H8Si8O12: A model for the vibrational structure of zeolite A

Abstract

The vibrational structure of the highly symmetrical octahydridosilasesquioxane has been investigated in detail, and a harmonic force field in terms of internal force constants has been determined, based on extensive IR and FT-Raman data and on a normal coordinate analysis of H~SisOl2 and DsSigOl2. Group frequencies have been assigned according to a potential energy analysis, and relations to group frequencies of comparable silicon compounds have been discussed. A step by step procedure starting from Oh-H~Sig012 to the frameworks Oh-(-O)8SigO12, D4h-(-0)8Si~012, D4h-(=Si0)8Si8012, and finally to Dw(*0)8T8012, T = Si or A1 and Si/Al = 1, has turned out to be an excellent, enlightening approach for qualitatively and quantitatively describing the vibrational structure of the zeolite A framework. NIR FT-Raman spectra of Na+-exchanged zeolite Y and of Na+-and Ag+-exchanged zeolite A have been measured and compared with each other. An improved force field is reported, and a correlation of the experimental and the calculated IR and Raman spectra of zeolite A has allowed one to assign group frequencies to all fundamental modes. All fundamentals between 11 10 and 950 cm-l belong to antisymmetric T-0-T stretching vibrations while the symmetric T-O-T stretching modes are at 860-830 cm-l, 740-680 cm-l, and 610-570 cm-l. The fundamentals between 490 and 100 cm-l can be described as 0-T-0 bendingvibrations-with the exception of a double four ring and two sodalite cage breathing modes and the 8-ring pore opening-whereas the T-O-T bending vibrations and the torsional modes are below 100 cm-1.

Synthesis and Catalytic Properties of Hybrid Mesoporous Materials Assembled from Polyhedral and Bridged Silsesquioxane Monomers

“…The assignment of vibrational bands to the presence of double four‐membered rings (D4R) in the framework of different zeolite materials has been discussed in several publications and, in general, such an assignment is still a controversial topic 39. 40 However, it is accepted that it is possible to detect the bands that are due to the skeletal vibration of D4R units (550–600 cm −1 ) 41. 42 More specifically, theoretical models of pure silica zeolite structures have estimated that the ring‐opening vibration frequency for D4R units is centered at 581 cm −1 43.…”

“…[39,40] However, it is accepted that it is possible to detect the bands that are due to the skeletal vibration of D4R units (550-600 cm À1 ). [41,42] More specifically, theoretical models of pure silica zeolite structures have estimated that the ring-opening vibration frequency for D4R units is centered at 581 cm À1 . [43] In our case, the mesoporous materials that were based on POSS blocks showed vibrational bands at around 580 cm À1 , which would confirm that silsesquioxane double four-member rings (D4R) were present in the framework of the hybrid materials, even in the presence of aryl building blocks (Figure 6 a).…”

Characterization of the benzene‐insoluble fraction of the hydrolyzate of phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide

“…Galeener and Geissberger21 suggested about 600 cm −1 for a 6‐member ring, whereas Bornhauser and Calzaferri20 suggested about 400 cm −1 for a 10‐member ring. Bornhauser and coworkers20, 23 calculated that the in‐phase 8‐member ring vibrations of H and deuterium (D) derivatives would appear at 456 and 452 cm −1 , respectively. The difference between D and H (Fig.…”

Optical absorption, EPR, infrared and Raman spectral studies of clinochlore mineral

“…Spectral and magnetic studies of minerals provide a wealth of information on the crystal chemistry of transition metal ions in naturally occurring minerals [1][2][3][4][5][6]. Generally, some paramagnetic transition ions such as Fe 3C , Cr 3C , Mn 2C etc., are present in natural minerals.…”