Synthesis, Crystal Structure, Magnetic Properties, and EPR of Cu(bp3ca)Br(2).H(2)O (bp3ca = 2,2'-Bipyridine-3,3'-dicarboxylic Acid). Ferromagnetic Interactions via Unsymmetrical Bromide Bridges.

Cu(bp3ca)Br(2).H(2)O crystallizes in the triclinic space group P&onemacr; with a = 10.622(2) Å, b = 10.832(2) Å, c = 14.684(2) Å, alpha = 106.13(1) degrees, beta = 105.91(1) degrees, gamma = 102.74(1) degrees, and Z = 2. The asymmetric unit consists of a bis &mgr;-bromo unsymmetrically dibridged dimer which is further linked to its inversion-related partner to form a dimer of dimers. Weak intertetramer contacts are also observed. The magnetic data for this compound were fit to a linear tetramer model to give J(1) = J(3) = -8.69 x 10(-)(3) cm(-)(1), J(2) = 91.52 cm(-)(1), and the intertetramer interaction J' = -1.187 cm(-)(1) with g = 1.93. EPR data are consistent with the magnetic data. This system is compared to its previously reported chloro counterpart, which differs markedly in both structure and magnetic properties.