ALKALINE-EARTH-METAL(II) COMPLEXES WITH HYDROXIDE AND FLUORIDE IN MOLTEN NH4NO3-CENTER-DOT-1.5H(2)O AT 50-DEGREES-C

The formation of alkaline-earth-metal(II) hydroxide and fluoride compl exes in molten NH4NO3.1.5H(2)O has been investigated by potentiometric , NMR and Raman spectroscopic methods at 50 degrees C. Complexes with the formal composition MgOH+, Mg2OH3+ and CaOH+ were detected in the h ydroxide systems. The formal stability constants are: beta(11)[MgOH+] = 3.2 +/- 0.1 kg mol(-1), beta(21) [Mg2OH3+] - 1.6 +/- 0.5 kg(2) mol(- 2), beta(11)[CaOH+] = 0.8 +/- 0.1 kg mol(-1) obtained from potentiomet ric measurements. In the fluoride systems the following complexes were detected: MgF+, MgF2, Mg2F3+, CaF+, CaF2, SrF+, Sr2F3+ and BaF+ with formal stability constants: beta(11)[MgF+] = 3.3 +/- 0.5 x 10(2) kg mo l(-1), beta(11)[MgF2] = 1.2 +/- 0.2 x 10(6) kg(2) mol(-2), beta(21)[Mg 2F3+] = 2.5 +/- 0.2 x 10(2) kg(2) mol(-2) beta(11)[CaF+] = 1.0 +/- 0.2 x 10(2) kg mol(-1), beta(12)[CaF2] = 2.9 +/- 0.6 x 10(5) kg(2) mol(-) , beta(11)[SrF+] = 1.5 +/- 0.2 kg mol(-1), beta(21)[Sr2F3+] = 0.9 +/- 0.2 kg(2) mol(-2) and beta(11)[BaF+] = 0.7 +/- 0.1 kg mol(-1). F-19 NM R experiments reveal only small changes in the F-19 chemical shift upo n addition of Mg2+ or Ca2+, a fact which indicates a predominantly ion ic M-F bonding character in the complexes formed. N-14 NMR and Raman s pectroscopy experiments using M(NO3)(2).3H(2)O-NH4NO3.1.5H(2)O melts ( M = Mg, Ga, Sr, Ba) indicate that nitrate ions are weakly coordinated to the metal ions and suggest the following order of increasing metal ion-nitrate interaction: Ba2+ < Sr2+ < Ca2+ < Mg2+. Difference Raman s pectra of melts with magnesium or calcium ions, with and without fluor ide present, show that nitrate ions, rather than water molecules, are most likely released upon metal-fluoride complex formation according t o: M(H2O)(x)(NO3)(y)(2-y) + nF reversible arrow MF(n)(H2O)(x)(NO3)(y-z )(2-n-y+z) + zNO(3)-.