Two scandium–biuret complexes: [Sc(C2H5N3O2)(H2O)5]Cl3·H2O and [Sc(C2H5N3O2)4](NO3)3

The scandium(III) cations in the structures of pentaaqua(biuret‐κ²O,O′)scandium(III) trichloride monohydrate, [Sc(C₂H₅N₃O₂)(H₂O)₅]Cl₃·H₂O, (I), and tetrakis(biuret‐κ²O,O′)scandium(III) trinitrate, [Sc(C₂H₅N₃O₂)₄](NO₃)₃, (II), are found to adopt very different coordinations with the same biuret ligand. The roles of hydrogen bonding and the counter‐ion in the establishment of the structures are described. In (I), the Sc³⁺ cation adopts a fairly regular pentagonal bipyramidal coordination geometry arising from one O,O′‐bidentate biuret molecule and five water molecules. A dense network of N—H...Cl, O—H...O and O—H...Cl hydrogen bonds help to establish the packing, resulting in dimeric associations of two cations and two water molecules. In (II), the Sc³⁺ cation (site symmetry 2) adopts a slightly squashed square‐antiprismatic geometry arising from four O,O′‐bidentate biuret molecules. A network of N—H...O hydrogen bonds help to establish the packing, which features [010] chains of cations. One of the nitrate ions is disordered about an inversion centre. Both structures form three‐dimensional hydrogen‐bond networks.