Mixed-valence Platinum Complexes Research Articles

Near-infrared vapochromism in lipid-packaged mixed-valence coordination polymers.

Reversible vapochromism in the NIR region is achieved for a mixed-valence platinum complex with lipid counterions, from which exclusion of crystallization water by organic vapor alters the lipid molecular orientation, which amplifies the information to changes in the 1D coordination structure and the electronic state.

Synthesis and characterization of binuclear Pt(IV) complexes and tetranuclear mixed valence complexes of Platinum(II)-Platinum(IV)

The binuclear platinum(IV) complexes [NBu4]2[PtIV2(μ-Cl)2(C6F5)4Cl4] (2) and [PtIV2(μ-C8H6N4)2(C6F5)4Cl4] (4) have been synthesized by oxidative addition of chlorine to the binuclear platinum(II) species, but [NBu4]2[PtIV2(μ-OH)2(C6F5)4Cl4] (3) has been synthesized by substitution of the chloride bridges of the platinum(IV) complex. The square planar platinum environments of the Pt(II) starting materials change, as expected, to Pt(IV) octahedral environments with the chloride ligands in trans-position. Only minor changes in the Pt-X (X = Clbridge, OH) interatomic distances are produced because of the oxidation.Depending on the size of the bridging ligands and also probably the anionic character of the diplatinum(IV) complexes, the apical chloride ligands can still act as bridges toward other Pt centers. Thus, the organometallic tetra-nuclear mixed-valence platinum(IV)-platinum(II) complexes with formulas [NBu4]2[{PtIV(μ-X)(C6F5)2}2(μ-Cl)4{PtII(C6F5)2}2] [X = Cl (5), OH (6)] were obtained by reaction of 2 and 3 with cis-[PtII(C6F5)2(thf)2]. The structures of complexes 2, 4 and 6 have been determined by single-crystal X-ray diffraction studies. These crystal structures confirm that the oxidative addition of the chlorine molecule to the platinum(II) complexes 2 and 3 takes place on the axial positions of the platinum centers suggesting a SN2 mechanism. On the other hand, the central core of the anion of 6 has a chair like conformation and the long Pt⋯Pt distances (>3.2 Å) clearly exclude any Pt.···Pt interaction.On the other hand, cis-[(C6F5)2Pt(μ-C8H6N4)Pt(C6F5)2] (1) can be reduced either electrochemically or by reacting with [CoCp2] to the anion [Pt2(μ-C8H6N4)(C6F5)4]- which in the last case, can be isolated as complex 7. According to the EPR studies the anion is not a mixed Pt(II)/Pt(I) compound but a binuclear Pt(II) derivative with the anion [C8H6N4]- as bridging ligand.

Redetermination of the crystal structure of catena-poly[[[bis-(ethyl-enedi-amine)-platinum(II)]-μ-iodido-[bis-(ethyl-enedi-amine)-platinum(IV)]-μ-iodido] tetra-kis-(octane-1-sulfonate) dihydrate

The structure of the title compound, which represents a mixed-valence platinum(II,IV) complex, {[Pt(II)Pt(IV)I2(C2H8N2)4][CH3(CH2)7SO3]4·2H2O} n , has been redetermined in a different space group. In contrast to the previously reported determination in the space group P21 cn [Matsushita & Taira (1999 ▸). Synth. Met. 102, 1787-1788], the current model was refined in the centrosymmetric space group Pmcn using the original diffraction data. The title compound has a linear chain structure composed of square-planar [Pt(en)2](2+) and elongated octa-hedral trans-[PtI2(en)2](2+) cations (en is ethyl-enedi-amine) stacked alternately, bridged by the I atoms, parallel to the c axis. Inorganic layers aligned parallel to the bc plane, composed of the Pt-complex columns, the -SO3 (-) part of the octane-1-sulfonate anion, and the water mol-ecule of crystallization, are stacked alternately with organic layers composed of the long-chain alkyl groups along the a axis. The Pt and I sites are located on the same mirror plane whereby the I site is equally disordered over two positions. The Pt and I atoms form a slight zigzag ⋯I-Pt(IV)-I⋯Pt(II)⋯ chain, with Pt(IV)-I bond lengths of 2.6888 (17) and 2.7239 (17) Å, Pt(II)⋯I contacts of 3.2065 (17) and 3.1732 (16) Å, and Pt(IV)-I⋯Pt(II) angles of 178.3 (3) and 176.7 (2)°. The mixed-valence state of the Pt site is expressed by the structural parameter δ = (Pt(IV)-I)/(Pt(II)⋯I), with values of 0.839 and 0.858 for the two independent I atoms. In the crystal, N-H⋯O hydrogen bonds involving the cationic chains, the sulfonate groups and water mol-ecules of crystallization, stabilize the columnar structure.

Wavepacket Dynamics at Low Temperature in Localized Excitons of the Quasi-One-Dimensional Br-Bridged Pt Complex Studied by Femtosecond Luminescence Spectroscopy

We report on the femtosecond time-resolved luminescence spectroscopy in a quasi-one-dimensional halogen-bridged mixed valence platinum complex, [Pt(en) 2 ][Pt(en) 2 Br 2 ](ClO 4 ) 4 at low temperatures. From the temperature dependence of the lifetime of the self-trapped excitons (STEs), we estimated the potential barrier height in the direction to the non-radiative path to be 99±10 meV. The observed time-evolutions of the luminescence excited by 1.57 eV photons at 4 K show complicated behavior, which is considerably different from that at room temperature. From Fourier transform of the time domain data, a low frequency mode was found at 0.7 THz in addition to the main mode at 3.4 THz, which has been assigned to the motion of the halogen ions in the self-trapped excitons. Incorporating two modes into the model based on the theory of resonant secondary radiation, the experimental data are well reproduced. This result shows that the wavepacket moves on the two-dimensional adiabatic potential surface of the s...

A template-directed synthetic approach to halogen-bridged mixed-valence platinum complexes on artificial peptides in solution

A template-directed synthetic approach to halogen-bridged mixed-valence platinum complexes has been performed in organic media using, for instance, a synthetic peptide bearing two bis(ethylenediamine)-based Pt(IV) complexes with two axial bromide anionic ligands, [(Pt(IV)Br2(en))2](RSO3)4, and a [Pt(II)(en)2](RSO3)2 complex (R = (C12H25OCH2)2CHO(CH2)3-).

Supramolecular solvatochromism. Effect of solvents on the self-assembly and charge transfer absorption characteristics of lipid-packaged, linear mixed-valence platinum complexes

Lipid-packaged, mixed-valence linear platinum complexes are dispersed in chloroform, chlorocyclohexane and in methylcyclohexane. They show indigo-colors, which are identical to solid samples. These lipid-complexes display supramolecular thermochromism, resulting from heat-induced dissociation and recovery of coordination chains. Unexpectedly, reassembled samples show altered CT absorption spectra. In chloroform, the reassembled complex gives indigo-color, while the chlorocyclohexane and methylcyclohexane dispersions show blue and red-colors, respectively. These color changes indicate enhanced solvation of lipid-packaged platinum complexes after the heat treatment. The thermal re-assembly also affects the aggregate morphology, and leads to the formation of nanowires, nanofibers and nanoparticles depending on the solvents employed. The conversion of pseudo one-dimensional (1D) inorganic complexes to lipophilic supramolecular assemblies thus gives solvatochromic properties, which are elements not existing in the conventional solid-state inorganic chemistry.

Self-Assembled Nanowires of Lipid-packaged Halogen-bridged Platinum Complexes Formed by One-pot Oxidation of Pt(en)2 complexes by Au(III) Ions

Abstract A solution-phase synthesis of lipid-packaged mixed valence platinum complexes is newly developed. Addition of aqueous HAuCl4 or AuBr3 to Pt(en)2[1]2 complex dissolved in dichloromethane affords halogen-bridged linear complexes [Pt(en)2][Pt(en)2X2][1]4 (X = Cl or Br). Formation of self-assembled nanowires was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy.

Mixed-Valence State of a One-Dimensional Platinum Complex with a Counter Ion Having Two Alkyl Chains and its Liquid Crystal Phase

We have investigated optical property and crystal structure of a one-dimensional halogen-bridged platinum complex (MX chain compound) with a counter ion having two alkyl chains, [Pt(en) 2 ][PtCl 2 (en) 2 ]{(CH 3 (CH 2 ) 7 CO 2 ) 2 CH 2 CHSO 3 } 4 2H 2 O, to elucidate influence of molecular fastener effect of the long alkyl chain on mixed-valence state of the platinum atoms. Thermal-behavior observations of the complex were also performed using a polarizing optical microscope without and with crossed nicols to examine thermal change of the mixed-valence state and appearance of the liquid crystal phase. Consequently, the complex has exhibited that the interaction between the platinum atoms is strengthened and the Pt II -Pt IV distance is shortened by doubling the number of alkyl chains around the platinum complex moieties compared with a corresponding PtCl chain complex with a single alkyl chain counter ion. We have also observed a texture of liquid crystal at about 200C. Mixed-Valence State One-Dimensional Halogen-Bridged Platinum Complex Long Alkyl Chain Molecular Fastener Effect Liquid Crystal Phase

Ultrafast relaxation dynamics of neutral soliton pairs in a quasi-one-dimensional halogen-bridged mixed-valence platinum complex [Pt(en)2][Pt(en)2Br2](ClO4)4

Ultrafast optical response of photoexcited states is studied by femtosecond pump and probe spectroscopy in a quasi-one-dimensional halogen-bridged mixed-valence platinum complex, [Pt(en)2][Pt(en)2Br2](ClO4)4 (en=ethylenediamine). We observed two kinds of photo-induced absorption (PA) signals, and both of the PA signal intensities follow non-exponential decay profiles. The signals are ascribed to two kinds of neutral soliton pairs with different configurations, that is, a spatially confined soliton and antisoliton pair and a noncorrelated soliton and antisoliton pair. Their formations are found to be closely related with both the excitation energy and the excitation density.

Decay Processes of a Photo-Excited State in a Strong Electron-Phonon Coupling System Trans-[Pt(en)2Cl2](ClO4)2

A quasi one-dimensional compound of halogen-bridged mixed-valence platinum complexes [Pt(en)2][Pt(en)2X2] (ClO4)4 (X=Cl, Br, and I, and en denotes ethylenediamine, hereafter we abbreviate as Pt–X) is known to show a strong charge-transfer (CT) absorption. By the optical excitation of the CT band, one can make a CT exciton on a one-dimensional chain. The CT exciton relaxes, without a barrier, to localized ed exciton (STE) states and the relaxation process was observed as a series of Raman lines followed by a large broad luminescence band. Recent spectroscopic measurement of femtosecond time resolved luminescence by Tomimoto et al. revealed a wave-packet oscillation in an adiabatic potential well associated with a self-trapped exciton. 3) The time constants of cooling from the photo-excited states to the STE states were identified as 0.21 and 0.43 ps for Pt–Cl and Pt–Br, respectively. Recently, optical spectra were measured at a He temperature on a crystal of trans-[Pt(en)2Cl2](ClO4)2 which consists of the same chemical composition as the Pt–Cl. The absorption band observed at the lowest energy of 3.3 eV was due to the d-d transition on a platinum atom. 5) The luminescence spectrum had a Gaussianlike lineshape formed by the superposition of phonon side bands more than 20 series. The energy of phonons observed in the luminescence was quite close to that of a breathing mode of chlorines centered around the platinum ion (44.9meV) observed on the Raman spectrum. On the other hand, no phonon structures were observed on the luminescence of both one-dimensional Pt– Cl and Pt–Br. The electron phonon coupling strength (Huang-Rhys factor) of trans-[Pt(en)2Cl2](ClO4)2 was obtained to be 9.52. These results show that trans[Pt(en)2Cl2](ClO4)2 is a strong electron-phonon coupling system and that one of most suitable materials for the studies of the dynamical decay processes of photo-excited states in a strong electron-phonon coupling system. Special interest is at the point of comparison with onedimensional Pt–X. In this report, time resolved luminescence spectra of trans-[Pt(en)2Cl2](ClO4)2 are for various temperatures and the photo-excited state is shown to be cool-down on the adiabatic potential surface of the excited state at about 1 ns. self-trapp

Organization of One-Dimensional Mixed-Valence Platinum Complexes at the Air-Water Interface and in Langmuir-Blodgett Films

Surface monolayers consisting of cationic, halogen-bridged linear platinum complex and anionic amphiphiles are formed at the air-water interface. Lipophilic polyion complex prepared from lipid and one-dimensional platinum complex is dispersed in chloroform as an indigo-colored solution, which color is ascribed to charge transfer (CT) absorption of the halogen-bridged complex (PtII→PtIV). Upon heating the solution, the indigo color disappeared due to dissociation of the linear complex into molecular unit complexes. Oriented surface monolayer is formed on water by spreading the colorless chloroform solution. Appearance of the CT band in reflectance spectra of monolayers indicates that the one-dimensional halogen-bridged complex is reformed at the air-water interface. The present technique opens an avenue to dimension-controlled organization of linear halogen-bridged complexes.

Femtosecond dynamics of self-trapped excitons in quasi-one-dimensional halogen-bridged Pt complexes

Dynamics of the self-trapped excitons (STE) in quasi-one-dimensional halogen-bridged mixed-valence platinum complexes [Pt(en) 2][Pt(en) 2X 2](ClO 4) 4 (en=ethylenediamine, X=Cl or Br) has been studied by luminescence up-conversion technique. Time evolution of the luminescence from STE has been studied from 0.79 to 2.1 eV in the X=Cl system with a time resolution of 180 fs. The cooling time of hot STEs was determined as 210 fs, and the formation time of STE was found to be shorter than 140 fs, which is limited by our time resolution. In the X=Br system, we achieved a time resolution of 90 fs and succeeded in observing the wave packet oscillation in the adiabatic potential well of STE by luminescence for the first time. The period of the local mode oscillation is 290 fs (97 cm −1) and the damping time constant is 430 fs. Usefulness of the up-conversion spectroscopy for wave packet observation is demonstrated.

Structural and spectroscopic characterisation of the mixed valence platinum complex PtdabI 3 (dab= o-diaminobenzene)

The new mixed valence platinum complex PtdabI 3 (dab= o-diaminobenzene) ( 1) has been prepared and characterised. The crystal structure consists of separate units of planar Pt(II)dabI 2 and octahedral Pt(IV)dabI 4 molecules. The latter are arranged in linear chains with rather short intermolecular I⋯I-contacts (3.478 Å) which are responsible for charge transfer interactions. In the resonance Raman spectrum strong intensity enhancements and extended overtone progressions of the symmetric I–Pt–I stretching mode have been observed.

Supramolecular Assemblies Comprised of One-Dimensional Mixed Valence Platinum Complex and Anionic Amphiphiles in Organic Media

Abstract A novel class of one-dimensional supramolecular assembly dispersed in organic media was prepared from halogen-bridged mixed valence platinum complex and anionic amphiphiles. Their intervalence absorption characteristics and nanostructures varied depending on the chemical structure of amphiphiles.

Electrocrystallization of a halogen-bridged mixed-valence platinum complex

Electrocrystallization of [Pt(en) 2][PtCl 2(en) 2](ClO 4) 4 (1), which is a halogen-bridged mixed-valence platinum complex having Pt II ··· X − Pt IV − X ··· chains, is reported. Electrochemical reduction of trans-[PtCl 2(en) 2]Cl 2 in an aqueous solution of perchloric acid at a potential of −1.5 to −1.6 V vs Pt counter electrode gave red needle crystals of (1) which are several mm long. The crystals appeared not only on the electrode but also away from it. On the other hand, electrochemical oxidation of a Pt II complex gave no crystals of (1) and the reason for this result is discussed.

Resonance Raman enhancement for photoinduced polaronic states of a quasi-one-dimensional mixed-valence platinum complex.

Resonance Raman enhancement for photoinduced polaronic states of a quasi-one-dimensional mixed-valence platinum complex.

Excitation energy dependence of the photoluminescence from self-trapped excitons in halogen-bridged mixed-valence platinum complexes

The excitation energy dependence of the photoluminescence (PL) of self-trapped excitons has been investigated in [Pt(en) 2][Pt(en) 2Cl 2(1− x) Br 2 x ](ClO 4) 4 ( x = 0, 0.08, 0.15) single crystals. The peak energy of the PL shifts to higher energy with increasing excitation photon energy from 2.4 to 2.6 eV. When the excitation energy is above 2.6 eV, the position of the peak energy is independent of the excitation energy and becomes almost constant. The magnitude of the peak energy shift increases with the molar fraction of bromine. These results are well understood by the distribution of the electron-hole separation which may depend on the excitation energy.

The Electron-Lattice Coupling in Quasi-One-Dimensional Halogen-Bridged Mixed-Valence Platinum Complexes (HMPC's)11The project supported by National Natural Science Foundation of China.

The effect of site-diagonal and site-off-diagonal electron-lattice coupling on polaronic binding energy in quasi-one-dimensional halogen-bridged mixed-valence platinum complexes (HMPC's) is investigated. It shows that the site-diagonal part is determinative in this kind of material, and agreeable with experiments.

Design of Hydrogen Bond Network in Halogen-Bridged Mixed-Valence Platinum Complexes by Substitution of Counter Ion

Abstract Sulfates in one-dimensional halogen-bridged mixed-valence platinum complexes were synthesized in order to elucidate contributions of hydrogen bonds between in-plane ligand amines and counter ions to the mixed-valence state. Their intervalence charge-transfer bands measured by using the single crystals and their structures determined by single crystal X-ray diffraction analyses show that the energy difference of dz 2 orbitals between the PtII and the PtIV becomes larger with decreasing linkages between the Pt units by the hydrogen bonds, comparing with perchlorates and hydrogensulfates.

PHOTO-INDUCED ABSORPTION BAND IN QUASI-ONE-DIMENSIONAL HALOGEN-BRIDGED MIXED-VALENCE PLATINUM COMPLEXES

Photo-induced absorption states in quasi-one-dimensional halogen-bridged mixed valence platinum complex is investigated. Based on the experimental data, a mechanism for photo-induced absorption is presented. Photo-induced absorption spectra both deformations of alternative and polaron induced for halogen ions are calculated. The comparison with experiments is made.