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

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)xCl1.5 (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.