Magnetic properties of 4,4-bipiperidinediium tetrahalocuprates: crystal structures of 4,4-bipiperidinediium tetrabromocuprate(II) monohydrate and bis(4,4-bipiperidinediium) hexabromodicuprate(I)

Reaction of 4,4-bipiperidine (bipip) with copper(II) bromide in aqueous HBr yielded the salts (H(2)bipip)CuBr4<bold>H</bold>2O (2) and (H(2)bipip)(2)Cu2Br6 (3). Compound 2 crystallizes in the space group P2(1)/m and forms alternating layers of the H(2)bipip cations and CuBr4 anions with the water molecules located in the anionic layer. Compound 3 contains Cu(I) and crystallizes in the space group P2(1)/c and comprises stacks of H(2)bipip cations alternating with stacks of Cu2Br64- anions. Temperature-dependent magnetic measurements on 2 and its chloride analog, 1, show distinctly different behaviors supported by the two-halide superexchange pathway. The chloride compound (1) is best described as weakly interacting antiferromagnetic dimers (J similar to-13K), while the bromide compound (2) exhibits very weak ferromagnetic interactions best modeled as a uniform chain with J=2.45 (9)K (using the H=-J(AB)sigma SA<bold>S</bold>B Hamiltonian). [GRAPHICS] .