We present a combined photoelectron spectroscopy and first-principles theory study on the structural and electronic properties and chemical bonding of B3O3-/0 and B3O3H-/0 clusters. The concerted experimental and theoretical data show that the global-minimum structures of B3O3 and B3O3H neutrals are very different from those of their anionic counterparts. The B3O3-anion is characterized to possess a V-shaped OB-B-BO chain with overall C-2v symmetry (1A), in which the central B atom interacts with two equivalent boronyl (B O) terminals via B-B single bonds as well as with one O atom via a B=O double bond. The B3O3H- anion has a C-s (2A) structure, containing an asymmetric OB-B-OBO zig-zag chain and a terminal H atom interacting with the central B atom. In contrast, the C-2v (1a) global minimum of B3O3 neutral contains a rhombic B2O2 ring with one B atom bonded to a BO terminal and that of neutral B3O3H (2a) is also of C-2v symmetry, which is readily constructed from C-2v (1a) by attaching a H atom to the opposite side of the BO group. The H atom in B3O3H-/0 (2A and 2a) prefers to interact terminally with a B atom, rather than with O. Chemical bonding analyses reveal a three-center four-electron (3c-4e) pi hyperbond in the B3O3H-(2A) cluster and a four-center four-electron (4c-4e) pi bond (that is, the so-called o-bond) in B3O3 (1a) and B3O3H (2a) neutral clusters. (C) 2016 AIP Publishing LLC.