Direct Observation of Molecular‐Level Template Action Leading to Self‐Assembly of a Porous Framework

Abstract

The molecular steps involved in the self-assembly of Cu(3)(BTC)(2) (BTC=1,3,5-benzenetricarboxylic acid) metal-organic frameworks that enclose Keggin-type H(3)PW(12)O(40) heteropolyacid molecules were unraveled by using solution (17)O, (31)P, and (183)W NMR spectroscopy, small-angle X-ray scattering, near-IR spectroscopy, and dynamic light scattering. In aqueous solution, complexation of Cu(2+) ions with Keggin-type heteropolyacids was observed. Cu(2+) ions are arranged around the Keggin structure so that linking through benzenetricarboxylate groups results in the formation of the Cu(3)(BTC)(2) MOF structure HKUST-1. This is a unique instance in which a templating mechanism that relies on specific molecular-level matching and leads to explicit nanoscale building units can be observed in situ during formation of the synthetic nanoporous material.

Tuning the growth of metal-organic framework nanocrystals by using polyoxometalates as coordination modulators

“…Upon adding Cu (II) cations, the 31 P resonance of the POM anions shows a significant shift from -10.15 to -29.97 ppm (Fig. 1c), indicating the change of local environment of the central P atom in the POM anion [29]. Such impact is the result of the interaction with Cu(II) cations, and the peak broadening might be attributed to the intricately or randomly orienting of Cu(II) cations around the surface of POM anions.…”

Simple synthesis recipes of porous materials

“…4). Additional evidence for Cu 2+ -Keggin interaction was obtained from 17 O NMR, 183 W NMR, Small Angle X-ray Scattering (SAXS), UV-Vis and Near Infra Red (NIR) experiments all of which have been discussed in detail in our previously published work [62].…”

“…3). We could show that a template directed positioning of transition metal centres occurs already during the formation of these hierarchical structures which allows to discard the hydrothermal synthesis of the HKUST-1 framework [Cu 3 (BTC) 2 (H 2 O) 3 ] in favour of a quick, room temperature self-assembly procedure [62]. Within minutes after mixing an ethanol based BTC solution with an acidic solution of Cu-decorated Keggin anions (H 8Àx XM 12 O 40 ), 3 micron-sized, highly crystalline Keggin incorporated [Cu 3 (BTC) 2 (H 2 O) 3 ] particles can be obtained.…”

The role of synchrotron radiation in examining the self-assembly of crystalline nanoporous framework materials: from zeolites and aluminophosphates to metal organic hybrids

“…Finally we note that whilst not in situ Bajpe et al 77 have for the first time utilized SAXS at room temperature to examine the role of an organic template in the formation of Cu 3 (BTC) 2 materials containing Keggin-type HPAs Fig. 12 The first example of a fully in situ synchrotron-based study of a MOF material.…”