Self-assembly of {W2O4}2 +: Syntheses and structures of high-valent tungsten compounds

Abstract Oxidation of K 3 [W III 2 Cl 9 ] in the mixture of concentrated hydrochloric acid and pyridine in the presence of hydrazinium dichloride afforded (PyH) 5 [W V OCl 4 (H 2 O)] 3 Cl 2 (PyH +  = pyridinium cation, C 5 H 5 NH + ) ( 1 ), obtained as emerald green needle-shaped crystals. The compound contains mononuclear octahedrally shaped [WOCl 4 (H 2 O)] − ions. In contrast to its molybdenum analog, 1 shows a marked instability in the air. Solvothermal reaction of a tetrabutylammonium salt of the [WOCl 4 (H 2 O)] − ion with pyridine at 115 °C afforded a small amount of orange crystals of [W V 8 W VI 2 O 26 (Py) 8 ]·Py ( 2 ) (Py = pyridine, C 5 H 5 N). The W V centers can be clearly distinguished from the W VI sites, namely they are grouped into four metal–metal bonded {W V 2 O 4 } 2 + cores. The structure of the cluster is virtually identical with the analogous molybdenum complex, [Mo 10 O 26 (Py) 8 ]. The isolation of [W 10 O 26 (Py) 8 ]·Py ( 2 ) confirms that the {W 2 O 4 } 2 + core forms from the [WOCl 4 (H 2 O)] − ions upon the substitution of the labile ligands.