Three novel Cu₆S₆ cluster-based coordination compounds: Synthesis, framework modulation and the sensing of small molecules and Fe³⁺ ions

Three novel Cu₆S₆ cluster-based coordination compounds formulated as [CuI3(mpymt)₃]₂ (1), {(CuI4Br₄)[CuI6(mpymt)₆]}_n (2), and {(CuI6I₆)[CuI6(mpymt)₆]}_n (3) (Hmpymt = 4-methylpyrimidine-2-thione), have been synthesized under solvothermal conditions and characterized by elemental analysis, infrared (IR) spectroscopy, thermal gravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. Structural analysis reveals that compound 1 shows a distorted octahedral core of six copper atoms (Cu₆S₆) constructed from four α and two β type NC-SH parts from six mpymt^- anions. Compound 2 displays an interesting 3D framework constructed from Cu₆S₆ and Cu₄Br₄ Cu(i) clusters simultaneously, interestingly, six mpymt^- with α type NC-SH parts are involved in the formation of Cu₆S₆. Compound 3 displays an infinite 1D framework constructed from Cu₆S₆ and Cu₆I₆ Cu(i) clusters, notably, four α and two β type NC-SH parts are involved in the formation of the Cu₆S₆ cluster, however, only mpymt^- ligands containing α type NC-SH parts form the bridged Cu₆I₆ cluster. The experimental results reveal that halogen ions finely modulate the structural features of compounds 1-3. The fluorescent properties of compounds 1-3 in the solid state and in various solvent emulsions were investigated in detail, the results of which indicate that compounds 1-3 are all highly sensitive naked eye colorimetric sensors for NB, 2-NT and Fe³⁺ (NB = nitrobenzene and 2-NT = 2-nitrotoluene).