Soluble Heteropolyniobates from the Bottom of Group IA

Abstract

Surprising solubility: While it is already well known that [Nb(6)O(19)](8-) salts exhibit an unusual solubility trend, that is, Cs>Rb>K>Na>Li, the heteropolyniobates of Cs and Rb had not yet been crystallized. These very soluble entities have now been obtained from solution by a simple and universal process. New polyoxoniobate geometries are thus unveiled, and the [SiNb(12)O(40)](16-) Keggin ion is characterized in solution for the first time.

Two Members of the {X4Nb16O56} Family (X = Ge, Si) Based on [(GeOH)2Ge2Nb16H2O54]12– and [K(GeOH)2Ge2Nb16H3O54]10–

“…Two trimetal clusters are the bow and stern, and two pentametal clusters form the bottom and hull of the boat ( Figure S1 in the Supporting Information). Each niobium atom has a distorted {NbO 6 (6) Å. Furthermore, bond valence sums (BVS) for niobium, germanium, and oxygen atoms were calculated by using the parameters given by Brown, [21] which showed that all the Nb and Ge atoms remain in their highest oxidation states, and could also mean that the Nb species have low activity.…”

“…However, PON chemistry studies have focused on isopolyniobate chemistry, which is dominated by the Lindquisttype [Nb 6 O 19 ] 8-anions. [2,3] To date, heteropolyanion chemistry has been dominated by heteropolymolybdates, -tungstates, and -vanadates, which are usually prepared by precipitation from aqueous, acidified solutions at ambient temperature and pressure.…”

“…They are chiefly impeded by a lack of soluble precursors, the inertness of Nb species, the narrow window of the working pH range, and limited chemistry with most addenda metals. [5][6][7] Even so, several groups have been quite active in this area. The synthesis and structural characterization of a heteropolyanion-type compound Na 14 10-building blocks, respectively.…”

“…Subsequently, the Nyman and Cronin groups have reported many heteropolyoxoniobate compounds, such as K 12 2 ]}·17H 2 O (en = ethylenediamine). [6,[9][10][11][12][13][14][15][16][17] Our group has also recently made a deeper study on the reactivity of polyoxoniobates in acidic solutions and obtained some mixed-addendum heteropolyniobates. [18] Furthermore, Ge IV -containing polyoxometalates have been known for several decades, and most of the published work was based on the Keggin-type germanotungstates [GeW 12 O 40 ] 4-and its lacunary derivatives.…”

PolyoxometalatesUpdate based on the original article by Michael T. Pope,Encyclopedia of Inorganic Chemistry© 2005, John Wiley & Sons, Ltd.

“…100 Mo or W atoms as individual clusters of three to eight metal centers. 3,4 Until comparatively recently, POMs were restricted to (and numerically dominated by) the elements of groups 5 and 6 usually in their highest oxidation states (d 0 ), but several examples based on d 8 and actinyl metal centers have now been reported, and this new area is currently under active investigation. As the chemistry and structures of the latter bear little relationship with those of the former, it seems appropriate to discuss them separately.…”