Recently, 1D halogen-bridged mixed-valence dinuclear metal complexes, so-called MMX chain compounds, have attracted significant attention as quasi-1D electronic systems characterized by strong electron ± phonon, electron ± electron, and magnetic interactions. Only two families of MMX chain compounds, namely [{A 4 [Pt 2 (pop) 4 X] ¥ n H 2 O} I ] (pop P 2 O 5 H 2 2À , A Li, K, Cs, NH 4 , X Cl, Br, I) [1] and [{M 2 (dta) 4 I} I ] (dta CH 3 CS 2 À , M Ni, Pt) [2] have been reported. These compounds are 1D chain systems based on a mixed-valence dinuclear unit with a formal oxidation number of 2.5 and a metal ± metal bond with a formal bond order of 1/2. An important feature of MMX chain compounds is the increase in internal degrees of freedom upon introducing a dinuclear unit in the mixed-valence state. This property enables a variety of electronic structures, represented by the extreme valence-ordering states shown in Figure 1. These valence-ordering structures would be classified based on the periodicity of the 1D chains as follows. The averaged valence (AV) and charge-polarization (CP) states, in which the periodicity of 1D chains is M-M-X-, correspond to a metallic state with an effective half-filled conduction band mainly composed of M ± Mds* ± Xp z -hybridized orbitals or to the Mott ± Hubbard semiconducting state. In contrast, the periodicity of 1D chains in the charge density wave (CDW) and alternate charge-polarization (ACP) states is doubled, and these electronic structures are regarded as Peierls and spin-Peierls states, [3] respectively.Kitagawa et al. have reported that [{Pt 2 (dta) 4 I} I ] exhibits metallic conducting behavior above 300 K in an AV state. [2d] On the results of a 129 I Mˆssbauer spectroscopic study, the valence-ordering structure of this compound at temperatures assembly of TiO 2 particles 20 ± 30 nm diameter in size, that is of highly porous morphology. After annealing at 673 K for 1 h the electrodes were modified with pyrene-functionalized gold nanoparticles by immersing into a THF solution of the nanoparticles overnight. The electrodes were washed thoroughly with THF to remove any unbound gold nanoparticles. These electrodes are referred to as OTE/TiO 2 /1. Absorption spectra were recorded with a Shimadzu 3101 spectrophotometer, transmission electron micrographs (TEM) with a Hitachi H600 transmission electron microscope. For the spectroelectrochemical experiments a Princeton applied research model 175 galvanostat/potentiostat was used, details of which can be found elsewhere. [22] The fluorescence from the nanostructured gold film was monitored with an SLM S-8000 photoncounting spectrofluorimeter in a front-face geometry. The other components of the cell were a Pt counter electrode, a saturated calomel reference electrode (SCE) and acetonitrile containing 0.1m tetrabutylammonium perchlorate (TBAP) as electrolyte.

A new one-dimensional (1-D) halogen-bridged mixed-valence diplatinum(II,III) compound, Pt(2)(EtCS(2))(4)I (3), has been successfully synthesized from [Pt(2)(EtCS(2))(4)] (1) and [Pt(2)(EtCS(2))(4)I(2)] (2). These three compounds have been examined using UV-visible-near-IR, IR, polarized Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray crystal structure analyses (except for 1). Compound 3 was further characterized through electrical transport measurements, determination of the temperature dependence of lattice parameters, X-ray diffuse scattering, and SQUID magnetometry. 3 crystallizes in the monoclinic space group C2/c and exhibits a crystal structure consisting of neutral 1-D chains with a repeating -Pt-Pt-I- unit lying on the crystallographic 2-fold axis parallel to the b axis. The Pt-Pt distance at 293 K is 2.684 (1) A in the dinuclear unit, while the Pt-I distances are essentially equal (2.982 (1) and 2.978 (1) A). 3 shows relatively high electrical conductivity (5-30 S cm(-1)) at room temperature and undergoes a metal-semiconductor transition at T(M-S) = 205 K. The XPS spectrum in the metallic state reveals a Pt(2+) and Pt(3+) mixed-valence state on the time scale of XPS spectroscopy ( approximately 10(-17) s). In accordance with the metal-semiconductor transition, anomalies are observed in the temperature dependence of the crystal structure, lattice parameters, X-ray diffuse scattering, and polarized Raman spectra near T(M-S). In variable-temperature crystal structure analyses, a sudden and drastic increase in the Pt-I distance near the transition temperature is observed. Furthermore, a steep increase in U(22) of iodine atoms in the 1-D chain direction has been observed. The lattice parameters exhibit significant temperature dependence with drastic change in slope at about 205-240 K. This was especially evident in the unit cell parameter b (1-D chain direction) as it was found to lengthen rapidly with increasing temperature. X-ray diffraction photographs taken utilizing the fixed-film and fixed-crystal method for the metallic state revealed the presence of diffuse scattering with line shapes parallel to the a* axis indexed as (-, n + 0.5, l) (n; integer). Diffuse scattering with k = n + 0.5 is considered to originate from the 2-fold periodical ordering corresponding to -Pt(2+)-Pt(2+)-I-Pt(3+)-Pt(3+)-I- or -Pt(2+)-Pt(3+)-I-Pt(3+)-Pt(2+)-I- in an extremely short time scale. Diffuse lines corresponding to 2-D ordering progressively decrease in intensity below 252 K and are converted to the diffuse planes corresponding to 1-D ordering near T(M-S). Furthermore, diffuse planes condensed into superlattice reflections below T(M-S). Polarized Raman spectra show temperature dependence through a drastic low-energy shift of the Pt-I stretching mode and also through broadening of bands above T(M-S).

A new one-dimensional iodo-bridged mixed-valence diplatinum(II,III) complex (MMX chain compound) with dithiobutanoate (n-PrCS2-) as a ligand, Pt2(n-PrCS2)4I, was found to undergo a structural phase-transition at 358–359 K by the differential scanning calorimetry (DSC) measurement and X-ray crystal structure analyses. In X-ray diffraction photographs measured using synchrotron radiation of the SPring-8 facility, the weak but distinct Bragg spots corresponding to the periodicity of 2-fold repetition length of a –Pt–Pt–I– unit were observed at 300 K and changed to diffuse scattering at 350 K. The electric conductivity deviates from the typical semiconducting behavior in the temperature region above 330 K.

We present a comprehensive study of the synthesis, heat capacity, crystal structures, UV-vis-NIR and mid-IR spectra, DFT calculations, and magnetic and electrical properties of a one-dimensional (1D) rhodium(I)-semiquinonato complex, [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2]∞ (3), where 3,6-DBSQ-4,5-(MeO)2(•-) represents 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato radical anion. The compound 3 comprises neutral 1D chains of complex molecules stacked in a staggered arrangement with short Rh-Rh distances of 3.0796(4) and 3.1045(4) Å at 226 K and exhibits unprecedented bistable multifunctionality with respect to its magnetic and conductive properties in the temperature range of 228-207 K. The observed bistability results from the thermal hysteresis across a first-order phase transition, and the transition accompanies the exchange of the interchain C-H···O hydrogen-bond partners between the semiquinonato ligands. The strong overlaps of the complex molecules lead to unusually strong ferromagnetic interactions in the low-temperature (LT) phase. Furthermore, the magnetic interactions in the 1D chain drastically change from strongly ferromagnetic in the LT phase to antiferromagnetic in the room-temperature (RT) phase with hysteresis. In addition, the compound 3 exhibits long-range antiferromagnetic ordering between the ferromagnetic chains and spontaneous magnetization because of spin canting (canted antiferromagnetism) at a transition temperature T(N) of 14.2 K. The electrical conductivity of 3 at 300 K is 4.8 × 10(-4) S cm(-1), which is relatively high despite Rh not being in a mixed-valence state. The temperature dependence of electrical resistivity also exhibits a clear hysteresis across the first-order phase transition. Furthermore, the ferromagnetic LT phase can be easily stabilized up to RT by the application of a relatively weak applied pressure of 1.4 kbar, which reflects the bistable characteristics and demonstrates the simultaneous control of multifunctionality through external perturbation.