The crystal structure of potassium heptafluoroprotactinate(V) and bonding in ML9 complexes

Abstract

Potassium heptafluoroprotactinate(V) is monoclinic, space group C2/c, with four formula units of K₂PaF₇ in a cell of dimensions a= 13·760, b= 6·742, c= 8·145 Å, β= 125·17°. The structure was solved by Patterson and difference syntheses, and refined by least-squares methods. R is 0·067 for 580 independent reflections. Each protactinium is surrounded by nine fluorines in a slightly distorted trigonal (prism plus equatorial triangle) array, of which the only strict (crystallographic) symmetry is a diad axis. These PaF₉ groups are linked by unsymmetrical two-fluorine bridges into infinite chains. The geometry and bonding of this and related structures are discussed.