Our group focuses on investigatingmagnetostructural correlations, and recently a family of pyrazine-bridged copper(II) chains has caught our attention. This family can be partitioned into two types: [CuL2pz(H2O)2](ClO4) and [CuL4pz](ClO4), where pz = pyrazine and L = n-methyl-2-pyridone with n = 3, 4, 5, or 6. Itwas selected for analysis via powder and single-crystal EPR studies, in addition to SQUID magnetometry, due to its moderate superexchange interactions and significant isolation between chains. Preliminary EPR studies demonstrated drastic variation in electronic structure between compounds. Moreover, one compound, for which a Jahn-Teller elongation effect has been identified via single-crystal X-ray diffractometry, yielded particularly interesting results. While its geometry agrees with a rhombic system, EPR data for powder (collected at X-band and Q-band) and single-crystal (collected at X-band) samples indicate that its electronic structure agrees with an axial system. In two compounds, powder EPR results agree with the presence of a Jahn-Teller compression effect, but single-crystal X-ray diffractometry for these compounds are still in process. Although the chemical formulae across compounds in this family are analogous, their crystal packing varies greatly. Of the five compounds for which crystal structures have been solved, four of them are in distinct space groups. The consistent morphology of the crystals allowed for development of a methodology for orienting single-crystal EPR samples that was applicable throughout the family. The unit cell is well aligned with the molecular frame; gx, gy, and gzare all aligned well with bond axes, with g-factor values inversely correlated to bond length. Compounds for which the crystal structure suggests opposing chain orientation within a unit cell demonstrated split single-crystal EPR signals despite expected collapse into a single signal as a result of exchange between chains. The presence of both signals indicates that the copper(II)-pyrazine chains are extremely well-isolated.

EPR studies of pyrazine-bridged copper(II) chains with pyridone ligands

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.