Cubic and rhombohedral heterobimetallic networks constructed from uranium, transition metals, and phosphonoacetate: new methods for constructing porous materials

Four heterobimetallic U(VI)/M(II) (M = Mn, Co, Cd) carboxyphosphonates have been synthesized. M₂[(UO₂)₆(PO₃CH₂CO₂)₃O₃(OH)(H₂O)₂]·16H₂O (M = Mn(II), Co(II), and Cd(II)) adopt cubic three-dimensional network structures with large cavities approximately 16 Å in diameter that are filled with co-crystallized water molecules. [Cd₃(UO₂)₆(PO₃CH₂CO₂)₆(H₂O)₁₃]·6H₂O forms a rhombohedral channel structure with hydrated Cd(II) within the channels. The cubic compound (Co) displays differential gas absorption with a surface area for CO₂ uptake of 40 m² g⁻¹ at 273 K, and no uptake of N₂ at 77 K.