Masahiro Yamashita

Control of CDW state in halogen-bridged metal complexes

Abstract Chemical modifications of one-dimensional (1D) halogen-bridged mixed-valence metal complexes have been made in order to control the amplitude of the charge density wave (CDW) state in -M-X-chains (M = Pt, Pd or Ni, and X = Cl, Br or I). By changing chemical parameters, such as strength of hydrogen-bonds between the ligands and the counter anions, and the ionic radii of M and X, the characteristic diagram of the amplitude of CDW has been obtained as a function of the M-X-M distances. This provides a new basic idea for understanding the 1D electronic state of the M-X compounds, especially as related to dynamical phenomena originated in the charge transfer instability in the ground state and the photo-excited state.

Valence structure of one-dimensional halogen bridged —PtPtXPtPtX— type complexes studied by 31P solid NMR

Abstract 31 P MAS NMR spectra in the solid state were measured on halogen-bridged one-dimensional complexes (NH 4 ) 4 [Pt 2 X(pop) 4 ] (pop: P 2 O 5 H 2− 2 ; X: Cl, Br, I) together with the corresponding binuclear Pt II and Pt III monomer complexes containing [Pt 2 (pop) 4 ] 4− and [Pt 2 X 2 (pop) 4 ] 4− (X: Cl, Br, I) ions, respectively. The polymer complexes afforded two kinds of 31 P resonance lines with chemical shifts of 20–40 and 50–70 ppm, values which are close to those in the monomer Pt II and Pt III complexes, respectively. From the analysis of spectra and spin—lattice relaxation data, a mixed-valence —Pt II Pt II X Pt III Pt III X— type chain structure was concluded for the polymer complexes.

Synthesis, X-ray molecular structure analysis, and study on ligand scrambling reactions of new thiolatogold(I) complexes with various phosphines

Abstract Treatment of Au(PPh3)Cl, (AuCl)2(trans-dpen) and (AuCl)2(dppfe) with Sn(SPh)(n-Bu)3 and/or PhSH/KOH affords Au(PPh3)(SPh) (1), (AuSPh)2(μ-trans-dpen) (2), (AuSPh)2(μ-dppfe) (3), (AuSPh)(μ-trans-dpen)(AuCl) (4), and (AuSPh)(μ-dppfe)(AuCl) (5) in good yields. All these thiophenolates are characterized by single crystal X-ray analysis, 1H and 31P NMR spectroscopy. 1 forms tetramer through Au⋯Au interaction and π–π interaction between the phenyl group in SPh and one of the phenyl groups in PPh3 in the solid state. An infinite chain structure is formed for 2 through intermolecular aurophilicity and these chains are connected by partial overlap (π–π interaction) of neighboring phenyl groups in SPh to give two-dimensional networks in the solid state. Similar infinite chains are formed through aurophilicity, but two-dimensional networks are not formed for 4 in the solid state. No multidimensional structure is formed for 3 and 5 in the solid state. 1H and 31P NMR spectroscopy of CDC13 solutions of 2, 3, 4, and 5 has revealed that rapid ligand scrambling takes place for 4 and 5.

The metallic state in a MMX-chain complex, Pt2(dta)4I

Abstract Transport, optical, magnetic, and structural properties of the MMX-type halogen-bridged mixed-valence complex, Pt 2 (dta) 4 I (dta = CH 3 CS 2 − ) were investigated. This complex exhibits metallic conduction between 300 and 340 K, which is the first observation in halogen-bridged 1-D transition-metal complexes. Below 300 K, a metal-semiconductor transition was observed. This salt undergoes an order-disorder phase transition at 340 K. The mixed-valence state is discussed.

Crystal structures of linear-chain halogen-bridged binuclear platinum complexes, dihydrate forms of K4[Pt2X(pop)4] ·nH2O (X=Cl and Br)

Abstract Crystal structures of the potassium catena-μ-halogenotetrakis(μ-diphosphonato-P,P)-diplatinum(4−) dihydrate, K 4 [Pt 2 X(pop) 4 ]·2H 2 O (X=Cl ( 1 ) and Br ( 2 ); pop=P 2 O 5 H 2 2− ), have been determined by the single crystal X-ray diffraction method. The complexes are isomorphous to each other and crystallize in orthorhombic, space group Pbnm , Z =4: for 1 , a =9.553(2), b =15.440(3), c =17.123(3) A, V =2525.6(8) A 3 at room temperature; for 2 , a =9.510(1), b =15.338(2), c =17.125(2) A, V =2497.9(6) A 3 at 125 K. The structures consist of linear chains with a repeating unit of ··· Pt II Pt II ··· XPt III Pt III X ··· along the c axes. The linear chains are not straight but a little bent to form zigzag chain structures, the bent angles defined by the PtPt bonds and the c axes being 3.34(1)° for 1 and 3.11(1)° for 2 , respectively. The PtPt separations, which are bridged by four pyrophosphato ligands (P 2 O 5 H 2 2− ), are 2.835(1) A for 1 and 2.834(1) A for 2 . The bridging halogen atoms are disordered over two sites in the chains, giving short PtX and long Pt ··· X separations: 2.406(4) and 3.362(4) A for 1 and 2.539(1) and 3.217(1) A for 2 , respectively. The deviations of the bridging halogen atoms from the midpoints between two Pt dimers are significantly larger than those of the trihydrate modifications.

Mixed-Valence States in MMX-Chains Complex, Pt2(dta)4I

Abstract Physical and structural properties of the MMX-type halogen-bridged mixed-valence complex, Pt2(dta)4I (dta = CH3CS2 −) were investigated. This complex exhibits metallic conduction above room temperature, which is the first observation in halogen-bridged 1-D transition-metal complexes. Below 300 K, the metal-semiconductor transition was observed. The mixed-valence state of this compound is discussed.

Electrical conductivity of one-dimensional halogen-bridged metal complexes at high pressures

Abstract The resistivity of four one-dimensional halogen-bridged metal complexes, Pt 2 (CH 3 CS 2 ) 4 I and M(chxn) 2 X 3 (M = Ni, Pd, Pt; X = Br; I; chxn = 1R, 2R-cyclohexanediamine), has been studied up to 7 GPa under quasi-hydrostatic conditions. The resistivity of Pt 2 (CH 3 CS 2 ) 4 I and Ni(chxn) 2 Br 3 with regular chains monotonically decreased with increasing pressure. On the other hand, the resistivity of Pd(chxn) 2 Br 3 and Pt(chxn) 2 I 3 with alternating lienar chains rapidly decreased in the low pressure region. The activation energy of the four metal complexes was in the range 0.03–0.05 eV at 7 GPa. Metallic behavior was not observed even at high pressures. The electrical conduction of the complexes is discussed.

One-dimensional spin dynamics in a halogen-bridged mixed-valence palladium (II), (IV) complex studied by 1H NMR

Abstract The 1 H NMR spin—lattice relaxation time T 1 of [Pd(chxn) 2 ][PdBr 2 (chxn) 2 ]Br 4 (chxn = 1R,2R-cyclohexanediamine) in the solid state was measured between 90 K and room temperature at Larmor frequencies of 10–60 MHz. The presence of thermally activated diffusive spins formed on paramagnetic Pd III sites along the halogen-bridged 1D chain was revealed from the Larmor frequency dependence of T 1 . The diffusion rates were estimated to be 2 × 10 13 , 9 × 10 11 , and 6 × 10 10 rad s −1 at 303, 198 and 125 K, respectively. The rate observed around room temperature showed an Arrhenius-type temperature dependence with an activation energy of ≈1700 K. It is shown that the diffusive spin is delocalized over several Pd sites. The observed spin motion is attributable to the neutral soliton by referring to the electrical conductivity data.

Competition between electron correlation of NiIII states and electron-phonon interaction of PdII-PdIV mixed-valence states in quasi-one-dimensional halogen-bridged mixed-metal complexes, Ni1-xPdX(chxn)2Br3

A series of single crystals of quasi-one-dimensional halogen-bridged Ni-Pd mixed-metal compounds, Ni1-xPdx(chxn)2Br3 (chxn equals 1R, 2R- cyclohexanediamine) have been obtained by electrochemical oxidation methods. In order to investigate the competition between the electron-correlation in the NiIII states (SDW states) and the electron-phonon interaction in the PdII-PdIV mixed-valence states (CDW states) in the Ni-Pd mixed-metal compounds, the single-crystal electrical conductivities, IR, resonance Raman spectra, ESR, magnetic susceptibilities, and XPS, have been measured. The electrical conductivities of these compounds show semiconducting behavior with the conductivities maximized and the activation energies minimized at x equals ca. 0.5. The IR, resonance Raman spectra, and XPS show that the PdII- PdIV mixed-valence states are influenced and approaching to the PdIII states with the increase of the NiIII components.

Photogeneration of Solitons and Polarons in MX Chains

Abstract The effects of the electron-lattice (e-1) coupling and the interchain interaction on the gap states in the one-dimensional Peierls-Hubbard system have been investigated by the photo-induced absorption (PA) measurements of the halogen-bridged metal complexes (the MX chains; M=Pt and X=Cl, Br or I). In the complexes having small amplitude of CDW, three PA bands named a1 , a2 and b are observed. The PA bands a1 and a2 , which are insensitive to the interchain interaction, are assigned to polarons. The decrease of the interchain coupling of CDW leads to a midgap band b, which is attributable to charged-solitons. While, in the complexes having large amplitude of CDW, there are observed the two PA bands A and B having the long life time. Spectral shapes and excitation profiles of these PA bands are considerably different from those of the a1 , a2 and b bands. These results suggest that generation processes and stabilization energies of the gap states are strongly dependent on the magnitude of e-1 inter...