Effect of counteranions on the crystal structures of Zn II coordination polymers with 1,3-bis(1 H -imidazol-1-yl)benzene

Two new coordination compounds, catena-poly[[[diaquazinc(II)]-bis[μ-1,3-bis(1H-imidazol-1-yl)benzene]] bis(tetrafluoroborate)], {[Zn(C₁₂H₁₀N₄)₂(H₂O)₂](BF₄)₂}n, 1, and catena-poly[[[diaquazinc(II)]-bis[μ-1,3-bis(1H-imidazol-1-yl)benzene]] hexafluorotitanate], {[Zn(C₁₂H₁₀N₄)₂(H₂O)₂][TiF₆]}n, 2, have been synthesized and structurally characterized. Both compounds exhibit analogous cationic 1D coordination chains, {[Zn(L)₂(H₂O)₂]²⁺}n, where L is 1,3-bis(1H-imidazol-1-yl)benzene. However, the identity of the counteranion, i.e. BF₄⁻ in 1 and [TiF₆]²⁻ in 2, significantly influences the supramolecular architecture and porosity due to differences in size, geometry and charge. In 1, the small monovalent BF₄⁻ anion stabilizes an extended conformation of the ligand and occupies channels without causing disruption, facilitating the assembly of a nonporous supramolecular framework through hydrogen-bonding interactions. Conversely, the larger [TiF₆]²⁻ dianion in 2 induces a more compact conformation of the ligand, occupies potential pore spaces and promotes inter-chain hydrogen bonds, resulting in a dense layered structure. However, the face-to-face packing of these layers creates an open porous architecture. This study highlights the role of anions as templates in modulating hierarchical assembly, ligand conformation and the resultant porosity in coordination polymers.