Electronic Structures, Vibrational and Thermochemical Properties of Neutral and Charged Niobium Clusters Nb n, n= 7− 12 (original) (raw)
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Photoelectron Spectra and Geometric Structures of Small Niobium Cluster Anions
Physical Review Letters, 1996
Photoelectron spectroscopy measurements and density functional theory calculations are combined to determine structures of Nb 2 n (n 3 8) clusters. A detailed comparison between observed and calculated electronic binding energies shows that the clusters have low-symmetry compact 3D structures and the lowest possible total spin, except for the three-and five-ato clusters which are in triplet states. We fin evidence for the coexistence of two isomers of Nb 2 8 under some experimental conditions. This approach shows great promise for structural characterization of small clusters.
Inorganic Chemistry, 2006
We report here the synthesis and crystal and electronic structures of the Na 2 (Sc 4 Nb 2 )(Nb 6 O 12 ) 3 niobium oxide whose structure is related to that of Ti 2 Nb 6 O 12 . It constitutes a new member of the larger A n BM 6 L 12 (Z) families (A ) monovalent cation located in tetrahedral cavities of units, B ) monovalent or trivalent cations located in octahedral cavities of units, M ) rare earth, Zr, or Nb, Z ) interstitial except for M ) Nb). The structural relationships between the A n BM 6 L 12 (Z) series (M 6 L i 12 L a 6 unit-based compounds with a M 6 L i 6 L i-a 6/2 L a-i 6/2 cluster framework) and Chevrel Phases (M 6 L i 8 L a 6 unit-based compounds with a M 6 L i 2 L i-a 6/2 L a-i 6/2 cluster framework) are shown in terms of M 6 L 18 and M 6 L 14 unit packing. Despite a topology similar to that encountered in Chevrel Phases, intercalation properties are not expected in the Nb 6 O i 6 O i-a 6/2 O a-i 6/2 cluster framework-based compounds. Finally, it is shown, from theoretical LMTO calculations, that a semiconducting behavior is expected for a maximum VEC of 14 in the Nb 6 O i 6 O i-a 6/2 O a-i 6/2 cluster framework.
Structure, stability, and electronic properties of niobium-germanium and tantalum-germanium clusters
Journal of Molecular Modeling, 2019
The structural, electronic and magnetic properties of niobium and tantalum doped germanium clusters MGen (M = Nb, Ta and n = 1-19) are investigated by first principles calculations within the Density Functional Theory approach (DFT). The growth pattern behaviors, stabilities, and electronic properties are presented and discussed. Endohedral cagelike structures in which the metal atom is encapsulated are favored for n ≥ 10. The doping metal atom contributes largely to strengthen the stability of the germanium cage-like structures with the binding energy ordered as follows BE(Gen+1) < BE (VGen) < BE(NbGen) < BE(TaGen). Our results highlight the relative high stability of NbGe15, TaGe15 and VGe14.
Journal of Fluorine Chemistry, 2001
We have synthesized by solid state chemistry and structurally characterized by single crystal X-ray diffraction two new cluster compounds, KNb 6 Cl 10 F 5 and CsNb 6 Cl 8 F 7. KNb 6 Cl 10 F 5 is a Ta 6 Cl 15 derived structure, whereas CsNb 6 Cl 8 F 7 exhibits a primitive framework derived from Nb 6 F 15. In both structures,¯uorine and chlorine are randomly distributed on the ligand positions, but in CsNb 6 Cl 8 F 7¯u orine fully occupies the apical positions. The comparison between the geometrical parameters of the title compounds and those observed in previously isolated Nb 6 chloro¯uorides, halides and¯uorides, allows speci®cation of the in¯uence of¯uorine in niobium cluster chemistry.
Inorganic Chemistry, 2006
We report here the synthesis and crystal and electronic structures of the Na 2 (Sc 4 Nb 2 )(Nb 6 O 12 ) 3 niobium oxide whose structure is related to that of Ti 2 Nb 6 O 12 . It constitutes a new member of the larger A n BM 6 L 12 (Z) families (A ) monovalent cation located in tetrahedral cavities of units, B ) monovalent or trivalent cations located in octahedral cavities of units, M ) rare earth, Zr, or Nb, Z ) interstitial except for M ) Nb). The structural relationships between the A n BM 6 L 12 (Z) series (M 6 L i 12 L a 6 unit-based compounds with a M 6 L i 6 L i-a 6/2 L a-i 6/2 cluster framework) and Chevrel Phases (M 6 L i 8 L a 6 unit-based compounds with a M 6 L i 2 L i-a 6/2 L a-i 6/2 cluster framework) are shown in terms of M 6 L 18 and M 6 L 14 unit packing. Despite a topology similar to that encountered in Chevrel Phases, intercalation properties are not expected in the Nb 6 O i 6 O i-a 6/2 O a-i 6/2 cluster framework-based compounds. Finally, it is shown, from theoretical LMTO calculations, that a semiconducting behavior is expected for a maximum VEC of 14 in the Nb 6 O i 6 O i-a 6/2 O a-i 6/2 cluster framework.
Theoretical study of small niobium sulphide clusters, NbnSm (n, m=1, 2)
Journal of Atomic and Molecular Sciences, 2014
In this study, the structures and electronic properties of simple prototype Ge n S m (n, m=1, 2) clusters are studied in their neutral, anionic and cationic states. The geometries of these small clusters are optimized by generalized gradient approximation. Their stabilities are discussed by calculating the binding energies per atom and fragmentation energies against dissociation to S atom. Various electronic parameters such as the HOMO-LUMO gap (band gap), electron affinity, ionization potential, chemical potential and chemical hardness are calculated and discussed.
Journal of Materials Science, 2018
In the present report, the structures, energetics and electronic properties of neutral and cationic Nb-doped Ge n (n = 7-18) clusters are systematically investigated under the first-principles density functional theory approach. The isomers in which the Nb atom is encapsulated inside a germanium cage are relatively stable compared to the exohedral surface doping. The thermodynamic stability and chemical activity of the ground-state isomers are analyzed through various energetic parameters. The results highlight the enhanced stability of the neutral NbGe 12 hexagonal prism-like structure with D 6h symmetry and cationic NbGe 16 fullerene isomers. The negative nucleus-independent chemical shift can explain the enhanced stability of neutral NbGe 12. However, the enhanced stability of cationic NbGe 16 is explained by shell closing model associated with the quasi-spherical geometry with a sequence 1S 2 1P 6 1D 10 1F 6 1G 12 2S 2 2P 6 IF 8 IG 6 2D 10 following Hund's rule. To understand the effect of hybridization on stability, we have calculated density of states (DOS) and projected DOS (PDOS). From PDOS, it is clear that Nb-p and Ge-s and p orbitals are mainly take part in hybridization; however, near below Fermi level, the dominating contribution comes from Nbd orbitals. In addition, IR and Raman spectra of clusters are also calculated to explain their vibrational properties of the isomers. Specifically, IR spectrum of the clusters in the range of 12-16 shows the possible application of these clusters in the IR sensing device.
Structures and vibrations of Nb3O and Nb3O−: A density functional study
The Journal of Chemical Physics, 2004
Density functional calculations of neutral and anionic niobium trimer monoxides are presented. The calculations were performed employing scalar quasirelativistic effective core potentials. In order to test the accuracy of the used effective core potentials in the framework of density functional theory the pulsed field ionization-zero electron kinetic energy photoelectron spectrum of Nb 3 O was simulated and compared to experiment. Different isomers of Nb 3 O and Nb 3 O Ϫ were studied in order to determine the ground state structures. For both neutral and anionic systems a planar C 2v structure with an edge-bound oxygen atom was found as a ground state. Equilibrium structure parameters, harmonic frequencies, and adiabatic electron affinity are reported. The calculated electron affinity and frequencies are in good agreement with the available experimental data obtained recently from vibrationally resolved negative ion photoelectron spectroscopy.