Niobium pentaisopropoxide

The NMR spectrum of niobium pentaisopropoxide at room temperature indicates a broad resonance and an average donblet which at low temperatnres was resolved into peaks of the dimer (at S 1.25 and 4.90) and monomer (at S 1.19 and 4.68). Although the monomer/dimer equilibrium for niobium pentaisopropoxide also existed in benzene solution, the value of the equilibrium constant at a given temperatnre was about 100 times greater for niobium than for tantalum isopropoxide, thereby demonstrating the greater degree of dissociation of niobium isopropoxide into monomeric species. 

The NMR spectra of the isopropoxides of niobium and tantalum were found to be both temperature (Fig. 2.5) and concentration (Fig. 2.6) dependent, consistent with the equilibrium M2(OPF) 2M(OPF)5. For example the pentaisopropoxide of tantalum in cyclohexane solution gave three septets in the range 8 4.7-5.0. The intensity of the high-field signals increased on raising the temperature at the expense of the... 

Compared to the tetra-alkoxoaluminates, the corresponding hexa-alkoxoniobate and -tantalate derivatives of most of the metals are less stable. Of these two, the niobate products tend to disproportionate more readily this is reflected in the conductivity curves obtained in the titrations of niobium and tantalum pentaisopropoxide with alkali (Na, K) isopropoxides in isopropyl alcohol (see Fig. 3.2). 

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See also in sourсe #XX -- [ , ]

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