Four organic–inorganic compounds based on polyoxometalates: crystal structures and catalytic epoxidation of styrene
Abstract
<div><p>Four compounds based on polyoxometalates, [Cu(4-bpo)(H<sub>2</sub>O)][Cu<sub>2</sub>(<i>μ</i><sub>2</sub>-Cl)(4-bpo)<sub>2</sub>(H<sub>2</sub>O)][SiW<sub>12</sub>O<sub>40</sub>][N(CH<sub>3</sub>)<sub>4</sub>]<sub>2</sub>·H<sub>2</sub>O (<b>1</b>), [Cu(4-bpo)]<sub>4</sub>[P<sub>2</sub>W<sub>18</sub>O<sub>62</sub>][N(CH<sub>3</sub>)<sub>4</sub>]<sub>2</sub>·6H<sub>2</sub>O (<b>2</b>), [Cu<sub>2</sub>(<i>μ</i><sub>2</sub>-OH)(4-bpo)<sub>2</sub>(Hina)(H<sub>2</sub>O)<sub>2</sub>]<sub>2</sub>[P<sub>2</sub>W<sub>18</sub>O<sub>62</sub>]·4H<sub>2</sub>O (<b>3</b>), and [Cu<sub>2</sub>(Hina)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>][H<sub>2</sub>P<sub>2</sub>W<sub>18</sub>O<sub>62</sub>](Hina)·11H<sub>2</sub>O (<b>4</b>) (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 <b>1</b> is composed by Keggin-type polyoxoanions {SiW<sub>12</sub>} and two types of infinite chains, {Cu(4-bpo)(H<sub>2</sub>O)}<sub><i>n</i></sub> and {Cu<sub>2</sub>(<i>μ</i><sub>2</sub>-Cl)(4-bpo)<sub>2</sub>(H<sub>2</sub>O)}<sub><i>n</i></sub>, through hydrogen bonds. Compound <b>2</b> has a 3-D rigid framework which is fabricated by Wells–Dawson type polyoxoanions {P<sub>2</sub>W<sub>18</sub>} and Cu-(4-bpo) chains through covalent bonds. Compound <b>3</b> contains an infinite {Cu<sub>2</sub>(<i>μ</i><sub>2</sub>-OH)(4-bpo)<sub>2</sub>(Hina)(H<sub>2</sub>O)<sub>2</sub>}<sub><i>n</i></sub> double-chain and {P<sub>2</sub>W<sub>18</sub>} polyoxoanions immobilized in the voids between the chains. Compound <b>4</b> exhibits a 3-D supramolecular network directed by hydrogen bonds between {P<sub>2</sub>W<sub>18</sub>} polyoxoanions and the double paddle-wheel {Cu<sub>2</sub>(Hina)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>}. Compounds <b>1–4</b> were tested as heterogeneous catalysts for the epoxidation of styrene using <i>tert-</i>butyl hydroperoxide (TBHP) as oxidant. The compounds show catalytic activity with <b>2</b> giving the highest yield of styrene oxide.</p></divSimilar works
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