INFRARED-SPECTRA OF ALUMINOGERMANATE-SODALITE AND ALUMINATE-SODALITE AND A RE-EXAMINATION OF THE RELATIONSHIP BETWEEN T-O BOND LENGTH, T-O-T ANGLE AND THE POSITION OF THE MAIN IR ABSORPTION-BAND FOR COMPOUNDS WITH FRAMEWORK STRUCTURES

Cell parameters and i.r. data are presented for 6 aluminogermanate-sodalites, 11 aluminate-sodalites and for Na8(Ga6Ge6O24)Br2 and Na8(Ga8Si6O24)Br2. Apart from the borate-sodalites the framework absorption bands of the sodalite family can be grouped into three sets: νas TOT between 800 and 1000 cm-1, νs TOT between 500 and 800 cm-1 and δ OTO between 300 and 500 cm-1 (T =tetrahedral framework cation). The aluminogermanate-sodalites have one νas TOT mode and two vs TOT and δ OTO modes. Cubic aluminate-sodalites with ∼ 9 Å cells are similar but with only one δ OTO mode; aluminate-sodalites without cubic ∼9 Å cells showed broadening of the vas TOT mode, which has several maxima and additional vs TOT bands. Compounds with framework structures having AlO, (Al, Ge)O, (Al, Si)O, (Ga, Ge)O, GeO and SiO framework bonds, when grouped into those with TOT angles close to either 125° or 145°, show good correlations between the wave numbers of their main absorption bands and their mean TO distances. © 1979.