Nanoporous, Interpenetrated Metal-Organic Diamondoid Networks

Reactions of Cd(NO(3))(2).4H(2)O with 4-cyanopyridine in the presence of ethanol or pyrazine guest molecules under hydro(solvo)thermal conditions afford two new cadmium coordination polymers, [Cd(isonicotinate)(2)(EtOH)][EtOH], 1, and [Cd(isonicotinate)(2)(H(2)O)][pyrazine], 2. The Cd centers in both 1 and 2 are seven-coordinate with distorted pentagonal bipyrimidal structures via coordination to two pyridyl nitrogen atoms, one oxygen atom from a solvent molecule, one chelating carboxylate, and one semichelating carboxylate group. The bridging isonicotinate groups link each Cd center to four adjacent Cd centers, resulting in three-dimensional polymeric networks based on doubly interpenetrated diamondoid structures. One molecule of ethanol or pyrazine is also included in 1 or 2, respectively, to fill the void space left within the solid after the twofold interpenetration. Thermogravimetric analyses (TGA) showed that the included and coordinated ethanol molecules in 1 could be removed stepwise at 100 and 160 degrees C, respectively. After the removal of the guest ethanol molecules, the resulting nanoporous solid exhibits the same X-ray powder diffraction (XRPD) pattern as 1. Guest ethanol molecules can be reintroduced into the evacuated sample of 1 via exposure to ethanol vapor at room temperature. Further heating results in the loss of coordinated ethanol molecules and the collapse of the polymeric network structure. On the other hand, XRPD shows that removal of pyrazine in 2 is accompanied by the loss of the coordinated water molecules and, consequently, the collapse of the polymeric network structure. These results demonstrate that nanopores can be designed based on interpenetrated coordinated networks. Crystal data for 1: orthorhombic space group Pbca, a = 12.691(1) Å, b = 15.545(1) Å, c = 18.342(1) Å, and Z = 8. Crystal data for 2: orthorhombic space group Pbca, a = 12.081(1) Å, b = 15.323(2) Å, c = 19.705(3) Å, and Z = 8.