Ternary B2X2H2 (X = O and S) rhombic clusters and their potential use as inorganic ligands in sandwich-type (B2X2H2)2Ni complexes

Abstract

Based upon global searches and electronic structure calculations at the B3LYP and CCSD(T) levels, we present the global-minimum structures of two ternary B–O–H and B–S–H rhombic clusters: D_2h B₂O₂H₂ (1, ¹A_g) and C_2v B₂S₂H₂ (2, ¹A₁). Both species feature a B₂X₂ (X = O or S) four-membered ring as the core, with two H atoms attached terminally. The former cluster is perfectly planar, whereas the latter undergoes a slight butterfly distortion. Bonding analyses reveal a four-center four-electron (4c–4e) o-bond in these clusters, which are 4π systems in a nonbonding/bonding combination, in contrast to an antibonding/bonding combination in a classical 4π antiaromatic hydrocarbon such as cyclobutadiene (C₄H₄). Clusters 1 and 2 are considered to be aromatic. The present results also help elucidate the bonding nature in the relevant heteroatomic ring B₂N₂H₄ system and suggest that it is not appropriate to consider B₂N₂H₄ as an inorganic cyclobutadiene, a conception that has been in existence in the literature for over 40 years. The electronic properties of the global-minimum clusters 1 and 2 are predicted. It is shown that B₂O₂H₂ (1) and B₂S₂H₂ (2) may serve as effective inorganic ligands to form sandwich-type transition metal complexes, such as D_2d [B₂O₂H₂]₂Ni (3) and D_2d [B₂S₂H₂]₂Ni (4).