Syntheses, crystal structures and optical spectroscopy of Ln2(SO4)3·8H2O (Ln=Ho, Tm) and Pr2(SO4)3·4H2O

The lanthanide sulphate octahydrates Ln2(SO4)3·8H2O (Ln=Ho, Tm) and the respective tetrahydrate Pr2(SO4)3·4H2O were obtained by evaporation of aqueous reaction mixtures of trivalent rare earth oxides and sulphuric acid at 300 K. Ln2(SO4)3·8H2O (Ln=Ho, Tm) crystallise in space group C2/c (Z=4, aHo=13.4421(4) Å, bHo=6.6745(2) Å, cHo=18.1642(5) Å, βHo=102.006(1) Å3 and aTm=13.4118(14) Å, bTm=6.6402(6) Å, cTm=18.1040(16) Å, βTm=101.980(8) Å3), Pr2(SO4)3·4H2O adopts space group P21/n (a=13.051(3) Å, b=7.2047(14) Å, c=13.316(3) Å, β=92.55(3) Å3). The vibrational and optical spectra of Ho2(SO4)3·8H2O and Pr2(SO4)3·4H2O are also reported.

In the lanthanide sulphate octahydrates the cations form slightly undulated layers. Between the layers are voids in which sulphate tetrahedra and water molecules are located. The holmium compound exhibits an Alexandrite effect.Figure optionsDownload as PowerPoint slideHighlights
► Determination of the optimum conditions for the growth of single-crystals of Ln2(SO4)3·8H2O (Ln=Ho, Tm) and Pr2(SO4)3·4H2O.
► Single-crystal structure elucidation of Ln2(SO4)3·8H2O (Ln=Ho, Tm) including hydrogen bonds.
► Single-crystal structure determination of Pr2(SO4)3·4H2O including hydrogen bonds.
► UV–vis spectra of Ho2(SO4)3·8H2O and Pr2(SO4)3·4H2O recorded and interpreted: Assignation of bands and clarification of the Alexandrite effect of the Ho compound.
► IR and Raman spectra of Ln2(SO4)3·8H2O (Ln=Ho, Tm) and Pr2(SO4)3·4H2O recorded and interpreted.