Optical Spectra,Electrical Conductances,Densities,and Viscosities of Glass-Forming Melts

Abstract

The charge-transfer bands of I⁻ in thin film spectra of MCl₂ (M = Mn, Co, and Ni)-rich mixtures of tetra-n-alkyl* (A* = butyl, pentyl, hexyl, and heptyl, respectively), and tributylpropyl-ammonium iodides have been found to resemble those of crystalline potassium-, rubidium-, and cesium-iodides.¹ (The band separation corresponds to 0.87 to 0.97 eV as against 0.94 to 1.15 eV found in the spectra of crystalline KI, RbI, and CsI, and 0.94 eV for 5²P_3/2 ← 5²P_1/2 transitions in the case of iodine atom.) In addition to the usual d-d bands, the charge-transfer bands of CoX₄⁻ and NiX₄⁻ which are ordinarily obscured by the absorption of X⁻ are also observed. The band assignments of NiX₄⁻ have been made in the light of the calculated electronic energy levels of tetrahalonickel (II) complexes using the Liehr-Ballhausen secular determinants for the d⁸ system in a cubic tetrahedral field based on the four ligand-field parameters (NiCl₄⁻: λ = −275, B = 740.00, C/B = 3.97, Dq = 358; NiCl₂Br₂⁻: λ = −275, B = 713.75, C/B = 3.93, Dq = 346; and NiCl₂ I₂⁻: λ = −275, B = 637.75, C/B = 4.7, Dq = 346 cm⁻¹). Similarly, the charge-transfer bands of Br⁻ and Cl⁻ are also obtained in thin film spectra of MCl₂ (M = Mn, Co, and Ni) in tetrabutyl-, and trioctylpropyl-ammonium bromides, and tetrabutyl-ammonium chloride, respectively. The degree of dissociation of MX₄⁻ is negligible in pure (A₄N⁺)₂MX₄⁻ (where A stands for either the same or different alkyl groups) as apparent from the decrease in the electrical conductances with [MX₂]. The species, (A₄N⁺)₂MX₄⁻, appear to be held together with increased intermolecular forces at low temperatures as evident from the (increase in the E_η;, energy of activation of viscosity) kinematic viscosity measurements. The data on the energies of activation of conductances and viscosities as functions of composition and temperature suggest an increased molecular association (as their ratio E_η;/EΛ ≈ 1) in such systems. The conductances and viscosities have been analyzed in terms of different functional forms based on the free volume model. The Walden's product rule has been found applicable in these systems.