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Dititanium‐Containing 19‐Tungstodiarsenate(III) [Ti 2 (OH) 2 As 2 W 19 O 67 (H 2 O)] 8− : Synthesis, Structure, Electrochemistry, and Oxidation Catalysis
Author(s) -
Hussain Firasat,
Bassil Bassem S.,
Kortz Ulrich,
Kholdeeva Oxana A.,
Timofeeva Maria N.,
de Oliveira Pedro,
Keita Bineta,
Nadjo Louis
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700043
Subject(s) - monoclinic crystal system , acetonitrile , octahedron , chemistry , aqueous solution , crystal structure , crystallography , electrochemistry , cyclic voltammetry , nuclear chemistry , stereochemistry , electrode , chromatography
The dititanium‐containing 19‐tungstodiarsenate( III) [Ti 2 (OH) 2 As 2 W 19 O 67 (H 2 O)] 8− ( 1 ) has been synthesized and characterized by IR, TGA, elemental analysis, electrochemistry, and catalytic studies. Single‐crystal X‐ray analysis was carried out on Cs 8 [Ti 2 (OH) 2 As 2 W 19 O 67 (H 2 O)] ⋅ 2 CsCl ⋅ 12 H 2 O (Cs‐ 1 ), which crystallizes in the monoclinic system, space group P 2 1 / m , with a =12.7764(19), b =19.425(3), c =18.149(3) Å, β =110.234(3)°, and Z =2. Polyanion 1 comprises two ( B‐ α ‐ As III W 9 O 33 ) Keggin moieties linked through an octahedral {WO 5 (H 2 O)} fragment and two unprecedented square‐pyramidal {TiO 4 (OH)} groups, leading to a sandwich‐type structure with nominal C 2 v symmetry. Synthesis of 1 was accomplished by reaction of TiOSO 4 and K 14 [As 2 W 19 O 67 (H 2 O)] in a 2:1 molar ratio in aqueous, acidic medium (pH 2). Polyanion 1 could also be isolated as a tetra‐ n ‐butyl ammonium (TBA) salt, {( n ‐C 4 H 9 ) 4 N} 5 H 3 [Ti 2 (OH) 2 As 2 W 19 O 67 (H 2 O)] (TBA‐ 1 ). TBA‐ 1 was studied by cyclic voltammetry in acetonitrile (MeCN) solutions containing 0.1 M LiClO 4 and compared with the results obtained with Cs‐ 1 in aqueous media. In MeCN, the Ti IV and W VI waves could not be separated distinctly. An important adsorption phenomenon on the glassy carbon working electrode was encountered both in cyclic voltammetry and in controlled potential electrolysis and was confirmed by Electrochemical Quartz Crystal Microbalance (EQCM) studies on a carbon film. TBA‐ 1 , dissolved in MeCN, reacts with H 2 O 2 to give peroxo complexes stable enough for characterization by UV‐visible spectroscopy, cyclic voltammetry, and EQCM. TBA‐ 1 shows high catalytic activity (TOF=11.3 h −1 ) in cyclohexene oxidation with aqueous H 2 O 2 producing products typical of a heterolytic oxidation mechanism. The stability of TBA‐ 1 under turnover conditions was confirmed by using IR, UV‐visible spectroscopy as well as cyclic voltammetry.