Electronic and geometric structures of Co2Cn− and V2Cn−: Initial growth mechanisms of late and early 3d transition-metal carbide clusters

Abstract

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Structures and magnetic moments of Fe-C clusters

“…The lowest-energy structure for FeC 2 has C 2v symmetry, which is in agreement with the previous theoretical calculations. 3,5,8 Analysis of the Mülliken population shows that 0.360e charge transfers from the Fe atom to the C atoms and that the magnetic moment, 2 B , lies primarily on the Fe atom.…”

“…For example, the early 3d TMs ͑Ti, V, Cr͒ easily form large stable carbide clusters such as met-cars, while late 3d TMs ͑Co, Ni͒ have no such tendency. To explain the initial growth mechanisms of early and late 3d TM carbide clusters, Tono et al 3 measured photoelectron spectra of Co 2 C N ͑N =2,3͒ and V 2 C N ͑N =2-4͒ ions and deduced their electronic states and geometric structures by density functional theory ͑DFT͒. The growth mechanisms of the 3d transition-metal carbide clusters were discussed on the basis of the structural models obtained.…”

“…Previously published theoretical works agreed in predicting that the ground states of MC 2 ͑M =Sc,V,Cr,Fe,Co,Ni͒ are isosceles triangles. 3,5,8 For MC 3 ͑M =Sc,V,Cr,Fe,Co,Ni͒ clusters, there are two kinds of competitive structures, one linear with the M atom at one end, 4,9 the other a C 2v ring structure. 6,8 In the present work, the geometries, binding energies, and magnetic moments of small FeC N ͑N =1-8͒ and Fe 2 C N ͑N =1-6͒ clusters are studied systematically using all-electron DFT.…”

Density-functional calculations of the structures, binding energies, and spin multiplicities of Fe–C clusters

“…So far, studies have found no difference between early and late 3d metals as regards the structures of monometallic di-and tri-carbides: MC 2 clusters (MϭSc, Ti, V, Fe, Co, and Ni͒ are isosceles triangles in the ground state, [11][12][13][14][15][16][17][18][19][20][21][22][23] and MC 3 clusters (MϭSc, Ti, V, Cr, Mn, Fe and Ni͒ have two-dimensional ''fan'' structures in which the M atom is bound to all three C atoms and the latter are bound together in a bent chain. 17,24 -26 Moreover, although in principle the early or late character of each M is expected to be more clearly manifested by dimetallic carbide clusters, extensive studies of M 2 C 2 clusters (MϭTi, V, and Co͒ using density-functional theory ͑DFT͒ have found no clear early-late difference: the ground-state geometries of V 2 C 2 and Co 2 C 2 , and the Ti 2 C 2 isomer of second-lowest energy, are all planar rings with transannular M-C bonds, [27][28][29] although ground-state Ti 2 C 2 is a planar ring with a transannular C-C bond. 29 However, recent experimental and DFT studies of Co 2 C 3 and V 2 C 3 by Tono et al 28 have shown that differences between early and late 3d metals are significant for M 2 C 3 , i.e., when the M/C proportion is the same as in met-cars, 1-7 whereas Co 2 C 3 has a C 2v -symmetric planar CoCCCCo-ring structure with a bent C 3 chain similar to free C 3 ͑Ref.…”

Vibrational spectrum of cyclic TiC3 in solid Ar

“…1 The discovery of the novel metallocarbohedrene or "metcar" ͑M 8 C 12 + , M = Ti, V, Zr, Hf, and Nb͒ molecular cluster ions by Guo et al 2,3 in the early 1990s has prompted numerous studies on the growth and formation of these and the smaller transition-metal-carbon clusters that could be building blocks for the larger structures. 4 Mass spectrometric studies 5 suggested that MC 2 is a building unit, and subsequent experimental and theoretical work on small Ti n C m clusters has been motivated in part by the objective of learning more about the structure and bonding of this and other potential building blocks for the formation of titanium metallocarbohedrenes. 6 In an early theoretical study on small Ti n C m molecules using a linear combination of atomic orbitals molecular orbital approach, Reddy and Khanna 7 reported the structures for TiC, TiC 2 , Ti 2 C 2 , and Ti 2 C 3 .…”