Abstract
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 {M(4)O(4)} units resembling the structure of oxide surfaces. This work investigated the oligomerization of [MoO(4)](2-) and [WO(4)](2-) oxyanions in aqueous solutions in the presence of {Ru(C(6)H(6))}(2+) 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(C(6)H(6))}(4)Mo(4)O(16)] (1), [{Ru(C(6)H(6))(OH)}(3)HMoO(4)][MoO(4)] (2), [{Ru(C(6)H(6))}(4)H(2)Mo(5)O(20)] (3), [{Ru(C(6)H(6))}(4)W(2)O(10)] (4), Na(6)[{Ru(C(6)H(6))}(2)H(2)W(8)O(30)] (5), [{Ru(C(6)H(6))}(5)H(2)W(6)O(24)] (6), and [{Ru(C(6)H(6))(OH)}(6)W(2)O(7)][{Ru(C(6)H(6))}(2){Ru(C(6)H(6))(OH(2))}(2)H(2)W(8)O(30)](2) (7). They comprise small, reactive iso-polyoxometalate building blocks that are capped by {Ru(C(6)H(6))}(2+) cations, resulting in cubane-like {Ru(3)MO(4)}, {Ru(2)M(2)O(4)}, or {RuM(3)O(4)} (M = Mo or W) structural motifs. Moreover, the molecular crystal of 1 contains extensive C-H···O hydrogen bonds, and it undergoes a reversible crystal-to-amorphous-to-crystal transition upon dehydration-hydration cycles.