Construction and structural diversity of Cd-MOFs with pyrazole based flexible ligands and positional isomer of naphthalenedisulfonate

• Synthesis of novel cadmium-organic coordination polymer with conformationally flexible bispyrazole and flexible bent bispyrazole.
• Comparative study of versatile coordination behaviour of positional isomeric naphthalenedisulfonates to the metal center.
• Effect of versatile coordination behaviour of naphthalenedisulfonates on conformational change in H2BPz and H2MBPz has been studied.

In the present communication, we have reported the construction of a series of Cd(II)-MOFs using conformationally flexible ligand (CFL); 3,3′,5,5′-tetramethyl-4,4′-bipyrazolyl (H2BPz), flexible bent ligand (FBL); methylenebis-(3,5-dimethylpyrazole) (H2MBPz) and positional isomer of naphthalene disulfonic acid salt ligands (1,5-NDS, 2,6-NDS). By using these ligands, four new coordination polymers namely [Cd(H2MBPz)2∙ 1,5-NDSA]n (NDS-MOF-1), [Cd(H2BPz)∙ 1,5-NDSA]n (NDS-MOF-2), {[Cd(H2MBPz)2]2 +∙ 2,6-NDSA2 −}n (NDS-MOF-3) and {[Cd(H2BPz)2]2 +∙ 2,6-NDSA2 −}n (NDS-MOF-4) have been synthesized. The crystal structure analysis revealed that the employment of positional isomeric naphthalene disulfonic acid salts resulted in different architectures ranging from one dimensional chain to two dimensional grid network and further connected into a three dimensional supramolecular structure through intermolecular hydrogen bonds, π⋯π and C–H⋯π interactions. In addition, the photophysical properties and thermal stability studies for all the NDS-MOFs 1–4 were also investigated.

The MOFs 1–4, [Cd(MBPz)2∙ 1,5-NDSA]n (NDS-MOF-1), [Cd(BPz)∙ 1,5-NDSA]n (NDS-MOF-2), {[Cd(MBPz)2]2 +∙ 2,6-NDSA2 −}n (NDS-MOF-3) and {[Cd(BPz)2]2 +∙ 2,6-NDSA2 −}n (NDS-MOF-4) were synthesized from cadmium nitrate and respective mixed ligands system i.e. 1,5-NDS and 2,6-NDS system by means of layering techniques. Furthermore, photophysical properties and thermal stability of frameworks were also investigated. Comparative study of Cis-Trans conformation of H2BPz and H2MBPz ligand by changing the position of sulfonate from α to β position of naphthalenedisulfonate was scrutinized.Figure optionsDownload as PowerPoint slide