SYNTHESES AND STRUCTURES OF THE TUNGSTOBORATE ANIONS

A new tungstoboric species, [BW13O46H3](8-), which was identified in s olution, is an intermediate between [BW11O39H](8-) and the so-called h exagonal acid. This heteropolyacid was obtained in high yield by a new synthetic route. A single-crystal X-ray diffraction study showed that its formula is H-21[B3W39O132]. 69H(2)O. The heteropolyanion is forme d by three BW13O46 subunits linked together by sharing vertices leadin g to C-3h symmetry. Each subunit is constituted by a undecatungstic an ion derived from the Keggin structure, capped by a mu-oxoditungstic gr oup, W2O11. The BO4 tetrahedron is significantly distorted, one of the B-O bonds being longer (1.58 Angstrom) than the three others (1.46 An gstrom). The conversions between the three species [BW11O39H](8-), [BW 13O46H3](8-) and [B3W39O132](21-) are rapid and reversible. On the con trary, the irreversible formation of the Keggin heteropolyanion, alpha -[BW12O40](5-), is observed by heating of the solution of [BW13O46H3]( 8-) at PH 1-5.