Experimental and Theoretical Evidence for the Formation of Zinc Tricarbonyl in Solid Argon

Zinc carbonyls are extremely rare. Here we report experimental and theoretical evidence of unprecedented zinc tricarbonyl, Zn(CO)₃, the next member of the series of 18-electron metal carbonyls Cr(CO)₆ → Fe(CO)₅ → Ni(CO)₄, whereas there is no evidence for the formation of the zinc mono- and dicarbonyls Zn(CO)_n (n = 1, 2). DFT calculations predict that the Zn(CO)₃ molecule has a singlet ground state with D_3h symmetry. The formation of Zn(CO)₃ involves 4s → 4p promotion of the Zn atom, which increases the Zn−CO bonding by decreasing the σ repulsion and significantly increasing the Zn 4sp hybrid orbitals → CO π* back-donation.