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The structure, susceptibility, and high-field magnetization of μ-quinoxalinecopper(II) dibromide are reported. The compound crystallizes in the space group C2/c as a coordination polymer of neutral Cu2Br4 dimers bridged into chains by quinoxaline molecules forming a ladder structure. The susceptibility data are well described by a spin-ladder model with two antiferromagnetic exchange strengths 2J⊥=35.0 K within the dimers, and 2J=30.3 K through the quinoxaline groups. The ratio of exchange strengths, R J⊥/J=1.16, is the closest to unity yet found for a spin ladder. The magnetization study shows the compound at low temperatures to be in a non-magnetic singlet state for low fields, but that a phase transition to a magnetized state occurs near 14 T, indicating the presence of an energy gap Δ≈20 K. |
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