Unexpected isotopic effect of a deuteriumed countercation on the spin-Peierls-type transitions in quasi-one-dimensional bis(maleonitriledithiolato)nickelate monoanion spin systems

摘要

Two deuteriumed quasi-one-dimensional (quasi-lD) spin-Peierls-type compounds, 4-X-benzylpyridinium-d_5 bis(maleo-nitriledithio-lato)nickelate (the substituent X = Br or Cl), were structurally characterized. Compared with the corresponding non-deuteration compounds, the transition temperature T_c shifts to higher temperature. The isotopic effect of countercations on T_c is probably related to the change of phonon frequency ω_0 and 'chemical pressure' resulted from the substitution of pyridine by pyridine-d_5.