Abstract:Physical and structural properties of the MMX-type halogen-bridged mixedvalence complex, Ptz(dta)4I (dta = CH~CSZ-) were investigated. This complex exhibits metallic conduction above room temperature, which is the first observation in halogenbridged 1-D transition-metal complexes. Below 300 K, the metal-semiconductor transition was observed. The mixed-valence state of this compound is discussed.
“…Experimental studies and previous theoretical calculations showed that the twisting of the dta ligand could account for the Peierls distortion in Pt 2 (dta) 4 I. ,, One major piece of evidence reflecting the role of this distortion is the structural phase transition in the temperature range 255−375 K, resulting from the disorder in the helical structure of Pt dimers. , These structural changes are accompanied by a semiconductor−metal transition. In our previous theoretical approach, the dta ligand geometry was optimized for different twisting-angle values through ab initio SCF-type calculations.…”
Section: Vibronic Interactions In the Pt2(dta)4i Chainmentioning
confidence: 95%
“…More recently, an emerging class of new compounds known as MMX chains has attracted considerable attention. − The alternation of metallic dimers with a direct metal−metal bond and halogen ions shapes the backbone of MMX compounds and is shown in Figure . The coordination sphere of metals is completed by four μ-bridging ligands L (L = CH 3 CS 2 - (dta), − EtCS 2 - (dtp),30a n -PrCS 2 - (dtbu),30a or P 2 O 5 H 2 2- (pop) 16-22 ), leading to the common stoichiometry (M 2 (L) 4 X) n - . 1 Schematic representation of MMX chains.…”
Section: Introductionmentioning
confidence: 99%
“…Unlike the pop compounds, the chains with dta, dtp, and dtbu ligands are neutral, giving rise to short-range interactions and quasi-1D species. Since the formal oxidation state of the transition metal is +2.5, MMX chains may exhibit different types of ordered valence structures. , The results obtained for the Pt 2 (dta) 4 I chain from different experimental techniques are often contradictory. Several X-ray studies agree on equal Pt−I distances within the standard deviation (2.975 and 2.981 Å). ,, At the same time, on the basis of XPS 28,29 and Mössbauer 30b spectral conclusions, it is now assumed that the low-temperature phase consists of halogen-bridged head-to-head dipoles Pt II −Pt III (...−Pt II Pt III −I−Pt III Pt II −I−Pt II Pt III ...).…”
We here present a quantum chemical analysis of the possible Peierls distortions accompanying charge redistribution in the Pt 2 (dta) 4 I infinite chain. Starting with the building block calculations, we point out the participation of the CH 3 CS 2 -(dta) ligand in the mechanism of electron transfer. As the chain grows, the position and the geometry of the equatorial dta ligands are significantly altered. These changes indirectly control the Pt-I distances and lead to noticeable reduction of electron-phonon coupling through bridging halogen. These results agree with experimental data suggesting the involvement of internal degrees of freedom in the electron trapping phenomenon.
“…Experimental studies and previous theoretical calculations showed that the twisting of the dta ligand could account for the Peierls distortion in Pt 2 (dta) 4 I. ,, One major piece of evidence reflecting the role of this distortion is the structural phase transition in the temperature range 255−375 K, resulting from the disorder in the helical structure of Pt dimers. , These structural changes are accompanied by a semiconductor−metal transition. In our previous theoretical approach, the dta ligand geometry was optimized for different twisting-angle values through ab initio SCF-type calculations.…”
Section: Vibronic Interactions In the Pt2(dta)4i Chainmentioning
confidence: 95%
“…More recently, an emerging class of new compounds known as MMX chains has attracted considerable attention. − The alternation of metallic dimers with a direct metal−metal bond and halogen ions shapes the backbone of MMX compounds and is shown in Figure . The coordination sphere of metals is completed by four μ-bridging ligands L (L = CH 3 CS 2 - (dta), − EtCS 2 - (dtp),30a n -PrCS 2 - (dtbu),30a or P 2 O 5 H 2 2- (pop) 16-22 ), leading to the common stoichiometry (M 2 (L) 4 X) n - . 1 Schematic representation of MMX chains.…”
Section: Introductionmentioning
confidence: 99%
“…Unlike the pop compounds, the chains with dta, dtp, and dtbu ligands are neutral, giving rise to short-range interactions and quasi-1D species. Since the formal oxidation state of the transition metal is +2.5, MMX chains may exhibit different types of ordered valence structures. , The results obtained for the Pt 2 (dta) 4 I chain from different experimental techniques are often contradictory. Several X-ray studies agree on equal Pt−I distances within the standard deviation (2.975 and 2.981 Å). ,, At the same time, on the basis of XPS 28,29 and Mössbauer 30b spectral conclusions, it is now assumed that the low-temperature phase consists of halogen-bridged head-to-head dipoles Pt II −Pt III (...−Pt II Pt III −I−Pt III Pt II −I−Pt II Pt III ...).…”
We here present a quantum chemical analysis of the possible Peierls distortions accompanying charge redistribution in the Pt 2 (dta) 4 I infinite chain. Starting with the building block calculations, we point out the participation of the CH 3 CS 2 -(dta) ligand in the mechanism of electron transfer. As the chain grows, the position and the geometry of the equatorial dta ligands are significantly altered. These changes indirectly control the Pt-I distances and lead to noticeable reduction of electron-phonon coupling through bridging halogen. These results agree with experimental data suggesting the involvement of internal degrees of freedom in the electron trapping phenomenon.
“…Kitagawa et al − reported the first observation of a metallic property in [Pt 2 (dta) 4 I] (dta: dithioacetato, R = CH 3 −). The electrical conductivity and thermoelectric power measurements for a single crystal of [Pt 2 (dta) 4 I] parallel to the chain axis b revealed that this complex exhibits a metallic temperature dependence above a metal−semiconductor transition temperature T M - S = 300 K. This metal−semiconductor transition was also confirmed by magnetic susceptibility measurement for a polycrystalline sample. , Furthermore, temperature dependence of the electrical conductivity and thermoelectric power measurements showed a first-order phase transition around 360 K. From single-crystal X-ray structure analyses, it was revealed that a first-order phase transition occurs at T trs = 365 K from the LT phase with space group C 2/ c to the HT phase with A 2/ m , in which the cell volume is a half of that of the LT phase.…”
Section: 6 Mixed-valence MMX Type Complexesmentioning
“…Two main families of the MMX-chain compounds have so far been reported: A 4 [Pt 2 (pop) 4 X 4 ]· n H 2 O (A = Li, K, Cs, NH 4 ; pop = diphosphonate, H 2 P 2 O 5 2- ; X = Cl, Br, I) − and M 2 (dta) 4 I (M = Ni, Pt; dta = dithioacetate, CH 3 CS 2 - ). − Interestingly, electrical conductivity and thermoelectric power measurements for a single crystal of Pt 2 (dta) 4 I parallel to the chain axis b 24,25,28,29 revealed that this complex indicates a metallic temperature dependence above a metal−semiconductor transition temperature T M - S = 300 K. Polarized reflectance spectra of a single crystal at room temperature 24,28 also indicated that a Drude-like reflectance associated with interbinuclear charge transfer was observed for the polarization parallel to the chain axis ( E || b ), which suggests that Pt 2 (dta) 4 I is a one-dimensional metal. A metallic behavior was first observed in Pt 2 (dta) 4 I among halogen-bridged one-dimensional transition-metal complexes.…”
Heat capacity of the halogen-bridged mixed-valence complex Pt 2 (dta) 4 I (dta ) CH 3 CS 2 -) has been measured in the temperature region between 6 and 386 K. The complex exhibited a phase transition of order-disorder type at T trs ) 373.4 K, from being arranged in an ordered helical form of four dta ligand planes around the central Pt-Pt axis to dynamically jumping between two orientations. Neither latent heat nor distinct thermal hysteresis was observed for the phase transition, suggesting that the phase transition is of higher-order rather than of first-order. The transition enthalpy and entropy were determined to be ∆ trs H ) 1.91 ( 0.02 kJ mol -1 and ∆ trs S ) 5.25 ( 0.07 J K -1 mol -1 , respectively. The transition entropy close to R ln 2 () 5.76 J K -1 mol -1 ), where R is the gas constant, implies that the twisting motion of the four dta ligands takes place in a synchronized way. No thermal anomaly was detected around 300 and 90 K, where a Mott transition from the one-dimensional metallic phase to the semiconducting phase and a spin-Peierls-like transition have been expected. The reason for the absence of these transitions in calorimetry is discussed briefly. † Contribution No. 51 from the Research Center for Molecular Thermodynamics.
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