Theoretical calculations are performed to probe the geometric and electronic properties of diniobium boride clusters, Nb 2 B x -/0 (x = 1-6). Generalized Koopmans' theorem is utilized to predict vertical detachment energies (VDEs) and to simulate the photoelectron spectra (PES). Density functional theory (DFT) calculations are carried out at the BP86 level to hunt for the most stable structures of the abovementioned species. A fascinating structural evolution is observed in Nb 2 B x -(x = 1- [a] 942 in which the Nb-Nb bond length is 2.217 Å and the Nb-B distances are 2.081 Å. Its corresponding triplet state (C 2v , 3 A 1 ) (Figure 1b) is computed to be 0.15 eV higher at the BP86 level. The results of CCSD(T) single-point calculations are in line with the aforementioned DFT results, making the C 2v ( 1 A 1 ) state 0.19 eV more stable than the triplet C 2v ( 3 A 1 ) state. The neutral Nb 2 B ground state (Figure 1c) is found to be a doublet C 2v ( 2 A 1 ) struc-Eur. J. Inorg. Chem. 2018, 940-950 www.eurjic.org