Structure and magnetic properties of (5BAP)(2)CuBr4: magneto-structural correlations of layered S=1/2 Heisenberg antiferromagnets

The synthesis, structure and magnetic behavior of (5BAP)(2)CuBr4 are report ed (5BAP = 2-amino-5-bromopyridinium). (5BAP)(2)CuBr4 is a member of a fami ly of CuX42- (X = Cl, Br) compounds which form C-centered lattices with two -dimensional (2D) antiferromagnetic interactions. Crystallographic data: mo noclinic, C2/c, a = 13.28 Angstrom, b = 8.719 Angstrom, c = 16.11 Angstrom, beta = 95.40 degrees, Z = 4. The structure was solved by direct methods an d refined to R = 0.0346 (R-w = 0.0827) for 1749 observed unique reflections and 105 parameters. The CuBr42- ions exist as distorted tetrahedra and are related by centering parallel to the C-face giving rise to a square magnet ic lattice. Magnetic susceptibility measurements over the temperature range of 2.1-100 K correspond to an intra-planar magnetic exchange constant of - 6.94(6) K and indicate a transition to 3D order at 4.0(2) K. The effects of structural variations upon the magnetic properties of the CuX42- layered c ompounds are considered. (C) 2001 Elsevier Science B.V. All rights reserved .