Dicarboxylate-bridged (Mo2)n (n = 2, 3, 4) paddle-wheel complexes: potential intermediate building blocks for metal–organic frameworks

Abstract

The treatment of the dimeric paddle-wheel (PW) compound [Mo₂(NCCH₃)₁₀][BF₄]₄1 with oxalic acid (0.5 equiv.), 1,1-cyclobutanedicarboxylic acid (1 equiv.), 5-hydroxyisophthalic acid (1 equiv.) (m-bdc–OH) or 2,3,5,6-tetrafluoroterephthalic acid (0.5 or 1 equiv.) leads to the formation of macromolecular dicarboxylate-linked (Mo₂)_n entities (n = 2, 3, 4). The structure of the compounds depends on the length and geometry of the organic linkers. In the case of oxalic acid, the dimeric compound [(CH₃CN)₈Mo₂(OOC–COO)Mo₂(NCCH₃)₈][BF₄]₆2 is formed selectively, whereas the use of 2,3,5,6-tetrafluoroterephthalic acid affords the square-shaped complex [(CH₃CN)₆Mo₂(OOC–C₆F₄–COO)]₄[BF₄]₈3. Bent linkers with a bridging angle of 109° and 120°, respectively, lead to the formation of the molecular loop [(CH₃CN)₆Mo₂(OOC–C₄H₆–COO)]₂[BF₄]₄4 and the bowl-shaped molecular triangle [(CH₃CN)₆Mo₂(m-bdc–OH)]₃[BF₄]₆5. All complexes are characterised by X-ray single crystal diffraction, NMR (¹H, ¹¹B, ¹³C and ¹⁹F) and UV-Vis spectroscopy.