A Discrete Spirocyclic (H2O)9 Cluster and 1D Novel Water Chain with Tetrameric and Octameric Clusters in Cationic Hosts

Two mixed-ligand Ag(I) coordination polymers (CPs), [Ag2(bpp)2(suc)·12H2O]n (1) and [Ag2(bpe)2(suc)·9H2O]n (2) (where bpp = 1,3-bis(4-pyridyl)propane, bpe = 1,3-bis(4-pyridyl)ethane, and H2suc = succinic acid), have been synthesized and structurally characterized. Both structures consist of cationic layers with Ag···π interacted chains of alternating metal and bis(pyridyl) ligands. The noncoordinated succinate (suc2−) in 1 or 2 serves as an anionic template driving surrounding water molecules to aggregate into an ordered 2D water-suc anionic layer. The interlamellar anions and cationic layers are stacked through weak electrostatic interaction and hydrogen bonds. One novel 1D water chain constructed from alternating water tetramer with uudd configuration and rare octamer exists in the anionic layer of 1. Each octameric water cluster consists of a pair of fused hexameric water clusters, and each water hexamer assumes a rare bag-shaped conformation. A discrete spirocyclic nonameric water cluster featuring two vertex-sharing pentamers, which shows a similar structure to organic hydrocarbon spiro[4.4] nonane, was observed in 2. All water clusters have not been structurally documented so far and illustrate new modes of supramolecular association of water molecules. What is more important is that the present observations demonstrate that the spacer length of N-donor ligands has a significant influence on the final formation of water aggregates.