted) with AsF5 or I2 produces small concentrations (0.2-4 spins/100 monomers) of polarons (partially delocalized radical cations). Fitting the Brillouin function to the magnetization behavior of these polaronic materials provides a method of obtaining the spin state without the need of an estimate of the concentration of polarons present. A spin state of S = 2.2 for AsF5-doped PMOT-18 was found at 1.95 K, while I2-doped PMPOT-6 and PMPOT-18 fit to a Brillouin function with S = 1.2 - 1.3. This is consistent with a net ferromagnetic coupling between 2-4 polarons. Temperature-dependent magnetic susceptibility measurements indicate the presence of both antiferro- and ferromagnetic interactions at temperatures below ca. 50 K. This is interpreted in terms of a model in which doping produces clusters of polarons that interact ferromagnetically. There is also a weaker, antiferromagnetic interaction between clusters that is apparent at low temperatures.
Bibliographical Information:

Advisor:Dennis A. Dougherty; Robert H. Grubbs

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis



Date of Publication:05/10/1990

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