First-row Transition Metal Cations Research Articles

Density functional study of ammonia activation by late first-row transition metal cations.

Density functional theory (DFT) in its B3LYP implementation is used to investigate the reaction of ammonia with the late (Co(+), Ni(+), and Cu(+)) first-row transition metal cations in both high- and low-spin states. The potential energy surfaces (PES's) leading to three different exit channels are closely examined. The binding energies for the reaction products are calculated and compared with the corresponding experimental values. A comparison with our earlier works covering the reactivity of the Sc-Fe series of cations is made in order to underline similarities and differences of the reaction mechanisms as well as to establish trends along the row.

Condensation reaction vs. ligand exchange with first-row transition metal cations: a theoretical study of Cu + heteroleptic model complexes

Analysis of the evolution of the binding energy to a late first-row transition metal cation M + shows that the third ligand is significantly less strongly bound than the two first. The present study suggests that a new type of cluster-assisted reactions could be induced by the metal center when it is tri-coordinated. Cu + complexes have been chosen as models for the quantum chemical calculations (density functional and post-Hartree–Fock ab initio). First, an emphasis is made on the analysis of the evolution of the binding energy as the coordination number n varies from 1 to 4 in Cu +(H 2O) n and Cu +(CO) n . The evolution of the electronic repulsion between the σ donating orbitals of the ligands and the 3d orbitals is discussed in details. Second, we consider the successive substitution reactions of CO by H 2O ligand from Cu +(CO) n ( n=1–4). Our calculations suggest that rather than the simple substitution reaction of CO by ROR′ (R, R′=H, alkyl), formation of an acid or ester could occur in the coordination sphere of the metal. Whereas kinetics is likely to be unfavorable in the case of Cu +, such condensation reaction of ROR′ and CO could be observed with late first-row transition metal cations such as Fe +.

Reactivity of 3d transition metal cations in diethylene glycol solutions. Synthesis of transition metal ferrites with the structure of discrete nanoparticles complexed with long-chain carboxylate anions.

Study of the reactivity of 3d transition metal cations in diethylene glycol solutions revealed several key features that made it possible to develop a new method for synthesis of the nanocrystalline transition metal ferrites. The 3-7 nm particles of [MFe2O4]n[O2CR]m, where M = Mn, Fe, Co, Ni, and Zn, ligated on their surface with long-chain carboxylate anions, have been obtained in an isolated yield of 75-90%. The key features are the following. Complexation of the first-row transition metal cations with diethylene glycol at a presence of alkaline hydroxide is sufficient to enable control over the rate of their hydrolysis. The reaction of hydrolysis leads to the formation of metal oxide nanocrystals in colloidal solution. The nanoparticles growth is terminated by an added long-chain carboxylic acid, which binds to their surface and acts as a capping ligand. The isolated nanocrystalline powders are stable against agglomeration and highly soluble in nonpolar organic solvents.

Insertion Reaction of Mn+ Bare Metal Cation into the N−H and C−H Bonds of Ammonia and Methane

The Potential Energy Surfaces of the dehydrogenation reaction of NH3 and CH4 molecules by the first-row transition metal cations Mn+ (7S, 5S) were investigated employing the Density Functional (B3LYP) and the CCSD(T) levels of theory. A close description of the reaction paths leading to three dissociation products was given, including several minima and key transition states. The reactions proceed to give dehydrogenation products by oxidative addition of the metal cation into one of the H−X bonds (X = N,C) and formation of the H−M+−XHn-1, hydrido intermediates, which in these cases are also confirmed to represent stable minima along the quintet surface. Because the spin state of the reactants is different from that of intermediates and products an intersystem crossing is proposed to occur. The binding energies of reaction products were calculated and compared with available experimental data to calibrate the quality of our approach.

Isomerically Pure α1-Monosubstituted Tungstodiphosphates: Synthesis, Characterization and Stability in Aqueous Solutions

Isomerically pure samples of α1-P2W17O61M were prepared, in which M represents CaII and mainly the first-row transition metal cations: MnII, FeIII, CoII, NiII, CuII, ZnII. The formula is α1-P2W17O62M for VV and MoVI. The compounds were characterised by elemental analysis, IR, UV/Vis and 31P NMR spectroscopy. The stability of these complexes was monitored by cyclic voltammetry and/or UV/Vis spectroscopy. All the compounds proved to be stable for at least 24 h in a pH = 3 medium, even in the presence of 0.2 M Na+, except for the precursor lacunary species itself and the CaII-substituted derivative. In this medium, the transformation of the lacunary heteropolyanion yielded a mixture of α-[P2W18O62]6− and [H2P2W12]12−. The same species were obtained, but at a much slower rate, through the decomposition of α1-P2W17O61Ca. This difference in stability between the lacunary and the CaII-substituted derivatives might be ascribed to size and charge effects, along with the rigidity of the vacant site. At pH = 5, the final product of the transformation of α1-[P2W17O61]10− is α2-[P2W17O61]10−. The presence of Li+ appears to be more favourable than Na+ for the stability of these complexes. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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.

Tetracyanomanganate(II) and its salts of divalent first-row transition metal ions.

The first known paramagnetic, tetrahedral cyanide complex, [Mn(II)(CN)(4)](2)(-), is formed by the photoinduced decomposition of [Mn(IV)(CN)(6)](2)(-) in nonaqueous solutions or by thermal decomposition in the solid state. In acetonitrile or dichloromethane, photoexcitation into the ligand-to-metal charge transfer band (lambda(max) = 25 700 cm(-1), epsilon = 3700 cm(-1) M(-1)) causes the homolytic cleavage of cyanide radicals and reduction of Mn(IV). Free cyanide in dichloromethane leads to the isolation of polycyanide oligomers such as [C(12)N(12)](2)(-) and [C(4)N(4)](-), which was crystallographically characterized as the PPN(+) salt C(40)H(30)N(5)P(2): monoclinic space group = I2/a, a = 18.6314(2) A, b = 9.1926(1) A, c = 20.8006(1), beta =106.176(2) degrees, Z = 4]. In the solid state Mn(IV)-CN bond homolysis is thermally activated above 122 degrees C, according to differential scanning calorimetry measurements, leading to the reductive elimination of cyanogen. The [Mn(II)(CN)(4)](2-) ion has a dynamic solution behavior, as evidenced by its concentration-dependent electronic and electron paramagnetic spectra, that can be attributed to aggregation of the coordinatively and electronically unsaturated (four-coordinate, 13-electron) metal center. Due to dynamics and lability of [Mn(II)(CN)(4)](2-) in solution, its reaction with divalent first-row transition metal cations leads to the formation of lattice compounds with both tetrahedral and square planar local coordination geometries of the metal ions and multiple structural and cyano-linkage isomers. alpha-Mn(II)[Mn(II)(CN)(4)] has an interpenetrating sphalerite- or diamond-like network structure with a unit cell parameter of a = 6.123 A (P43m space group) while a beta-phase of this material has a noninterpenetrating disordered lattice containing tetrahedral [Mn(II)(CN)(4)](2-). Linkage isomerization or cyanide abstraction during formation results in alpha-Mn(II)[Co(II)(CN)(4)] and Mn(II)[Ni(II)(CN)(4)] lattice compounds, both containing square planar tetracyanometalate centers. alpha-Mn(II)[Co(II)(CN)(4)] is irreversibly transformed to its beta-phase in the solid state by heating to 135 degrees C, which causes a geometric isomerization of [Co(II)(CN)(4)](2)(-) from square planar (nu(CN) = 2114 cm(-1), S = (1)/(2)) to tetrahedral (nu(CN) = 2158 cm(-1), S = (3)/(2)) as evidenced by infrared and magnetic susceptibility measurements. Mn(II)[Ni(II)(CN)(4)] is the only phase formed with Ni(II) due to the high thermodynamic stability of square planar [Ni(II)(CN)(4)](2)(-).

Reactivity of Cr+(6S,4D), Mn+(7S,5S), and Fe+(6D,4F): Reaction of Cr+, Mn+, and Fe+ with Water

The study of the reaction of water with the first-row transition-metal ions is continued in this work. Here we report the study of the reaction of water with the middle (Cr+, Mn+, and Fe+) first-row transition-metal cations in both high- and low-spin states. In agreement with experimental observations, the oxides are predicted to be more reactive than the metal ions, and no exothermic products are observed. Formation of endothermic products is examined. An in-depth analysis of the reaction paths leading to the observed products is given, including various minima, and several important transition states. All results have been compared with existing experimental and theoretical data, and our earlier works covering the (Sc+, Ti+, V+) + H2O reactions to observe existent trends for the early first-row transition-metal ions. The MO+ + H2 energy relative to M+ + H2O increases through the series from left to right. Additionally, the Fe+ case is seen to be significantly different from the entire Sc+−Mn+ series because both its low- and high-spin cases involve paired electrons, and Mn+ shows some differences because of the complete half-filling of its valence shell in the high-spin case.

Theoretical study of ammonia activation by M+ (M=Sc, Ni, Cu)

The reactions of the first-row transition metal cations, Sc+ (3D,1D), Ni+ (2D), Cu+ (1S), with NH3 have been studied by the multiconfigurational and multireference-based theories, to clarify the similarities and differences in the reactivity of early (Sc+) and late (Ni+, Cu+) transition metal cations. In all the cases, the ion–dipole complex, MNH3+, is initially formed with a C3v symmetry structure, which is the most stable complex in the respective potential energy surfaces except for Sc+ (1D). The M+–NH3 binding energy was evaluated as 42.4, 37.8, 50.9, and 48.1 kcal/mol for Sc+ (3D), Sc+ (1D), Ni+, and Cu+, respectively. In the second step, M+ is expected to activate one N–H bond of NH3, leading to the insertion complex, HMNH2+. In Sc+ (3D,1D), three different stationary points of HScNH2+, i.e., Cs (in-plane), Cs (out-of-plane), and C2v structures, were located, which correspond to a minimum point, a first-order saddle point, and a second-order saddle point, respectively. In these complexes, the singlet state originating from Sc+ (1D) is largely stabilized compared to the triplets. The singlet HScNH2+ (in-plane) is calculated to be the most stable compound. There are three dissociation channels from HScNH2+, i.e., →ScNH2++H, →ScH++NH2, and →ScNH++H2. The third dissociation occurs through the transition state of a four-centered structure, with a small activation barrier of 23 kcal/mol, in both singlet and triplet surfaces. As to the late transition metal cations Ni+ and Cu+, there is no intermediate complex of HMNH2+, thus, all the dissociations occur through highly vibrational excitations of MNH3+. The calculated results are consistent with experimental observations.

A [RuII(bipy)3]-[1,9-diamino-3,7-diazanonane-4,6-dione] two-component system, as an efficient ON–OFF luminescent chemosensor for Ni2+ and Cu2+ in water, based on an ET (energy transfer) mechanism

A dioxo-tetramine ligand (1,9-diamino-3,7-diazanonane-4,6-dione ≡ dioxo-2,3,2-tet) has been appended to a RuII(bipy)3 unit. This new system, 2, is water-soluble and capable of sensing Cu2+ and Ni2+ cations thanks to the strong quenching of the Ru(bipy)3 fluorescence, which takes place when a metal cation is coordinated by the dioxo-2,3,2-tet binding unit. Coordination requires the energetically expensive deprotonation of the amide nitrogens, so that only Cu2+ and Ni2+ are able to promote it among the series of divalent first-row transition metal cations. Moreover, the complexation reaction is pH-dependent and one can distinguish between the two metal cations on working at the proper pH. The quenching mechanism has been examined by measuring the lifetime of the excited state of the ruthenium luminophore both on the metal-free and metal-complexed system and by flash photolysis experiments carried out on the complexed systems. The results clearly indicate that an energy transfer mechanism holds both for the Cu2+ and Ni2+ complex. The characterization of 2 as a water soluble ON–OFF sensor for copper and nickel has also been checked for its lowest detection limit, finding that these two metals can be detected down to a 10–7 M concentration. Moreover, also system 3, containing a dioxo-2,3,2-tet ligand and the ReI(CO)3bipy(Cl) luminophore, has been examined as another possible water-soluble ON–OFF fluorescent sensor for the same transition metal cations. Again, only Cu2+ and Ni2+ are bound with a pH-dependent equilibrium, but incomplete luminescence quenching was observed, which prevented the determination of the quenching mechanism.

Transition-Metal Ethene Bonds: Thermochemistry of M+(C2H4)n(M = Ti−Cu,n= 1 and 2) Complexes

Complexes of the first-row transition-metal cations (Ti+−Cu+) with one and two ethene molecules are studied by guided ion beam mass spectrometry. Thermalized complexes are formed in a flow tube source and examined by energy-resolved collision-induced dissociation with Xe. The energy dependence of the CID cross sections is analyzed with consideration of multiple collisions, internal energy of the reactants, and lifetime effects. First, D0(M+−C2H4), and second, D0(C2H4M+−C2H4), adiabatic metal ion ethene bond energies, in eV, obtained in this study are 1.51 ± 0.11 for Ti (first bond only), 1.29 ± 0.08 and 1.32 ± 0.14 for V, 0.99 ± 0.11 and 1.12 ± 0.11 for Cr, 0.94 ± 0.12 and 0.91 ± 0.15 for Mn, 1.50 ± 0.11 and 1.57 ± 0.16 for Fe, 1.93 ± 0.09 and 1.58 ± 0.14 for Co, 1.89 ± 0.11 and 1.79 ± 0.15 for Ni, and 1.82 ± 0.14 and 1.80 ± 0.13 for Cu, respectively. These values include corrections for diabatic dissociation in the cases of Fe+(C2H4) and Mn+(C2H4)2, a point that is discussed in detail. Previous work obta...

Formation of Phenolate Complexes of Some First-Row Transition Metal Cations

We report in the present paper the result of our potentiometric studies on the complexation tendency of phenolate anion with divalent manganese, cobalt, nickel, and copper ions in aqueous sodium pperchlorate solutions of 0.1 M ionic strenght at 25.0°

Polyoxoanion Coordination Chemistry: Synthesis and Characterization of the Heterometallic, Hexanuclear Clusters [{Zn(bipy)(2)}(2)V(4)O(12)], [{Zn(phen)(2)}(2)V(4)O(12)].H(2)O, and [{Ni(bipy)(2)}(2)Mo(4)O(14)

The hydrothermal reactions of vanadium oxide and molybdenum oxide starting materials with divalent first-row transition metal cations in the presence of nitrogen donor chelating ligands yield the heterometallic hexanuclear clusters [{Zn(bipy)(2)}(2)V(4)O(12)] (2), [{Zn(phen)(2)}(2)V(4)O(12)].H(2)O (3.H(2)O), and [{Ni(bipy)(2)}(2)Mo(4)O(14)] (4). A similar reaction in the presence of excess 2,2'-bipyridine yields [Zn(bipy)(3)](2)[V(4)O(12)].11H(2)O (1.11H(2)O), a species with an isolated {V(4)O(12)}(4)(-) cluster. The structure of 2 consists of a {V(4)O(12)}(4)(-) ring covalently attached to each of two {Zn(bipy)(2)}(2+) moieties through the terminal oxo groups of alternate vanadium sites. In contrast, the structure of 3 exhibits a {V(4)O(12)}(4)(-) ring linked through oxo groups of adjacent vanadium sites to two {Zn(phen)(2)}(2+) moieties. The structure of 4 is constructed from two {Mo(2)O(7)}(2)(-) units linked through two {Ni(bipy)(2)}(2+) groups to form a cyclic 12-membered {Mo(4)Ni(2)O(6)} core. Crystal data: [Zn(bipy)(3)](2)[V(4)O(12)].11H(2)O (1.11H(2)O), a = 21.910(4) Å, b = 14.044(2) Å, c = 23.815(4) Å, beta = 106.15(1) degrees, monoclinic, C2/c, Z = 4; [{Zn(bipy)(2)}(2)V(4)O(12)] (2), a = 12.017(2) Å, c = 15.120(2) Å, tetragonal P4(2)/n, Z = 2. [{Zn(o-phen)(2)}(2)V(4)O(12)].H(2)O (3.H(2)O), a = 18.182(2) Å, b = 11.3668(9) Å, c = 23.455(2) Å, beta = 97.815(7) degrees, monoclinic P2(1)/c, Z = 4; [{Ni(bipy)(2){(2)Mo(4)O(14)] (4), a = 12.323(2) Å, c = 14.897(4) Å, tetragonal P4(2)2(1)2, Z = 2.

Theoretical Study on the Stability of Low-Spin Hydridomethyl Complexes of the First-Row Transition Metal Cations

Theoretical calculations have been performed in order to study the stability of the low-spin hydridomethyl complexes HMCH3+ for the first-row transition metals (M+ = Sc+−Cu+). Originally experimental results have been rationalized by assuming a low-spin hydridomethyl complex as a stable intermediate in the reactions of methane with singly charged metal cations. Recently, theoretical studies showed that for some late transition metals of the first row (Fe+ and Co+) no stable low-spin insertion product could be located on the potential energy surface. For the early elements of this row (Sc+−V+) the experimental cross section ratios σ(MH+)/σ(MCH3+) indicate that the elimination reactions for these cations proceed via a statistically behaved intermediate. Our CASPT2 calculations indeed confirm a stable hydridomethyl complex for these cations. The reason for the stability of the insertion complexes could be traced back to the relative position of the lowest lying low-spin s0dn state and the lowest lying low-spin s1dn-1 state in the electronic spectrum of the corresponding free transition metal cations. Further, an analysis of the wave function clearly reveals a correlation between the extent of the participation of the 4s orbital in the metal−ligand bonds and the experimentally observed dominance of the H2 elimination over the other elimination reactions for the cations Sc+ to Cr+. An explanation in terms of the frontier orbital approach is given.

Gas-Phase Chemistry of Hydrogen Peroxide and Alkyl Hydroperoxides with “Bare” First-Row Transition-Metal Cations Cr+−Co+. Generation of MO+ Cations Using H2O2 as Oxidant

The unimolecular reactions of “bare” first-row transition-metal cations Cr+−Co+ complexed to small alkyl hydroperoxides and hydrogen peroxide have been examined by means of tandem mass spectrometry. In the metal-mediated reactions of the methyl, ethyl, and isopropyl hydroperoxides disproportionations of the peroxides dominate which involve insertion of the metal ion into the weak O−O bond followed by β-hydrogen shifts. These processes lead to competitive losses of water, aldehydes, or ketones as thermochemically favored neutral products. In addition, for CH3OOH/M+ unimolecular dehydrogenation to yield M(OH2)(CO)+ takes place. The metal complexes of tert-butyl hydroperoxide give rise to methanol as a side product via an analogous β-methyl migration and subsequent reductive elimination of methanol. However, for this complex the major reaction channel corresponds to water loss, which is rationalized by a multistep rearrangement. Interestingly, the observed reactivity patterns remain essentially unchanged irrespective of the nature of the metal. This may be attributed to the high thermodynamic stability of the products and the absence of other competing reaction channels. In contrast to the alkyl hydroperoxides, the hydrogen peroxide/M+ complexes permit oxygen-atom transfer to the metal center to yield inter alia MO(OH)+, M(OH)+, and MO+ cations. As shown previously, the latter can further be used as oxidants in the oxygenation of hydrocarbons.

Molecular Orbital Study of the Reaction Mechanism of Sc+ with Methane. Comparison of the Reactivity of Early and Late First-Row Transition Metal Cations and Their Carbene Complexes

The reactions of Sc+ + CH4 and ScCH2+ + H2 have been studied with the CASSCF and MR-SDCI-CASSCF methods. The reaction of the ground state Sc+ with CH4 proceeds as Sc+(3D, s1d1) + CH4 → ScCH4+(3A‘‘) → TS2(1A‘) → HScCH3+(1A‘) → TS1 → (H2)ScCH2+(1A1) → ScCH2+(1A1) + H2 and is calculated to be endothermic by 24.8 kcal/mol. After formation of an ion−molecule complex ScCH4+, the reaction cannot proceed on the triplet surface because of a high barrier and has to cross over to singlet and reach the singlet transition state TS2 with a barrier of 28.6 kcal/mol. The insertion product HScCH3+, 4.9 kcal/mol more stable than the reactants Sc+ + CH4, produces most favorably an ion−molecule complex (H2)ScCH2+ with a barrier of 28kcal/mol, which can dissociate to give H2 and ScCH2+(1A1) with a small barrier of 3.2 kcal/mol. At higher temperatures, production of ScH+ + CH3 and ScCH3+ + H from HScCH3+ will dominate. The reverse reaction ScCH2+(1A1) + H2 proceeds very easily and leads to HScCH3+(1A‘), ScCH4+(3A‘), and Sc+(1D...

Face selectivity of the C-H bond activation of cyclohexane by the "Bare" first-row transition-metal cations Sc+-Zn+

Face selectivity of the C-H bond activation of cyclohexane by the "Bare" first-row transition-metal cations Sc+-Zn+

Variation in stability of monohalide complexes and some properties of the solvated cations within the Mn 2+-Zn 2+ series

The stability of the monohalide complexes of the divalent first-row transition metal cations in water as well as in other donor solvents follows the sequence: MnX + > FeX + > CoX + > NiX + < CuX + > ZnX +. Moreover, some of the properties of the M(solvent) 6 2+ solvo-cations may be rationalized in terms of the same series. The observed sequence is opposite to that known as the Irving—Williams series.

Interactions between metal cations and the ionophore lasalocid. Part 3.—Interactions of lasalocid with Mn2+, Fe2+, Co2+, Ni2+ and Zn2+ in methanol

The stability of complexes formed in methanol between the bacterial ionophore lasalocid and first-row transition-metal cations has been studied using potentiometry and, for manganese, electron spin resonance. Both AM+ and A2M complexes were obtained from the ionophore AH and the metal cation M2+. Comparison of the stability of the analogous salicylic acid complexes in the same medium suggests that the salicylic moiety in lasalocid is the main site of complexation for the cations studied here.

The chemistry of organosulphur compound types occurring in heavy oils: 4. the high-temperature reaction of thiophene and tetrahydrothiophene with aqueous solutions of aluminium and first-row transition-metal cations

In the reactions of thiophene and tetrahydrothiophene with aqueous solutions of first-row transition-metal and aluminium cations at 240 °C and 3.4 MPa all the metal species accelerated the decomposition of the thiophenes in relation to equivalent reactions with pure water. Al 3+, Sc 3+, VO 2+, Cr 3+, Ni 2+ and Cu 2+ were most reactive towards thiophene and Al 3+, VO 2+, Cr 3+ and Cu 2+ were most reactive towards tetrahydrothiophene. Principal products were H 2S and complex mixtures of organic products. The presence of CO 2 and oxygen-containing organic products revealed that water was involved in direct chemical reaction with the substrates. It is likely that these model reactions parallel more complex processes that occur during the steam-stimulated recovery of oil-sand bitumen and other high-sulphur oils.