Syntheses, structures and luminescence properties of novel metal-organic frameworks based on zinc(II), cadmium(II) or lead(II) and a 2,2′-dimethoxy-functionalised biphenyl linker

Three metal-organic frameworks (MOFs) based on zinc(II) (1), cadmium(II) (2) or lead(II) (3) and the functionalised biphenyl linker biphenyl-2,2'-dimethoxy-4,4'-dicarboxylate, [4,4'-(CO2)(2)-2,2'-(OMe)(2)-1,1'-(C6H3)(2)] (L), were synthesised. Compounds 1 and 3 exhibit different three-dimensional networks with the Zn4O(O2C)(6)(H2O) unit as the secondary building unit (SBU) in the Zn-based MOF [{(Zn4O)(L)(3)(H2O)}center dot 4.5DMF](n) (1) and Pb6O2(O2C)(4) clusters as SBU in the Pb-based MOF [{(Pb6O2)L-4}center dot 2EtOH](n) (3), as shown by X-ray analysis. The Cd-based MOF [{(Cd3L4)(2)(CdL2)}center dot 8DMF center dot 8Me(2)NH(2)center dot 2Cl](n) (2) exhibits two interpenetrated three-dimensional networks formed from two different types of secondary building units, Cd-3(mu-O2C)(6)(O2C)(2) and Cd(O2C)(4). Compounds 1-3 are thermally stable up to 420, 360 and 380 degrees C, respectively (according to DTA-TG). All compounds show bluish emissions visible with the naked eye, which could be assigned to S-1,S-2 -> S-0 transitions of the aromatic units by comparison with the luminescence properties of the free ligand.