Structure and Properties of New Gallium‐containing Polyoxotungstates with Hexanuclear and Tetranuclear Cores

Abstract

A series of new gallium‐containing silicotungstates was obtained from the one step reaction of the lacunary Na10[α‐SiW9O34]·15H2O Keggin‐type building block (SiW9) with gallium nitrate in aqueous solution. The sandwich‐type polyoxotungstate [Ga6(H2O)x{α‐SiW9O34(OH)y}2]n– (1) crystallizes first as a mixture of two similar polyoxometalates (1a and 1b), while [Ga4(H2O)2{α‐SiW10O38}2]12– (2) is generated from the mother liquor in a second step. Both newly obtained polyoxometalates with tetra‐ and hexanuclear gallium cores were structurally characterized with a wide range of methods encompassing single crystal and powder X‐ray diffraction techniques, FT‐IR spectroscopy, and thermal analysis. The solution stability of both dimeric POMs K10[Ga6(H2O)3{α‐SiW9O35(OH)2}2]·35.5H2O (1a) and K12[Ga4(H2O)2{α‐SiW10O38}2]·30H2O (2) was investigated with 183W NMR and HR ESI mass spectrometry, and the electrochemical properties of both compounds were determined by cyclic voltammetry.

Synthesis, Structure, and Characterization of In10-Containing Open-Wells–Dawson Polyoxometalate

“…Synthetic and structural studies of group 13 ion-containing POMs provide informative and definitive molecular models of group 13 metal clusters in solution. However, among all the Al-, Ga-, and In-containing POMs, formed by the substitution of several tungsten ions in the parent POMs with trivalent group 13 ions [28,[33][34][35][36][37][38][39][40], few well-characterized In-containing POMs have been reported to date [41][42][43]. Thus, In-containing POMs are intriguing target compounds from both a synthetic and a structural point of view.…”

Aluminum‐ and Gallium‐Containing Open‐Dawson Polyoxometalates

“…Bond valence sum (BVS) calculations11 suggested that the oxygen atoms (O67, O68, O69, O70, O71, and O72) are protonated (the BVS value; O67, 1.111; O68, 1.116; O69, 1.111; O70, 0.995; O71, 1.024; O72, 1.083; Table S2, Supporting Information). In contrast, it should be noted that Patzke 's group reported that the corner‐ and edge‐sharing oxygen atoms connecting to neighboring gallium atoms were di‐protonated, i.e., [{Ga 4 (H 2 O) 6 }Si 2 W 18 O 66 ] n – 6e. Each Ga atom is bonded to three oxygen atoms of the lacunary site in the open‐Dawson polyanion, [α,α‐Si 2 W 18 O 66 ] 16– [Ga–O average 2.014 Å].…”

“…The reaction condition of Ga 4 ‐ open was similar to that of Al 4 ‐ open with the exception of the metal source, Ga(NO 3 ) 3 · n H 2 O instead of Al(NO 3 ) 3 · 9H 2 O, and the counter cations of the precursor of trilacunary Keggin POM, i.e., K + vs. Na + . Patzke's group has previously obtained Ga 4 ‐ open only as a by‐product of the trigallium(III)‐substituted dimer, [Ga 6 (H 2 O) x {α‐SiW 9 O 34 (OH) y } 2 ] n – ( Ga 6 ‐ dimer ) and the di‐gallium(III) substituted dimer, [Ga 4 (H 2 O) 2 {α‐SiW 10 O 38 } 2 ] 12– ( Ga 4 ‐ dimer ) 6e. By using their synthetic method, Ga 4 ‐ open was not isolated as main product.…”

“…Furthermore, the Al sites in Al‐containing POMs act as Lewis acid sites,5b,5e and Al‐containing POMs are expected to be used as the Lewis‐acid catalysis. Despite their importance, only a few Al‐ and Ga‐containing POMs, in which addenda tungsten ions are substituted by Al 3+ and Ga 3+ ions, have been fully structurally characterized 5,6e. The Al‐substituted POMs whose structures are determined by X‐ray crystallography include K 6 H 3 [ZnW 11 O 40 Al] · 9.5H 2 O,5a TBA 3 H[γ‐SiW 10 O 36 {Al(OH 2 )} 2 (μ‐OH) 2 ] · 4H 2 O, TBA 3 [(C 5 H 5 N)H][γ‐SiW 10 O 36 {Al(C 5 H 5 N)} 2 (μ‐OH) 2 ] · 2H 2 O (TBA = tetrabutylammonium),5b K 6 Na[(A‐PW 9 O 34 ) 2 {W(OH)(OH 2 )}{Al(OH)(OH 2 )}{Al(μ‐OH)(OH 2 ) 2 } 2 ] · 19H 2 O,5c TBA 9 [{γ‐H 2 SiW 10 O 36 Al 2 (μ‐OH) 2 (μ‐OH)} 3 ], TBA 6 Li 3 [{γ‐H 2 SiW 10 O 36 Al 2 (μ‐OH) 2 (μ‐OH)} 3 ] · 18H 2 O,5d Rb 2 Na 2 [Al 4 (H 2 O) 10 (β‐As III W 9 O 33 H) 2 ] · 20H 2 O, (NH 4 ) 2 Na 2 [Al 4 (H 2 O) 10 (β‐Sb III W 9 O 33 H) 2 ] · 20H 2 O,5e TBA 6 [α‐PW 11 Al(OH)O 39 ZrCp 2 ] 2 ,5f and TMA 14 Na 2 [B‐α‐H 3 P 2 W 15 O 59 {Al(OH)} 2 {Al(OH 2 )}] 2 · 39H 2 O (TMA = tetramethylammonium) 5g.…”

“…However, the structurally characterized Ga‐substituted POMs by X‐ray crystallography are still one of the least reported compounds. Recently, Patzke et al reported the synthesis of tri‐ and di‐Ga‐substituted Keggin POM dimers, i.e., [Ga 6 (H 2 O) x {α‐SiW 9 O 34 (OH) y } 2 ] n– ( Ga 6 ‐ dimer ) and [Ga 4 (H 2 O) 2 {α‐SiW 10 O 38 } 2 ] 12– ( Ga 4 ‐ dimer ) 6e. In this context, Al‐ and Ga‐substituted POMs remain challenging targets from the synthetic and structural point of view.…”