Two New Helical Compounds Based on Pitch‐Tunable Keggin Clusters

Two isostructural compounds, {[Cu2(DF)2H2O]2SiW12O40}·2H2O (1) and {[Cu2(DF)2H2O]2GeMo12O40}·2H2O (2) (DF = 4,5‐diazafluoren‐9‐one), were synthesized and characterized by routine methods and single‐crystal X‐ray diffraction. In the compounds, each Keggin cluster links five copper dimers [Cu2(DF)2H2O]2+ in an unusual asymmetrical pentacoordination mode to form 3D networks with left‐ and right‐handed helical chains. Notably, by comparing 1 and 2 with other helical compounds with Keggin clusters as connectors, we found that the pitches of those compounds are mainly dominated by the coordination modes of the Keggin clusters, suggesting that the Keggin clusters are pitch‐tunable synthons. Furthermore, the luminescent and electrochemical properties of the title compound were studied. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)