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Carbometalates and related compounds

Carbometalates and related compounds

Dr. Enkhtsetseg Dashjav



The efficient development of the chemistry of ternary nitrides and nitridometalates in the past decades motivated us to investigate ternary carbides, especially carbometalates, which remained less explored until recently and present promising properties due to the high polarizability of the carbo-ligands. The characteristic features of carbometalates are usually affected by low oxidation states of of the transition metal elements participating in the formation of complex carbometalate units [(TyCz)n-] [1]. They are clearly distinguished from the metal–rich carbides, which may be viewed as interstitial carbides with broad homogeneity ranges and chemical bonding situations predominantly characterized by metal–metal interactions.


Besides the exploratory syntheses of new carbometalates the most important subjects of our investigations are the preparation of single phase materials. Due to the high thermal activation, the high melting points and the low solid state diffusion rates in these systems methods such as arc melting, high frequency induction heating, extended annealing at high temperatures and the flux methods are used for the preparation.

Characterization methods

The following methods for characterization of these compounds are used: X-ray diffraction, EDX, WDX, ICP-OES, electrical resistivity and magnetic susceptibility measurements, X-ray absorption-, Raman- and Mössbauer spectroscopy. The electronic structures are studied using DFT/LDA band structure methods followed by both orbital based COHP and topological analyses based on complete position space partitioning, such as the QTAIM (quantum theory of atoms in molecules) and the ELI-D (electron localizability indicator) methods.

Figure 1. a). The crystal structure of Pr2[MoC2]; part of the polyanion (left) and ELF diagram for the dimers right). Orange domains: Mo-C covalent bonds and lone pairs at C1 atom; green domains: weak multi-center metal-metal interactions. b). The crystal structure of Ce2[Mo2C3]; part of the polyanion(left) and ELF diagram for an unit cell (right). Orange domain: Mo-C covalent bonds and lone pairs at carbon atoms. c). The crystal structure of Pr2[Mo2C3]; part of the polyanion(left) and ELF diagram (right) Pink domains: Mo-C covalent bonds and lone pairs at the carbo-ligands.

Recent developments

The synthesis and characterization of a number of novel low-valency carbometalates RE2[TC2] (RE = Ce – Nd; T = Mo, W) and RE2[T2C3] (RE = Ce, Pr, Sm, Gd – Dy; T = Cr, Mo) within the past few years justified the development of concept of carbometalates [2-6]. Their crystal structures contain complex anions such as distorted TC4 tetrahedra, which are interconnected via vertex and edge sharing to form 2D or 3D polyanions. Examples: (see Fig. 1). The RE metals are located between the polyanionic layers or in holes of the anionic network donating their valence electrons to the polyanionic part. The metal atoms form distorted bcc arrangements with the carbo-ligands occupying fractions of the octahedral voids. Recent investigations in the systems RE-Fe-C [7] have shown the increasing importance of metal-metal (T-T) interactions even in carbometalates. A real example is given by the rare-earth iron carbide Dy15Fe8C26, which is characterized by a 2D anionic partial structure, with low oxidation states of Fe, and significant Fe–Fe interactions within the Fe6- units (Fig. 2).

Figure 2. Details of the polyanionic slab revealing the linkages of the different Fe-coordination polyhedra (left). ELI presentation for Dy15Fe8C26 (right): light brown domains (isovalue YD = 1.49) indicate covalent bonds Fe–C and lone pairs around the free ends of the C2-pairs and the monoatomic C; green domains (isovalue YD = 1.01) indicate multicenter metal-metal (Fe-Fe) interactions.

This work is done with the collaboration of

Ruediger Kniep (Principle Investigator)
Gudrun Auffermann (ICP-OES)
Horst Borrmann and Yurii Prots (Crystal structure)
Ulrich Burkhardt (Metallography)
Bambar Davaasuren (Preparation)
Stefan Hoffmann (DSC/DTA)
Guido Kreiner (Phase stability)
Slovakia Academy of Sciences, Bratislava, Slovakia: Marek Mihalkovic (First Principle Calculations)
Walter Schnelle (Magnetic susceptibility and electrical resistivity)
Frank R. Wagner (Electronic structure calculations)

[1] E. Dashjav, G. Kreiner, W. Schnelle, F. R.Wagner, R. Kniep, and W. Jeitschko, J. Solid State Chem. 180 (2007) 636.
[2] E. Dashjav, F. R. Wagner, W. Schnelle, G. Kreiner, and R. Kniep, Z. Anorg. Allg. Chem. 630 (2004) 689.
[3] E. Dashjav, F. R. Wagner, W. Schnelle, G. Kreiner, and R. Kniep, Z. Anorg. Allg. Chem. 630 (2004) 2277.
[4] E. Dashjav, F. R. Wagner, W. Schnelle, G. Kreiner, and R. Kniep, Z. Anorg. Allg. Chem. 633 (2007) 1349.
[5] E. Dashjav, W. Schnelle, G. Kreiner, and R. Kniep: Z. Kristallogr. NCS. 220 (2005) 129.
[6] E. Dashjav, Yu. Prots, G. Kreiner, W. Schnelle, F. R. Wagner, and R. Kniep, Sc. and Technol. Adv. Mater. 8 (2007) 364.
[7] B. Davaasuren, H. Borrmann, E. Dashjav, G. Kreiner, W. Schnelle, F.R.Wagner, and R. Kniep, Scientific Report 2006-2008, Max-Planck-Institut für Chemische Physik fester Stoffe, 2009.

Last modified on July 22, 2009 Print version         Top
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