PCU-type copper-rich open-framework chalcogenides: pushing up the length limit of the connection mode and the first mixed-metal [Cu7GeSe13] cluster

Abstract

We report four new copper-rich open-framework chalcogenides (COCs) with the formulas [Cu₈Ge₆Se₁₉](C₅H₁₂N)₆ (1a), [Cu₈Sn₆Se₁₉](C₆H₁₂N₂)₄(H₂O)₁₃ (1b), [Cu₁₆Ge₁₂S₃₆][Ni(en)₃]₄(en)_xCl_1.5 (1c), and [Cu₇Ge₄Se₁₃](C₆H₂₁N₄) (2). Single-crystal X-ray diffraction analyses suggest that all of these compounds with pcu-type topology are completely built on icosahedral clusters. Of particular interest, the connection units linking the icosahedral clusters in 1a–1c are pure dimeric units in three axial directions. Such a case is unprecedented among previously reported COCs and pushes up the length limit of the connection mode, thereby resulting in the largest solvent-accessible space in COCs. Compound 2 is built on an intriguing and unprecedented mixed-metal Cu₇GeSe₁₃ cluster. The copper-rich nature of these compounds gives rise to a narrow band gap in the near-infrared range, making them hold promise for photoelectric applications.