INFRARED-SPECTRA OF THE AMMONIUM ION IN AMMONIUM HEXAVANADATE (NH4)2V6O16

The infrared bands of the NH+4 and ND+4 groups in (NH4)2V6O16 and its deuterated analogue can be assigned with a fair amount of certainty at 90 K under the space group P21/m(C22h). The ND stretching modes of isotopically dilute NH3D+ ions in the crystal are in agreement with the predicted splitting into Cs, Cs and C1(2) components. The frequencies, shapes and temperature dependence of these modes suggest that both normal and bifurcated hydrogen bonds are formed. The latter closely resembles corresponding bonds in NH4VO3, but the normal hydrogen bonds are not as strong as the similar bonds in NH4VO3. This can be expected as NH+4 ions are dynamic in character in (NH4)2V6O16 and remain so down to temperatures of 90 K. © 1990.