A uudd Cyclic Water Tetramer and an Opened Octameric Water Cluster in the Charge-Transfer Salts of the Bipyridinium Cation

Abstract

Two novel charge-transfer salts, [(Bpyph)(SCN)2]·2H2O 1 and {(HBpyph)[Fe(CN)6]}·5.5H2O 2, have been synthesized and characterized using elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction studies. Compound 1 is the first bipyridinium charge-transfer salt containing a cyclic water tetramer, in which the uudd cyclic water tetramers built from four symmetry related water molecules join the Bpyph2+ cations to the dimer by hydrogen bonds between the water molecules and the nitrogen atoms of Bpyph2+. The cooperation of the hydrogen-bonding and π–π stacking interactions between the pyridyl groups results in the formation of an infinite ribbon with a herringbone arrangement. An opened water octamer has been observed in 2. It presents a new association mode of water molecules that is not predicted theoretically nor found experimentally. The water octamer is hydrogen-bonded to two HBpyph3+ cations and two [Fe(CN)6]3− anions to form water octamer-bridged HBpyPh-Fe(CN)6 dimers, which are further connected to each other via π–π offset stacking interactions to generate an infinite one-dimensional ribbon.