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

The treatment of the dimeric paddle-wheel (PW) compound Mo(2)(NCCH(3))(10)]BF(4)](4)1 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 (Mo(2))(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 (CH(3)CN)(8)Mo(2)(OOC-COO)Mo(2)(NCCH(3))(8)]BF(4)](6)2 is formed selectively, whereas the use of 2,3,5,6-tetrafluoroterephthalic acid affords the square-shaped complex (CH(3)CN)(6)Mo(2)(OOC-C(6)F(4)-COO)](4)BF(4)](8)3. Bent linkers with a bridging angle of 109° and 120°, respectively, lead to the formation of the molecular loop (CH(3)CN)(6)Mo(2)(OOC-C(4)H(6)-COO)](2)BF(4)](4)4 and the bowl-shaped molecular triangle (CH(3)CN)(6)Mo(2)(m-bdc-OH)](3)BF(4)](6)5. All complexes are characterised by X-ray single crystal diffraction, NMR ((1)H, (11)B, (13)C and (19)F) and UV-Vis spectroscopy.