Vibrational Spectroscopic and X-Ray Single Crystal Diffraction Investigation of Tetra-n-Alkylammonium Hydrogen Selenates

Abstract

Two novel semi-organic salts of tetra-n-propylammonium (1+) and tetra-n-butylammonium (1+) hydrogen selenate have been prepared and characterised. Tetra-n-propylammonium (1+) hydrogen selenate (a = 15.7949(6) A, b = 15.3876(6) A, c = 40.4384(17) A, V = 9828.4(7) A3, Z = 8 for 8775 observed reflections) and tetra-n-butylammonium (1+) hydrogen selenate (a = 15.0870(3) A, b = 15.3380(4) A, c = 17.4750(4) A, V = 4043.79(16) A3, Z = 8, R = 0.0432 for 3335 observed reflections) crystallise in the centrosymmetric space groups Pbcn and Pccn of the orthorhombic system, respectively. Both salts were also characterised by the methods of vibrational spectroscopy (IR and Raman). The interpretation of the vibrational spectra is based on ab initio calculations of the isolated cations. The crystal structure of the third analogous compound, tetra-n-ethylammonium(1+) hydrogen selenate was redetermined at 150 K (a = 8.2109(17) A, b = 9.072(2) A, c = 9.431(3) A, α = 77.13(3)o, β = 74.43(2)o, γ = 63.62(3)o, V = 601.89(3) A3, Z = 2, R = 0.0167 for 2237 observed reflections). This compound crystallises in centrosymmetric space group P-1 of the triclinic system and was previously studied only at room temperature. The preparation and detailed characterisation (using the combination of diffraction and spectroscopic methods) of salts of tetra-n-alkylammonium hydrogen selenates (alkyl = propyl, butyl).