Quadrupole Effects in the EPR Spectra of Bis [1,3-di(p-n-Octyloxyphenyl Propane-1,3 Dionato] Cu-(II): Role in Phase Transitions

ABSTRACT

X band studies of alkyl/alkloxy phenyl substituted Cu complexes indicate that only C₈O-Cu exhibits a complex hyperfine structure (h. f. s.) at 300K. It also undergoes a first-order phase transition around 213K. However, the complex h. f. s. could not be delineated at X band. In the Q band, in addition to the four permitted h. f. lines, 10 forbidden lines due to quadrupole effects are observed. Further, the forbidden lines disappear in the discophase but the permitted h. f. lines remain. This difference between C₈O-Cu and C₈Cu could be explained from their crystal structures. In C₈O-Cu, the repeating unit is a Cu dimer, as opposed to a single Cu atom placed at the inversion centre in C_nCu. Distortion in the dimer, possibly accounts for the observed quadrupole effects.