Takuya Kawashima

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.

ESR observation of averaged-valence and charge-density-wave states in quasi-one-dimensional halogen-bridged binuclear metal complexes

Abstract Electron spin resonance (ESR) measurements have been performed on quasi-one-dimensional iodo-bridged binuclear metal complexes (MMX-chain compounds) A4[Pt2(pop)4I]·nH2O (A=Li, Na, K, Rb, Cs; pop=P2O5H22−). ESR signals show a clear distinction between averaged-valence (AV) and charge-density-wave (CDW) states predicted from optical studies in these complexes. While spin susceptibility χ of the CDW states shows Curie-like behavior, χ of the AV states shows a crossover from Curie to weakly temperature-dependent behavior at high temperatures, characteristic of the Heisenberg antiferromagnetic chains. The Na (n=2) and Cs (n=0) compounds are typical ones exhibiting the characters of the AV and CDW states, respectively. Furthermore, a signal around g=4 is observed, which is more remarkable in the CDW states, suggesting the formation of the state with S=1 or higher spin values as a defect state with a continuous fine-structure parameter distribution.

Electronic structures of quasi-one-dimensional halogen-bridged NiIII complexes with strong electron-correlations

Abstract In the quasi-one-dimensional halogen-bridged metal complexes, the Pt and Pd compounds have charge density wave (CDW) states or the M II –M IV mixed-valence states where the bridging halogens are distorted from the midpoints between neighboring two metal ions due to the stronger electron–phonon interaction. However, Ni compounds have spin density wave (SDW) states or the M III states where the bridging halogens are located at the midpoints between neighboring two metal ions, due to the stronger electron-correlation. These Ni compounds are not Mott-insulators but charge-transfer-insulators. The electronic structures in [Ni III (chxn) 2 X]Y 2 (chxn=cyclohexanediamine; X=Cl, Br and mixed-halides; Y=Cl, Br, mixed-helides, NO 3 , ClO 4 and BF 4 ) are tuned by substituting the bridging halogens and counteranions. The competition between the SDW states in Ni III sites and the CDW states in Pd II –Pd IV sites in the Ni–Pd mixed-metal compounds, Ni 1− x Pd x (chxn) 2 Br 3 , has been investigated. The Pd II –Pd IV states are approaching the Pd III states with increase of the Ni components in this system due to the stronger electron-correlation in Ni III sites.

Syntheses and physical properties of quasi-one-dimensional chloro-bridged Ni–Pd mixed-metal MX-chain compounds, Ni1−xPdx(chxn)2Cl3

Abstract A series of single crystals of quasi-one-dimensional chloro-bridged Ni–Pd mixed-metal MX-chain compounds, Ni 1− x Pd x (chxn) 2 Cl 3 (chxn=1 R ,2 R -diaminocyclohexane) have been obtained by electrochemical oxidation methods. In order to investigate the competition between the electron correlation in the Ni(III) states and the electron–phonon interaction in the Pd(II)–Pd(IV) mixed-valence states in the Ni–Pd mixed-metal compounds, the infrared spectra, resonance Raman spectra, X-ray photoelectron spectra and Auger spectra have been measured. These results show that the Pd(II)–Pd(IV) mixed-valence states are influenced by Ni(III) and gradually approaching to the Pd(III) states with the increase of the Ni(III) components as observed in Br-bridged complexes, Ni 1− x Pd x (chxn) 2 Br 3 .

Competition between electron-correlation in Ni(III) and electron-lattice interaction in Pd(II)-Pd(IV) in mixed-metal MX-chain, Ni1−xPdx(chxn)2Br3

Abstract The electrical conductivities, IR, XPS and resonance Raman spectra of a series of Ni-Pd mixed-metal MX-chain compounds, Ni1−xPdx(chxn)2Br3 have been measured in order to investigate the competition between the electron-correlation in Ni(III) and the electron-lattice interaction in Pd(II)-Pd(IV) states. In these compounds, at x=0.4, the activation energy in electrical conductivity is minimized. And at x=0.4 or below, the vN-H does not split, while at x with larger than 0.5, vN-H shows triplet. This result suggests that the Pd(II)-Pd(IV) mixed-valence states are effectively influenced by Ni(III) states, approaching toward the Pd(III) states.

Crystal and Electronic Structures of Quasi-One-Dimensional Halogen-Bridged Binuclear Platinum Complexes, {(C n H 2n+1 ) 2 NH 2 } 4 [Pt 2 (pop) 4 I] (n=2-6)

The crystal structures of {(C n H 2n+1 ) 2 NH 2 } 4 [Pt 2 (pop) 4 I] (pop=O(PO 2 H) 2 2− , n=2-6) have been determined. Judging from the results of the X-ray structural analyses and Raman spectra, 1-D electronic structures of these compounds are consider to be …Pt 2+ -Pt 3+ -X …Pt 2+ -Pt 3+ -X… charge-polarized states.

Charge Fluctuation in MMX Chain Compounds, R4[Pt2(pop)4I]

Abstract A series of quasi-one-dimensional I-bridged binuclear platinum compounds, R 4 [Pt 2 (pop) 4 I].nH 2 O (R=Li, Na, K, NH 4 , Rb, Cs etc.: pop=P 2 O 5 H 2 ) have been synthesized. Resonance Raman spectra revealed that the compounds with Li and Na take -Pt 2.5+ -Pt 2.5+ -I-Pt 2.5+ -Pt 2.5+ -(a) while the compounds with Rb and Cs take …Pt 2+ -Pt 2+ …I-Pt 3+ -Pt 3+ -I.(b). Interestingly, the compound with NH 4 shows the phase transition between (a) at room temperature and (b) at 10K.

Competition between electron-phonon interaction and electron-correlation in Ni-Pd mixed-metal MX chain compounds

Abstract The IR, XPS and resonance Raman spectra of a series of Ni-Pd mixed-metal MX-chain compounds, Ni 1−x Pd x (chxn) 2 Br 3 have been measured in order to investigate the competition between the electron-correlation in Ni III and the electron-phonon interaction in Pd II –Pd IV states. The splitting of doublet signals of the Pd II –Pd IV in IR spectra and the integrated intensity of the Pd IV -Br stretching in Raman spectra decrease with decrease of Pd components. These results suggest that the Pd II –Pd IV mixed-valence states are effectively influenced by Ni III states, approaching toward the Pd III states.

Charge Fluctuation in Quasi-One-Dimensional Halogen-Bridged Platinum Binuclear Mixed-Valence Compounds, A4[Pt2(pop)4I]·nH2O

Abstract New quasi-one-dimensional halogen-bridged platinum binuclear mixed-valence compounds, A4[Pt2(pop)4I]·nH2O (A=alkaline metal and NH4, and; n=0, 2 and 4) have been synthesized. The Li, Na and K compounds take structures -Pt2.5+-Pt2.5+-X-Pt2.5+-Pt2.5+-X- (a). On the other hand, the Cs and Rb compounds take structures …Pt2+-Pt2+…X-Pt3+-Pt3+-X… (b). Interestingly, the NH4 compound takes a phase transition between (a) and (b) around 200K.

Creations of Solitons and Polarons in MX-Chain Compounds, {[Pt(en) 2 ][PtX 2 (en) 2 ]} 3 (CuX 4 ) 4 (X=Cl and Br)

The creations of solitons and polarons in the {[Pt(en) 2 ][PtX 2 (en) 2 ]} 3 (CuX 4 ) 4 (X=Cl and Br) which consist of the double linear chain structures of the main one-dimensional halogen-bridged Pt(II)-Pt(IV) mixed-valence units and one-dimensional counteranions of trigonal bipyramidal Cu(I) ions, have been investigated by the absorption spectra, photo-induced absorption spectra, and ESR spectra. The ESR signals of the Pt(III) and Cu(II) species, which were introduced during the synthetic process, are observed in these compounds. The relative intensities of d-d transitions and ESR spectra of Cu(II) species in counteranions are consistent with each other in the Cl-bridged compounds obtained by pH control. The photo-induced absorption of the Cl-bridged compound is observed in the mid-gap region, which is attributable to the soliton. The doping effect by Br 2 was investigated of d-d transition and ESR spectra in Cu(II) increase with increasing exposure time. However, the electrical conductivities do not increase. Therefore, the induced Pt(III) species are attributable to neutral solitons.