Ligand Excess "Inverse-Defected" Zr Tetrahedral Tetracarboxylate Framework and Its Thermal Transformation.

A new porous coordination polymer (PCP/MOF), , based on a tetrahedral 1,3,5,7-tetra(carboxyphenyl)benzene ligand (HL) was synthesized using formic or acetic acids as modulators. The low symmetry (2/) framework, [Zr(μ-O)(μ-OH)(L)(HL)(OH)(HO)], is built upon a rare 10-connected Zr cluster. Two-thirds of the ligands bear one nondeprotonated carboxy group, and the framework has a complex trinodal 3,4,10-c, {4.6.8}{4}{4.6}, underlying net. Supercritical CO drying and mild degassing at 120 °C yielded a porous material with = 1190 m g. When heated up to ∼200 °C, converts to another crystalline framework, . The latter was identified to be identical to the expected fluorite () observed previously for other tetrahedral ligands. The high symmetry (4/m) framework is built upon 8-connected Zr clusters and has a formula of [Zr(μ-O)(μ-OH)(OH)(L)]. The complicated trinodal network of and the simple net in are topologically interrelated via the operation of the merging of two neighbor three-connected nodes to one four-connected one. The thermally induced conversion of proceeds with expulsion of one ligand per Zr node in the pores of the framework, resulting in a relatively low = 585 m g for the activated HL@. A mixed ligand approach for was attempted using 1,3,5-tetra(carboxyphenyl)benzene (HL), which is a truncated analog of HL with one missing branch. The monocrystalline sample of obtained in small yields demonstrated only minor inclusion of HL. However, the high-yielding (∼80%) procedure with HCl as a modulator allows near proportional incorporation of the ligands. The formed materials are semiamorphous with powder XRDs intermediary between pure and . Thermal treatment of the semiamorphous materials increases their crystallinity and allows = 400-550 m g surface areas to be reached for pure HL and HL or their mixture alike. The approach proposes a viewpoint on the HL trifunctional ligand as a model of a ligand platform, suitable for bearing a large functionality on the fourth "truncated" branch. The significance of as a material for postsynthetic introduction of metal-based cluster functionality and as a model of functionality encapsulation, an alternative to the ship-in-the-bottle method, is discussed.