Aluminum‐ and Gallium‐Containing Open‐Dawson Polyoxometalates

Abstract

Al-and Ga-containing open-Dawson polyoxometalates (POMs), K 10 [{Al 4 (μ-OH) 6 }{α,α-Si 2 W 18 O 66 }]·28.5H 2 O (Al 4 -open) and K 10 [{Ga 4 (μ-OH) 6 }(α,α-Si 2 W 18 O 66 )]·25H 2 O (Ga 4 -open) were synthesized by the reaction of trilacunary Keggin POM, [A-α-SiW 9 O 34 ] 10-, with Al(NO 3 ) 3 ·9H 2 O or Ga(NO 3 ) 3 ·nH 2 O, and unequivocally characterized by single-crystal X-ray analysis, 29 Si and 183 W NMR, and FT-IR spectroscopy as well as elemental analysis and TG/ DTA. Single-crystal X-ray analysis revealed that the {M 4 (μ-OH) 6 } 6+ (M = Al, Ga) clusters were included in an open pocket of the open-Recently, the open-Dawson POMs have been reported as an emerging class of POMs. [2] The conventional Dawson structural POMs are regarded as an assembly of two trilacunary Keggin POMs via six W-O-W bonds. In 2014, Mizuno et al. reported that the conventional Dawson POM with highly charged guest SiO 4 4-, TBA 8 [α-Si 2 W 18 O 62 ]·3H 2 O, was synthesized by dimerization of a trilacunary Keggin POM, [SiW 9 O 34 ] 10-, in an organic solvent. [3a] However, in aqueous media, the electrostatic repulsion between the halves, induced by the highly charged guest XO 4 4-(X = Si, Ge), is so strong that it inhibits the assembly of the usual Dawson structure. [3b] Therefore, the two trilacunary Keggin units with XO 4 4-(X = Si, Ge) are linked by only two W-O-W bonds, forming open-Dawson structural POMs. The open pocket of the open-Dawson POMs can accommodate multiple metals (1 to 6 metals), and several compounds have been reported so far that contain metal ions in the open pocket, e.g., V 5+ , [2f]542 crystallization water molecules were also observed in the crystal structures of Al 4 -and Ga 4 -open, forming a 3D network structure in the crystal ( Figure 5).

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

“…Bond valence sum (BVS) [44] calculations suggest that the corner-and edge-sharing oxygen atoms that are linked to the In atoms (corner-sharing: O135, O136, O139, O140, O141, O142, O143, O144, O145, O146, O147, O148, and O149; edge-sharing: O133, O134, O137, and O138) are protonated, i.e., they are ascribed to the hydroxide groups. On the other hand, the terminal oxygen atoms on the indium atoms (O150, O151, O152, O153, O154, O155, O156, and O157) are ascribed to the water groups (Table S1) and Ga4-open (56.110°) [28]. The difference between the bite angles of Al4-, Ga4-, and In10-open is caused by the difference in the ionic radii of the Al (0.53 Å), Ga (0.76 Å), and In (0.94 Å) ions [45,46].…”

“…Recently, open-Wells-Dawson POMs have been reported as an emerging class of POMs [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. These compounds are a dimerized species of the trilacunary Keggin POMs, [XW 9 O 34 ] 10´( X = Si, Ge).…”

“…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.…”

β,β-Isomer of Open-Wells–Dawson Polyoxometalate Containing a Tetra-Iron(III) Hydroxide Cluster: [{Fe4(H2O)(OH)5}(β,β-Si2W18O66)]9−

“…Recently, the open-Wells-Dawson POMs have been an emerging class of POMs [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] [29]. However, in aqueous media, the electrostatic repulsion induced by the highly charged guest XO 4 4´( X = Si, Ge) inhibits the assembly of the standard Wells-Dawson structure [30].…”

“…However, in aqueous media, the electrostatic repulsion induced by the highly charged guest XO 4 4´( X = Si, Ge) inhibits the assembly of the standard Wells-Dawson structure [30]. Therefore, the two trilacunary Keggin units with XO 4 4´( X = Si, Ge) [19], Mn 2+ [16,21], Fe 3+ [19], Co 2+ [14,16,20,21,25,27], Ni 2+ [16,21,24,27], Cu 2+ [15][16][17], Zn 2+ [23], Al 3+ [28], Ga 3+ [28], and lanthanoid (Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ ) [22,26]. The standard Wells-Dawson structural POM is one of the most deeply studied POMs.…”