Design, Synthesis, Structure, and Gas (N₂, Ar, CO₂, CH₄, and H₂) Sorption Properties of Porous Metal-Organic Tetrahedral and Heterocuboidal Polyhedra

A strategy based on assembling metal ions and organic carboxylate links has been applied for the design and synthesis of a new class of porous, truncated tetrahedral and heterocuboidal polyhedra, whose pore size and functionality can be systematically varied. The synthesis of this series of metal-organic polyhedra (MOPs) employs sulfate-capped oxygen-centered iron-carboxylate trimers, Fe₃O(CO₂)₃(SO₄)₃, as rigid nodes separated by linear (phenyl, biphenyl, terphenyl, and tetrahydropyrene) or trigonal (benzenetriphenyl) links to yield five highly crystalline polyhedra of general formula [NH₂(CH₃)₂]₈[Fe₁₂O₄(SO₄)₁₂(link)_x(py)₁₂]·G (x = 6 for linear or 4 for trigonal, py = pyridine, G = guests). In this series, the size of each polyhedron has been varied from 20.0 to 28.5 Å (on edge), and the corresponding pore diameter from 7.3 to 13.3 Å. Gas sorption isotherms were measured for three members of this series to reveal significant uptake of gases (N₂, Ar, CO₂, H₂, CH₄) and benzene and exhibit Type I sorption behavior that is indicative of permanent porosity. The apparent surface areas for these compounds range from 387 to 480 m²/g.