Syntheses and structures of Zr4 tetrahedral clusters containing direct Zr–Zr bonds: the missing cluster in the series Zrn (n = 2–6)

Abstract

The reduction of [(μ₂-H)( μ₃-H)(Cp*ZrCl)]₄ by excess Na/Hg led to the isolation of the mixed-valence Zr(III)/Zr(IV) Zr₄ cluster [(μ₂-H)₈(μ₂-Cl)₂(Cp*Zr)₄], 1, and the Zr(II)/Zr(III) Zr₄ cluster [(μ₂-H)₆(Cp*Zr)₄], 2. The proton NMR data supports the diamagnetic property of both clusters in solution and the solid state structure of each cluster revealed a distorted tetrahedral skeleton comprised of four Zr atoms and the presence of direct Zr–Zr bonds. The hydride-bridged Zr–Zr bond distances are in the range of 3.0516(6)–3.0585(6) Å in 1 and 3.0525(13)–3.0864(13) Å in 2. The chloride-bridged Zr–Zr distances in 1 are 3.5514(6) and 3.5643(6) Å. The existence of Zr–Zr bonds in both clusters was further confirmed by DFT calculations. 1 and 2 represent the first examples of Zr₄ tetrahedrons containing direct Zr–Zr bonds.