X-ray photoelectron spectroscopic (XPS) and differential thermal analysis (DTA) studies of a series of diamine dihydrochlorides have shown that a linear relationship exists between the N(1 s) and Cl(2p3/2) binding energy shifts and the melting points of these salts. A theoretical model is presented to verify this empirical correlation. It is apparent that such binding energy shifts and melting points are also dependent upon intrinsic electronic and bonding features of these salts such as quaternary nitrogen substituent inductive effects, charge delocalisation within the cation, cation-anion interaction and salt hydration.
