Structure, Phase Transition And Properties Of The One-Dimensional Antiferromagnet Cu(2,6-Dimethylpyrazine)Br-2

We report the crystal structure and properties of the one-dimensional S = 1/2 antiferromagnet Cu(2,6-dimethylpyrazine)Br-2 with strong intra-chain exchange. At room temperature, its linear spin chains are formed by Cu2+ ions via the non-bonding BrMIDLINE HORIZONTAL ELLIPSISBr contacts. Interestingly, a phase transition from Pmmn to P21/n structure occurs at T-S approximate to 248 K below which the [CuBr2](n) spin chains become non-linear and the magnetic susceptibility abruptly increases, reflecting the weakening of antiferromagnetic exchange strength. This result evidences the Goodenough-Kanamori rules which claim that a linear super-exchange pathway produces stronger antiferromagnetic coupling. From magnetic susceptibility measurements we find the average intra-chain exchange strength is J/k(B) approximate to -88.18 K in the low temperature phase. Both magnetic and specific measurements show the absence of magnetic ordering down to 2 K, implying the excellent magnetic one-dimensionality of Cu(2,6-dimethylpyrazine)Br-2. We also performed ultra-violet (UV) absorption and photoluminescence measurements which give a semiconducting band gap Delta approximate to 2.79 eV which is consistent with theoretical calculations.