Interaction of the early 3d transition metals Sc, Ti, V, and Cr with N2: an ab initio study

The interaction of the early 3d transition elements M=Sc, Ti, V, and Cr with N2(X 1Sigmag+) has been studied by coupled-cluster and multiconfigurational techniques in conjunction with quantitative basis sets. We investigated both triatomic (MN2) and tetratomic (M2N2) species but focused mainly on high-spin linear and T-shaped triatomics. The lowest bound states of ScN2(4B1),TiN2(5Delta), and VN2(6Sigma+) correlate to the first excited state of the M atom, with M-N2 binding energies (De) of 24, 14, and 8 kcal/mol, respectively. In CrN2, the first bound state (7) product operator correlates to the sixth excited state of the Cr atom (7P) with De = 27 kcal/mol. The M-N2-M bond strength of high-spin linear tetratomics is twice as large the binding energy of the corresponding M-N2 linear triatomics, M = Sc, Ti, V, and Cr.     

Negative ions of transition metal-halogen clusters

A systematic density functional theory based study of the structure and spectroscopic properties of neutral and negatively charged MX(n) clusters formed by a transition metal atom M (M=Sc,Ti,V) and up to seven halogen atoms X (X=F,Cl,Br) has revealed a number of interesting features: (1) Halogen atoms are bound chemically to Sc, Ti, and V for n≤n(max), where the maximal valence n(max) equals to 3, 4, and 5 for Sc, Ti, and V, respectively. For n>n(max), two halogen atoms became dimerized in the neutral species, while dimerization begins at n=5, 6, and 7 for negatively charged clusters containing Sc, Ti, and V. (2) Magnetic moments of the transition metal atoms depend strongly on the number of halogen atoms in a cluster and the cluster charge. (3) The number of halogen atoms that can be attached to a metal atom exceeds the maximal formal valence of the metal atom. (4) The electron affinities of the neutral clusters abruptly rise at n=n(max), reaching values as high as 7 eV. The corresponding anions could be used in the synthesis of new salts, once appropriate counterions are identified.     

Electronic structure and bonding of the 3d transition metal borides, MB, M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu through all electron ab initio calculations

The electronic structure and bonding of the ground and some low-lying states of all first row transition metal borides (MB), ScB, TiB, VB, CrB, MnB, FeB, CoB, NiB, and CuB have been studied by multireference configuration interaction (MRCI) methods employing a correlation consistent basis set of quintuple cardinality (5Z). It should be stressed that for all the above nine molecules, experimental results are essentially absent, whereas with the exception of ScB and CuB the remaining seven species are studied theoretically for the first time. We have constructed full potential energy curves at the MRCI/5Z level for a total of 27 low-lying states, subsequently used to extract binding energies, spectroscopic parameters, and bonding schemes. In addition, some 20 or more states for every MB species have been examined at the MRCI/4Z level of theory. The ground state symmetries and corresponding binding energies (in kcal/mol) are 5Sigma-(ScB), 76; 6Delta(TiB), 65; 7Sigma+(VB), 55; 6Sigma+(CrB), 31; 5Pi(MnB), 20; 4Sigma-(FeB), 54; 3Delta(CoB), 66; 2Sigma+(NiB), 79; and 1Sigma+(CuB), 49.     

Ab initio investigation of the ground and low-lying states of the diatomic fluorides TiF, VF, CrF, and MnF

The electronic structure of the ground and low-lying states of the diatomic fluorides TiF, VF, CrF, and MnF was examined by multireference and coupled cluster methods in conjunction with extended basis sets. For a total of 34 states we report binding energies, spectroscopic constants, dipole moments, separation energies, and charge distributions. In addition, for all states we have constructed full potential curves. The suggested ground state binding energies of TiF(X (4)Phi), VF(X (5)Pi), CrF(X (6)Sigma(+)), and MnF(X (7)Sigma(+)) are 135, 130, 110, and 108 kcal/mol, respectively, with first excited states A (4)Sigma(-), A (5)Delta, A (6)Pi, and a (5)Sigma(+) about 2, 3, 23, and 19 kcal/mol higher. In essence all our numerical findings are in harmony with experimental results. For all molecules and states studied it is clear that the in situ metal atom (M) shows highly ionic character, therefore the binding is described realistically by M(+)F(-).     

Theoretical study of the geometric and electronic structure of neutral and anionic doped silver clusters, Ag5X with X = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni

Density functional theory (DFT) has been applied to investigate the low-lying electronic states of neutral and anionic transition metal doped silver clusters Ag₅X^0,− with X = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni using the B3LYP functional with the Stuttgart SDD basis sets. The structural features, frontier orbital energy gaps (HOMO and LUMO), vertical detachment energies, and vertical and adiabatic electronic affinities are evaluated. For all doped silver clusters, both in neutral and anionic states, two-dimensional and three-dimensional low-energy isomers are found to coexist. For neutral clusters, dopant Sc, Ti, V, and Mn atoms largely decrease the frontier orbital energy gaps, while they are markedly increased by Sc and Fe atoms in the anionic clusters. A completely quenched dopant magnetic moment is found in Ag₅Sc, while high spin magnetic moments are located on the other dopant atoms in Ag₅X^0,−.     

Naked (C5Me5)2M cations (M = Sc, Ti, and V) and their fluoroarene complexes

The ionic metallocene complexes [Cp*(2)M][BPh(4)] (Cp* = C(5)Me(5)) of the trivalent 3d metals Sc, Ti, and V were synthesized and structurally characterized. For M = Sc, the anion interacts weakly with the metal center through one of the phenyl groups, but for M = Ti and V, the cations are naked. They each contain one strongly distorted Cp* ligand, with one (V) or two (Ti) agostic C-H...M interactions involving the Cp*Me groups. For Sc and Ti, these Lewis acidic species react with fluorobenzene and 1,2-difluorobenzene to yield [Cp*(2)M(kappaF-FC(6)H(5))(n)][BPh(4)] (M = Sc, n = 2; M = Ti, n = 1) and [Cp*(2)M(kappa(2)F-1,2-F(2)C(6)H(4))][BPh(4)], the first examples of kappaF-fluorobenzene and kappa(2)F-1,2-difluorobenzene adducts of transition metals. With the perfluorinated anion [B(C(6)F(5))(4)](-), both Sc and Ti form [Cp*(2)M(kappa(2)F-C(6)F(5))B(C(6)F(5))(3)] contact ion pairs. The nature of the metal-fluoroarene interaction was studied by density functional theory (DFT) calculations and by comparison with the corresponding tetrahydrofuran (THF) adducts and was found to be predominantly electrostatic for all metals studied.     

On the ground and some low-lying excited states of ScB: a multiconfigurational study

The electronic structure of a series of low-lying excited triplet and quintet states of scandium boride (ScB) was examined using multireference configuration interaction (including Davidson's correction for quadruple excitations) and single-reference coupled cluster (CC) methods with averaged natural orbital (ANO) basis sets. The CC approach was used only for the lowest quintet state. The authors have analyzed eight low-lying triplets 3Sigma-(2), 3Sigma+, 3Pi(3), and 3Delta(2) dissociating to Sc(2D)/B(2P) atoms and eight low-lying quintet states 5Sigma-, 5Sigma+, 5Pi(2), 5Phi, and 5Delta(3) dissociating to Sc(4F)/B(2P) atoms. They report the potential energy curves and spectroscopic parameters of ScB obtained with the multireference configuration interaction (MRCI) technique including all singly and doubly excited configurations obtained with the ANO-S basis set. For the two lowest states they obtained also improved ANO-L spectroscopic constants, dipole and quadrupole moments as well as scalar relativistic effects based on the Douglas-Kroll-Hess Hamiltonian. They provide the analysis of the bonding based on Mulliken populations and occupation numbers. Since the two lowest states, 3Sigma- and 5Sigma-, lie energetically very close, their principal goal was to resolve the nature of the ground state of ScB. Their nonrelativistic MRCI(Q) (including Davidson correction) results indicate that the quintet is more stable than the triplet by about 800 cm(-1). Inclusion of scalar relativistic effects reduces this difference to about 240 cm(-1). The dissociation energies for 5Sigma- ScB range from 3.20 to 3.30 eV while those for the 3Sigma- range from 1.70 to 1.80 eV.     

Calculated and experimental geometries and infrared spectra of metal tris-acetylacetonates: vibrational spectroscopy as a probe of molecular structure for ionic complexes. Part II

Following on from our previous work on Sc, Fe, Cr, and Al (Part I; see J. Phys. Chem. A, 105 (2001) 238), the geometries and infrared spectra of the trivalent metal tris-acetylacetonate complexes (M[O2C5H7]3; M = Ti, V, Mn, Co) have been studied both experimentally and theoretically using nonlocal hybrid density functional theory with a split-valence plus polarization basis for the ligand and valence triple-zeta for the metal. Unlike the D3 complexes studied in Part I, those of Ti, V and Mn are candidates for Jahn-Teller distortion due to fractional d-shell occupancy. Using scale factors transferred from Part I, our calculated frequencies are in very good agreement with experimentally observed fundamentals. Our investigation shows that the V and Mn complexes distort to C2 ground states, but D3 Ti tris-acetylacetonate is stable. Further investigation of the weak band observed around 800 cm(-1) in the Fe complex (and present in almost all studied first-row transition metal tris-acetylacetonates), which we were unable to assign theoretically in Part I, supports the argument that this band is not a fundamental but is due to Fermi resonance.     

Electronic structure of cobalt carbide, CoC

The ground and 18 low lying excited states of the diatomic molecule cobalt carbide, CoC, have been examined by multireference variational methods (MRCI) combined with quantitative basis sets. All calculated states are bound and correlate adiabatically to the ground-state atoms, Co(a4F) + C(3P). We report complete potential energy curves, equilibrium bond distances, dissociation energies (De), spectroscopic constants, electric dipole moments and spin-orbit splittings. The bonding character of certain states is also discussed with the help of Mulliken distributions and valence-bond-Lewis diagrams. We are practically certain that the ground state is of 2Sigma+ symmetry with a state of 2Delta symmetry lying less than 3 kcal/mol higher, in agreement with the relevant experimental findings. Our best estimate of the X 2Sigma+ dissociation energy is De(D0) = 83(82) kcal/mol at r(e) = 1.541 A, 0.02 A shorter than the experimental bond length.     

Anionic Fischer-type carbene complexes as bidentate (N,O) ligands

New polynuclear complexes, (L1)3M2 [M2 = Cr(III) (4a,4b), Fe(III) (5), Co(III) (8)], (L1)2M2(L2)2 [M2 = Co(II) (7), Ni(II) (9)], (L1)2M2(O)L2 [M2 = V(IV) (6)] and L1M2Cp2 [M2 = Ti(III) (10)] with L1 = (CO)5M1=C[C=NC(CH3)=CHS](O-)(M1 = Cr or W) and L2 = 4-methylthiazole or THF, are described. The molecular structures of these complexes determined by X-ray diffraction show that the Fischer-type carbene complexes act as bidentate ligands towards the second metal centre, coordinating through C(carbene)-attached O-atoms and imine N-atoms of the thiazolyl groups to form five-membered chelates with the oxygen atoms in the mer configuration. Isostructural complexes have similar characteristic band patterns in their far-IR spectra. Cyclic voltammetry of selected complexes reveals the oxidation of the carbene complex ligand between 1.01 and 1.29 V. Oxidation of the central metal (M2) takes place at 0.56 and 0.86 V for 7 and 9, respectively. Three stepwise reductions of Cr(III) to Cr(0) occur for 4a and 4b in the region -0.51 to -1.58 V. These new ligand types and other variants thereof should find application in ligand design with the first metal -- and other ligands attached thereto -- in the carbene complex ligand, playing an important role.     

The geometric, electronic, and magnetic properties of Ag5X+ (X = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) clusters

Density functional theory calculations are performed on small cationic transition metal doped silver clusters, Ag5X+ (X = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) using the B3LYP and BP86 functionals. Several two-dimensional and three-dimensional isomers with the dopant at a high coordinated site are found to be close in energy. The relative energy of the isomers is checked with CCSD(T). The interaction between the dopant 3d electrons and the host is discussed by considering the density of states and the shape of the molecular orbitals. A large local spin magnetic moment on the dopant atom is predicted.     

Density functional study of the stable oxidation states and the binding of oxygen in MO4 clusters of the 3d elements

The tetraoxide clusters with stoichiometry MO(4), and the structural isomers with side-on and end-on bonded dioxygen, are studied by DFT with the B1LYP functional. Diperoxides M(O(2))(2) are the most stable clusters at the beginning (Sc, Ti) and at the end of the row (Co-Cu), the latter being planar. For V, Cr, and Mn, the dioxoperoxides O(2)M(O(2)) are the most stable isomers. Low-spin states are dominant for the nonplanar diperoxides M(O(2))(2) and dioxoperoxides O(2)M(O(2)), and the local magnetic moment at the metal cations is small. The local charge on the metal cation center is higher in the diperoxides of Sc and Ti; it drops significantly in the dioxoperoxides of V and Cr. The iron dioxosuperoxide in the (3)A' state, which contains end-on bonded dioxygen, OOFeO(2), is an exception with higher charge on Fe. In the planar diperoxides of Co, Ni, and Cu, oxygen-to-metal charge transfer is significant, and the local charge on the metal cation is close to 1. In all tetraoxygen clusters of the 3d elements, the cation center remains strongly electrophilic and interacts with Ar atoms from the inert-gas matrix, where the clusters are trapped for IR spectral studies. Significant frequency shifts in the matrix are found for the dioxoperoxide of vanadium, O(2)V(O(2)), the dioxosuperoxide of iron, OOFeO(2), and the nickel diperoxide, Ni(O(2))(2).     

Homonuclear transition-metal trimers

Density-functional theory has been used to determine the ground-state geometries and electronic states for homonuclear transition-metal trimers constrained to equilateral triangle geometries. This represents the first application of consistent theoretical methods to all of the ten 3d block transition-metal trimers, from scandium to zinc. A search of the potential surfaces yields the following electronic ground states and bond lengths: Sc3(2A1',2.83 A), Ti3(7E',2.32 A), V3(2E",2.06 A), Cr3(17E',2.92 A), Mn3(16A2',2.73 A), Fe3(11E",2.24 A), Co3(6E",2.18 A), Ni3(3A2",2.23 A), Cu3(2E',2.37 A), and Zn3(1A1',2.93 A). Vibrational frequencies, several low-lying electronic states, and trends in bond lengths and atomization energies are discussed. The predicted dissociation energies DeltaE(M3-->M2+M) are 49.4 kcal mol(-1)(Sc3), 64.3 kcal mol(-1)(Ti3), 60.7 kcal mol(-1)(V3), 11.5 kcal mol(-1)(Cr3), 32.4 kcal mol(-1)(Mn3), 61.5 kcal mol(-1)(Fe3), 78.0 kcal mol(-1)(Co3), 86.1 kcal mol(-1)(Ni3), 26.8 kcal mol(-1)(Cu3), and 4.5 kcal mol(-1)(Zn3).     

Ground and lowest-lying electronic states of CoN. A multiconfigurational study

The lowest-lying X1Sigma+, a3Phi, b3II, c5Delta, A1Phi, and B1II electronic states of CoN have been investigated at the ab initio MRCI and MS-CASPT2 levels, with extended atomic basis sets and inclusion of scalar relativistic effects. Among the singlet states, the A1Phi and B1II states have been described for the first time. Potential energy curves, excitation energies, spectroscopic constants, and bonding character for all states are reported. Comparison with other early transition-metal nitrides (ScN, TiN, VN, and CrN), isoelectronic (NiC) and isovalent (RhN and IrN) species has been made, besides analyzing the B1II <=> X1+ electronic transition in terms of Franck-Condon factors, Einstein coefficients, and radiative lifetimes. At both levels of theory, the following energetic order has been obtained: X1Sigma+, a3Phi, b3II, c5Delta, A1Phi, and B1II, with good agreement with experimental results. In contrast, previous DFT and MRCI calculations predicted the ground state to be the 5Delta state.     

The electronic structure of vanadium carbide, VC

Within an energy range of 2.4 eV, we have explored 29 of the 36 states of the diatomic molecule VC that arise from the atoms in their ground state, V(4s23d3;4F)+C(2s2 2p2;3P). We use multireference methods with large atomic natural orbital basis sets. The ground state is of 2Delta symmetry with the first two excited states, 4Delta and 2Sigma+, located 4.2 and 7.0 kcal/mol above the X state. All the states examined in this work are relatively strongly bound and show significant charge transfer from V to C. The binding energy of the X 2Delta state is estimated to be 95.3 kcal/mol in good agreement with the experimental value.     

Laser ablation and secondary ion mass spectrometry of inorganic transition-metal compounds. Part I: comparison between static ToF-SIMS and LA-FTICRMS

Most of the first-row transition-metal oxides, M(A)O(B) (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) were examined by static secondary ion mass spectrometry (s-SIMS) and laser ablation/ionization Fourier transform ion cyclotron resonance mass spectrometry (LA-FTICRMS). Positive and negative ions show strong correlation between the studied oxide and the detected cluster ions. Specific M(x)O(y) (+/-) species were systematically observed with both MS techniques for each investigated M(A)O(B) transition-metal oxide. Moreover, the ion composition and ion distribution are greatly dependent on the ionization technique. Laser ablation (LA)/ionization leads to larger cluster ions (ionic species with nearly hundred atoms were in particular detected for Sc2O3 and Y2O3 oxides), whereas hydrogenated, dihydrogenated, and sometimes trihydrogenated species were observed in s-SIMS. However, the ion distribution for a given M(x)O(y) (+/-) ion series (i.e. ions including the same number of metal atoms M) generally presented important similarities in both techniques.Finally, it was demonstrated that the chemical state of metal atoms in the observed ionic species is closely dependent on the metal electronic valence shell. High valence states (+III, +IV, +V, and +VI) are favored for metals with a less-than-half full valence shell configuration, whereas for other first-row transition metals (manganese, iron, cobalt, nickel, copper and zinc) lower metal valence states (0, +I or, +II) are involved.     

Theoretical study of ammonia and methane activation by first-row transition metal cations M(+) (M = Ti, V, Cr)

The potential energy surfaces for the reaction of first-row transition metal cations Ti(+)((4)F,(2)F), V(+)((5)D,(3)F), and Cr(+)((6)S,(4)D) with NH(3) and CH(4) have been built up by using density functional theory. In all cases, the high-spin ion-dipole complex, which is the most stable species on the respective potential energy hypersurfaces, is initially formed. In the second step, a hydrogen shift process leads to the formation of the insertion products, which are more stable in a low-spin state. From these intermediates three dissociation channels have been considered. All the results have been compared with existing experimental and theoretical data and our earlier work on the reactivity of Sc(+), to clarify similarities and differences in the behavior of the transition metal ions considered.     

Synthesis,characterization, and crystal structures of iodides and polyiodides of scandium complexes with urea and acetamide

Iodides and polyiodides of scandium complexes containing urea (Ur) and acetamide (AA) have been synthesized and characterized by elemental analysis, IR spectroscopy, and X-ray diffraction. The trigonal crystals of [Sc(L)₆]I₃ (L?=?Ur, AA) and monoclinic crystals of [Sc(Ur)₆][I₃]₃ are isomorphous to the earlier reported [M(Ur)₆]I₃ (M?=?Ti, V, Cr, Fe) and [Ln(Ur)₆][I₃]₃ (Ln?=?Yb, Lu), respectively. Therefore, scandium in its complexes with urea and iodine links rows of 3d transition elements and rare-earth elements; it continues the tendency of formation of polyiodides with different structures from isomorphous iodides, which was found for other metal(III) urea complexes. In the orthorhombic crystals of [Sc(AA)₆][I₅][I₃]I, the first example of the M(III) acetamide polyiodide, metal ions in complex cations are located at the centers of distorted octahedral arrangements of oxygen atoms of acetamide; iodide ions are not coordinated. The crystals of [Sc(AA)₆][I₅][I₃]I contain V-shaped pentaiodide, linear triiodide, and isolated iodide anions.     

Ab initio investigation of the electronic and geometric structure of magnesium diboride, MgB2

Employing multireference variational (MRCI) and coupled cluster (CC) methods combined with quadruple-zeta quality correlation-consistent basis set, we have studied 36 states of the magnesium diboride (MgB(2)) molecule as well as 17 states of the experimentally unknown diatomic MgB. For all states of MgB(2), we report geometries, atomization energies, and dipole moments, while for the first 5 states, potential energy profiles have been also constructed. The ground state is formally of (1)A(1) V-shaped symmetry with an atomization energy of 108.1(109) kcal/mol at the MRCI(MRCI + Davidson correction) level. The first excited state ((3)B(1)) is less than 1 kcal/mol above the X(1)A(1) state, with the next state of linear Mg-B-B geometry (b(3)Sigma(-)) located 10 kcal/mol higher. In all states, bent or linear, the bonding is complicated and unconventional because of the extraordinary bonding agility of the boron atom(s).