Charge-Density-Wave to Mott−Hubbard Phase Transition in Quasi-One-Dimensional Bromo-Bridged Pd Compounds

Abstract

A -Pd(III)-Br-Pd(III)-Mott-Hubbard state was observed in a quasi-one-dimensional bromo-bridged Pd compound [Pd(en)2Br](C5-Y)2 x H2O (en = ethylenediamine, C5-Y = dipentylsulfosuccinate) for the first time. The phase transition between Mott-Hubbard and charge-density-wave states occurred at 206 +/- 2 K and was confirmed by using X-ray, ESR, Raman and electronic spectroscopies, electrical resistivity, and heat capacity. From X-ray powder diffraction patterns and Raman spectra of a series of Pd-Br compounds, [Pd(en)2Br](C(n)-Y)2 x H2O (n = 4, 5, 6, 7, 8, 9, and 12), chemical pressure from the alkyl chains of the counterions caused the phase transition.

Continuous Control of Optical Gaps in Quasi-One-Dimensional Bromide-Bridged Platinum Complexes by Utilizing Chemical Pressure

“…Preparation of Starting Materials. Sodium salts of the counterions Na(C n −Y) (n = 5, 6, 7, 9, 12) 11 and single crystals of [Pt(chxn) 2 Br]Br 2 (chxn = 1R,2R-diaminocyclohexane) 15 were synthesized following previously reported methods.…”

“…Although we used a racemic mixture of Na(C 6 −Y) as the starting material, the crystals used for an X-ray crystal structure analysis preferentially contained the R form of the C 6 −Y − group. In other words, [Pt(en) 2 11 The bridging Br ions are disordered and displaced from the midpoint between two neighboring Pt ions, indicating that this MX chain is in an MV state.…”

“…9 Although more than 300 complexes have been synthesized since Wolffram reported the first mixed-valence salt [Pt II (NH 2 C 2 H 5 ) 4 ][Pt IV Cl 2 (NH 2 C 2 H 5 ) 4 ]Cl 4 ·4H 2 O in 1900, 10 before our research, Pt and Pd MX chains had been found to be only in the MV states and Ni MX chains were only in AV states. 11 Okamoto et al have investigated the relationship between the electronic state and the features of the 1D chain structure in a series of MX chains. 9 Figure 1 shows the M−X distance as a function of L for different complexes.…”

“…As can be seen, X ions approach the midpoint, i.e., the difference between l 1 and l 2 becomes small, as L decreases, indicating that the compounds approach AV states when L becomes small. On the basis of this feature, we have recently prepared a Pd(III) chain in an AV state by applying chemical pressure between alkyl chains in the countercations to shorten L. 11 This result motivated us to adopt the same strategy to prepare the first Pt(III) AV state. In the present work, we synthesized Br-bridged Pt complexes with long alkyl chains in the countercations used to prepare the Pd(III) chains.…”

Novel Countercation in MMX-Type Mixed-Valence Chain Compound: Coexistence of Neutral and Protonated Amino Substituents

“…The other, made from lantern-type dinuclear complex (hereafter abbreviated as MMX chains) has ····M-M─X─M-M─X···· infinite 1D chain structure. MX chains has been attracting much attention because of their interesting physical properties, such as gigantic third-order nonlinear optical properties [9,10], midgap absorptions attributable to solitons and polarons [11], and charge-density-wave to Mott-Hubbard phase transition [12]. Compared with MX chains, the electrical conductivity of MMX chains is higher.…”