Scandium(III) p-toluenesulfonate hexahydrate, as well as the isomorphous yttrium(III) and six lanthanoid(III) (Sm, Gd, Dy, Ho, Er, and Yb) p-toluenesulfonate enneahydrates, were synthesized and their structures were determined by the single-crystal X-ray diffraction technique. The scandium salt was monoclinic with the space group P21⁄a, Z=4 (the cell constants were a=23.672(16), b=15.792(6), c=7.7543(12) Å, β=92.86(3)°, and the final R value was 0.059). The central metal atom is hexa-coordinated, being in an octahedral geometry, in which two unidentate sulfonate oxygen atoms (in cis-configuration) and four water oxygen atoms are ligated. The latter seven salts were also monoclinic with a space group of P21⁄n, and Z=4 (the cell constants of the holmium salt, for example, were a=25.058(19), b=7.476(2), c=17.802(10) Å, β=98.80(8)°, and its final R value was 0.039). The central metal atom of these complexes are octa-coordinated, being in a square-antiprism geometry in which two unidentate sulfonate and six water oxygen atoms are ligated. In both types of complexes, no ligand bridgings were found, and one in three sulfonate ions was not coordinated to the metal atom. In the respective lanthanoid(III) complexes, M–O(sulfonato) bonds are shorter than the M–O(water) ones. The corresponding M–O bonds of the respective complexes decrease, almost proportional to the sum of the Shannon’s ionic radii of the metal and oxygen, with the metal atomic numbers. Each M–O bond length of the yttrium(III) p-toluenesulfonate and 2-naphthalenesulfonate had the value expected from the corresponding bond lengths of the series of the respective isomorphous lanthanoid(III) salts, referring to its metal ionic radius.
