PREPARATION AND STRUCTURAL CHARACTERIZATION OF TRIRUBIDIUM OCTACHLORODIMOLYBDENUM . A BINUCLEAR STRUCTURE WITH STRONG METAL-METAL BONDING

The compounds Rb3Mo2Cl8 and Cs3Mo2Cl8 have been isolated and structurally characterized. The green-yellow crystall in e solids are obtained by treatment of Mo2(O2CCH3)4 with deoxygenated 12 N HCl at 60°, followed by addition of RbCl or CsCl and cooling to 0°. The cesium compound is obtained in practically quantitative yield. These compounds can be converted electrochemically into Rb3Mo2Cl9 and Cs3Mo2Cl9 in excellent yields; we believe this is the best way to prepare the latter compounds. Rb3Mo2Cl8 and Cs3Mo2Cl8 appear virtually certain to be isostructural. The structure of Rb3Mo2Cl8 has been solved and refined: space group P62c; a = 7.190 (5) Å, c = 16.662 (10) Å at 24°; dcaled(Z = 2) = 3.26 g cm-3; dobsd = 3.23 ± 0.04 g cm-3. The structure consists of Rb+ ions and discrete Mo2Cl83- ions. The latter are not related structurally to the Mo2Cl84- ion but may be described as Mo2Cl9 groups of the bioctahedron (W2Cl93-) type in which one-third of the bridging Cl atoms are missing. These defective binuclear entities are then rotationally disordered in the crystal. The Mo-Mo distance, 2.38 (1) Å, as well as the squashing together of the two octahedra, shows that there is strong metal-metal bonding, though not so strong as in Mo2Cl84- (Mo-Mo = 2.14 Å). © 1969, American Chemical Society. All rights reserved.