Structure of the mixed-valence platinum complexes [Pt II(en)(SCN) 2][Pt IV(en)(SCN) 2I 2] and cis-[Pt II(NH 3) 2(SCN) 2][Pt IV(NH 3) 2(SCN) 2I 2] studied by the method of radial distribution functions of atoms

Abstract

Using the method of radial distribution functions of atoms obtained by Fourier transform of powder X-ray patterns it has been shown directly that the structures of the mixed-valence complexes cis- [Pt II(NH 3) 2(SCN) 2][Pt IV(NH 3) 2(SCN) 2I 2] ( I) and [Pt II(en)(SCN) 2][Pt IV(en)(SCN) 2I 2] ( II) (en = ethylenediamine) contain the linear chains …IPt IVI…Pt II…IPt IV-I…Pt II…I, wherein square-planar complexes of Pt II alternate with octahedral complexes of Pt IV. Such a structure for I had earlier been proposed only on the basis of indirect spectroscopical data. The distances Pt IVI and Pt II…I have been determined. The first one is 2.70 Å in both the complexes and the second is 3.50 Å in I and 3.23 Å in II. The distances Pt II…I are considerably longer than corresponding distances in the similar mixed-valence complex of known structure [Pt II(en) 2][Pt IV(en) 2I 2](ClO 4) 4 ( IV) (about 3.10 Å). The elongation of the Pt II…I contact corresponds to the smaller bridge role of I atoms in the thiocianate complexes, to the smaller electron delocalization over the chain of Pt and I atoms and, hence, to a more pronounced division of the system into true complexes of Pt II and Pt IV than in IV.