Explanations are provided for the first time for the historically known locations of electrical conductivity maxima versus mixing ratio (mole fraction of acid, x) in mixtures of (i) acetic acid with water and (ii) acetic acid with pyridine. To resolve the question for the second system, density-functional-based molecular dynamic simulations were performed, at 1:1, 1:2, 1:3, 1:5, and 1:15 mixing ratios, to gain vital information about speciation. In a zeroth-order picture, the degree of ionization (and hence conductivity) would be maximal at x = 0.5, but these two examples see this maximum shifted to the left (water/acetic acid, x = 0.06), due to improved ion stability when the effective dielectric constant is high (i.e., water-rich mixtures), or right (pyridine/acetic acid x = 0.83), due to improved acetate stability via "self-solvation" with acetic acid molecules (i.e., acid-rich mixtures) when the dielectric constant is low. A two-parameter equation, with theoretical justification, is shown to reproduce the entire 0 < x < 1 range of data for electrical conductivity for both systems. Future work will pursue the applicability of these equations to other amine/carboxylic acid mixtures; preliminary fits to a third system (trimethylamine/acetic acid) give curious parameter values.

The phenomenon of electrical conductivity maxima of molten salts versus temperature during orthobaric (closed-vessel) conditions is further examined via ab initio simulations. Previously, in a study of molten BiCl3, a new theory was offered in which the conductivity falloff at high temperatures is due not to traditional ion association, but to a rise in the activation energy for atomic ions hopping from counterion to counterion. Here this theory is further tested on two more inorganic melts which exhibit conductivity maxima: another high-conducting melt (SnCl2, σmax = 2.81 Ω(-1) cm(-1)) and a low-conducting one (HgBr2, σmax = 4.06 × 10(-4) Ω(-1) cm(-1)). First, ab initio molecular dynamics simulations were performed and again appear successful in reproducing the maxima for both these liquids. Second, analysis of the simulated liquid structure (radial distributions, species concentrations) was performed. In the HgBr2 case, a very molecular liquid like water, a clear Grotthuss chain of bromide transfers was observed in simulation when seeding the system with a HgBr(+) cation and HgBr3 (-) anion. The first conclusion is that the hopping mechanism offered for molten BiCl3 is simply the Grotthuss mechanism for conduction, applicable not just to H(+) ions, but also to halide ions in post-transition-metal halide melts. Second, it is conjectured that the conductivity maximum is due to rising activation energy in network-covalent (halide-bridging) melts (BiCl3, SnCl2, PbCl2), but possibly a falling Arrhenius prefactor (collision frequency) for molecular melts (HgBr2).

In a continuing effort to master the reasons for conductivity maxima vs temperature in semicovalent molten halides, the structure and some transport properties of molten zinc halide are examined with ab initio molecular dynamics. Molten zinc halides are a special class of molten salts, being extremely viscous near their melting point (with a glassy state below it) and low electrical conductivity, and since they are also known (ZnI2) or predicted (ZnBr2 and ZnCl2) to exhibit conductivity maxima, they would be useful additional cases to probe, in case the reasons for their maxima are unique. Strong attractive forces in ZnX2 result in tight tetrahedral coordination, and the known mixture of edge-sharing vs corner-sharing ZnX4 tetrahedra is observed. In the series zinc chloride → bromide → iodide, (i) the ratio of edge-sharing vs corner-sharing tetrahedra increases, (ii) the diffusion coefficient of Zn2+ increases, and (iii) the diffusion coefficient of the anion stays roughly constant. A discussion of conductivity, with focus on the Walden product W = ηΛe, is presented. With predicted Haven ratios of 1–15 when heated toward their conductivity maxima, the physical chemistry behind molten zinc halide conductivity does not appear to be fundamentally different from other semicovalent molten halides.

The phenomenon of electrical conductivity maxima of molten salts versus temperature during orthobaric (closed-vessel) conditions is further examined. First, we summarize results from densityfunctional-based molecular dynamics simulations of molten SnCl 2 and HgBr 2 , which provided structural information but also succeeded in reproducing (i) previously published experimental conductivities to within an order of magnitude, and (ii) the conductivity maxima. The "hopping" mechanism we previously proposed is now termed a Grotthuss mechanism, which became quite clear in the simulations of the molecular liquid HgBr 2 which exhibited Grotthuss chains of bromide transfers. Second, we fit the experimental conductivities of 12 different molten salts with the equation

Misconclusions are corrected on Raman peak assignment and gauche-vs.-trans conformer ratio of ethylenediamine in liquid and aqueous phases. Peaks lost upon aqueous dilution are due to lost NH⋯N interactions. Both conformers exist in both phases.