Radii-volatility correlation

Method 7 Significant correlations exist between ionic radii in the solid state -or radii of electron orbitals of ions -and the sublimation enthalpies for various compound classes, especially for the halides. It is possible to calculate the standard sublimation enthalpy of transactinide compounds from their calculated ionic radii by making use of a radii-volatility correlation and of corresponding radii of the homologues [44], However, in this procedure it is important to use consistent sets of radii for all homologues, see e.g. Figure 7. 

Fig. 7. Radii-volatility correlation for group 4 elements and rutherfordium. The filled squares represent the radii of the outer orbital (r(orbit), top axis) the filled circles show the ionic radii in solid crystals (r(cryst), bottom axis). Included are predicted data for AH°sub (Rfpred.) from [44] (diamond) and rtcrysORf pred (triangle) from [49].

Eichler, B., Tiirler, A., Gaggeler, H.W. Radius-volatility correlation of tetrachlorides of Ti, Zr, Hf, 104, Th, and U. In PSI condensed matter research using large scale facilities annual report 1994, Annex IIIA, p. 76. Villigen (1995)... 

As one would expect, there is a strong correlation between solubility in non-polar solvents, volatility and molecular complexity of metal amide compounds. The degree of association can typically be related to empirical formula (ML ), metal covalent radius and the steric demand of the amide substituents. 

Several possible explanations can be offered to account for the ubiquitous correlation between the volatility of the complexes and the size of the metal ion. In the case of tris complexes with unsymmetrical ligands such as Ln(fod)3, the molecules have permanent molecular dipoles. Assuming that the size of the molecule decreases with the radius of the metal ion, the size of the molecular dipole should also decrease. Furthermore, all j -dike-tonate chelates, irrespective of the symmetry of the ligand, have small... 

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