Self-assembly of tetrabromoterephthalic acid with different metal system: diversity in dimensionalities, structures and gas adsorption

Abstract

A new series of coordination compounds of different dimensionalities, {Cd₂(TBTH)₂(TBT)(DMF)₆} (1), {Cu(TBT)(DMF)₂}_n (2), {Ni(TBT)(DMF)₂(EtOH)₂}_n (3) and {Mn(TBT)(DMF)}_n (4) have been synthesized under similar reaction conditions and stoichiometry using tetrabromoterephthalic acid (TBTH₂) as a building block. Single crystal X-ray diffraction study reveals 1 is a dimeric discrete complex whereas 2 and 3 are found to be 1D coordination polymers and all the three compounds extend to three dimensions by non-covalent (H-bonding and O⋯Br) interactions. Compound 4 has a 3D framework structure where {Mn(CO₂)}_n chains are cross-linked by TBT linkers and DMF molecule also acts as a bidentate bridging ligand. The difference in dimensionalities can be correlated to the metal ions (Cd^II, Cu^II, Ni^II and Mn^II) having different ionic radius. Compound 4 does not contain any guest solvent molecule but removal of bridging DMF molecules creates a 1D channel with dimension of 2.1 × 4.2 Å2. Adsorption studies reveal that the desolvated compound 4 (4′) with unsaturated MnII sites can uptake an appreciable amount of CO₂ at 195 K (15 wt.%), and H₂ at 77 K (∼0.4 wt.%) although surface area is not significant.