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

Abstract

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)}·4.5DMF]n (1) and Pb6O2(O2C)4 clusters as SBU in the Pb-based MOF [{(Pb6O2)L4}·2EtOH]n (3), as shown by X-ray analysis. The Cd-based MOF [{(Cd3L4)2(CdL2)}·8DMF·8Me2NH2·2Cl]n (2) exhibits two interpenetrated three-dimensional networks formed from two different types of secondary building units, Cd3(μ-O2C)6(O2C)2 and Cd(O2C)4. Compounds 1–3 are thermally stable up to 420, 360 and 380 °C, respectively (according to DTA–TG). All compounds show bluish emissions visible with the naked eye, which could be assigned to S1,2 → S0 transitions of the aromatic units by comparison with the luminescence properties of the free ligand.