Synthesis of ITQ-7 with a new template molecule and its crystal structure analysis in the as synthesized form

Song, Jiaqing; Marler, Β.; Gies, Hermann

doi:10.1016/j.crci.2004.10.029

Cited by 16 publications

(15 citation statements)

References 10 publications

(15 reference statements)

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“…14,19 In fact, recent NMR studies on ITQ-13 and STW-type silicogermanates delivered evidence for a presence of Ge-O-Ge linkages at relatively low overall Ge contents. 13,16 (2) Crystallographic investigations on SiO 2 -and GeO 2 -zeolites and mixed (Si,Ge) systems containing d4r units always located fluoride at the center of the cage, 12,17,23,[31][32][33] whereas some NMR studies have pointed to an off-center displacement in Ge-containing systems. 17,30 While there is no direct experimental evidence for the presence of Ge-F bonds, the computations performed by Sastre and co-workers, which were validated against experimental NMR data, predicted the existence of pentacoordinated germanium atoms in both GeO 2 -AST (d(Ge-F) ≈ 2.2 Å) and in mixed (Si,Ge) systems (d(Ge-F) ≈ 1.9 to 2.0 Å).…”

Section: Introductionmentioning

confidence: 99%

Local Environment and Dynamic Behavior of Fluoride Anions in Silicogermanate Zeolites: A Computational Study of the AST Framework

Fischer

2018

J. Phys. Chem. C

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In silicogermanate zeolites containing double four-ring (d4r) building units, the germanium atoms preferentially occupy the corners of these cube-like units. While this general behaviour is well known, the absence of long-range order precludes a determination of the preferred arrangements of Si and Ge atoms at the corners of d4r cages by means of crystallographic methods. If fluoride anions are present during the synthesis, these are incorporated into the d4r cages. Due to the sensitivity of the 19 F chemical shift to the local environment, NMR experiments can provide indirect insights into the predominant (Si,Ge) arrangements. However, conflicting interpretations have been reported, both with regard to the preference for, or avoidance of, Ge-O-Ge linkages, and concerning the equilibrium position of fluorine inside the cage, where fluorine might either occupy the cage centre or participate in a partly covalent Ge-F bond. In order to shed light on the energetically preferred local arrangements, periodic electronic structure calculations in the framework of dispersion-corrected density functional theory (DFT) were performed. The AST framework was used as a suitable model system, as this zeolite is synthetically accessible across the range of (Si 1-n ,Ge n)O 2 compositions (0 ≤ n ≤ 1). DFT structure optimisations for (Si,Ge)-AST systems containing fluoride anions and organic cations revealed that arrangements of Si and Ge at the cage vertices which maximise the number of Ge-O-Ge linkages are energetically preferred, and that fluorine tends to form relatively short (~2.2 to 2.4 Å) bonds to Ge atoms that are surrounded by Ge-O-Ge linkages. The preference for Ge-O-Ge linkages disappears in the absence of fluorine, pointing to a "templating" effect of the anions. In addition to the prediction of equilibrium structures, DFT-based Molecular Dynamics calculations were performed for selected AST models in order to analyse the dynamics of fluoride anions confined to d4r cages. These calculations showed that the freedom of movement of fluorine varies markedly depending on the local environment, and that it correlates with the average Ge-F distance (short Ge-F bonds = restricted motion). An analysis of the Ge-F radial distribution functions provided no evidence for a coexistence of separate local energy minima at the cage centre and in the proximity of a germanium atom for any of the systems considered. The computational approach pursued in this work provides important new insights into the local structure of silicogermanate zeolites with d4r units, enhancing the atomic-level understanding of these materials. In particular, the findings presented here constitute valuable complementary information that can aid the interpretation of experimental data.

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Section: Introductionmentioning

confidence: 99%

Local Environment and Dynamic Behavior of Fluoride Anions in Silicogermanate Zeolites: A Computational Study of the AST Framework

Fischer

2018

J. Phys. Chem. C

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“…6.16 ) [ 108 ]. The structure refi nement from single-crystal data immediately Later, in NMR experiments monitoring the synthesis of zeolite ITQ-7, it has been shown that the signal characteristic for the fl uoride anion in the D4R confi nement shows up long before the crystalline material could be detected in P-XRD experiments [ 109 ].…”

Section: The Clathrasil Octadecasil and The F Synthesis Of Zeolitesmentioning

confidence: 98%

Structure Analysis in Zeolite Research: From Framework Topologies to Functional Properties

Gies

Marler

2016

Green Chemistry and Sustainable Technology

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The solution and the refi nement of crystal structures of microporous materials are of prime interest for the synthesis and application community in porous solid research. The structure of a material reveals not only the geometry of the bonding network of the rigid framework but also the location of the nonframework constituents responsible for the porosity of the material. Analyzing the structure, therefore, unveils the synthesis protocol including nucleation and growth. The properties related to the porous net correspond to the local structure, i.e., the composition and the geometry of local confi gurations. It thus inspires ideas about possible properties and modifi cations to improve functionality.The chapter is intended to highlight the contribution of crystallographic analysis of microporous materials and in particular porous silicates to the success of this class of materials. It does not survey the continuous growth of materials in the fi eld but show how the insight gained from crystallographic studies acted as catalyst in the further development of the fi eld.

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“…X‐ray diffraction investigations of as‐synthesised samples prepared via the “fluoride route” have typically located the fluoride anions at, or close to, the centre of the d4r cage in all‐silica zeolites like octadecasil, [11,42] ITQ‐7, [43] ITQ‐12, [13] and ITQ‐13, [14] and in GeO 2 zeotypes like ASU‐7 (ASV), [44,45] ASU‐9 (AST), [44–46] FOS‐5 (BEC), [47] ITQ‐21, [48] and IM‐10 (UOZ) [49] . In AlPO 4 and GaPO 4 zeotypes, somewhat different locations have been reported for different structures: While the fluoride anions are situated at the centre of the cage in AlPO 4 ‐16 (AST) [50] and in cubic LTA‐type AlPO 4 [36] and GaPO 4 , [51] off‐centre displacements were observed in rhombohedrally distorted AlPO 4 ‐LTA [37] and in the gallophosphate cloverite [35] .…”

Section: Introductionmentioning

confidence: 99%

Local Distortions in a Prototypical Zeolite Framework Containing Double Four‐Ring Cages: The Role of Framework Composition and Organic Guests**

Fischer

Freymann

2020

ChemPhysChem

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Cube‐like double four‐ring ( d4r ) cages are among the most frequent building units of zeolites and zeotypes. In materials synthesised in fluoride‐containing media, the fluoride anions are preferentially incorporated in these cages. In order to study the impact of framework composition and organic structure‐directing agents (OSDAs) on the possible occurrence of local distortions of fluoride‐containing d4r cages, density functional theory (DFT) calculations and DFT‐based molecular dynamics simulations were performed for AST‐type zeotypes, considering four different compositions (SiO 2 , GeO 2 , AlPO 4 , GaPO 4 ) and two different OSDA cations (tetramethylammonium [TMA] and quinuclidinium [QNU]). All systems except SiO 2 ‐AST show significant deformations, with a pyritohedron‐like distortion of the d4r cages occurring in GeO 2 ‐ and GaPO 4 ‐AST, and a displacement of the fluoride anions towards one of the corners of the cage in AlPO 4 ‐ and GaPO 4 ‐AST. While the distortions occur at random in TMA‐containing zeotypes, they exhibit a preferential orientation in systems that incorporate QNU cations. In addition to providing detailed understanding of the local structure of a complex host‐guest system on the picosecond timescale, this work indicates the possibility to stabilise ordered distortions through a judicious choice of the OSDA, which might enable a tuning of the material's properties.

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Synthesis of ITQ-7 with a new template molecule and its crystal structure analysis in the as synthesized form

Cited by 16 publications

References 10 publications

Local Environment and Dynamic Behavior of Fluoride Anions in Silicogermanate Zeolites: A Computational Study of the AST Framework

Local Environment and Dynamic Behavior of Fluoride Anions in Silicogermanate Zeolites: A Computational Study of the AST Framework

Structure Analysis in Zeolite Research: From Framework Topologies to Functional Properties

Local Distortions in a Prototypical Zeolite Framework Containing Double Four‐Ring Cages: The Role of Framework Composition and Organic Guests**

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