Synthesis and structure of two tetranuclear osmium carbonyl isotopomers: a crystallographic isotope effect

Abstract

A synthetic route to [Os₄(µ-H)(µ-OH)(µ-CO)(CO)₁₂] (1) has been devised through the activation of [Os₄(CO)₁₄] with Me₃NO. The pyrolysis and photolysis of the reactant in the presence of a trace amount of water produces 1 in low yield. The solid-state structure of [Os₄(µ-H)(µ-OH)(µ-CO)(CO)₁₂·H₂O] (1·H₂O) reveals a butterfly Os₄ skeleton with bridging H, OH and CO ligands as well as hydrogen-bonded molecules of water in the crystal lattice. A low-temperature ¹³C{¹H} NMR spectroscopic study revealed a merry-go-round exchange of CO ligands around the Os₃ plane containing the asymmetric bridging CO. The exposure of 1·H₂O to D₂O yielded [Os₄(µ-H)(µ-OD)(µ-CO)(CO)₁₂] (2). Although the solid-state, intramolecular structure of 2 closely matched that of 1·H₂O, the intermolecular structure did not: its crystal lattice contained no water of crystallization, a previously unreported crystallographic isotope effect.