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Origin of the structure-directing effect resulting in identical topological open-framework materials.

ABSTRACT: In the synthesis of zeolites and related crystalline materials with open-frameworks, a single structure is obtained in the presence of many different templates, known as the "one-structure/multiple-templates" phenomenon. However, the reasons behind this phenomenon have yet to be elucidated. By analyzing the possible starting point of crystallization in several "one-structure/multiple-templates" systems and applying the molecular dynamics simulation to such systems, we found that the template-framework binding free energy level or charge transfer (exchange) degree was the key to the structure-directing effect of a template. This discovery explains why the structure-directing effect of a template can be affected by many variables, such as the nature of the source materials, molar composition of the initial reaction mixture (recipe), mineralizers, type of solvent, and heating temperature. In the synthesis of zeolites and related crystalline materials with open-frameworks, the template or organic additive played a topological structure-directing role instead of a structure-directing role.

SUBMITTER: Xin L

PROVIDER: S-EPMC4597409 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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Origin of the structure-directing effect resulting in identical topological open-framework materials.

Xin Liang L Sun Huai H Xu Ruren R Yan Wenfu W

Scientific reports 20151008

In the synthesis of zeolites and related crystalline materials with open-frameworks, a single structure is obtained in the presence of many different templates, known as the "one-structure/multiple-templates" phenomenon. However, the reasons behind this phenomenon have yet to be elucidated. By analyzing the possible starting point of crystallization in several "one-structure/multiple-templates" systems and applying the molecular dynamics simulation to such systems, we found that the template-fra ...[more]

PMID: 26447528

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Project description:The templated zeolite-analogue GaPO-34 (CHA structure type) crystallises from a gel precursor Ga2O3?:?2H3PO4?:?1HF?:?1.7SDA?:?70H2O (where SDA = structure directing agent), treated hydrothermally for 24 hours at 170 °C using either pyridine or 1-methylimizadole as SDA and one of either poorly crystalline ?-Ga2O3 or ?-Ga2O3 as gallium precursor. If the same gels are stirred for periods shorter than 2 hours but treated under identical hydrothermal conditions, then a second phase crystallises, free of GaPO-34. If ?-Ga2O3 is used as a reagent only the second phase is found to crystallise, irrespective of gel aging time. The competing phase, which we denote GaPO-34A, has been structurally characterised using synchrotron powder X-ray diffraction for the pyridine material, GaPO-34A(pyr), and using single-crystal X-ray diffraction for the 1-methylimiazole material, GaPO-34A(mim). The structure of GaPO-34A(pyr), P1[combining macron], a = 10.22682(6) Å, b = 12.09585(7) Å, c = 13.86713(8) Å, ? = 104.6531(4)°, ? = 100.8111(6)°, ? = 102.5228(6)°, contains 7 unique gallium sites and 6 phosphorus sites, with empirical formula [Ga7P6O24(OH)2F3(H2O)2]·2(C5NH6). GaPO-34A(mim) is isostructural but is modelled as a half volume unit cell, P1[combining macron], a = 5.0991(2) Å, b = 12.0631(6) Å, c = 13.8405(9) Å, ? = 104.626(5)°, ? = 100.346(5)°, ? = 101.936(4)°, with a gallium and a bridging fluoride partially occupied and two partially occupied SDA sites. Solid-state 31P and 71Ga NMR spectroscopy confirms the structural complexity of GaPO-34A with signals resulting from overlapping lineshapes from multiple Ga and P sites, while 1H and 13C solid-state NMR spectra confirm the presence of the protonated SDA and provide evidence for disorder in the SDA. The protonated SDA is located in 14-ring one-dimensional channels with hydrogen bonding deduced from the SDA nitrogens to framework oxygen distances. Upon thermal treatment to investigate SDA removal, structure collapse occurs, which may be due the large number of bridging hydroxides and fluorides in the as-made material, and the unequal amounts of gallium and phosphorus present.

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Origin of the structure-directing effect resulting in identical topological open-framework materials.

Publications

Origin of the structure-directing effect resulting in identical topological open-framework materials.

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