Syntheses and physical properties of quasi-one-dimensional halogen-bridged Cu^II-Pt^IV mixed-metal complexes [Cu(chxn)₂][PtX₂(chxn)₂]X₄

Quasi-one-dimensional halogen-bridged Cu^II-Pt^IV mixed-metal complexes of the form [Cu(chxn)₂] [PtX₂(chxn)₂]X₄, where chxn = 1R,2R-diaminocyclohexane and X is either Cl or Br, have been synthesized. The crystal structures of these compounds have been determined by single-crystal X-ray diffraction. The Cl-bridged compound crystallizes in the space group I222 with dimensions a = 24.237(1) Å, b = 5.103(1) Å, c = 6.854(1) Å, and V = 847.7(1) ų and with Z = 1. The Br-bridged complex crystallizes in the space group I222 with dimensions a = 23.700(8) Å, b = 5.344(5) Å, c = 6.978(8) Å, and V = 883.8(8) ų and with Z = 1. These structures are isomorphic to each other and to homometal [Pt(chxn)₂][PtX₂(chxn)₂]X₄ complexes. In these complexes, the planar [Cu(chxn)₂] and the octahedral [PtX₂(chxn)₂] groups are stacked alternatively with the axial bridging halogen ions, forming linear chain structures. The neighboring [Cu(chxn)₂] and [PtX₂(chxn)₂] moieties along the chains are linked by hydrogen bonds between amino hydrogens and the counteranions (X). Moreover, there are hydrogen bonds among the neighboring chains that form a two-dimensional hydrogen-bonded network parallel to the bc plane. Therefore, the Cu^II and Pt^IV units are two-dimensionally ordered. The b axes correspond to the Cu^II-Pt^IV separations, which are shorter than those of [Pt(chxn)₂][PtX₂(chxn)₂]X₄ due to the smaller ionic radius of the Cu^II ions. In the XP spectra, the Pt^IV 4f_7/2 and Pt^IV 4f_5/2 binding energies in homometal [Pt(chxn)₂][PtX₂(chxn)₂]X₄ are lower than those of [Cu(chxn)₂][PtX₂(chxn)₂]X₄ (X = Cl and Br), indicating that the electron-phonon interaction in Cu^IIPt^IV compounds is stronger than that in Pt^II-Pt^IV compounds. In the Raman spectra, v(Pt^IV-X) of the homometal Pt^II-Pt^IV complexes is lower than that of the Cu^II-Pt^IV complexes, indicating again that the electron-phonon interaction in Cu^II-Pt^IV compounds is stronger than that of Pt^II-Pt^IV compounds. The temperature-dependent magnetic susceptibilities of the Cu^II-Pt^IV complexes show weak antiferromagnetic interactions between Cu^II components along the chain axes.