Characterization of 2(0' )8(' 0 )2 by and 13C NMR spectroscopy, IR spectroscopy, and single-crystal X-ray diffraction (-100 °C) is reported. The compound crystallizes in the space group PI with a = 18.262 (4) Á, b = 19.883 (5) Á, c = 12.067 (3) Á, a = 98.59 (1)°, ß = 96.26 (1)°, y = 77.49 (1)°, and Z = 4. The unit cell contains four half-dimers in the asymmetric unit, all of which differ only in the rotational conformation about Zr-O and O-C bonds. In each dimer, the edge-shared bioctahedron has two µ-O'Pr groups. On opposite sides of this 2(µ-)2 plane, each dimer forms two hydrogen bonds, one each between a coordinated alcohol and a terminal alkoxide. The NMR spectra at 25 °C are so simple as to be structurally uninformative, a result of rapid fluxionality which includes, as one component, proton migration among all O'Pr units. At -80 °C in toluene, the NMR spectra are now too complex to be accounted for by a single edge-shared bioctahedral structure. The hafnium analogue is isomorphous with the zirconium compound. Although Ce2(0'Pr)8('Pr0H)2 is not isomorphous, it exhibits an analogous hydrogen-bonded structure in which the 0-0 distance is as short as it is in the Zr analogue, in spite of a metal-metal separation which is longer by 0.28 Á. It crystallizes in the space group PI with a = 1 1.385 (4) Á, b = 12.144 (5) Á, c = 9.009 (3) Á, a = 109.72 (1)°, ß = 111.54 (2)°, y = 65.70 (1)°, and Z = 1. The generality of hydrogen bonding between M-OR and M-0(H)R groups when they are aligned parallel in a metal cluster is reviewed.

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The acidic protons in Zr2(0R)8(ROH)2, R = Pri, serve as a controlled functionality and react with Ba metal and with LiNMe2 to give the hydrocarbon-soluble heterometallic alkoxides Ba22r4(0R)20 and LiZr2(OR),(ROH) which have been characterized in solution by NMR spectroscopy and in the solid state by X-ray diffraction: Zr2(OR), units bind the Li+ and Ba2+ via bridging alkoxides and, for Li+, a terminal alcohol ligand which hydrogen bonds to a terminal alkoxide on zirconium.

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