Two Zinc(II) Coordination Polymers Constructed with Rigid 1,4-Benzenedicarboxylate and Flexible 1,4-Bis(imidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene Linkers: From Interpenetrating Layers to Templated 3D Frameworks

Two new coordination polymers, [Zn(bdc)(bimx)]·1.5H₂O (1) and [Zn₂(bdc)₂(bimx)]·(H₂bdc) (2) (H₂bdc = 1,4-benzenedicarboxylic acid, bimx = 1,4-bis(imidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene), containing both rigid (bdc) and flexible (bimx) linkers were synthesized in aqueous media (hydrothermal conditions) and characterized by single-crystal and powder X-ray diffraction, FT-IR spectroscopy, and thermogravimetric/differential thermal analysis. While 1 is an essentially dense material consisting of stacked composite layers each being built from two mutually interpenetrating two-dimensional square-grid frameworks, 2 possesses a single (non-interpenetrated) three-dimensional open framework (α-Po net) with wide channels that are filled with H₂bdc template molecules. Formally, ring-penetrating bdc linkers are replaced by H₂bdc molecules when going from the structure of 1 to the structure of 2. The occluded H₂bdc molecules exhibit distinct interactions with the framework and can thus be regarded as template molecules or structure-directing agents. In line with these host−guest interactions, attempts to remove the template from as-synthesized 2 with retention of the framework structure by heat treatment or liquid exchange were not successful. These results give new impetus, however, to the recently discussed idea to use structure-directing effects, as they occur in zeolite synthesis, for the preparation of metal−organic framework materials.