The hydrogensulfate-sulfates Ln(HSO4)(SO4) (Ln: Sm, Eu, Gd, Tb, Dy) have been crystallized from sulfuric acid and their thermal decomposition behavior has studied. crystal structures for all members of the series were refined X-ray single-crystal diffraction data (for all: Tb(HSO4)(SO4) structure type, P21, Z=2, a≈6.66 Å, b≈6.63 c≈6.82 β≈104.6°). Optical spectra (Sm–Dy) magnetic susceptibilitie...