Organometallic oxides: preparation of the cluster [(eta-C5Me5)Mo](4)O-7 by reduction of [(eta-C5Me5)MoCl(O)](2)(mu-O) or (eta-C5Me5)MoCl2(O)

Reduction of [(eta-C5Me5)MoCl(O)](2)(mu-O) or (eta-C5Me5)MoCl2(O) with sodium or magnesium amalgam, magnesium turnings, or tributyltin hydride produced [(eta-C5Me5)Mo](4)O-7, with [(eta-C5Me5)Mo(O)(mu-O)](2) as a co-product. [(eta-C5Me5)Mo](4)O-7 was characterized by X-ray diffraction, mass spectrometry, H-1 NMR and IR spectroscopies, and magnetism. Crystals of [(eta-C5Me5)Mo](4)O-7 contained a tetrahedral [(eta-C5Me5)Mo](4) unit (Mo-Mo = 2.909 (3) Angstrom) with the Mo4O7 core having the structure Mo-4(mu(2)-O(b))(3)(mu(2)-O(c))(3)(mu(3)-O(a)) (3). Microcrystalline samples of [(eta-C5Me5)Mo](4)O-7 were paramagnetic over the temperature range 2-300 K, with an effective moment of 1.26 mu(B) at 300 K. [(eta-C5Me5)Mo](4)O-7 was also paramagnetic in chloroform solution, over the temperature range 223-298 K, with an effective moment of 1.43 mu(B) at 298 K. The H-1 NMR spectrum showed a broad resonance at 16.3 ppm (delta nu(1/2) = 113 Hz) and two narrow resonances at 1.89 ppm and 1.69 ppm (delta nu(1/2) = 5 Hz). The magnetism and NMR spectra showed that [(eta-C5Me5)Mo](4)O-7 existed in two forms which were in equilibrium in solution. One form was paramagnetic (S = 1), with the Mo4O7 core having the geometry 3, and the other was diamagnetic (S = 0), with the Mo4O7 core having the geometry 4.