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-kappa(2)O,O')scandium(III) trichloride monohydrate, [Sc(C(2)H(5)N(3)O(2))(H(2)O)(5)]Cl(3)center dot H(2)O, (I), and tetrakis(biuret-kappa(2)O,O')scandium(III) trinitrate, [Sc(C(2)H(5)N(3)O(2))(4)](NO(3))(3), (II), are found to adopt very different coordinations with the same biuret ligand. The roles of hydrogen bonding and the counterion in the establishment of the structures are described. In (I), the Sc(3+) 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 center dot center dot center dot Cl, O-H center dot center dot center dot O and O-H center dot center dot center dot Cl hydrogen bonds help to establish the packing, resulting in dimeric associations of two cations and two water molecules. In (II), the Sc(3+) cation (site symmetry 2) adopts a slightly squashed square-antiprismatic geometry arising from four O,O'-bidentate biuret molecules. A network of N-H center dot center dot center dot 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.