Ancillary ligand-assisted structural diversity of six new MOFs with 5-(4-carboxybenzoylamino)-isophthalic acid: syntheses, crystal structures and photoluminescence properties

Abstract

Solvothermal reactions of a tricarboxylate ligand 5-(4-carboxybenzoylamino)-isophthalic acid (H3L), dipyridyl linkers (bpe, bpa and bpy) and divalent metal ions (Co2+, Cd2+, Zn2+ and Ni2+) provided a highly efficient approach to the syntheses of multi-dimensional framework materials containing interesting structural motifs: [Co3L2(bpe)4]·2DMF·2H2O (1), [Cd3L2(bpe)4]·3H2O (2), [Zn2L(OH)(bpe)]·5.5H2O (3), [Co7L4(bpa)2(OH)2(H2O)4]·4H2O (4), Ni(HL)(bpa)(H2O) (5) and [Zn2(HL)2(bpy)2(H2O)2]·(bpy)·6H2O (6) (bpe = 1,2-bis(4-pyridyl)ethene, bpa = 1,2-bis(4-pyridyl)diazene, bpy = 4,4′-bipyridine). Solids 1 and 2 are isostructural and each features a three-dimensional (3D) pillar-layer architecture generated from bpe-pillared M-L3− layers. Complex 3 has a 3D structure in which the secondary building unit (SBU) is a rare example of a tetranuclear Zn4(μ3-OH)2(COO)6(bpe)4 unit, whereas 4 exhibits an interesting sandwich-shaped architecture with a trimeric unit [Co3(COO)4(OH)(N2)] serving as the SBU. Complex 5 provides an unusual example of a (4,4) grid layer structure bearing free carboxylic acid (–COOH) units. The layered structure of 6 is generated from hydrogen bonded [Zn(HL)(bpy)(H2O)] chains, with free bpy and guest water molecules accommodated inside. Furthermore, the thermal behavior, powder X-ray diffraction (PXRD) and solid state photoluminescence properties correlated with the corresponding structural features were investigated.