Mixed-valence Platinum Complexes Research Articles

Resonance Raman Spectra Interpretation by Molecular Coherent State Representation

In this paper the problem of exact summation over vibrational states of intermediate electronic level excited by resonance Raman scattering in a molecular system with an arbitrary number of vibrational modes is solved with the help of the coherent state representation. For matrix elements of the resonance Raman (RR) amplitude the expressions in the form of an integral and multiple series as well as recurrence relations are obtained. The interpretation of RR spectra of linear-chain mixed-valence platinum complexes is given as an illustration.

Nonlinear optical study of quasi-one-dimensional platinum complexes: Two-photon excitonic resonance effect

Third-harmonic generation measurements have been made for the first time on oriented films of halogen-bridged mixed-valence platinum complexes for the pump wavelength region from 0.6 to 1.0 μm. The ‖χ(3)(−3ω;ω,ω,ω)‖ spectra obtained by the Maker’s fringe method show a distinct peak at about 1.8 eV with the peak value of about 4×10−11 esu. From comparison with the electroabsorption data, this peak has been identified with the two-photon resonance peak with the forbidden exciton in the Pt-halogen chains. One-dimensional exciton states in this compound take an important role in the third-order optical nonlinearity, similar to the case in conjugated polymers.

Analysis of the excitation profiles of Raman bands of linear-chain mixed-valence complexes. The geometry of [Pt(en) 2][Pt(en) 2Br 2]Br 4 in the intervalence state

Calculations of the resonance Raman excitation profiles for the ν 1 band and its overtones have been performed for the linear- chain mixed-valence platinum complex [Pt(en) 2Br 2]Br 4. It is found that the Pt IV length increases by 0.075 Å in the intervalence state. A satisfactory fit to the excitation profiles requires the inclusion of a second excited state at 16500 cm −1, which we have assigned to Br→Pt IV charge transfer.

Structure of the mixed-valence platinum complexes [Pt II(en)(SCN) 2][Pt IV(en)(SCN) 2I 2] and cis-[Pt II(NH 3) 2(SCN) 2][Pt IV(NH 3) 2(SCN) 2I 2] studied by the method of radial distribution functions of atoms

Using the method of radial distribution functions of atoms obtained by Fourier transform of powder X-ray patterns it has been shown directly that the structures of the mixed-valence complexes cis- [Pt II(NH 3) 2(SCN) 2][Pt IV(NH 3) 2(SCN) 2I 2] ( I) and [Pt II(en)(SCN) 2][Pt IV(en)(SCN) 2I 2] ( II) (en = ethylenediamine) contain the linear chains …IPt IVI…Pt II…IPt IV-I…Pt II…I, wherein square-planar complexes of Pt II alternate with octahedral complexes of Pt IV. Such a structure for I had earlier been proposed only on the basis of indirect spectroscopical data. The distances Pt IVI and Pt II…I have been determined. The first one is 2.70 Å in both the complexes and the second is 3.50 Å in I and 3.23 Å in II. The distances Pt II…I are considerably longer than corresponding distances in the similar mixed-valence complex of known structure [Pt II(en) 2][Pt IV(en) 2I 2](ClO 4) 4 ( IV) (about 3.10 Å). The elongation of the Pt II…I contact corresponds to the smaller bridge role of I atoms in the thiocianate complexes, to the smaller electron delocalization over the chain of Pt and I atoms and, hence, to a more pronounced division of the system into true complexes of Pt II and Pt IV than in IV.

Optical response of excitons in one-dimensional semiconductors

Exciton effect on interband absorption in a one-dimensional semiconductor with a dimerization gap is studied theoretically. An important role of the delocalization length is pointed out, and the peculiarity of the lowest singlet exciton state is elucidated by calculating the one- and the two-photon spectra. Results are compared with experiments in polydiacetylene, polysilane, and halogen-bridged mixed-valence platinum complexes.

Polaronic states induced by photo-excitation and halogen-doping in quasi-one-dimensional, mixed-valence platinum complexes -drift mobilities of electron and hole polarons-

The drift mobilities of the quasi-one-dimensional halogen-bridged mixed-valence platinum complexes, were measured on both the pure and halogen-doped samples by the pulsed photoconductivity technique. The results show that the hopping mechanism dominates the electric conduction and that the halogen dopants produce hole polarons on chains and the ionized dopants entered between the chains become a hopping center.

Luminescence study of the self-trapped exciton polarons of mixed crystals of quasi-one-dimensional mixed-valence metal complexes

Mixed crystals of quasi-one-dimensional halogen-bridged mixed-valence platinum complexes [Pt 3−ϱ (en) 2] [Pt 3+ ϱ (Cl 1−xBr x) 2(en)] (ClO 4) 4 (0<×<1, 0<<ϱ≤1) were studied by luminescence measurements. The self-trapped states of the charge transfer excitons were of the “amalgamation” type as well as the free states. By comparing the line shapes with the calculated profiles using a model, the polaron size of the self-trapped exciton was estimated to be larger than four molecular units of [-Pt t− ϱ -x −-Pt 3+ ϱ -x −-] (X = Cl,Br). This result is consistent with our previous estimates from the lifetime and the quantum efficiency of the luminescence.

Synthesis and spectroscopy of linear-chain palladium(II,IV) and platinum(II,IV) complexes involving quadridentate ligands

The effects of the in-plane ligand, the metal atom, the bridging halogen atom and the counter-anion on the electronic structures of a series of linear-chain, halogen-bridged, mixed-valence complexes of platinum and palladium have been investigated. Complexes of the type [ML][MLX2]Y4, where M = Pd or Pt, X = Cl, Br or I, L = 3, 7-diazanonane-1,9-diamine, 4,7-diazadecane-1,10-diamine, 1,4,8,11-tetraazacyclotetradecane or 1,4,8,12-tetraazacyclopentadecane and Y = BF4, ClO4 or PF6, have been examined by means of electronic, Raman and resonance-Raman spectroscopy. The electronic spectra of the complexes each show an intense intervalence charge-transfer band in the visible region, occurring at higher energy, Eg, than it does for analogous bis(ethylenediamine) complexes; this implies greater localisation of valences for the quadridentate than for the bis(ethylenediamine) complexes, in agreement with conclusions drawn from the X-ray structural results. Resonance-Raman spectra of the complexes display long progressions in the symmetric chain stretching mode ν1, νsym(X–MIV–X), corresponding members occurring at higher wavenumbers than for the analogous en complexes. Progressions in ν1 reach at most to v1= 12 for X = Cl, v1= 9 for X = Br and v1= 5 for X = I. Both the trends in Eg and also those in v1(max) vary in the order I < Br < Cl, Pd < Pt and BF4⩽ ClO4 < Pf6, implying increased valence localisation to the right in each series.

DOPING AND ELECTRICAL CONDUCTIVITY IN HALOGEN-BRIDGED MIXED-VALENCE PLATINUM COMPLEX

A model Hamiltonian is presented to describe halogen-bridged mixed-valence platinum complex (HMPC), the Green function is used to calculate the electrical conductivity of doping HMPC, the dope induced defect states are discussed in detail, the results are in agreement with experiments satisfactorily.

Study of Mixed-Valence State in Halogen-Bridged Mixed-Valence Platinum(II,IV) Complexes by Temperature Dependence of Intervalence Charge-Transfer Spectra

Abstract The low-energy absorption edge due to the intervalence charge-transfer (IVCT) transition from PtII to PtIV has been investigated at 4.2 K and room temperature in single crystals of [Pt(en)2][PtBr2(en)2]Y4 {Y=ClO4(PBC), HSO4(PBHS)}, [Pt(en)2][PtI2(en)2](HSO4)4·4H2O (PIHS) and [Pt(en)2][PtX2(en)2](SO4)2·6H2O {X=Cl(PCSW), Br(PBSW), I(PISW)}. The IVCT absorption edges in PCSW, PBSW, and PISW shifted to the lower-energy side (i.e. red shift), while those in PBC, PBHS, and PIHS shifted to the higher-energy side (i.e. blue shift) with an increase in temperature. We consider that the thermal effect of the valence fluctuation of the Pt mixed-valence state causes a red shift of the IVCT absorption edge and that the thermal effect of the hydrogen bond between the PtII complex ion and the PtIV complex ion causes a blue shift of the IVCT absorption edge. These two effects coexist and compete with each other in one complex. The dominant effect of the two effects determines the direction of the shift of the IVCT absorption edge, namely, the temperature dependence of the Pt mixed-valence state.

Comparison between Optical Properties of Sulfates and Hydrogensulfates in Halogen-Bridged Mixed-Valence Platinum(II, IV) Complexes

Abstract Syntheses and optical properties of some new halogen-bridged mixed-valence platinum complexes analogous to Wolffram’s Red Salt, [Pt(en)2][PtBr2(en)2](HSO4)4 (PBHS), [Pt(en)2][PtI2(en)2](HSO4)4·4H2O (PIHS), and [Pt(en)2][PtX2](en)2](SO4)2·6H2O {X=Br(PBSW), I(PISW)}, are reported. The powder X-ray diffraction pattern shows that PBHS is isomorphous with [Pt(en)2][PtCl2(en)2](HSO4)4 (PCHS), and that PBSW and PISW are isomorphous. The hydrogensulfates PBHS and PIHS crystallize from an aqueous sulfuric acid solution, whereas the sulfates PBSW and PISW crystallize from an aqueous solution. The single crystal absorption spectra of PBHS, PIHS, PBSW, and PISW have been investigated at 4.2 K. The intense optical absorption due to intervalence charge-transfer transition from Pt(II) to Pt(IV) has been observed for the light polarized parallel to the Pt chain axis (E//chain). From the comparison of the energy of the intervalence charge-transfer absorption edges in PBHS, PBSW, and PISW, one can conclude that the influence of the substitution of the counterions HSO4− with SO42− on the Pt(II)–Pt(IV) mixed-valence state is no less better than that of the substitution of the bridging halogen. The role of the counterion on the mixed-valence state is explained by the hydrogen bond network (Pt–NH···counterion···HN–Pt) on individual chains.

Effects of Impurity-Induced Interchain Coupling on Polarons in Quasi-One-Dimensional Solids

When an impurity is placed between chains in quasi-one-dimensional solids, it can cause transfer of electrons between chains through itself. The effects of this impurity induced interchain coupling on polarons are studied by means of the continuum version of the Holstein model. It is found that when the coupling strength exceeds a certain critical value, the polaron wave function extends itself over plural chains surrounding the impurity, rather than being localized on a single chain. Higher conductivity in directions perpendicular to the chains than in the parallel direction observed quite recently in doped halogen-bridged mixed-valence platinum complexes lends support to the above-mentioned picture.

Polarons and soliton pairs (bipolarons) in halogen-doped quasi-one-dimensional mixed-valence platinum complexes.

The first experimental studies on halogen doping in quasi-one-dimensional, halogen-bridged, mixed-valence platinum complexes (HMPC) are presented. The electrical conductivity of the iodine compound increases over 7 orders of magnitude with iodine doping. The absorbance of the two optical-absorption bands near the midgap and the ESR intensity in dilute doped HMPC increase with the dopant concentration. In the dilute regime, halogen doping yields the same effects on optical absorption and ESR as does photoexcitation at an energy greater than or equal to the energy of the charge-transfer absorption band. The doping-induced states are located on single chains and have charge and spin. These results strongly suggest polaron formation by halogen doping. At high doping levels, a new doping-induced absorption appears at an energy of 1.55 eV at 77 K, and the ESR decreases in intensity as the doping proceeds. It appears that upon halogen doping, singly charged polarons are produced and the formation of confined charged soliton pairs (bipolarons) via the process ${P}^{+}$+${P}^{+}$\ensuremath{\rightarrow}${S}^{+}$+${S}^{+}$ (or ${B}^{2+}$) is favored.

Experimental evidence of polaronic states in halogen bridged mixed valence platinum complexes

Two midgap absorption bands are observed in the quasi one-dimensional semiconductor (Pt(en) 2) (Pt(en) 2X 2) (C10 4) 4 by the photo-excitation of the light of charge transfer absorption band or higher at nitrogen temperature. The photo-induced absorption bands are active only for the light polarized parallel to the chain axis, showing that the photo-induced defect states are not associated with interchain defects. The defect states have spin and charge. These suggest that the photo-induced defect states are polaronic ones.

Syntheses, crystal structures, and Raman and resonance Raman spectroscopy of platinum(II), platinum(IV), and halogen-bridged chain platinum(II,IV) complexes involving the terdentate ligand 3-methyl-3-azapentane-1,5-diamine(4Me-dien)

The effect of introducing a methyl substituent onto the central nitrogen atom of the ligand dien(dien = diethylenetriamine or 3-azapentane-1,5-diamine) on the ease of formation of mixed-valence chain complexes of platinum has been investigated. The chain complex prepared by partial oxidation of [Pt(4Me-dien)I]I, viz. [Pt(4Me-dien) I][Pt(4Me-dien)I3]I2(4)(4Me-dien = 3-methyl-3-azapentane-1,5-diamine), breaks down on recrystallisation to yield separate crystals of [Pt(4Me-dien)I]X [X = I3–(1) or I–(2)] and [Pt(4Me-dien)I3]I(3). X-Ray structural investigation of (1)–(3) and of similar discrete complexes of platinum reported previously indicate that dien co-ordinates in the planar (pseudo-mer) conformation in four-co-ordinate platinum(II) but in the bent (fac) conformation in six-co-ordinate platinum(IV) complexes, However, in mixed-valence chain complexes, dien is forced to co-ordinate to the platinum(IV) centre in the mer conformation. In the case of 4Me-dien the mer conformation around platinum(IV) is severely hindered; hence unless this species is trapped quickly between two platinum(II) entities it isomerises from mer to fac, thereby preventing the assembly of the mixed-valence chain complex. Complex (4) has a very intense Raman spectrum at resonance with the intervalence band, the principal observed progression being v1ν1[ν1(116.5 cm–1) is the symmetric stretching mode of the chain, νsym(I–PtIV–I)]. The wavenumber of ν1 found for this complex is lower than that of the analogous species with unsubstituted dien in accord with a lengthening of the PtIV–I linkage on N-methyl substitution of the ligand. Crystallographic data: (1), monoclinic, space group P21/n, a= 15.433(3), b= 7.856(5), c= 13.327(4)Å, β= 102.24(2)°, and Z= 4; (2), monoclinic, space group P21/c, a= 20.434(7), b= 8.267(2), c= 15.571(1)Å, β= 110.67(2)°, and Z= 8; (3), monoclinic, space group P21/m, a= 8.960(6), b= 10.561(4), c= 7.651(4)Å, β= 103.10(2)°, and Z= 2.

Photo-Induced Defect States in a Quasi One-Dimensional Mixed-Valence Platinum Complex

Photo-induced absorption effects have been investigated in [Pt(en) 2 ][Pt(en) 2 Cl 2 ] (ClO 4 ) 4 single crystals. When the crystals are irradiated at 77 K by the light within the charge-transfer absorption band (CT band) or higher, two absorption bands (A and B) are observed below the CT band. Their intensities increase linearly with the total excitation light flux at low excitation level. The photo-induced absorption bands are stable at 77 K, but are not observed at room temperature. The A and B bands are induced only by the light with E // chain and preferencially polarized for E // chain, suggesting that the photo-induced defect states are located on individual chains, and not associated with interchain defects. The results are discussed in terms of the photo-induced polaron and kink-soliton models.

Reflectance and Raman spectra of mixed crystals of quasi-one-dimensional mixed-valence platinum complexes [ Pt3− ϱ( en) 2][ Pt3+ ϱ( Cl1− xBrx) 2( en) 2]( ClO4) 4 (0 ≦ x ≦ 1, 0 ⪡ ϱ ≦ 1)

Mixed crystals of halogen-bridged mixed-valence platinum complexes [ Pt 3− ϱ ( en) 2][ Pt 3+ ϱ ( Cl 1− x Br x ) 2]( ClO 4) 4 (0 ≦ x ≦ 1, 0 ⪡ ϱ ≦ 1) are studied by reflectance and Raman scattering measurements. Quasi-one-dimensional charge transfer excitons in these mixed crystals are of the “amalgamation” type with large optical bowing. The energies of the phonons related to the Peierls distortion shift with composition x and their resonant Raman intensities diminish rapidly by the introduction of different halogens. These effects are discussed in terms of modulated charge density waves in one-dimensional mixed crystals.

電子密度解析の応用への夢 ＩＩＩ ハロゲン架橋一次元鎖状白金系混合原子価錯体

電子密度解析の応用への夢 ＩＩＩ ハロゲン架橋一次元鎖状白金系混合原子価錯体

Soliton Model for Halogen-Bridged Mixed-Valence Platinum Complexes

The quasi-one-dimensional chains of halogen-bridged mixed-valence platinum complexes (HMPC) have characteristic twofold degeneracy similar to the trans isomer of polyacetylene, which strongly suggests the presence of soliton-like excitations in HMPC. It is shown that the microscopic Hamiltonian proposed by Ichinose for HMPC, which naturally is different from the Su-Schrieffer-Heeger model of trans -polyacetylene, leads to the Takayama-Lin-Liu-Maki Hamiltonian when the continuum limit is taken. This theoretical result implies that we can expect various soliton processes found in trans -polyacetylene to take place in HMPC as well, though such experimental evidences are scarce as yet.

The syntheses, structures, and electronic and resonance-Raman spectroscopy of halogen-bridged platinum(II,IV) chain complexes involving equatorially co-ordinated terdentate amines: X- ray crystal structure of [Pt II (Me-dien)I][Pt IV (Me-dien)I3]I2, and spectroscopy of [Pt II (dien)(NO2)][Pt IV (dien)(NO2)Br2]Br2

Three chain platinum(II,IV) complexes of the type [PtL3X][PtL3XY2]Z2(L3= terdentate ligand, X = halogen or NO2–, Y = halogen, Z = monoanion) have been synthesised. Two of these have been studied in detail, one by X-ray and the other by spectroscopic methods. The first, [Pt(Me-dien)I]-[Pt(Me-dien)I3]I2(Me-dien =N-methyldiethylenetriamine), has been found to crystallize in the monoclinic space group P21/n, with a= 19.830(8), b= 12.220(5), c= 11.079(6)A, β= 96.49(4)°, and Z= 4. Refinement on 1 543 independent reflections led to a final R value of 0.043. The Pt–I chain distances are 2.679(3) and 2.691(3)A(PtIV) and 3.443(3) and 3.560(3)A(PtII) the chain deviating substantially at iodine and platinum(II) from linearity [PtIV–I–PtII= 150.5(1) and 149.1(1)°; I–PtII-I = 162.8(1)°], but not at platinum(IV)[I–PtIV–I = 179.4(1)°]. The second complex studied in detail, [Pt(dien)(NO2)][Pt(dien)(NO2) Br2] Br2(dien = diethylenetriamine), was found to yield a very intense resonance-Raman spectrum, the principal observed progression being v1ν1, where ν1(181.5 cm–1) is the symmetric stretching mode of the chain, νsym(Br–PtIV–Br). Analysis of these data yields ω1 and x11 values of 181.9 and –0.2 cm–1, respectively. Further, much weaker, progressions of the sorts v1ν1+νsym(NO2)(to v1= 5) and v1ν1+δsym(NO2)(to v1= 4) were also detected. The results add substantially to the few previously known data on halogenbridged mixed-valence chain complexes of platinum in which each unit carries a single positive charge.