The non-ring cations influence on silicooxygen ring vibrations M. Sitarz a, * , M. Handke a , W. Mozgawa a , E. Galuskin b , I. Galuskina b a University of Mining and Metallurgy (AGH), Department of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Krako ´w, Poland b University of Silesia, Museum of Earth, Department of Earth Science, ul. Be ˛dzin ´ska 60, 41-200 Sosnowiec, Poland Received 15 November 1999; revised 31 January 2000; accepted 31 January 2000 Abstract In this work IR spectra of synthetic and natural ring silicates (cyclosilicates) containing in their structure isolated sili- cooxygen rings of various numbers of members n  3; 4; 6 have been presented. By means of factor group analysis it has been shown that only one intensive band characteristic of ring structures (“ring band”) should be observed in the IR spectra of cyclosilicates. The ring band position is related to the number of ring members [M. Handke, M. Sitarz, W. Mozgawa, J. Mol. Struct. 450 (1998) 229] and strongly depends on the kind of non-ring cations connecting the rings. The existence of the cations such as Ti 4+ , Zr 4+ , Cu 2+ etc. in the cyclosilicates structure causes the conjugation of the vibrations, making the interpretation of the spectra more difficult. In this work we have shown that the presence of such non-ring cations causes the shifting of the “ring band” to the higher wavenumbers. In the case when Al 3+ are non-ring cations it is almost impossible to identify the “ring band” (6-membered cyclosilicates).  2000 Elsevier Science B.V. All rights reserved. Keywords: Vibrational spectroscopy; Ring silicate 1. Introduction Ring silicates (cyclosilicates) form a subgroup of oligosilicates. Cyclosilicates include isolated rings of different numbers of members in their structure. The rings are formed of small numbers of silicooxygen tetrahedra. Detailed analysis of vibrations of sili- cooxygen rings containing different numbers of members together with theoretical analysis was carried out by Lazariev [2], who took into account the influence of ring symmetry on the shape and number of bands in the spectra of cyclosilicates. With the increased Si–O–Si angle value (with the increased number of ring members) one can suppose that the frequency of asymmetric Si–O–Si vibrations will increase and the frequency of symmetric Si–O– Si vibrations will decrease [2]. In a previous work [1] we proposed the model of silicooxygen ring vibrations to simplify the interpretation of the spectra. It was established that in the case of all ideal rings there is only one IR-active vibrational mode, namely the one symmetric with respect to the axis of the highest fold, i.e. A 2 00 in the case of 3-membered rings and A 2u in the case of 4- and 6-membered rings. This is why only one intensive band due to silicooxygen rings can be observed. Calculations performed (PM3 method) indicated that only 3-membered rings are flat whereas higher membered rings are always deformed [3]. The main aim of this work is to estimate the influence of non-ring cations on the shape of cyclosilicate IR spectra. To establish this it was necessary to carry out model cyclosilicate spectroscopic analysis. We chose cyclosilicates containing almost ideal rings connected by the alkaline or alkaline earth cations. Journal of Molecular Structure 555 (2000) 357–362 0022-2860/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0022-2860(00)00621-9 www.elsevier.nl/locate/molstruc * Corresponding author. Tel.: +48-12-6172395; fax: +48-12- 6331593. E-mail address: msitarz@uci.agh.edu.pl (M. Sitarz).