Observation of the Properties of a Single Unit of a Limited CDW Structure in a PtII/PtIVHost-Guest Binary System Based on a Square-Shaped Complex

A macrocyclic tetranuclear platinum(II) complex [Pt(en)(4,4'-bpy)](4)(NO(3))(8) (1(NO(3))(8); en = ethylenediamine, 4,4'-bpy = 4,4'-bipyridine) and a mononuclear platinum(IV) complex [Pt(en)(2)Br(2)]Br(2) (2Br(2)) formed two kinds of Pt(II)/Pt(IV) mixed valence assemblies when reacted: a discrete host-guest complex 12Br(10) (3) and an extended 1-D zigzag sheet 1(2)(3)Br(8)(NO(3))(6) (4). Single crystal X-ray analysis showed that the dimensions of the assemblies could be stoichiometrically controlled. Resonance Raman spectra suggested the presence of an intervalence interaction, which is typically observed for quasi-1-D halogen-bridged M(II)/M(IV) complexes. The intervalence interaction indicates the presence of an isolated {Pt(II)X-Pt(IV)-XPt(II)} moiety in the structure of 4. On the basis of electronic spectra and polarized reflectance measurements, we conclude that 4 exhibits intervalence charge transfer (IVCT) bands. A Kramers-Kronig transformation was carried out to obtain an optical conductivity spectrum, and two sub-bands corresponding to slightly different Pt(II)-Pt(IV) distances were observed.