Giant Polyniobate Clusters Based on [Nb₇O₂₂]⁹⁻ Units Derived from a Nb₆O₁₉ Precursor

Abstract

Rational self-assembly of hexaniobate Lindqvist-type precursor [HNb6O19]7- with soluble Cu2+ salts utilizing different strategies produces a series of giant polyniobate clusters, namely, (H2en)1.25[Cu(en)2(H2O)]2Cl4[Nb24O72H21.5]7 H2O (1; en: ethylenediamine), [Cu(en)2]3[Cu(en)2(H2O)]9[{H2Nb6O19} subset{[({KNb24O72H10.25}{Cu(en)2})2{Cu3(en)3(H2O)3}{Na1.5Cu1.5(H2O)8}{Cu(en)2}4]6}]144 H2O (2), K12Na4[H23NaO8Cu24(Nb7O22)8]106 H2O (3), and K16Na12[H9Cu25.5O8(Nb7O22)8] 73.5 H2O (4). Their structures were determined and further characterized by single-crystal X-ray diffraction analysis, IR and Raman spectroscopy, thermogravimetric analysis (TGA), and elemental analysis. Structural analyses reveal that compound 2 comprises a giant capsule anion based on a wheel-shaped cluster encapsulating a Lindqvist diprotonated cluster [H2Nb6O19]6- unit, and forms a honeycomb-like structure with the inclusion of Lindqvist-type anions [H2Nb6O19]6- in the holes, whereas 3 and 4 represent an unprecedented giant cube-shaped framework. All the compounds are built from [Nb7O22]9- fundamental building blocks. Solution Raman spectroscopy studies of 2 and 3 reveal that the solid-state structures of these polyniobate cluster anions disassemble and exist in the form of the [Nb6O19]8- unit in solution. Magnetic susceptibility measurement of 3 shows antiferromagnetic coupling interactions between CuII ions with the spin-canting phenomenon.

Building Niobate Nanoparticles with Hexaniobate Lindqvist Ions

“…In previous reports in the literature, [30,[36][37][38][39][40] a simple method was reported to prepare hexaniobate ions in aqueous solution. Briefly, it was to dissolve amorphous Nb 2 O 5 ·xH 2 O in a strongly basic aqueous solution of inorganic alkali hydroxides (e.g.…”

“…8-, the most dominant and smallest of its kind, [30] has been well studied and used as the standard architecture for heteropolyniobates. [30,[36][37][38][39][40] 8-. [41,42] In this article, we present a general method to build niobate NPs by using hexaniobate ions as a niobium source.…”

Polyoxometallate als Bausteine für funktionelle Nanosysteme

“…[30] der auf zwei grundsätzlichen Strukturmotiven beruht, die als Baueinheiten für größere Cluster und ausgedehnte Strukturen dienen können: kondensierte {Nb 6 }-Oktaeder und ein offener {Nb 6 }-Ring. [31] Kürzlich haben wir die Polyoxoniobate [HNb 27 . [33] Dieser "Über-Lindqvist"-Cluster enthält 6 Nb-Zentren an den Spitzen eines Oktaeders und 12 Ti-Atome an den Kantenmitten.…”

A novel Lindqvist type polyoxoniobate coordinated to four copper complex moieties: {Nb6O19[Cu(2,2′-bipy)]2[Cu(2,2′-bipy)2]2}·19H2O

“…Recently, using [Nb 6 O 19 ] 8À as a precursor, Nyman and co-workers reported a new isopolyniobate cluster {Nb 24 O 72 H 9 } 15À [18] and five complexes based on the linkage of [Nb 6 O 19 ] clusters and [CuL x ] (L = ethylenediamine (en), NH 3 , H 2 O) [19]. Our research group had also synthesized giant polyniobate clusters based on [Nb 7 O 22 ] 9À units derived from Nb 6 O 19 precursor [20]. All these work use basic ligands (en, NH 3 ) coordinating to transition metals and then react with hexaniobate at basic conditions.…”

“…Flynn 3 } n ] (8Àn)À (M = Re, Mn), which contain two M(CO) 3 groups attached to the surface bridging oxygen atoms [11]. Attempts to introduce more than two M(CO) 3 [20]. All these work use basic ligands (en, NH 3 ) coordinating to transition metals and then react with hexaniobate at basic conditions.…”