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

The synthesis, structure and magnetic behavior of (5BAP)2CuBr4 are reported (5BAP=2-amino-5-bromopyridinium). (5BAP)2CuBr4 is a member of a family of CuX4 2− (X=Cl, Br) compounds which form C-centered lattices with two-dimensional (2D) antiferromagnetic interactions. Crystallographic data: monoclinic, C2/c, a=13.28 Å, b=8.719 Å, c=16.11 Å, β=95.40°, Z=4. The structure was solved by direct methods and refined to R=0.0346 (Rw=0.0827) for 1749 observed unique reflections and 105 parameters. The CuBr4 2− ions exist as distorted tetrahedra and are related by centering parallel to the C-face giving rise to a square magnetic 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 CuX4 2− layered compounds are considered.