REDETERMINATION OF BIS(2-AMINOPYRIMIDINIUM) TETRABROMOCOPPER(II) AT 200 AND 100 K

The structure of (C4H6N3)(2)[CuBr4] has been studied using X-ray diffr action techniques at 200 and 100 K. The molecular structure has ideal square-planar [CuBr4](2-) groups, bonded to protonated organic molecul es not only through hydrogen bonds, but also via the lone pair of one N atom through a coordinative Cu-N bond, so making the other N atom pr otonated. The copper coordination changes slightly at lower temperatur es towards an octahedral coordination. The compound presents Jahn-Tell er distortion as confirmed by magnetic measurements; there is antiferr omagnetic ordering at T-n = 30 K, with a broad peak indicating that th e system is one-dimensional.