Relationships among ionic lattice energies, molecular (formula unit) volumes, and thermochemical radii

The linear generalized equation described in this paper provides a further dimension to the prediction of lattice potential energies/enthalpies of ion ic solids. First, it offers an alternative (and often more direct) approach to the well-established Kapustinskii equation (whose capabilities have als o recently been extended by our recent provision of an extended set of ther mochemical radii). Second, it makes possible the acquisition of lattice ene rgy estimates for salts which, up until now, except for simple 1:1 salts, c ould not be considered because of lack of crystal structure data. We have g eneralized Bartlett's correlation for MX (1:1) salts, between the lattice e nthalpy and the inverse cube root of the molecular (formula unit) volume, s uch as to render it applicable across an extended range of ionic salts for the estimation of lattice potential energies. When new salts are synthesize d, acquisition of full crystal structure data is not always possible and po wder data provides only minimal structural information-unit cell parameters and the number of molecules per cell. In such cases, lack of information a bout cation-anion distances prevents use of the Kapustinskii equation to pr edict the lattice energy of the salt. However, our new equation can be empl oyed even when the latter information is not available. As is demonstrated, the approach can be utilized to predict and rationalize the thermochemistr y in topical areas of synthetic inorganic chemistry as well as in emerging areas. This is illustrated by accounting for the failure to prepare diiodin etetrachloroaluminum(III), [I-2(+)][AlCl4-] and the instability of triiodin etetrafluoroarsenic(III), [I-3(+)][AsF6-](-) A series of effective close-pa cking volumes for a range of ions, which will be of interest to chemists, a s measures of relative ionic size and which are of use in making our estima tes of lattice energies, is generated from our approach.