Preparation and Crystal Structures of 4-(4-Pyridylthio)-1-methylpyridinium Salts: Assembly of a Donor–AcceptorType Molecule Containing a Sulfide Bridge

RCrO4 oxides (R=Pr, Gd, Tb, Tm, and Yb) have been synthesized at 773 K using the corresponding nitrates as precursors. Xray diffraction data reveal that these samples are single phases and crystallize with the zircon-type structure, showing tetragonal symmetry, space group I41/amd. All the compounds are antiferromagnetic and the Néel temperature, which depends on the R3+ ion, takes values lower than 30 K. The presence of a canting appears to be responsible for the negative values of the magnetic susceptibility found below the compensation temperature. This uncommon phenomenon is named reversal of magnetization. It is field-dependent, being suppressed at 500 Oe for the TmCrO4 compound. The highest value of the compensation temperature (24 K) corresponds to the YbCrO4 oxide. A metamagnetic transition has been observed in all cases at critical fields ranging from 225 Oe (GdCrO4) to 1600 Oe (YbCrO4).