ChemInform Abstract: Two Novel Phases Containing Centered, Isolated Zirconium Clusters, Rb4Zr6Cl18C and Li6Zr6Cl18H

Abstract

The title compounds are synthesized by reaction of Zr, ArCl{sub 4} with RbCl plus graphite, or LiCl plus ZrH{sub 1.7} at {approximately} 850 or 700C, respectively. Stability of the rubidium phase is marginal, and the synthesis requires excess zirconium. The structures of the two have been established by single-crystal X-ray diffraction. Individual close-packed layers of isolated (Zr{sub 6}(C)Cl{sub 12}{sup i}Cl{sub 6}{sup a}){sup 4{minus}} clusters are present in the rubidium salt. However, the requirement of four cation sites results in offset, not close, packing of the layers, and the cations between these are bound more tightly to one layer than the other. The exo Zr-Cl{sup a} bonds (2.59 {angstrom}) are the shortest known because of weaker Cl{sup a} {hor ellipsis} Rb interactions. The rhombohedral Li{sub 6}Zr{sub 6}Cl{sub 18}H contains cubic-close-packed ((Zr{sub 6}(H)Cl{sup i}{sub 12})Cl{sub 6}{sup a}){sup 6{minus}} clusters with lithium in pseudooctahedral cavities between and within the layers. The Zr-cluster center distance, 2.257 {angstrom}, is at least 0.16 {angstrom} too large for good bonding of the hydride, and the solid-state {sup 1}H NMR shift ({approximately} 400 ppm vs Fe{sup 3+}(aq) at room temperature) is similar to that in Zr{sub 6}Cl{sub 12}H where a high hydrogen mobility is present. The sharp 11.8more » ppm absorption in the {sup 7}Li NMR spectrum (relative to LiCl) is consistent with the site symmetry deduced by X-ray diffraction and the nature of the nearest-neighbor chlorine atoms.« less