posted on 2018-08-29, 14:51authored byAbdul Malik P. Peedikakkal, Hong Sheng Quah, Stacey Chia, Almaz S. Jalilov, Abdul Rajjak Shaikh, Hasan Ali Al-Mohsin, Khushboo Yadava, Wei Ji, Jagadese J. Vittal
Reaction
of bpy (bpy = 4,4′-bipyridine) with Pb(OAc)2·3H2O in DMF (DMF = dimethylformamide) afforded a metal–organic
framework (MOF), [Pb2(μ-bpy)(μ-O2CCH3)2(μ-O2CCH3)2]·H2O (1). Reaction of bpy with Pb(O2CCF3)2 in a methanol and chloroform mixture furnished another MOF,
[Pb(μ-bpy)(μ-O2CCF3)2]·1/2CHCl3 (2). However, the reaction of bpy with Pb(OAc)2·3H2O in the presence of trifluoroacetic acid in
a similar reaction condition yielded a hydrogen-bonded zwitter-ionic
complex of Pb(II), [Pb(bpy-H)2(O2CCF3)4] (3). All compounds
have been characterized by single crystal X-ray crystallography, FT-IR,
and 1H NMR spectroscopies. Compound 1 forms
four heptacoordinated Pb(II) joined by (OCCH3)-O–
linkages, resulting in a 3D noninterpenetrated MOF net with a four-connected
uninodal sra (SrAl2) topology. However, in 2, tetra-connected Pb4(O2CCF3)8 cluster units are linked further through eight
bpy ligands to furnish a doubly interpenetrated MOF with a new topology
but having the very similar connectivity of 1, whereas 3 forms a zigzag hydrogen-bonded chain structure. The variation
of carboxylate anions, pH of the reaction medium, and the ratio of
the reactants profoundly affected the final topological structure
of the compounds synthesized. The solid-state photoluminescence of 1–3 was investigated at room temperature.
Interestingly 1, 2, and 3 achieved
close to white light emission when excited at 329, 376, and 330 nm,
respectively. The systematic understanding of the photophysical properties
of analogous Pb-based compounds may open new perspectives for developing
single-phase white-light-emitting materials using Pb(II) based MOFs.