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

Acta Cryst. (2008). C64, m205–m208 [doi:10.1107/S010827010800824X]

Scandium(III) shows unusual flexibility in its coordination number in complexes, and six-, seven-, eight- and nine-coordinate species are known. When combined with biuret and water molecules, distinctive, near regular, pentagonal bipyramidal [Sc(H₂O)₅(C₃H₅N₂)]³⁺ and square antiprismatic [Sc(C₃H₅N₂)₄]³⁺ geometries arise, suggesting that the counter-ion may play some role in defining the metal coordination preference.

W.T.A. Harrison