Preparation and spectroscopic characterization of sodium pentacyano(phosphane/phosphite)ferrates(III)

Sodium pentacyanoferrates(III) of the type Na-2[Fe(CN)(5)L] (L = phosphane or phosphite) have been prepared from sodium pentacyanoferrates(II), Na-3[F e(CN)(5)L], by bromine oxidation and characterized by Mossbauer, IR, and el ectronic spectroscopy. Isomer shifts and quadrupole splittings lie within t he range commonly found in low-spin iron(III) complexes. A linear correlati on was round between isomer shifts and CN stretching and Fe-CN bending freq uencies, respectively. The spectroscopic parameters show that the d(pi)-d(p i) back bonding of the Fe-P bonds is synergetically strengthened with incre asing sigma donor capability of the phosphorus ligands.