Holding Open Micropores with Water: Hydrogen-Bonded Networks Supported by Hexaaquachromium(III) Cations

To form any porous solid requires payment of an energetic penalty to create voids through either strong bonds or many weak interactions working in concert. Here, we present a porous solid that is composed, after pore activation, of 27 wt % water and sustained by charge-assisted hydrogen bonds between hexaaquachromium(III) cations and organophosphonate anions. The network forms a pillared layered motif including guest solvents, as confirmed crystallographically. Although aquo ligands are an integral part of the hydrogen-bonding network that sustains the pores, activation under high vacuum is possible, and the network demonstrates reversible CO2 sorption. The stability of the network is attributed to the inertness of the octahedral d(3) Cr(III) center in combination with high degrees of complementarity and cooperativity of hydrogen bonds. The sub-nanometer pores are guest selective on the basis of size, shape, and chemical functionality.