W0044

On Deuterium Isotope Enrichment From Water Solutions of Zwitterionic Dimolybdenum(II,II) Tetracarboxylate. Boris Udovic, via Timignano 42, 34128 Triest, Italy, borisudovic@email.si.

The natural abundance of deuterium ²₁H in water is unfavourably low (c. 150 mg dm^-3), neither the tritium isotope ³₁H can be easily recovered from conventionally enriched and extremely expensive tritiated water solutions.

At some point of crystal growth attempts, the viscous matrix solution of zwitterionic dimolybdenum(II,II) 3,5-diaminobenzoate tetracarboxylate Mo₂(O₂CC₆H₃(NH₃⁺)₂)₄Br₈·xH₂O was equilibrated at –22 ºC, its aqueous constituent was isolated on high vacuum working line and analysed with mass spectrometer. A depletion shift in deuterium content was found at the extent δ(²₁H)~ -112.4 ‰ if referred to the ocean water standard, where:

δ(‰) = {[isotope ratio (sample) - isotope (standard)]/[isotope ratio (standard)]}×10³

A plausible explanation on the origins of congruently isolated and isotopically depleted water involves efficient incorporation of deuterium ²₁H in place of hydrogen ¹₁H across quadruply bonded dimers Mo₂⁺ by isotopic exchange and oxidative addition reactions in strongly acidic media. A rapid pre-equilibrium with ionic pairs formation through protonated-deuterated species is highly favoured in concentrated and reactive matrix solutions of strong hydrohalogenic acids as HCl, HBr and HI. The Hammett acidity function H₀ was considered to be a reliable quantitative measure of the solution acidity and a significant parameter within the overall isotopic exchange pathway. The observed absorption peak (ε ~ 4×10³ M^-1cm^-1, 25 °C) at λ_max = 446 nm (in comparison with λ_max = 520 nm of well known Mo₂Cl₈^4- anionic species), was assigned to a δ→δ^* transition in the inner side of the zwitterionic tetrakis(3,5-diaminobenzoate)dimolybdenum(II,II) complex. This peak disappeared gradually as the oxidative addition reaction with breaking of the δ component of the quadruple metal-metal bond advanced to a higher extent. Isotope enrichment via chemical exchange and hydride-deuteride intermediates make possible an alternative proposal to known procedures of electrolysis, electromigration, thermal diffusion, centrifuging etc. to accomplish separations of light isotopes as deuterium ²₁H and tritium ³₁H directly from water solutions.