Structure, phase transition and properties of the one-dimensional antiferromagnet Cu(2,6-dimethylpyrazine)Br2?

RSC Advances Pub Date: 2021-06-25 DOI: 10.1039/D1RA02318G

Abstract

We report the crystal structure and properties of the one-dimensional S = 1/2 antiferromagnet Cu(2,6-dimethylpyrazine)Br2 with strong intra-chain exchange. At room temperature, its linear spin chains are formed by Cu2+ ions via the non-bonding Br?Br contacts. Interestingly, a phase transition from Pmmn to P21/n structure occurs at TS ≈ 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/kB ≈ ?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)Br2. We also performed ultra-violet (UV) absorption and photoluminescence measurements which give a semiconducting band gap Δ ≈ 2.79 eV which is consistent with theoretical calculations.

Graphical abstract: Structure, phase transition and properties of the one-dimensional antiferromagnet Cu(2,6-dimethylpyrazine)Br2
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