No abstract

The reduction of [(μ(2)-H)( μ(3)-H)(Cp*ZrCl)](4) by excess Na/Hg led to the isolation of the mixed-valence Zr(III)/Zr(IV) Zr(4) cluster [(μ(2)-H)(8)(μ(2)-Cl)(2)(Cp*Zr)(4)], 1, and the Zr(II)/Zr(III) Zr(4) cluster [(μ(2)-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 Zr(4) tetrahedrons containing direct Zr-Zr bonds.