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.