A Soluble Phosphorus‐Centered Keggin Polyoxoniobate with Bicapping Vanadyl Groups

Abstract

A water-soluble tetramethylammonium (TMA) salt of a novel Keggin-type polyoxoniobate has been isolated as TMA9[PV2Nb12O42]·19H2O (1). This species contains a central phosphorus site and two capping vanadyl sites. Previously only a single example of a phosphorus-containing polyoxoniobate, [(PO2)3PNb9O34](15-), was known, which is a lacunary Keggin ion decorated with three PO2 units. However, that cluster was isolated as an insoluble structure consisting of chains linked by sodium counterions. In contrast, the [PV2Nb12O42](9-) cluster in 1 is stable over a wide pH range, as evident by (31)P and (51)V NMR, UV/Vis spectroscopy, and ESI-MS spectrometry. The ease of substitution of phosphate into the central tetrahedral position suggests that other oxoanions can be similarly substituted, promising a richer set of structures in this class.

Unprecedented High‐Nuclear Transition‐Metal‐Cluster‐Substituted Heteropolyoxoniobates: Synthesis by {V8} Ring Insertion into the POM Matrix and Antitumor Activities

“…The terminal M=O t (M = V, Nb) vibrations appear at ṽ = 953/905, and 865 cm À1 for 1, 948 and 863 cm À1 for 2, 951 and 876 cm À1 for 3, and 951 and 865 cm À1 for 4, respectively. [6][7][8][9][10][11][12]18] The characteristic peaks at ṽ = 667 and 492 cm À1 (1), 680 and 502 cm À1 (2), 696 and 521 cm À1 (3), and 686 and 470 cm À1 (4) can be attributed to the bridging M-O b -M vibrations, respectively. [6][7][8][9][10][11][12]18] Bands at ṽ = 1030 cm À1 for 1, 1033 cm À1 for 2, 1043 cm À1 for 3, and 1047 cm À1 for 4 can be assigned to the X-O c vibrations, respectively.…”

“…[6][7][8][9][10][11][12]18] The characteristic peaks at ṽ = 667 and 492 cm À1 (1), 680 and 502 cm À1 (2), 696 and 521 cm À1 (3), and 686 and 470 cm À1 (4) can be attributed to the bridging M-O b -M vibrations, respectively. [6][7][8][9][10][11][12]18] Bands at ṽ = 1030 cm À1 for 1, 1033 cm À1 for 2, 1043 cm À1 for 3, and 1047 cm À1 for 4 can be assigned to the X-O c vibrations, respectively. [11,21] The characteristic absorption bands of the organic groups appear at ṽ = 1107-1585 cm À1 , 1281-1586 cm À1 , 1101-1584 cm À1 , and 1104-1589 cm À1 for 1-4, respectively.…”

“…[5] For-tunately, increasing attention has been paid to the design and synthesis of PONs following the pioneering work of Nyman and others. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Consequently, isopolyoxoniobate (IPN) chemistry has progressed greatly, and members of a series of IPNs, such as {Nb 6 }, {Nb 10 }, {Nb 20 }, {Nb 24 }, {Nb 27 }, {Nb 31 }, and {Nb 32 } IPNs, have been successfully synthesized. [6,7] On the other hand, since the first HPN, [Ti 2 O 2 ][SiNb 12 O 40 ] 12À , was reported by Nyman et al,[XNb 12 O 40 ] (X= Si, Ge) and their derivatives, have been reported.…”

“…[10] Very recently, the central tetrahedral position of HPNs has been successfully substituted by P V and V V heteroatoms, resulting in the P V -and V V -centered Keggin-type HPNs [PNb 12 V 2 O 42 ] 9À and [V 3 Nb 12 O 42 ] nÀ . [11,12] As is well known, the introduction of transition metal (TM) clusters into POMs or POM-based inorganic-organic hybrid materials provides a means of functionalizing POM matrices. [13,14] However, the exploration of TM-substituted PONs is hampered by limitations on the co-existence of TM cations and PON precursors under alkaline conditions, and the difficulty in activating the surface oxygen atoms of PONs.…”

“…In this field, the fact that TM cations can be introduced into the HPN system through surface decoration or capping (mostly based on V and Cu) seems to hold great promise. [11,12] Also, lacunary HPNs, such as [X 4 Nb 16 O 56 ] 14À (X = Si, Ge) [8a, 20] and [P 4 Nb 9 O 40 ] 15À , [21] have been reported in the literature, which might be potential inorganic polydentate ligands for the construction of high-nuclear TM clusters. These examples indicate that exploration of high-nuclear TM-clustersubstituted HPNs should be a promising research field.…”