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 AgNO 3 with 1,4-benzenedicarboxylic acid (1,4-H 2 BDC) and 1,2-bis(4-pyridyl)ethylene (bpe) (molar ratio = 1:1:1) with 6 M HNO 3 followed by hydrothermal treatment at 170 °C afforded a one-dimensional (1D) coordination polymer {[Ag 2 (bpe) 2 ](1,4-BDC)·(1,4-H 2 BDC)} n ( 1 ). Photochemical [2 + 2] cycloaddition reaction of 1 through UV irradiation followed by dissolving the photolysis product in 6 M HNO 3 and hydrothermal treatment at 170 °C led to the formation of a three-dimensional (3D) coordination polymer {[Ag 4 (4,4′-tpcb) 3 ][(NO 3 ) 4 (H 2 O) 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 1 consists of a 1D 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 4 n + 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 [(NO 3 ) 4 (H 2 O) 6 ] 4− anions. The formation of such a cluster anion may provide some insight into the nature of hydration of nitrate in H 2 O.