Directing the Linkage of Small Polyoxometalate Building Blocks Using (Benzene)ruthenium Cations.

Oligomerization of monomeric molybdate and tungstate oxyanions in the presence of organometallic cations produces a group of organometallic-polyoxometalate clusters, which have diverse structures based on cubane-like {MO} units resembling the structure of oxide surfaces. This work investigated the oligomerization of [MoO] and [WO] oxyanions in aqueous solutions in the presence of {Ru(CH)} as the organometallic structure-directing agents. The reactions produced a mixture of several species, and fractional crystallization by adjusting crystallization temperature and molar ratios of Ru:Mo or Ru:W allowed the isolation of seven types of (benzene)ruthenium-polyoxometalate complexes: [{Ru(CH)}MoO] (), [{Ru(CH)(OH)}HMoO][MoO] (), [{Ru(CH)}HMoO] (), [{Ru(CH)}WO] (), Na[{Ru(CH)}HWO] (), [{Ru(CH)}HWO] (), and [{Ru(CH)(OH)}WO][{Ru(CH)}{Ru(CH)(OH)}HWO] (). They comprise small, reactive -polyoxometalate building blocks that are capped by {Ru(CH)} cations, resulting in cubane-like {RuMO}, {RuMO}, or {RuMO} (M = Mo or W) structural motifs. Moreover, the molecular crystal of contains extensive C-H···O hydrogen bonds, and it undergoes a reversible crystal-to-amorphous-to-crystal transition upon dehydration-hydration cycles.