Valence-Ordering Structures and Magnetic Behavior of Metallic MMX Chain Compounds

Abstract

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.

Intrinsic electrical conductivity of nanostructured metal-organic polymer chains

“…The fitting values are I 0 =0.12 nA, α =0.937 (the critical exponent for the density of states) and G N =0.185 × 10 −7 S, which represents a parallel conductance. Unfortunately, temperature-dependent measurements in these samples are challenging and difficult to interpret due to a crystal structural transition near room temperature34. A complete identification of such 1D behaviour would require temperature-dependent studies on nanoribbons, and work in this respect is currently underway.…”

1-(2-Chlorobenzyl)pyridinium bis(maleonitriledithiolato)nickelate(III)

“…In recent years many new effects have been found, especially for low-dimensional spin systems (Caneschi et al, 2001;Wolf et al, 2002;Mitsumi et al, 2002;Lorenz et al, 2002). Our aim is to construct quasi-one-dimensional molecule-based magnetic materials formed by plate-like maleonitriledithiolene (mnt) anionic metal complexes [M(mnt) 2 ] À (M is Ni 3+ , Pd 3+ or Pt 3+ ).…”

“…Data collection: SMART (Siemens, 1996); cell re®nement: SMART (Siemens, 1996); data reduction: SAINT (Siemens, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL. In recent years many new effects have been found especially for low-dimensional spin systems (Caneschi et al, 2001;Wolf et al, 2002;Mitsumi et al, 2002;Lorenz et al, 2002). Our aim is to construct quasi-one-dimensional molecule- We have found that the topology and size of the [R-BzPy] + ion, which is related to its molecular conformation, can be modulated by systematic variation of the substituents on the aromatic rings.…”

1-(2-Bromobenzyl)pyridinium bis(maleodinitriledithiolato)nickelate(III)

“…Several interesting physical phenomena, such as slow relaxation of magnetization and hysteresis effects not associated with three-dimensional order (Caneschi et al, 2001), valenceordering structure (Mitsumi et al, 2002), spin-charge separation state (Lorenz et al, 2002), and distinct magnetization plateaus (Wolf et al, 2002), have been found in recent years for low-dimensional spin systems. Investigations of these phenomena have motivated corresponding theoretical research in this ®eld (Clay et al, 2003;Orignac & Citro, 2003).…”