The name/synonym for ligand NI (curated from ChEBI, PubChem, and PDB databases):

1NICKEL(2+)
2NI(2+)
3NICKEL (II) ION
4NICKEL, ION (NI2+)
5NICKELOUS ION
6NI2+
7NICKEL(2+) ION
8NICKEL(II) CATION