BeM(CO)₃⁻ (M = Co, Rh, Ir) and BeM(CO)₃ (M = Ni, Pd, Pt): Triply bonded terminal beryllium in zero oxidation state.

This article focuses on the theoretical investigation of bonding in beryllium-transition metal carbonyl complexes, specifically BeM(CO)₃⁻ (M = Co, Rh, Ir) and BeM(CO)₃ (M = Ni, Pd, Pt). Using advanced computational methods including CASPT2 and energy decomposition analysis combined with natural orbitals for chemical valence (EDA-NOCV), the study identifies four stable complexes—BeCo(CO)₃⁻, BeRh(CO)₃⁻, BeIr(CO)₃⁻, and BePt(CO)₃—that exhibit a Be≡M triple bond composed of one strong σ-dative bond and two weaker π-dative bonds, with beryllium in an unusual zero oxidation state. Radial orbital-energy slope (ROS) analysis reveals that the highest occupied molecular orbital (HOMO) in these complexes is slightly antibonding, which precludes assigning a quadruple bond despite EDA-NOCV indicating four bonding components; this finding also revises previous claims of quadruple bonding in related BeM(CO)₄ complexes. The results suggest that electropositive s-block metals like beryllium can form multiple bonds under appropriate coordination environments, highlighting these complexes as promising targets for future experimental studies in s-block multiple bonding chemistry.