Ab initio search for global minimum structures of neutral and anionic B4H5 clusters. Optical isomerism in B4H5 and B4H5-

► We conducted an unbiased search for global minimum structures of B4H5 and B4H5-. ► Optical isomers were found for neutral and anionic B4H5 clusters. ► Chemical bonding analysis reveals 2c-2e σ, 3c-2e σ and π, and 4c-2e σ and π bonds. ► Calculated theoretical VDEs for B4H5- can help interpret future PES study of B4H5-.