Preparation of monodispersed nanoparticles by electrostatic assembly of keggin-type polyoxometalates and 1,4,7-triazacyclononane-based transition-metal complexes

Sayaka Uchida, Shiro Hikichi, Takeo Akatsuka, Toshiyuki Tanaka, Ryosuke Kawamoto, Aides Lesbani, Yoshinao Nakagawa, Kazuhiro Uehara, Noritaka Mizuno

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29 Citations (Scopus)

Abstract

Complexation of Keggin-type polyoxometalates (POMs), [α-PW 12O40]3- (PW), [α-SiW12O 40]4- (SiW), and [γ-SiV2W 10O38(OH)2]4- (SiVWH) with cationic transition-metal complexes having a triazacyclononane ligand, [M(tacn) 2]n+ (M-tacn; M = CoIII and NiII; tacn = 1,4,7-triazacyclononane), yields fine particles of inorganic-organic composites. The strong electrostatic interaction between the highly negatively charged POMs and the +2- or +3-charged [M(tacn)2]n+ as well as the hydrophobicity of [M(tacn)2]n+ results in the formation of the water-insoluble binary composites. The crystal structure of the 1:1 (=the molar ratio of POM to M-tacn) composite [Co(tacn)2] [α-PW12O40]·2H2O (1·H 2O) shows the close packing of PW and Co-tacn in the crystal lattice. The guest sorption properties of the corresponding anhydrous compound 1 show that the amounts of hydrophobic molecules sorbed are comparable to that of water. The reaction of SiVWH with Co-tacn yields fine particles of [Co(tacn)2]2[γ-SiV2W10O 40]·6H2O (2· H2O), and the molar ratio of POM to M-tacn is 1:2. The reaction of SiW with +2-charged Ni-tacn yields fine particles of [Ni(tacn)2]2[α-SiW 12O40]·4H2O (3·H2O). The crystal structure of 3·H2O shows the honeycomb packing of SiW and Ni-tacn, and the ionic components are closely packed in the crystal lattice. The reaction of SiVWH with Ni-tacn yields fine particles of [Ni(tacn)2]2[γ-SiV2W10O 38(OH)2]· 3H2O (4·H 2O). The crystal structure of 4·H2O is analogous to that of 3·H2O. Compound 4·H2O can heterogeneously catalyze the epoxidation of olefins with H2O 2, maintaining the stereoselectivity of the tetra-n-butylammonium salt of SiVWH in the homogeneous reaction system. On the other hand, 2·H2O is inactive probably because the POM in 2·H 2O is deprotonated.

Original languageEnglish
Pages (from-to)4694-4701
Number of pages8
JournalChemistry of Materials
Volume19
Issue number19
DOIs
Publication statusPublished - 2007 Sep 18
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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