Open-framework beryllium phosphates with a zeolitic CrB4 topology and their structural analogues containing 12-ring channels

Abstract

Two new open-framework beryllium phosphates, formulated as MV·Be₂(HPO₄)₂(H₂PO₄)₂ (1) and EV·Be₂(HPO₄)₂(H₂PO₄)₂ (2), have been synthesized under solvothermal conditions, where MV = methylviologen and EV = ethylviologen. The two compounds have large 16-membered ring (16 MR) channels with a zeolitic CrB₄ topology. They contain in situ generated viologen dications from the alkylation of 4,4′-bipyridine (4,4′-bpy) molecules as the structure-directing agents (SDAs). In comparison, the use of 4,4′-bpy and 2,2′-bpy as the SDAs results in the formation of two different open-framework compounds, (4,4′-H₂bpy)₂·Be₅(HPO₄)₇ (3) and (2,2′-H₂bpy)_0.5·Be₃(OH)(HPO₄)₃ (4). Compounds 3 and 4 have different framework structures with 12 MR channels. The presence of large 4¹⁰8⁴12⁴ cages in the structure of 3 is worth noting.