Encapsulation of Unusual Nitrate-Water Cluster [(NO3)4(H2O)6]4- Anions into Cages of a Three-Dimensional Cationic Coordination Polymer

Acidification (pH = 3) of a solution containing AgNO3 with 1,4-benzenedicarboxylic acid (1,4-H2BDC) and 1,2-bis(4-pyridyl)ethylene (bpe) (molar ratio = 1:1:1) with 6 M HNO3 followed by hydrothermal treatment at 170 degrees C afforded a one-dimensional (ID) coordination polymer {[Ag-2(bPe)(2)](1,4-BDC)center dot(1,4-H2BDC)}(n) (1). Photochemical [2 + 2] cycloaddition reaction of 1 through UV irradiation followed by dissolving the photolysis product in 6 M HNO3 and hydrothermal treatment at 170 degrees C led to the formation of a three-dimensional (3D) coordination polymer {[Ag-4(4,4'-tpcb)(3)][(NO3)(4)(H2O)6]}(n) (4,4'-tpcb = tetrakis(4-pyridyl)-cyclobutane) (2). Compounds 1 and 2 were characterized by elemental analysis, IR, and single crystal X-ray diffraction. Compound I consists of a ID linear chain extending along the [011] plane in which Ag(I) ions are bridged by bpe molecules. Compound 2 contains the 2-fold interpenetrating 3D cationic [Ag-4(4,4'-tpcb)(3)](n)(4n+) net with the Schlafli symbol of (6(3))(4)(6(2)8(4))(3). Within the cages of this net occupy the uncommon nitrate-water cluster [(NO3)(4)(H2O)(6)](4-) anions. The formation of such a cluster anion may provide some insight into the nature of hydration of nitrate in H2O.