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Synthesis of open shell organic molecules for magnetic materials applications and investigations

Paul R Serwinski, University of Massachusetts - Amherst

Abstract

A variety of molecules were investigated to help determine structure-property relationships governing the limits of unpaired electron delocalization and interaction. ^ Nitreno-radicals were synthesized and examined by ESR. Connectivites of nitrene groups were correlated to ZFS :D/hc: and :E/ hc: values. Meta-connected quartet state systems showed larger :D/hc: compared to para-connectivity. Calculations did not show more delocalization in either connectivity. Prepared quartets were studied by ESR Curie analysis over 4–70 K. ^ Nitrosonium perchlorate complexes of azidophenyl nitronyl nitroxides were studied by X-ray crystallography and found to be more planar than their radical precursors. Magnetic susceptibility measurements showed little response, confirming oxidation to cation. ^ Prepared para-connected rigid dinitrenes were studied by ESR and Curie analysis. 1,4-Bis-(nitrenophenyl)-1,3-butadiyne (29 ) showed an excited-state triplet biradical spectrum, and is presumably a ground-state singlet. This proves that the unpaired π-electrons in 29 are strongly exchange coupled and strongly delocalized. 1,4-Bis-(4-nitrenophenylethynyl)-benzene (30) showed an excited-state quintet spectrum but is also presumed to be a ground-state singlet. The quintet spectrum indicates that the unpaired π-electrons in 30 are not strongly exchange coupled, and do not delocalize to the central phenyl ring. A rigid dinitrene, 1,5-dinitrenonaphthalene ( 113), was found to rearrange to a cumulated alkene with terminal nitrile groups. No biradical state was observed. Apparently 113 exhibits strong exchange delocalization of its unpaired π-electrons to favor a singlet state over the triplet, since the triplet is not observed: computations support a singlet ground-state. ^ Septet trinitrene 1,3-dicyano-5-methyl-2,4,6-trinitrenobenzene ( 115) was prepared and studied by ESR and Curie analysis. A high-spin ground state was observed with estimated ZFS of :D/hc: = 0.090 cm−1 and :E/hc: ≈ 0 cm −1. The azide groups photolyze in step-wise fashion giving triplet mononitrene, quintet, and septet. There is sufficient delocalization of the nitrene π-electrons to favor the septet state in the overall system. ^ An iminoyl nitroxide with a hydrogen-bonding 6-uradinyl group ( 119) was prepared. X-ray crystallography showed planarity dominated by two-point hydrogenbonding. Room temperature solution ESR shows seven lines (aN = 8 G, 3 G) compared to five lines (typical aN = 7 G) that result from a nitronyl nitroxide. ^

Subject Area

Chemistry, Organic|Chemistry, Physical

Recommended Citation

Paul R Serwinski, "Synthesis of open shell organic molecules for magnetic materials applications and investigations" (January 1, 2003). Doctoral Dissertations Available from Proquest. Paper AAI3110550.
http://scholarworks.umass.edu/dissertations/AAI3110550

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