Optical properties of single crystals of quasi-one-dimensional halogen-bridged mixed-valence platinum and palladium compounds

Chemical pressure-induced PtIII-I Mott-Hubbard nanowire, [Pt(en)2I](Asp-Cn)2·H2O (13 ≤ n), detected via polarized infrared spectroscopy

The electronic states of iodo-bridged platinum nanowire complexes have been studied using polarized FT-IR spectroscopy. The N-H symmetrical stretching mode was found to be highly sensitive to the electronic states, distinguishing mixed-valence (MV) and averaged-valence (AV) states. The first Pt(III) nanowire complexes have been realized by the chemical pressures of the counter-anions.

Thermally Induced Electron-Hole Dissociation Dynamics in Quasi-One-Dimensional Bromo-Bridged Palladium(III) Mott-Insulator [Pd(en)2Br](Suc-Cn)2·H2O (Cn-Y = dialkylsulfosuccinate; n = 5 and 6)

Current-voltage characteristics and dielectric properties were studied on bromo-bridged one-dimensional compounds, [Pd(en)2Br](Suc-C5)2·H2O, exhibiting mixed-valence and averaged valence (MV-AV) phase transition. In the AV phase, a clear nonlinear current-voltage characteristics was...

Interdigitated Pt-Br chains with π-stacking: an approach toward Robin-Day class I mixed valency in MX-chain complexes

The first interdigitated MX-type chain complex with infinite π-stacked arrays was synthesized. The synchronization between a Pt-Br⋯ chain and π-stacking periodicities led to the longest M-X-M distance (6.6978(15) Å) and nil or negligible intervalence charge transfer, which is essential to realize the Robin-Day class I mixed valence state in MX chains.

Observation of charge bistability in quasi-one-dimensional halogen-bridged palladium complexes by X-ray absorption spectroscopy

We performed X-ray absorption fine structure (XAFS) measurements on three representative bromo-bridged palladium compounds. In the X-ray absorption near-edge structure (XANES) spectra, the averaged-valence (AV) compound, [Pd3+(dabdOH)2Br]Br2 (1: dabdOH = (2S,3S)-2,3-diaminobutane-1,4-diol), and the mixed-valence (MV) compound, [Pd2+(en)2][Pd4+(en)2Br2](ReO4)4 (2), showed significant differences in their spectra. In [Pd(en)2Br](Suc-C5)2·H2O (3: en = ethylenediamine, Suc-C5 = dipentylsulfosuccinate), which exhibits an MV-AV phase transition, on the other hand, the spectroscopic difference between below and above the phase transition temperature was hardly observed due to the subtle difference in the oxidation states. In the extended X-ray absorption fine structure (EXAFS) spectra, a clear difference in the Pd-Br correlation region was observed upon the phase transition.

Band-Gap Tuning of Organic-Inorganic Hybrid Palladium Perovskite Materials for a Near-Infrared Optoelectronics Response

Organic-inorganic hybrid material is a recent hot topic in the scientific community. The best band gap for the entire solar absorption spectrum is about 1.1 eV. However, the lead perovskite band gap is about 1.5 eV. Therefore, developing organic-inorganic hybrid material toward the broader light harvesting of the solar spectrum is extremely urgent. In this study, we prepare three kinds of organic-inorganic hybrid palladium perovskite materials, including (CH₃NH₃)₂PdCl₄, (CH₃NH₃)₂PdCl_4-x Br _x , and CH₃NH₃PdI₃, for an optoelectronic response. The absorption cut offs of (CH₃NH₃)₂PdCl₄, (CH₃NH₃)₂PdCl_4-x Br _x , and CH₃NH₃PdI₃ are approximately 600, 700, and 1000 nm, respectively. The band gaps of (CH₃NH₃)₂PdCl₄, (CH₃NH₃)₂PdCl_4-x Br _x , and CH₃NH₃PdI₃ are determined to be approximately 2.15, 1.87, and 1.25 eV, respectively. To the best of our knowledge, this is the first study that discusses adsorption properties and photoelectric behavior of organic-inorganic hybrid palladium perovskite materials. Interestingly, the photoelectric response of the devices based on CH₃NH₃PdI₃ reaches 950 nm. The results will attract attention in the fields of optical recorders, optical memory, security, light capture, and light treatment.

Charge-bistable Pd(iii)/Pd(ii,iv) coordination polymers: phase transitions and their applications to optical properties

This paper reviews the recent progress in charge-bistable Pd(iii)/Pd(ii,iv) coordination polymers (MX chains). The temperature-, pressure- and photo-induced phase transitions have been demonstrated, proposing MX chains as a material for optical switching devices.

Stabilization of Pd(III) states in nano-wire coordination complexes

In spite of a long history of quasi-one-dimensional halogen-bridged complexes (MX-chains), all Pt and Pd complexes form the charge-density wave (CDW) state (-X...M(II)...X-M(IV)-X...), while all Ni complexes form Mott-Hubbard (MH) states (-X-Ni(III)-X-Ni(III)-X-), without exception. We have succeeded in stabilizing the Pd(iii) MH state for the first time by utilizing the following two methods: partial substitution with Ni(iii) ions, [Ni(1-x)Pd(x)(chxn)(2)Br]Br(2), and chemical pressure via long alkyl chains introduced as counter-anions, [Pd(en)(2)Br](C(n)-Y)(2).H(2)O. In both systems, it has been revealed that the electronic state of bromo-bridged Pd compounds are determined by the PdPd distances, in other words, CDW and MH states are stabilized when PdPd distances are longer and shorter than 5.26 A, respectively.

Structural study of electronic states in quasi-one-dimensional halogen-bridged mixed-metal complexes [Ni(1-x)Pd(x)(chxn)(2)Br]Br(2)

The electronic structures of quasi-one-dimensional halogen-bridged mixed-metal compounds [Ni(1-x)Pd(x)(chxn)(2)Br]Br(2) were investigated by means of powder X-ray diffraction measurements. Unit cell lengths of all directions obeyed a linear relationship when x < 0.9, whereas those deviated when x > 0.9 especially in the case of the b and c axes. This deviation can be explained by a phase change from an M(III) Mott-Hubbard state to an M(II)-M(IV) charge-density-wave state because of chemical pressure caused by the substitution of Pd ions into [Pd(chxn)(2)Br]Br(2) with smaller Ni ions.

Observation of the properties of a single unit of a limited CDW structure in a Pt(II)/Pt(IV) host-guest binary system based on a square-shaped complex

A macrocyclic tetranuclear platinum(II) complex [Pt(en)(4,4'-bpy)](4)(NO(3))(8) (1(NO(3))(8); en = ethylenediamine, 4,4'-bpy = 4,4'-bipyridine) and a mononuclear platinum(IV) complex [Pt(en)(2)Br(2)]Br(2) (2Br(2)) formed two kinds of Pt(II)/Pt(IV) mixed valence assemblies when reacted: a discrete host-guest complex 12Br(10) (3) and an extended 1-D zigzag sheet 1(2)(3)Br(8)(NO(3))(6) (4). Single crystal X-ray analysis showed that the dimensions of the assemblies could be stoichiometrically controlled. Resonance Raman spectra suggested the presence of an intervalence interaction, which is typically observed for quasi-1-D halogen-bridged M(II)/M(IV) complexes. The intervalence interaction indicates the presence of an isolated {Pt(II)X-Pt(IV)-XPt(II)} moiety in the structure of 4. On the basis of electronic spectra and polarized reflectance measurements, we conclude that 4 exhibits intervalence charge transfer (IVCT) bands. A Kramers-Kronig transformation was carried out to obtain an optical conductivity spectrum, and two sub-bands corresponding to slightly different Pt(II)-Pt(IV) distances were observed.

Effect of an in-plane ligand on the electronic structures of bromo-bridged nano-wire Ni-Pd mixed-metal complexes, [Ni(1-x)Pd(x)(bn)2Br]Br2 (bn = 2S,3S-diaminobutane)

Single crystals of quasi-one-dimensional bromo-bridged Ni-Pd mixed-metal complexes with 2S,3S-diaminobutane (bn) as an in-plane ligand, [Ni(1-x)Pd(x)(bn)(2)Br]Br(2), were obtained by using an electrochemical oxidation method involving mixed methanol/2-propanol (1:1) solutions containing different ratios of [Ni(II)(bn)(2)]Br(2) and [Pd(II)(bn)(2)]Br(2). To investigate the competition between the electron-correlation of the Ni(III) states, or Mott-Hubbard states (MH), and the electron-phonon interaction of the Pd(II)-Pd(IV) mixed valence states, or charge-density-wave states (CDW), in the Ni-Pd mixed-metal compounds, X-ray structure analyses, X-ray oscillation photograph, and Raman, IR, ESR, and single-crystal reflectance spectra were analyzed. In addition, the local electronic structures of Ni-Pd mixed-metal single crystals were directly investigated by using scanning tunneling microscopy (STM) at room temperature and ambient pressure. The oxidation states of [Ni(1-x)Pd(x)(bn)(2)Br]Br(2) changed from a M(II)-M(IV) mixed valence state to a M(III) MH state at a critical mixing ratio (x(c)) of approximately 0.8, which is lower than that of [Ni(1-x)Pd(x)(chxn)(2)Br]Br(2) (chxn = 1R,2R-diaminocyclohexane) (x(c) approximately 0.9) reported previously. The lower value of x(c) for [Ni(1-x)Pd(x)(bn)(2)Br]Br(2) can be explained by the difference in their CDW dimensionalities because the three-dimensional CDW ordering in [Pd(bn)(2)Br]Br(2) observed by using X-ray diffuse scattering stabilizes the Pd(II)-Pd(IV) mixed valence state more than two-dimensional CDW ordering in [Pd(chxn)(2)Br]Br(2) does, which has been reported previously.

Solitons, polarons and their dynamics in mixed-valence halogen-bridged MX-chains

This article describes the photo-generation processes of elementary excitations such as solitons and polarons, and their dynamics in the one-dimensional (1D) halogen-bridged Pt compound [Pt(en)2Br](ClO4)2. Spin-solitons were photo-generated via relaxation processes of CT excitons and self-trapped excitons, made evident by photo-induced absorption and photo-induced electron spin resonance spectra. Polarons were not generated from CT excitons. Diffusion of spin-solitons on the 1D chain was studied quantitatively by analysing 1H NMR spin-lattice relaxation times (T1).