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Title: Ternary rare earth and actinoid transition metal carbides viewed as carbometalates

Abstract

Ternary carbides A{sub x}T{sub y}C{sub z} (A=rare earth metals and actinoids; T=transition metals) with monoatomic species C{sup 4-} as structural entities are classified according to the criteria (i) metal to carbon ratio, (ii) coordination number of the transition metal by carbon atoms, and (iii) the dimensionality of the anionic network [T{sub y}C{sub z}]{sup n-}. Two groups are clearly distinguishable, depending on the metal to carbon ratio. Those where this ratio is equal to or smaller than 2 may be viewed as carbometalates, thus extending the sequence of complex anions from fluoro-, oxo-, and nitridometalates to carbometalates. The second group, metal-rich carbides with metal to carbon ratios equal to or larger than 4 is better viewed as typical intermetallics (''interstitial carbides''). The chemical bonding properties have been investigated by analyzing the Crystal Orbital Hamilton Population (COHP). The chemical bonding situation with respect to individual T-C bonds is similar in both classes. The main difference is the larger number of metal-metal bonds in the crystal structures of the metal-rich carbides.

Authors:
 [1];  [1];  [1];  [1];  [2];  [3]
  1. Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, D-01187 Dresden (Germany)
  2. Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, D-01187 Dresden (Germany), E-mail: Kniep@cpfs.mpg.de
  3. Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Wilhelm-Klemm-Strasse 8, D-48149 Muenster (Germany), E-mail: jeitsch@uni-muenster.de
Publication Date:
OSTI Identifier:
21015694
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 2; Other Information: DOI: 10.1016/j.jssc.2006.11.019; PII: S0022-4596(06)00602-5; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANIONS; CARBIDES; CHEMICAL BONDS; COORDINATION NUMBER; CRYSTALS; INTERMETALLIC COMPOUNDS; INTERSTITIALS; RARE EARTH COMPOUNDS; TRANSITION ELEMENT COMPOUNDS

Citation Formats

Dashjav, Enkhtsetseg, Kreiner, Guido, Schnelle, Walter, Wagner, Frank R., Kniep, Ruediger, and Jeitschko, Wolfgang. Ternary rare earth and actinoid transition metal carbides viewed as carbometalates. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2006.11.019.
Dashjav, Enkhtsetseg, Kreiner, Guido, Schnelle, Walter, Wagner, Frank R., Kniep, Ruediger, & Jeitschko, Wolfgang. Ternary rare earth and actinoid transition metal carbides viewed as carbometalates. United States. doi:10.1016/j.jssc.2006.11.019.
Dashjav, Enkhtsetseg, Kreiner, Guido, Schnelle, Walter, Wagner, Frank R., Kniep, Ruediger, and Jeitschko, Wolfgang. Thu . "Ternary rare earth and actinoid transition metal carbides viewed as carbometalates". United States. doi:10.1016/j.jssc.2006.11.019.
@article{osti_21015694,
title = {Ternary rare earth and actinoid transition metal carbides viewed as carbometalates},
author = {Dashjav, Enkhtsetseg and Kreiner, Guido and Schnelle, Walter and Wagner, Frank R. and Kniep, Ruediger and Jeitschko, Wolfgang},
abstractNote = {Ternary carbides A{sub x}T{sub y}C{sub z} (A=rare earth metals and actinoids; T=transition metals) with monoatomic species C{sup 4-} as structural entities are classified according to the criteria (i) metal to carbon ratio, (ii) coordination number of the transition metal by carbon atoms, and (iii) the dimensionality of the anionic network [T{sub y}C{sub z}]{sup n-}. Two groups are clearly distinguishable, depending on the metal to carbon ratio. Those where this ratio is equal to or smaller than 2 may be viewed as carbometalates, thus extending the sequence of complex anions from fluoro-, oxo-, and nitridometalates to carbometalates. The second group, metal-rich carbides with metal to carbon ratios equal to or larger than 4 is better viewed as typical intermetallics (''interstitial carbides''). The chemical bonding properties have been investigated by analyzing the Crystal Orbital Hamilton Population (COHP). The chemical bonding situation with respect to individual T-C bonds is similar in both classes. The main difference is the larger number of metal-metal bonds in the crystal structures of the metal-rich carbides.},
doi = {10.1016/j.jssc.2006.11.019},
journal = {Journal of Solid State Chemistry},
number = 2,
volume = 180,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • The existence of further metal-rich condensed cluster compounds in R-Z-Te systems has been synthetically explored for R = Sc, Y, Pr, Dy, Er, Tm, Yb, Lu and, mainly, Z = Ru, Rh, Pd, Ag, Ir, Pt, Au. Ten new examples of orthorhombic Er{sub 7}Ni{sub 2}Te{sub 2}-type (Imm2) have been identified and that for Dy{sub 7}Ir{sub 2}Te{sub 2} has been refined. Seven new examples of other ternary structure types plus X-ray powder pattern evidence for 14 unknown phases have also been identified. To date the family of ternary R-Z-Te phases appears to be limited to those for R = Sc, Y,more » and Dy-Lu, a trend that is parallel to but more emphatic than those variations found among parallel cluster halide systems. Stability trends among the halide and especially the telluride series follow the I1 + I2 sums for the R elements well, the larger values of which are considered to reflect better mixing of R and Z valence d orbitals in the more stable phases.« less
  • The carbides R{sub 2}ReC{sub 2} (R = Y, Ce-Nd, Sm, Gd-Tm, Lu) were prepared by arc-melting of cold-pressed pellets of the elemental components. They crystallize with the orthorhombic space group Pnma and Z = 4 formula units per cell. The lattice constants for Pr{sub 2}ReC{sub 2} are: a = 655.69(6) pm, b = 509.46(5) pm, c = 984.42(8) pm. The crystal structure was determined from quantitative evaluations of Guinier powder data for Y{sub 2}ReC{sub 2} and Pr{sub 2}ReC{sub 2}, which refined to conventional residuals of R = 0.088 and R = 0.072, respectively. The structure of the isotypic carbide Er{submore » 2}ReC{sub 2} was determined from single-crystal diffractometer data: R = 0.032 for 842 structure factors and 26 variable parameters. The positions of the metal atoms correspond to those of the Co{sub 2}Si-branch of the anti-PbCl{sub 2} structure. The carbon atoms are isolated from each other and occupy two different octahedral voids (4R + 2Re, 5R + 1Re).« less
  • The ternary rare earth boride carbides R{sub 2}B{sub 4}C (R=Tb, Dy, Ho, Er) have been synthesized by reacting the elements at temperatures between 1800 and 2000K. The crystal structure of Dy{sub 2}B{sub 4}C has been determined from single-crystal X-ray diffraction data. It crystallizes in a new structure type in the orthorhombic space group Immm (a=3.2772(6) A, b=6.567(2) A, c=7.542(1) A, Z=2, R1=0.035 (wR{sub 2}=0.10) for 224 reflections with I{sub o}>2{sigma}(I{sub o})). Boron atoms form infinite chains of fused B{sub 6} rings in [100] joined with carbon atoms into planar, two-dimensional networks which alternate with planar sheets of rare earth metalmore » atoms. The electronic structure of Dy{sub 2}B{sub 4}C was also analyzed using the tight-binding extended Hueckel method. - Graphical abstract: Dy{sub 2}B{sub 4}C crystallizes a new structure type where planar 6{sup 3}-Dy metal atom layers alternate with planar non-metal layers consisting of ribbons of fused B{sub 6} hexagons bridged by carbon atoms. Isostructural analogues with Tb, Ho and Er have also been characterized.« less
  • The ternary rare-earth metal boride carbides RE{sub 15}B{sub 6}C{sub 20} (RE=Pr, Nd) were synthesized by co-melting the elements. They exist above 1270 K. Their crystal structures were determined from single-crystal X-ray diffraction data. Both crystallize in the space group P1-bar , Z=1, a=8.3431(8) A, b=9.2492(9) A, c=8.3581(8) A, {alpha}=84.72(1){sup o}, {beta}=89.68(1){sup o}, {gamma} =84.23(1){sup o} (R1=0.041 (wR2=0.10) for 3291 reflections with I{sub o}>2{sigma}(I{sub o})) for Pr{sub 15}B{sub 6}C{sub 20}, and a=8.284(1) A, b=9.228(1) A, c=8.309(1) A, {alpha}=84.74(1){sup o}, {beta}=89.68(1){sup o}, {gamma}=84.17(2){sup o} (R1=0.033 (wR2=0.049) for 2970 reflections with I{sub o}>2{sigma}(I{sub o})) for Nd{sub 15}B{sub 6}C{sub 20}. Their structure consists ofmore » a three-dimensional framework of rare-earth metal atoms resulting from the stacking of slightly corrugated and distorted square nets, leading to cavities filled with unprecedented B{sub 2}C{sub 4} finite chains, disordered C{sub 3} entities and isolated carbon atoms, respectively. Structural and theoretical analyses suggest the ionic formulation (RE{sup 3+}){sub 15}([B{sub 2}C{sub 4}]{sup 6-}){sub 3}([C{sub 3}]{sup 4-}){sub 2}(C{sup 4-}){sub 2}.11e. Accordingly, density functional theory calculations indicate that the compounds are metallic. Both structural arguments as well as energy calculations on different boron vs. carbon distributions in the B{sub 2}C{sub 4} chains support the presence of a CBCCBC unit. Pr{sub 15}B{sub 6}C{sub 18} exhibits antiferromagnetic order at T{sub N}=7.9 K, followed by a meta-magnetic transition above a critical external field B>0.03 T. On the other hand, Nd{sub 15}B{sub 6}C{sub 18} is a ferromagnet below T{sub C}{approx}40 K. - Graphical abstract: The ternary rare-earth metal boride carbides RE{sub 15}B{sub 6}C{sub 20} (RE=Pr, Nd) were synthesized by co-melting the elements. They exist above 1270 K. Their structure consists of a three-dimensional framework of rare-earth metal atoms resulting from the stacking of slightly corrugated and distorted square nets, leading to cavities filled with unprecedented B{sub 2}C{sub 4} finite chains, disordered C{sub 3} entities and isolated carbon atoms, respectively. Structural and theoretical analyses suggest the ionic formulation (RE{sup 3+}){sub 15}([B{sub 2}C{sub 4}]{sup 6-}){sub 3}([C{sub 3}]{sup 4-}){sub 2}(C{sup 4-}){sub 2} 11e. Pr{sub 15}B{sub 6}C{sub 18} exhibits antiferromagnetic order at T{sub N}=7.9 K, followed by a meta-magnetic transition above a critical external field B>0.03 T. On the other hand, Nd{sub 15}B{sub 6}C{sub 18} is ferromagnetic below T{sub C}{approx}40 K.« less
  • The ternary rare-earth boride carbides R{sub 15}B{sub 4}C{sub 14} (R=Y, Gd-Lu) were prepared from the elements by arc-melting followed by annealing in silica tubes at 1270 K for 1 month. The crystal structures of Tb{sub 15}B{sub 4}C{sub 14} and Er{sub 15}B{sub 4}C{sub 14} were determined from single crystal X-ray diffraction data. They crystallize in a new structure type in space group P4/mnc (Tb{sub 15}B{sub 4}C{sub 14}: a=8.1251(5) A, c=15.861(1) A, Z=2, R{sub 1}=0.041 (wR{sub 2}=0.088) for 1023 reflections with I{sub o}>2{sigma}(I{sub o}); Er{sub 15}B{sub 4}C{sub 14}: a=7.932(1) A, c=15.685(2) A, Z=2, R{sub 1}=0.037 (wR{sub 2}=0.094) for 1022 reflections with I{submore » o}>2{sigma}(I{sub o})). The crystal structure contains discrete carbon atoms and bent CBC units in octahedra and distorted bicapped square antiprisms, respectively. In both structures the same type of disorder exists. One R atom position needs to be refined as split atom position with a ratio 9:1 indicative of a 10% substitution of the neighboring C{sup 4-} by C{sub 2}{sup 4-}. The actual composition has then to be described as R{sub 15}B{sub 4}C{sub 14.2}. The isoelectronic substitution does not change the electron partition of R{sub 15}B{sub 4}C{sub 14} which can be written as (R{sup 3+}){sub 15}(C{sup 4-}){sub 6}(CBC{sup 5-}){sub 4{center_dot}}e{sup -}. The electronic structure was studied with the extended Hueckel method. The investigated compounds Tb{sub 15}B{sub 4}C{sub 14}, Dy{sub 15}B{sub 4}C{sub 14} and Er{sub 15}B{sub 4}C{sub 14} are hard ferromagnets with Curie temperatures T{sub C}=145, 120 and 50 K, respectively. The coercive field B{sub C}=3.15 T for Dy{sub 15}B{sub 4}C{sub 14} is quite remarkable. - Graphical abstract: The ternary rare earth boride carbides R{sub 15}B{sub 4}C{sub 14} (R=Y, Gd-Lu) were prepared from the elements by arc-melting followed by annealing in silica tubes at 1270 K for 1 month. Tb{sub 15}B{sub 4}C{sub 14} is a new member of the rare-earth metal boride carbide series in which the finite quasi-molecular CBC entities as well as isolated C atoms are embedded in the voids of the metal atom matrix. The structure of Tb{sub 15}B{sub 4}C{sub 14} contains two types of slabs: one slab contains finite bent CBC units and isolated carbon atoms whereas another is formed only from octahedral coordinated single carbon atoms. The electronic structure for the idealized composition corresponds to an electron partitioning according to (Tb{sup 3+}){sub 15}(C{sup 4-}){sub 6}(CBC{sup 5-}){sub 4{center_dot}}e{sup -} giving rise to a single electron per formula for Tb-Tb framework bonding. The magnetism of the ternary rare earth boride carbides R{sub 15}B{sub 4}C{sub 14} (R=Tb, Dy, Er) is characterized by the onset of ferromagnetic order below T<150 K.« less