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.

Microwave assisted hydrothermal synthesis of a novel CuI-sulfate-pyrazine MOF

“…Open-framework metal-organic polymers, derived from the combination of selected transition metal and multidentate bridging ligands, have attracted much attention in the last decades due to their potential as purpose-built materials with practical properties such as gas storage [1][2][3][4], catalysis [5], optics [6] and magnetisms [7]. In addition, they have been recently investigated as novel nanomaterials [8][9][10][11][12].…”

“…It is noteworthy that microwave assisted synthesis produces monocrystals suitable for X-ray diffraction studies, reducing reaction time and with higher yield than the classical hydrothermal procedures. The compound presented here, [Cu 2 (pyz) 2 (SO 4 )(H 2 O) 2 ] n (pyz = pyrazine), has been crystallographically characterised to be a threefold interpenetrated three-dimensional coordination (10,3)-b network.Open-framework metal-organic polymers, derived from the combination of selected transition metal and multidentate bridging ligands, have attracted much attention in the last decades due to their potential as purpose-built materials with practical properties such as gas storage [1-4], catalysis [5], optics [6] and magnetisms [7]. In addition, they have been recently investigated as novel nanomaterials [8][9][10][11][12].…”

Calorimetric Study of a Halogen-Bridged MMX Chain Complex Having Alkyl Chains, Pt2(n-PrCS2)4I (n-Pr = Propyl Group)

“…Representatives of the MMX chain compounds having been studied are A 4 [Pt 2 (pop) 4 X]‚nH 2 O (A ) Li, K, Cs, NH 4 ; pop ) H 2 P 2 O 5 2-, diphosphonato; X ) Cl, Br, I), [4][5][6][7][8] and M 2 (RCS 2 ) 4 I (M ) Pt, Ni; R) alkyl chain). [9][10][11][12][13][14][15][16][17][18][19][20][21][22] M 2 (RCS 2 ) 4 I has four alkyl chains (R) in ligands. Elongation of alkyl chains in ligands is considered to enhance the onedimensionality of the electronic system on the MMX chains because of weak van der Waals S-S contacts between neighboring chains.…”

“…The dithiocarboxylato groups show a structural disorder concerning their twist with respect to the Q1D MMX chain, as in a manner similar to that of Pt 2 (n-BuCS 2 ) 4 I. 20 On cooling from the HT phase, the resistivity and thermoelectric power exhibit a jump around 359 K due to a phase transition. At room temperature, the electric conductivity of Pt 2 (n-PrCS 2 ) 4 I is ca.…”

“…This periodicity describes only the structural disorder concerning the dithiocarboxylato groups and the propyl chains belonging to only the center complex in a unit cell length, similarly to Pt 2 (n-BuCS 2 ) 4 I. 20 Four dithiocarboxylato groups belonging to the two ordered complexes are twisted right or left. That is, the linear chain structure is represented by the twisted manner of Pt 2 (n-PrCS 2 ) 4 I units as a sequence of -disorder-right-left-as in Pt 2 (n-BuCS 2 ) 4 I.…”