Ligand Excess "Inverse-Defected" Zr 6 Tetrahedral Tetracarboxylate Framework and Its Thermal Transformation.

A new porous coordination polymer (PCP/MOF), ZRTE-10 , based on a tetrahedral 1,3,5,7-tetra(carboxyphenyl)benzene ligand (H ₄ L ⁴ ) was synthesized using formic or acetic acids as modulators. The low symmetry ( C 2/ c ) framework, [Zr ₆ (μ ₃ -O) ₄ (μ ₃ -OH) ₄ (L ⁴ )(HL ⁴ ) ₂ (OH) ₂ (H ₂ O) ₂ ], is built upon a rare 10-connected Zr ₆ cluster. Two-thirds of the ligands bear one nondeprotonated carboxy group, and the framework has a complex trinodal 3,4,10-c, {4 ¹⁴ .6 ²⁴ .8 ⁷ }{4 ³ } ₂ {4 ⁵ .6}, underlying net. Supercritical CO ₂ drying and mild degassing at 120 °C yielded a porous material with S _BET = 1190 m ² g ^-1 . When heated up to ∼200 °C, ZRTE-10 converts to another crystalline framework, ZRTE-11 . The latter was identified to be identical to the expected fluorite ( flu ) observed previously for other tetrahedral ligands. The high symmetry ( I 4/m) framework is built upon 8-connected Zr ₆ clusters and has a formula of [Zr ₆ (μ ₃ -O) ₄ (μ ₃ -OH) ₄ (OH) ₄ (L ⁴ ) ₂ ]. The complicated trinodal network of ZRTE-10 and the simple flu net in ZRTE-11 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 ZRTE-10 proceeds with expulsion of one ligand per Zr ₆ node in the pores of the framework, resulting in a relatively low S _BET = 585 m ² g ^-1 for the activated H ₄ L ⁴ @ ZRTE-11 . A mixed ligand approach for ZRTE-10,11 was attempted using 1,3,5-tetra(carboxyphenyl)benzene (H ₃ L ³ ), which is a truncated analog of H ₄ L ⁴ with one missing branch. The monocrystalline sample of ZRTE-10 obtained in small yields demonstrated only minor inclusion of H ₃ L ³ . 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 ZRTE-10 and -11 . Thermal treatment of the semiamorphous materials increases their crystallinity and allows S _BET = 400-550 m ² g ^-1 surface areas to be reached for pure H ₄ L ⁴ and H ₃ L ³ or their mixture alike. The approach proposes a viewpoint on the H ₃ L ³ trifunctional ligand as a model of a ligand platform, suitable for bearing a large functionality on the fourth "truncated" branch. The significance of ZRTE-10 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.