Hydrothermal Syntheses:  A Route to the Stepwise Condensation of Reduced Keggin Polyanions. From Reduced β-[H_mSiMo₁₂O₄₀]^n- Monomers to Bicapped Dimerized [Si₂Mo₂₈O₈₄(H₂O)₂]^6- Anions

Abstract

The five reduced polyoxomolybdate anions [HSiMo 12 O 40 ] 4-(HI β ), [H 2 SiMo 12 O 40 ] 4-(H 2 II β ), [H 5 SiMo 12 O 40 ] 3-(H 5 IV β ), [SiMo 14 O 44 ] 4-(SiMo 14 ), and [Si 2 Mo 28 O 84 (H 2 O) 2 ] 6-(Si 2 Mo 28 ) have been synthesized as tetramethylammonium salts, by hydrothermal reactions, and characterized by IR spectroscopy, redox titrations (HI β , H 2 II β ), and X-ray crystal structure analyses. Crystal data: (TMA) 4 HI β ‚1.5H 2 O, monoclinic space group P2 1 /n, a ) 12.2487-(3) Å, b ) 39.9307(11) Å, c ) 12.4761(3) Å, β ) 116.542(1)°; (TMA) 4 H 2 II β ‚2H 2 O, monoclinic space group P2 1 /n, a ) 12.7930(2) Å, b ) 21.6171(2) Å, c ) 19.7222(2) Å, β ) 96.017(1)°; (TMA) 3 H 5 IV β ‚2H 2 O, monoclinic space group P2 1 /n, a ) 12.7763(5) Å, b ) 20.2277(8) Å, c ) 20.9784(9) Å, β ) 98.037(1)°; (TMA) 4 SiMo 14 , monoclinic space group P2 1 /n, a ) 12.0502(4) Å, b ) 11.7500(4) Å, c ) 19.8001(5) Å, β ) 100.525(1)°; (TMA) 6 Si 2 Mo 28 ‚2H 2 O, monoclinic space group P2 1 /n, a ) 19.3591(2) Å, b ) 13.1119(2) Å, c ) 21.1265(2) Å, β ) 101.124(1)°. HI β , H 2 II β , and H 5 IV β are respectively one-, two-, and four-electron-reduced {SiMo 12 O 40 } anions with the β-Keggin type structure. SiMo 14 and Si 2 Mo 28 are two novel anions containing R-Keggin cores; in SiMo 14the Keggin core is capped by two {MoO 2 } units while in Si 2 Mo 28 two bicapped anions are linked through terminal oxo groups. A comparison of the molecular structures of the five anions shows the role of the protonation, the reduction, and the aggregation of capping {MoO 2 } units on the structural features of the Keggin core. The condensation process is discussed in terms of Lewis-type interactions between reduced, highly charged basic polyanions and reactive {MoO 2 } 2+ units.

Recent Advances in Synthesis, Characterization, Structure and Applications of Polyoxometalates

“…Large number of organic-inorganic hybrid materials based on oxometalates with 1D and 2D framework have been reported by Zubeita and co-worker [37]. [42][43][44][45][46][47][48]. Polyoxometalates compounds with divalent cation of 3d transition metal as capping atoms have been scarcely reported [49].…”

Hydrothermal Synthesis and Crystal Structure of an Unusual Compound: [Cu(en)2]4[SiMo8VV4O40(VIVO)2][MoO4]2·5H2O

“…It is noteworthy that weak coordination interactions exist between the Cu 2+ and the terminal oxygen atoms of polyoxoanions with the average distance of Cu-O 2.776 Å . Furthermore, there exist weak hydrogen bonds among the N(1)Á Á ÁO (8), N(1)Á Á ÁO (4), N(2)Á Á ÁO (8), and N(2)Á Á ÁO(4) with the distances of 2.991, 3.328, 2.893, and 3.312 Å , respectively. Owing to these weak coordinative interactions and hydrogen bonds, polyoxoanions and counter ions are linked together with regular space array (see Fig.…”

Bi-antimony capped Keggin polyoxometalate modified with Cu-ligand fragment

“…The introduction of the hydrothermal technique for the synthesis of POMbased compounds has been proved as a successful strategy and has also led to the appearance of various inorganic capped Keggin-type derivatives. Up to now, a number of Keggin clusters with the capping groups have been reported, such as bi-, tri-, tetra-and hexa-capped structures [5][6][7][8][9][10][11]. The capping groups in these derivatives are mainly restricted to high oxidation states metal (V) and divalent transition metals (Ni and Cu).…”