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

Abstract

Three novel Cu₆S₆ cluster-based coordination compounds formulated as [Cu^I₃(mpymt)₃]₂ (1), {(Cu^I₄Br₄)[Cu^I₆(mpymt)₆]}_n (2), and {(Cu^I₆I₆)[Cu^I₆(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).