Scandium in Neutral and Positively Charged Ammonia Complexes: Balancing between Sc2+ and Sc3.

High-level quantum chemical approaches are performed to study the stability and electronic structure of tri-, di-, monocationic, and neutral scandium ammonia complexes. The calculated binding energies of all Sc(NH3)1-83+,2+,+,0 complexes reveal the higher stability of hexa- and octacoordinated systems. The ground states of Sc(NH3)6,82+ and Sc(NH3)6,8 have a Sc2+(3d1) center, while there are two competitive electronic states for Sc(NH3)6,8+ with a Sc2+(3d1) or a Sc3+ center. The remaining electrons occupy an outer diffuse s-type orbital (1s). The lower lying states involve 3d-3d transitions for Sc(NH3)6,82+ but outer 1s-1p transitions for Sc(NH3)6,8+,0. The addition of one electron to Sc(NH3)6,83+,2+,+ reduces the binding energies but shortens the Sc-N bond lengths. The comparison with the vanadium and yttrium ammonia complexes (studied earlier) reveal the unique identity of scandium balancing between a d- and s-block element.