Synthesis, X-ray crystal structures and inclusion properties of a hydrogen-bonded coordination polymer [Ni(SCN)2(pppeH)2]·(guest)x

Abstract

This study reports three inclusion compounds [Ni(SCN)₂(pppeH)₂]·(guest)_x (1–3) and a guest-free crystal [Ni(SCN)₂(pppeH)₂] (4), where pppeH = trans-3-[4-(4-pyridyl)phenyl]propenoic acid and guest = dibenz[a,h]anthracene (x = 1/2) (1), p-bromobenzoic acid (x = 1) (2) and 4,4′-dibromobiphenyl (x = 1) (3). The crystal structures of 1–4 are best described as consisting of layers. The layer, [Ni(SCN)₂(pppeH)₂]_∞, is formed by R²₂(8) O–H⋯O hydrogen bonding between the pppeH ligands coordinating to Ni²⁺ ions of adjacent 1D coordination polymers. The layers of 1–3 have cavities surrounded by two pppeH dimers and four μ-1,3-SCN ligands with the dimensions of ca. 25.5 × 6.2–7.6 Ų. On the other hand, the layer of 4 does not. This indicates that the guests act as templates for the formation of the cavity. Interlayer connection of the cavities gives channels penetrating through the crystals where the guests are arranged one-dimensionally. Detailed investigation on the crystal structures of 1–3 and [Ni(SCN)₂(pppeH)₂]·(benz[a]anthracene)_2/3 (5) reported previously has revealed that the stacking manner of the layers, the interlayer separation and the structure of the layer are adjusted in response to the guests, and simultaneously the guests adjust their positions and orientations to form a close-packed structure.