Four organic–inorganic compounds based on polyoxometalates: crystal structures and catalytic epoxidation of styrene

Four compounds based on polyoxometalates, [Cu(4-bpo)(H2O)][Cu2(μ2-Cl)(4-bpo)2(H2O)][SiW12O40][N(CH3)4]2·H2O (1), [Cu(4-bpo)]4[P2W18O62][N(CH3)4]2·6H2O (2), [Cu2(μ2-OH)(4-bpo)2(Hina)(H2O)2]2[P2W18O62]·4H2O (3), and [Cu2(Hina)4(H2O)2][H2P2W18O62](Hina)·11H2O (4) (4-bpo=2,5-bis(4-pyridyl)-1,3,4-oxadiazole, ina=isonicotinic acid), have been hydrothermally synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. The 3-D framework of 1 is composed by Keggin-type polyoxoanions {SiW12} and two types of infinite chains, {Cu(4-bpo)(H2O)}n and {Cu2(μ2-Cl)(4-bpo)2(H2O)}n, through hydrogen bonds. Compound 2 has a 3-D rigid framework which is fabricated by Wells–Dawson type polyoxoanions {P2W18} and Cu-(4-bpo) chains through covalent bonds. Compound 3 contains an infinite {Cu2(μ2-OH)(4-bpo)2(Hina)(H2O)2}n double-chain and {P2W18} polyoxoanions immobilized in the voids between the chains. Compound 4 exhibits a 3-D supramolecular network directed by hydrogen bonds between {P2W18} pol...