Metal–organic frameworks built from a carborane linker isolating ideal one-dimensional large-spin chains of Co (S = 3/2) or Ni (S = 1)

Abstract

One-dimensional (1D) antiferromagnetic chains are fascinating because of their exotic quantum phenomena. However, isolating large-spin S chains remains challenging as even minimal interchain interaction J′ tends to drive unwanted long-range ordering. Here, we report on the synthesis, crystal structure, magnetism, optical, and electronic properties of two isostructural metal–organic frameworks (MOFs), [M2(mCB-L)2(μ2-H2O)2(DMF)4]n·solv (M = Co(II) (mCB-Co) or Ni(II) (mCB-Ni)), which feature water-bridged Co (S = 3/2) or Ni (S = 1) spin chains that are effectively separated by bulky carborane linkers (1,7-di(4-carboxyphenyl)-1,7-dicarba-closo-dodecaborane, mCBLH2). The temperature-dependent susceptibility reveals strong antiferromagnetic interactions with significant intrachain coupling, JCo/kB = −4.65 K (mCB-Co) and JNi/kB = −23.36 K (mCB-Ni), yet confirm the absence of long-range order down to 0.3 K due to negligible interchain interactions, as corroborated by specific heat data. This indicates extremely small J′, with J′/J < 4.7 × 10−4 (3.7 × 10−5) for Co (Ni) MOFs, making these new materials nearly ideal 1D antiferromagnets. Additionally, optical band gaps were estimated via the Kubelka–Munk method, yielding an increase from 3.83 eV for mCB-Co to 4.20 eV for mCB-Ni, showcasing tunable electronic properties across the two MOFs.

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ORCID for Mark E. Light: orcid.org/0000-0002-0585-0843

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