MOLAR REFRACTIVITY AS A DIAGNOSTIC TOOL FOR DETERMINING COMPOSITION OF TRANSITION ELEMENT FLUORIDE COMPLEXES

The composition of alkali (and ammonium) fluoride complexes of the tetravalent d- and f-transition elements Zr, Ce, Th, U, and Pt can be determined from their molar refractivities, R. A simple linear rule applies: RnAF·MF = nRAF + RMF. The absolute value of the refractivity depends on the tetravalent element M and the mole ratio (n) of alkali fluoride (AF) to MF4. The increment in refractivity per mole of a given alkali fluoride in the complex is a constant. For some 45 compounds it was found that RAF is equivalent to RA+ plus RF-, Fajans' refractivities for the aqueous ions. Thus, a close estimate of the molar refractivity for many compounds can be obtained by adding multiples of Fajans' aqueous refractivities for the alkali and fluoride ions to the measured refractivity of the tetrafluoride. The RnAF·MF values for analogous compounds reflect the sequence RCeF > RUF ≈ RPtF > RThF > RZrF. Additivity also applies to RnAF· MF and RnAF· MF the molar refractivities of trivalent and pentavalent fluoride complexes. A model for statistical treatment of refractivity data is given. © 1969, American Chemical Society. All rights reserved.