Structural, magnetic, and optical studies of new mixed-valence copper(II)–platinum(IV) complexes with one-dimensional chain structures

Abstract

The crystal structures of halogen-bridged one-dimensional copper(II)–platinum(IV) complexes [Cu(en)₂][PtX₂(en)₂][ClO₄]₄(en = ethylenediamine, X = Cl or Br) have been determined by X-ray structure analyses. The chloro-bridged complex (1) crystallizes in the orthorhombic space group Icma with unit-cell dimensions a= 13.645(1), b= 10.787(1), c= 9.645(1)Å, and Z= 2. The bromo-bridged complex crystallizes as two different non-stoicheiometric compounds (2a) and (2b) depending on the preparation conditions. Both compounds crystallize in the orthorhombic space group Icma with a= 13.599(1), b= 10.917(1), c= 9.657(1)Å, and Z= 2 for (2a) and a= 13.625(2), b= 10.905(2), c= 9.651 (1)Å, and Z= 2 for (2b). In (1), (2a), and (2b), the copper(II) and platinum(IV) complexes which are bridged by a halogen atom are stacked alternately, leading to a one-dimensional chain structure. The X-ray structure analyses using a full-matrix least-squares method revealed the non-stoicheiometric structures, in which the Cu^II and Pt^IV are partially replaced by Pt^II. The temperature dependence of the magnetic susceptibilities and e.s.r. measurements show no strong magnetic interaction between the copper atoms. Single-crystal reflectance spectra of complex (1) show a polarized band (parallel to the chain direction) at 2.7–2.8 eV corresponding to Cu^II→ Pt^IV charge transfer. A progression of peaks (313, 625, and 940 cm^–1) due to the totally symmetric stretching mode of Cl–Pt^IV–Cl was observed in the resonance-Raman spectrum of complex (1).