Rectangular two-dimensional antiferromagnetic systems: Analysis of copper(II) pyrazine dibromide and dichloride

The structure of copper pyrazine dibromide (or dichloride) consists of dihalide-bridged copper chains parallel to the c-axis with the copper sites linked in a perpendicular direction by bridging pyrazine molecules parallel to the b-axis. Superexchange interactions are propagated through both halides and pyrazine so the magnetic structure is a rectangular layer with two exchange strengths, J and J′ (J′ = αJ), where 0 < α < 1. The susceptibility of a rectangular antiferromagnetic Heisenberg lattice with S = 1/2 has been simulated using Quantum Monte Carlo techniques and the results compared to the experimental data. Best fits of the magnetic susceptibility data to the simulated data yield: for Cu(pz)Br₂, α = 0.20(5), C = 0.430(1) emu K/mol, 2J = ?46(1) K, and 2J′ = ?9(2) K and for Cu(pz)Cl₂, α = 0.30(5), C = 0.426(1) emu K/mol, 2J = ?28(1) K, and 2J′ = ?8(2)) K. The values are in good agreement with the literature and thus demonstrate the effectiveness of the technique for rectangular lattices.