ENTHALPIES OF MIXING IN SYSTEMS CONSISTING OF NEUTRAL ORGANOPHOSPHORUS COMPOUNDS AND LANTHANIDE(III) AND YTTRIUM(III) NITRATE SOLVATES

The enthalpies of mixing in systems consisting of neutral organophosph orus compound (NOPC) [NOPC = triisoamyl phosphate (TIAP), diisooctyl m ethylphosphonate (DIOMP), diisoamyl methylphosphonate (DIAMP), and dib utyl butylphosphonate (DBBP)] end lanthanide(III) nitrate solvates [Ln (NO3)(3) . 3S] (S = TIAP, DIOMP, DIAMP, and DBBP) were determined calo rimetrically at 298.15 K. The enthalpies of mixing (h(E)) are describe d by the equation h(E) = A(h)X(d)X(S), where X(d) and X(S) are the mol e fractions of the diluent and solvate, respectively. The values of A( h) become more negative with a decrease in the lanthanide(III) ionic r adius and in the length of phosphonate radicals.