Noriyoshi Kimura

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.

Spin solitons in halogen-bridged one-dimensional mixed-valence complexes, [MII(en)2][MIVBr2(en)2](ClO4)4 (M: Pt, Pd) studied by 1H NMR and EPR

Temperature and Larmor frequency dependences of 1H NMR spin–lattice relaxation time (T1) in 1-D mixed-valence complexes [M(en)2][MBr2(en)2](ClO4)4 (M: Pt, Pd; en: ethylenediamine) were observed in the ranges 90–330 K and 15–60 MHz. EPR spectra observed for the Pd complex showed the presence of paramagnetic PdIII sites of a temperature independent concentration of 10−4 per Pd site, and a motional narrowing upon heating attributable to thermally activated motions of these sites. The NMR T1 data giving an ω1/2 frequency dependence in the range 100–150 K were successfully analysed by applying the Devreuxs treatment of rapidly 1-D diffusing electron spins. Comparing the present results with the electrical conductivity data, the diffusing paramagnetic spins could be explained by kink-type neutral solitons analogous to the spin soliton model reported for trans-polyacetylene. Diffusion rates of 1012–1013 and 1013–1014 rad s−1 were estimated in Pt and Pd complexes, respectively, below ca. 150 K. This diffusion in the present 1-D structure complexes was shown to be much easier than that in [Pd(chxn)2][PdBr2(chxn)2]Br4 (chxn: 1R,2R-cyclohexanediamine) with 2-D hydrogen bond networks.

Metal valence structures in 1-D mixed-metal complexes [Ni1-xPdxX(chxn)2]X2 studied by solid NMR

13C magic-angle-spinning NMR spectra in solid were measured in mixed-metal 1-D complexes [Ni 1-x Pd x X(chxn) 2 ]X 2 (X: Cl, Br; 0.0≤x ≤1.0) where the antiferromagnetically coupled paramagnetic -X-Ni 3+ -X-Ni 3+ - chains are formed at x=0.0, while the mixed-valence -X-Pd 2+ -X-Pd 4+ - state is made at x=1.0. Upon increasing x from 0.0, 13 C spectra in the C α position in the chxn ligand was broadened and shifted from original Pd 2+ and Pd 4+ positions indicating the fluctuation of Pd valency in mixed states. A marked spectrum broadening observed in C β is also attributable to the effect from the partial mixing of paramagnetic Pd 3+ sites in consistent with reported ESR results.

Electron spin dynamics in the new halogen-bridged one-dimensional complex, Ni2(CH3CS2)4I studied by 1H NMR

Abstract We measured temperature and Larmor frequency(ω) dependences of the 1 H NMR spin-lattice relaxation time T 1 in solid Ni 2 (CH 3 CS 2 ) 4 I which contains the one-dimensional(1-D) chain of -Ni-Ni-I-Ni-Ni-I- with no Peierls distortion. Almost temperature independent T 1 values of ca. 180 ms observed at ω = 40.98 MHz and in the range of 90–300 K are attributable to the relaxation due to the fluctuation of antiferromagnetically coupled unpaired electron spin formed at each -X-Ni-Ni- unit in consistent with the 1-D Mott-Hubbard type structure. T 1 in this temperature range showed the Larmor frequency dependence of ω 1 2 explainable by rapid spin diffusion along the 1-D chain. Applying the Devreuxs treatment on the low-dimensional spin dynamics, the diffusion rate and activation energy for the 1-D hopping of electron spins were evaluated.

Control of Charge Instabilities in Quasi-One-Dimensional Halogen-Bridged Nickel Compounds

Abstract Quasi-one-dimensional halogen-bridged nickel compounds with nitrate counteranions, Ni(chxn)2X(NO3)2 (chxn=cyclohexanediamine; X=C; and Br), and with perchlorate counteranions, Ni(chxn)2X(C104)2 (X=Cl and Br) have been synthesized in order to control the charge instabilities. The Ni(chxn)2X(NO3)2 were synthesized by both chemical and electrochemical methods. The crystal structure of Ni(chxn)2Br(NO3)2 has been determined by single-crystal X-ray diffraction method. In this compound, the Ni(chxn)2 moieties are bridged by Br− ions to construct linear-chain structures and the hydrogen-bond networks of NH…O-N-0…HN which hold the chains are extended over the chains two-dimensionally. The bridging Br− ions are located at the midpoints between neighboring two Ni atoms along the chains with no Peierls distortion. The Ni(chxn)2X(C104)2 were synthesized by halogenation of 70% HC104 solution of Ni(chxn)2(C104)2. The lattice constants of Ni(chxn)2Cl(C104)2 were determined by X-ray powder pattern. The Ni-Cl-Ni d...

Spin solitons in a halogen-bridged 1-D Pt complex

Abstract Temperature and Larmor frequency dependences of 1 H NMR relaxation time T 1 were measured in a 1-D halogen-bridged complex [Pt(en) 2 ][PtX 2 (en) 2 ](ClO 4 ) 4 in ranges of 90 – 300 K and 15 – 60 MHz, respectively. The observed main and long T 1 component was explainable by the magnetic dipolar relaxation due to electron spins diffusing along the 1-D chain containing paramagnetic Pt III sites with a concentration of 10 −4 in molar ratio. These spins attributed to neutral spin solitons were shown to diffuse more rapidly than those in [Pd(chxn) 2 ][PdBr 2 (chxn) 2 ]Br 4 forming 2-D H-bond networks

Molecular motions and phase transitions in halogen-bridged one-dimensional complexes [Pt(en)2][PtX2(en)2](ClO4)4 (X: I, Br)

1H and 2H NMR and thermal measurements were performed on crystalline [Pt(en)2][PtI2(en)2](ClO4)4 in which protonated and partially deuterated ethylenediamines H2N(CH2)2NH2, D2N(CH2)2ND2 and H2N(CD2)2NH2 were used as the ligand “en”. A metastable crystalline phase of [Pt(en)2][PtBr2(en)2](ClO4)4 with conformational disorder of the en chelate rings was shown to have a different phase transition at ca. 380 K to the stable crystalline form of the ordered structure. NMR spectra and relaxation times showed that the distribution of the en conformation is not static but dynamic in both I and Br complexes where a puckering motion of en chelate rings was shown to take place between asymmetric potential wells.

Valence structure and magnetic interaction in MMX-type 1D complexes, A4[Pt2I(P2O5H2)4]·nH2O, studied by 31P solid NMR

31P MAS-NMR spectra and spin-lattice relaxation time T 1 in solid were measured on A 4 [Pt 2 I(P 2 O 5 H 2 ) 4 ].nH 2 O (A: Cs, Rb, K, Na and Li). Continuous spectrum changes in both line and splitting widths were observed with changing the cation size and the number of crystalline water. Complexes with A: Cs (n=0) and Rb (n=2) afforded two kinds of 31 P resonance lines with chemical shifts close to those in the Pt 3+ and Pt 2+ monomer complexes indicating a mixed valence structure. On the other hand, complexes with A: Na (n=2) and Li (n=4) yielded a broad single line suggesting the formation of paramagnetic Pt sites with an averaged valence of Pt 2.5+ . An analogous continuous change was observed in 31 P T 1 in consistent with the above analysis. The observed spectra and T 1 depending on the cation size and the H 2 O number suggest valence fluctuation due to spin jumps in and between Pt-Pt units sensitively influenced by crystal packings and hydrogen bonding.

Electron spin carriers in halogen-bridged 1-D complexes with nondegenerate CDW ground state

We measured temperature dependences of ESR spectra and 1 H NMR spin-lattice relaxation time T 1 on recently prepared mixedvalence hetero-metal complexes [Pd(en) 2 ][PtX 2 (en) 2 ](ClO 2 ) 4 (en: ethylenediamine; X: Cl, Br) which consist of a 1-D structure of-X-Pd II -X-Pt IV -X-Pd II -X-Pt IV -X-chain giving a non-degenerated electronic ground state. The observed low-concentration of paramagnetic M III sites and also long 1 H NMR T 1 compared with those in homo-metal complexes [M II (en) 2 ][M IV X 2 (en) 2 ](ClO 4 ) 4 (M: Pt, Pd; X: Cl, Br) having the degenerated ground state, can be explained well by the hindrance of the formation of domainwall type spin solitons in the hetero-metal complexes. This result supports our previous conclusion of the neutral soliton formation in the homo-metal halogen-bridged complexes.

Solid state 1H NMR in one dimensional neutral complex: [PtCl2(en)][PtCl4(en)]

Abstract The 1 H NMR spin-lattice relaxation time T 1 of [PtCl 2 (en)][PtCl 4 (en)] (en = ethylenediamine) has been measured from 110 to 330 K at Larmor frequencies 25.1 and 54.0 MHz. A BPP-type frequency dependency of T 1 due to magnetic dipolar interactions was observed above ca . 200 K and could be attributed to the puckering motion of the ethylenediamine chelate rings. The DTA and X-ray powder diffraction measurements showed that onset of this puckering motion is associated with a second or higher order phase transition located at ca . 210 K. The nonexponential recovery of 1 H magnetization observed in the low-temperature range was well explained by almost fixed paramagnetic Pt(III) sites of a low concentration formed along the 1-D chain.