Host–guest key–lock hydrogen-bonding interactions: a rare case in the design of a V-shaped polycarboxylate Ni(ii)-based chiral coordination polymer

Abstract

A rare case in the design of a V-shaped polycarboxylate Ni(II)-based chiral coordination polymer from achiral ligands is described. Four metal–organic coordination networks, namely [Ni₂(hfdpa)(bpypip)₂(H₂O)₂](bpypip)·2.5H₂O (1), [Ni₃(Hodpa)₂(bpypip)₃(H₂O)₉] (2), [Ni₂(odpa)(bpypip)₂(H₂O)₂] (3), and [Cd₂(bptc)(bpypip)₂(H₂O)₂]·H₂O (4), where H₄hfdpa = 4,4′-(hexafluoroisopropylidene)diphthalic acid, H₄odpa = 4,4′-oxydiphthalic acid, H₄bptc = benzophenone-3,3′,4,4′-tetracarboxylic acid, and bpypip = N,N′-bis(pyrid-4-yl)piperazine, were prepared via a hydrothermal process. The structure of 1 exhibits a chiral three-dimensional porous framework, featuring left-handed Ni–O₂C 2₁-screw helical chains along the crystallographic b axis and rectangular-shaped tubular open channels occupied by the uncoordinated bpypip and water molecules. Compound 2 possesses a 2-fold 2D + 2D → 2D interwoven sheet structure that is arranged interdigitally along the crystallographic a axis, forming an extensive three-dimensional supramolecular network through hydrogen-bonding. The structure of 3 shows a complicated 1D + 1D → 3D polyrotaxane coordination polymer entanglement, which suits a four-connected {6⁴8²}-net resembling the topology of a cds-net. Compound 4 has a complicated 2D + 2D → 3D coordination framework, which is simplified into a six-connected {4⁹6⁴8²}-net. In comparison with the crystal structures of the products, the uncoordinated bpypip ligands in 1, along with the guest water molecules, acts as a key for interacting with the coordinated V-shaped polycarboxylate hfdpa and coordinated bpypip ligands through simultaneous C–H⋯F, C–H⋯O, and C–H⋯N hydrogen-bonding, thereby assisting the generation of the chiral Ni^II coordination polymer. This type of host–guest key–lock interaction is unique and is observed for the first time by controlling the formation of a chiral coordination polymer.