A Noble‐Metalate Bowl: The Polyoxo‐6‐vanado(V)‐7‐palladate(II) [Pd₇V₆O₂₄(OH)₂]⁶⁻

Abstract

Polyoxometalates (POMs) are discrete nanosized metal oxoanions with an enormous structural diversity and a multitude of interesting properties that lead to potential and real applications in catalysis, analytical chemistry, magnetism, nanotechnology, and medicine.[1]Recently we reported a novel subclass in POM chemistry: polyanions composed of square-planar d 8 noble-metal ions.[2]In all cases the synthetic strategy was based on the con , to open basket-, shell-, ring-, and cage-like host systems suitable for the uptake of neutral, cationic, and anionic guests. The structural flexibility of polyoxovanadates is based on the ability of vanadium to adopt different coordination geometries from tetrahedral to square-pyramidal and octahedral, and to form POMs in both + 5 and + 4 oxidation states, thus leading to mixed-valent or even fully reduced polyanions that can behave as nanoscale magnets.[1a,b,d,g,j, 4] Moreover, it is well known that vanadium can easily replace one or more addenda atoms in polyoxomolybdates and -tungstates.[ 6À (Pd 7 V 6 ), which was prepared by heating Pd(OAc) 2 and either sodium meta-or orthovanadate in a potassium acetate solution (2 m, pH 7.5), and which was crystallized as the hydrated mixed potassium and sodium salt K 5 Na[Pd 7 V 6 O 24 (OH) 2 ]·7 H 2 O (1). At least three main competing processes occur in the reaction mixture: 1) selfassembly of Pd 7 V 6 , 2) formation of potassium decavanadate (which is always present as a side product), and 3) aggregation of Pd II aqua and hydroxo complexes with formation of insoluble Pd(OH) 2 . To minimize the third process we used an excess of vanadate ions in the synthesis of Pd 7 V 6 , and indeed this resulted in a higher yield of 1. The isolation of pure crystalline 1 can be achieved by fractional crystallization; here the evaporation rate of the solvent is rather important (see the Experimental Section for details). Compound 1 is soluble in water and is stable in the solid state and after redissolution when exposed to air and light.The IR spectrum of 1 shows strong bands at 564 and 456 cm À1 that correspond to the {PdO 4 } groups. The sharp band at 918 cm À1 is due to the stretching vibrations of terminal V=O groups, while the peaks at 788, 746, and 636 cm À1 are attributed to symmetric and asymmetric V À O À V and Pd À O À V vibrations. [6] Pd 7 V 6 is bowl-shaped with idealized C 2v symmetry, and is composed of two identical {Pd 3 V 3 O 11 } units (Figure 1, upper left), linked through four m 2 -oxo bridges and one additional Pd II center that forms the bottom of the "bowl".[7] The[*] Dr.

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

“…The central metal guest in such structures is octacoordinated with perfect or slightly distorted cubic symmetry in the case of all 3d metal ions and lanthanides, including Pd II (for LX = As V Ph (Figure 16b). 80 Very recently, an isostructural selenium(IV) derivative has been reported and studied in solution as well as the gas phase. 81 No Pt II analogs have yet been reported, although the anion [Pt 12 O 8 (SO 4 ) 12 ] 4− (with six {Pt 2 } 6+ centers, Figure 16c) has been isolated from a sealed tube reaction of Pt(NO 3 ) 2 with concentrated sulfuric acid at 350 • C. 82…”

Discrete Silver(I)‐Palladium(II)‐Oxo Nanoclusters, {Ag4Pd13} and {Ag5Pd15}, and the Role of Metal–Metal Bonding Induced by Cation Confinement

“…Polyoxopalladates(II), in particular,r epresent by far the largest subclass of polyoxo-noble-metalates.G enerally,t heir structural types can be classified into two categories,namely, the nanocube-shaped [MPd 12 O 32 L 8 ] nÀ , [6b,7] and the nanostarshaped [MPd 15 O 40 L 10 ] nÀ [8] (M = central Pd II or guest metal ion, L = heterogroup), as well as af ew derivatives. [9] Recent advances elucidated that the respective size of the guest M allows the detailed condensation arrangement of the peripheral Pd II -oxo shell to be tuned. [10] Nevertheless,asystematic study on the structure-directing effects induced by other noble metal ions besides Pd II has thus far been rather unexplored, although we have demonstrated that it is possible to merge Pd II and Au III into one polyanion.…”

Erdalkalimetalle als Gastionen in der Polyoxopalladatchemie: vom Nanowürfel über eine offenschalige Struktur zum Nanostern

“…[5] Man kann davon ausgehen, dass die würfelfçrmige Pd 12 -Form und die sternfçrmige Pd 15 -Form aufgrund ihrer hohen Symmetrie (T d bzw. [5] Man kann davon ausgehen, dass die würfelfçrmige Pd 12 -Form und die sternfçrmige Pd 15 -Form aufgrund ihrer hohen Symmetrie (T d bzw.…”

“…[1,[3][4][5]8] Ein pH-Wert von 5.0-5.3 ist für die Synthese von Na-SrPd 12 besonders günstig, wohingegen eine Erhçhung des pH-Wertes die Bildung des Pd 13 -Nebenprodukts fçrdert. [1,[3][4][5]8] Ein pH-Wert von 5.0-5.3 ist für die Synthese von Na-SrPd 12 besonders günstig, wohingegen eine Erhçhung des pH-Wertes die Bildung des Pd 13 -Nebenprodukts fçrdert.…”

“…Die benachbarte Hüllkurve mit einem Zentrum bei m/z 1000.90 kann der Natrium-Form von SrPd 12 zugeschrieben werden ({Na(H 2 O)5 -SrPd 12 } 3À ). Es kçnnte jedoch auch sein, dass zwei flüchtige Acetatgruppen in der SrPd 12 -Struktur durch Wasser ersetzt wurden und somit zu diesem Signal beitragen.Um diese Theorie zu bestätigen und weitere Strukturinformationen über die synthetisierten Polyoxopalladate zu erhalten, wurde Elektrospray-Ionisations-Massenspektrometrie (ESI-MS) angewendet, welche es häufig ermçglicht, den Großteil der in wässriger Lçsung und in der Gasphase vorliegenden Strukturen zu charakterisieren.…”