Occurrence of Uncommon Infinite Chains Consisting of Edge-Sharing Octahedra in a Porous Metal Organic Framework-Type Aluminum Pyromellitate Al4(OH)8[C10O8H2] (MIL-120): Synthesis, Structure, and Gas Sorption Properties

A new metal organic framework (MOF)-type aluminum pyromellitate or Al-4(OH)(8)[C10O8H2]center dot 4.8-5H(2)O (called MIL-120) has been hydrothermally synthesized at 210 degrees C for 24 h. Its structure was analyzed by single-crystal microdiffraction using the synchrotron radiation beamline at ID 13 station (ESRF, Grenoble). It consists of infinite chains of aluminum centers in octahedral coordination connected to each other through the pyromellitate linker. The structural feature is the existence of the AlO2(OH)(4) octahedra linked to each other via a common edge consisting of two mu(2)-hydroxo groups, along the [102] direction. The different positions of the common edge in the two distinct Al crystallographical sites induce a cis-trans connection mode of the octahedral units, and zigzag chains are generated. All the carboxylate groups of the pyromellitate molecules are perpendicularly connected to the inorganic chains, and it results in the formation of channels running along the c axis (5.4 x 4.7 angstrom), in which water molecules are encapsulated. Al-27 solid state NMR revealed two well resolved signals with two distinct quadrupolar coupling constants (C-Q = 8.07 and 4.77 MHz) related to 2 two Al sites. Brunnauer-Emmett-Teller (BET) surface area is 308(4) m(2) g(-1) (Langmuir: 432(1) m(2)g(-1)). H-2 adsorption is 1.3 wt % oat 77 K and 3 MPa. CH4 or CO2 adsorptions are 1.8 mmol g(-1) and 4.8 mmol g(-1), respectively, at 303 K (under 1 MPa).