Thermochemical and spectroscopic studies of some gold and tellurium complexes

Abstract

Using an isoperibol solution reaction calorimeter the enthalpies of aquation of selected anhydrous alkali tetrahaloaurates were measured and AHf(MAuX4(s)) derived from this and ancillary data as follows: (AHf(KAuCl4(s)) = -608.8 + 0.3 kj mol-1; AHf(RbAuCl4(s)) = -613.9 + 1.0 kj mol-1; AHf(KAuBr4(s)) = -486.1 + 1.3 kj mol-1; AHf(RbAuBr4(s)) = -497.5 i 1.8 kj mol-1). From the measured enthalpies of reduction of Me4NAuBr2 and Et4NAuBr2 (with aqueous FeSO4 soln.), and Et4NAuI2 (with aqueous SO2 soln.), the standard enthalpies of formation of the dihaloaurates were calculated. (AHf (Me4NAuBr2(s)) = -291.3 +/-0.1 kj mol-1;AHt (Et4NAuBr2(s)) = -428.4 - 0.1kJ mol-1; AHf(Et4NAuI2(s) ) = -353.92 - 0.20 kj mol-1)."Thermochemical radii" of the ions AuCl-4, AuBr4 and AuBr2 have been calculated by the Kapustinskii-Yatsimirskii procedure in order to estimate the lattice energies of the above salts, and the standard enthalpies of formation of the gaseous AuCl4, AuBr4 and AuBr2 ions. Additional standard enthalpies of formation and lattice energies of alkali metal salts containing these ions have been calculated. The reaction between aqueous tetrahaloaurate and ferrous sulphate in acid medium (X = Cl, Br) has been investigated by means of a thermometric titration; this was found to have only one rate limiting step in agreement with the induced chloride exchange of the AuCl4 (aq.) data reported by Rich and Taube. Raman investigations revealed no reaction between AuCl3 and SbCl5, or AuCl3 and AsCl3.The syntheses of tellurium dichloride dibroraide and the tellurium tetrahalide salts TeCl2Br2AlCl3; TeBr4AlBr3 TeBr3AlCl3, TeBr4SbBr5, TeBr4SbCl5; TeCl4AlBr3, TeCl4AlCl3 and TeCl4SbCl5 were attempted, using a technique involving halogenation and coraplexation in a number of chlorinated solvents. Raman investigations of the isolated products revealed: 1. the formation of an impure TeClBr2+Cl- (s) product. 2. the possible formation of an impure, covalent TeCl2BrAlBr2Cl2 product. 3. the formation of an impure TeBr3+ AlBr4 (s) product from CS2 medium. 4. no reaction of TeBr4 with AlCl3. 5. no reaction of TeBr4 with SbBr5. 6.chlorination of tellurium tetrabromide by antimony pentachloride to yield a product with Br:Cl ratio of 1:27. 7. no complexation between the tellurium tetrachloride and AlBr3. 8. an unidentified product from TeCl4 and AlCl3 which thermally decomposed in a laser beam of wavelength 647.1 nm. 9. the formation of an impure TeCl3+ SbCl6- product.Purification of the tetrahalides and complexes by distillation under reduced pressure and recrystallisation from glacial acetic acid/acetic anhydride or toluene was attempted. In all cases thermal decomposition took place.