Ultrafast optical response in a quasi-one-dimensional halogen-bridged mixed-valence complex [Pd(en)2] [PdCl2(en)2] (ClO4)4

Syntheses and physical properties of quasi-one-dimensional halogen-bridged Cu(II)(-)Pt(IV) mixed-metal complexes [Cu(chxn)(2)][PtX(2)(chxn)(2)]X(4)

Quasi-one-dimensional halogen-bridged Cu(II)-Pt(IV) mixed-metal complexes of the form [Cu(chxn)(2)][PtX(2)(chxn)(2)]X(4), 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) A, b = 5.103(1) A, c = 6.854(1) A, and V = 847.7(1) A(3) and with Z = 1. The Br-bridged complex crystallizes in the space group I222 with dimensions a = 23.700(8) A, b = 5.344(5) A, c = 6.978(8) A, and V = 883.8(8) A(3) and with Z = 1. These structures are isomorphic to each other and to homometal [Pt(chxn)(2)][PtX(2)(chxn)(2)]X(4) complexes. In these complexes, the planar [Cu(chxn)(2)] and the octahedral [PtX(2)(chxn)(2)] groups are stacked alternatively with the axial bridging halogen ions, forming linear chain structures. The neighboring [Cu(chxn)(2)] and [PtX(2)(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)][PtX(2)(chxn)(2)]X(4) 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)][PtX(2)(chxn)(2)]X(4) are lower than those of [Cu(chxn)(2)][PtX(2)(chxn)(2)]X(4) (X = Cl and Br), indicating that the electron-phonon interaction in Cu(II)-Pt(IV) compounds is stronger than that in Pt(II)-Pt(IV) compounds. In the Raman spectra, nu(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.

Tuning of Charge Density Wave Strengths by Competition between Electron-Phonon Interaction of Pd(II)-Pd(IV) Mixed-Valence States and Electron Correlation of Ni(III) States in Quasi-One-Dimensional Bromo-Bridged Ni-Pd Mixed-Metal MX Chain Compounds Ni(1)(-)(x)()Pd(x)()(chxn)(2)Br(3)

A series of single crystals of quasi-one-dimensional bromo-bridged Ni-Pd mixed-metal MX chain compounds Ni(1)(-)(x)()Pd(x)()(chxn)(2)Br(3) (chxn = 1(R),2(R)-diaminocyclohexane) have been obtained by electrochemical oxidation methods of the mixed methanol solutions of parent Ni(II) complex [Ni(chxn)(2)]Br(2) and Pd(II) complex [Pd(chxn)(2)]Br(2) with various mixing ratios. To investigate the competition between the electron correlation of the Ni(III) states (or spin density wave states) and the electron-phonon interaction of the Pd(II)-Pd(IV) mixed-valence states (or charge density wave states) in the Ni-Pd mixed-metal compounds, IR, Raman, ESR, XP, and Auger spectra have been measured. The IR, resonance Raman, XP, and Auger spectra show that the Pd(II)-Pd(IV) mixed-valence states are influenced and gradually approach the Pd(III) states with the increase of the Ni(III) components. This means that in these compounds the electron-phonon interaction in the Pd(II)-Pd(IV) mixed-valence states is weakened with the strong electron correlation in the Ni(III) states.

Tuning of Spin Density Wave Strengths in Quasi-One-Dimensional Halogen-Bridged Ni(III) Complexes with Strong Electron Correlations, [Ni(III)(chxn)(2)X]Y(2)

A series of quasi-one-dimensional halogen-bridged Ni(III) complexes, [Ni(chxn)(2)X]Y(2) (chxn = 1R,2R-diaminocyclohexane; X = Cl, Br, and mixed halides; Y = Cl, Br, mixed halides, NO(3), BF(4), and ClO(4)) have been synthesized in order to investigate the effect of the bridging halogens and counteranions on their crystal, electronic structures, and moreover the spin density wave strengths. In the crystal structures, the [Ni(chxn)(2)] moieties are symmetrically bridged by halogen ions, forming linear-chain Ni(III)-X-Ni(III) structures. The hydrogen bonds between the aminohydrogens of chxn and the counteranions are constructed not only along the chains but also over the chains, forming the two-dimensional hydrogen-bond networks. While the Ni(III)-X-Ni(III) distances or b axes are almost constant in the compounds with the same bridging halogens, the c axes which correspond to the interchain distances in the directions of the interchain hydrogen bonds are remarkably lengthened with the increase of the ionic radius of the counterions; X < NO(3) < BF(4) < ClO(4). These compounds show the very strong antiferromagnetic interactions among spins on Ni 3d(z)2 orbitals through the superexchange mechanisms via the bridging halogen ions. Judging from the results of X-ray photoelectron spectra (XPS), Auger spectra, and single-crystal reflectance spectra, these Ni compounds are not Mott-insulators but charge-transfer-insulators. Their electronic structures or the spin density wave strengths are found to be tuned by the combinations of the counteranions and the bridging halogens.