Metal Valence Electrons Research Articles

Suppressing Defects‐Induced Non‐Radiative Recombination for Activating the Near‐Infrared Photoactivity of Red Polymeric Carbon Nitride

AbstractMany cases of light absorption modification exceeding 700 nm or near‐infrared (NIR) light are reported for capturing more than half of the solar energy, however, very few modifications can produce NIR photoactivity due to the inevitably introduced defects‐induced non‐radiative recombination. Here, taking four kinds of C/O co‐doped red polymeric carbon nitride as examples, defect‐repairing is carried out using alkali metal molten‐salts (LiCl/NaCl and LiCl/KCl) or solid‐salt (KCl) to activate their NIR photoactivity. The defect repair results from the passivation of alkali metal valence electron pairing and the formation of crystalline polyheptazine imide structure with more complete polymerization. More importantly, it sharply eliminates bulk defects (such as carbon vacancy and nitrogen vacancy) introduced by C/O co‐doping. Since structural defects are inevitably introduced in most photocatalysts during expanding light absorption, this proposed strategy is bound to be universal in suppressing defects‐induced non‐radiative recombination to activate NIR photoactivity.

Donor-acceptor electron transfers and bonding performance of cyclopentadienyl and cyclo-P5 middle decks in (CpFeE5)ML3 and (CpFeE5)FeCb (E5 = Cp, P5 and ML3 = Cr(CO)3, Mo(CO)3, CrBz, MnCp, MoBz) triple-decker complexes: Bonding and energy decomposition analysis

Density functional theory (DFT) calculations using BP86 and B3LYP* methods have been applied on a series of isoelectronic (CpFeCp’)ML3, (CpFeP5)ML3, (CpFeCp’)FeCb and (CpFeP5)FeCb (Cb = Cyclobutadiene, ML3 = Cr(CO)3, Mo(CO)3, CrBz, MBz, MnCp and Bz = Benzene) triple-decker complexes of 30-MVE (metal valence electrons) count to investigate the electronic structure and the bonding and exploiting the energy decomposition analysis (EDA). The optimized structures for the considered complexes are comparable to those experimentally characterized by X-ray diffraction. The bonding is evaluated through the interactions between the (cyclo-P5−) or Cp− and ML3 metallic fragments pinpointing the σ-donor and π-acceptor performance of the (cyclo-P5−) and Cp− ligands as potential 6 electron donors on one hand and that of the metallic fragments of 12-MVE count on other hand. The natural charges and the localization of the molecular orbitals have been used to predict the variation of the interactions with the nature of the metal fragment. The electrostatic and orbital interaction contributions and the role of σ-donor and π acceptor into the bonding are for a huge importance with regard to the energy decomposition analysis (EDA). For both (cyclo-P5−) and Cp−, the bonding was revealed to be equally ionic and covalent related to the percentage of ΔEelstat and ΔEorb into the total of attractive interactions (ΔEelstat + ΔEorb). The π bonding is strong than σ one, which contributes significantly by about 75% and more into the total orbital interactions.The σ-donation (Cp → M and P5 → M) and π-backdonation (Cp ← M and P5 ← M) are evaluated based on the donor–acceptor electrons transfers, revealing that are more significant for P5− than those for Cp−.

Transition metals based metalides TM-Janus-TM (where TM=Sc–Zn and Janus=F6C6H6); A theoretical study of nonconventional metalides with excellent static and dynamic nonlinear optical properties

Continuous progress is being made to bring forward the novel strategies for designing materials with excellent stability and exceptional nonlinear optical response. For the first time, 3d-transition series (Sc–Zn) is doped as source of excess electrons to design novel class of TM-JN-TM (TM = Sc–Zn) metalides based upon Janus-type all-cis1,2,3,4,5,6-hexafluorocyclohexane (JN) molecule. DFT calculations are performed at M06-2X/6-31+G(d,p) level of theory to explore the electronic and NLO properties of these complexes. The obtained novel metalides show excellent thermal stabilities than those of conventional alkalides and their interaction energies ranging from −3.50 to −88.33 kcal mol−1. Under the large facial polarization of JN, the valence electrons of transition metals (TM) on fluorine face serve as source of excess electron to TM metals on hydrogen face. With the excellent electronic stabilities, these complexes show significant decreased HOMO-LUMO gaps and, the performed NBO analysis also reveals their metalide character where the negative charge is observed at metal (TMH) on hydrogen face of complex C, D, G, H, and I. Among the designed metalides (TM-JN-TM), the significant first and second hyperpolarizability values of 2.43 × 106 au and 1.72 × 109 au are observed for Fe-JN-Fe complex. Simple excess electron complexes have better NLO response than that of true metalides. The observed dynamic first hyperpolarizabilities β(ω) values are much pronounced at smaller dispersion frequency (1064 nm). The frequency-dependent second hyperpolarizability γ(ω) value increased up to 5.75 × 1010 au for V-JN-V. At 1300 and 1900 nm, significant dynamic second hyperpolarizability γ(ω) values are observed. The scattering hyperpolarizability (βHRS) show significant value (2.0 × 107 au) for Fe-JN-Fe complex. We hope this work could open up new possibilities for NLO material design by using transition metals as source excess electron and, on the other hand, encourage greater experimental efforts in the laboratory to synthesize such stable compounds.

Electron transfers’ assessment between stannol ring of triple-decker complexes and M(CO)5 (M = Cr, Mo, W), MnCp(CO)2 and CoCp(CO) metallic fragments: Bonding and energy decomposition analysis

Density functional theory (DFT) calculations using BP86 and B3LYP* functionals have been performed on a series of triple-decker complexes [(M’Cp)2(C4Sn)](R) (M’ = Fe, Ru and R = Cr(CO)5, Mo(CO)5, W(CO)5, MnCp(CO)2 and CoCp(CO)) of 30-MVE (metal valence electrons) count to investigate the electronic structure, the bonding and the energy decomposition. The bonding is evaluated through the interactions between Sn(II) and R metallic fragments. The optimized structures for the considered complexes are comparable to the available X-ray data. The bonding energies have been calculated for all considered systems and their dependence on the nature of the metal cation of the R metallic fragment and its environment has been discussed. The increase of the MVE of the R fragments conducts to a remarkable increase of Sn-metal interactions. The natural charges and the localization of the molecular orbitals have been used to predict the variation of the interactions with the nature of the metal fragment. The σ-donation (L → M) and π-backdonation (L ← M) (L = (M’Cp)2(C4Sn) and M = the metal of the R metallic fragment) are evaluated based on the donor–acceptor electrons transfers showing the strength of the former and the cancellation or partial cancellation of the later. The electrostatic and orbital interaction contributions and the role of σ donor and π acceptor bonding are for a great significance in relationship with the energy decomposition analysis (EDA). The Sn-Metal bonding was revealed to be more ionic than covalent in relationship with the proportion of ΔEelstat and ΔEorb into the total of attractive interactions (ΔEelstat + ΔEorb) and it is well correlated to its bond distance and its Wiberg bond index. The π bonding for Cr(CO)5, Mo(CO)5 and W(CO)5 is weak but not totally suppressed, contrarily to that for MnCp(CO)2 and CoCp(CO) which contributes significantly by about 22% and 26%, into the total orbital interactions, respectively.

Hydrogen trapping and storage in the group IVB-VIB transition metal carbides

The transition metal carbides have been known to act as traps for hydrogen in steels as well as potential materials for hydrogen storage. Despite numerous experimental and a few theoretical studies, what impacts hydrogen trapping and storage in the transition metal carbides is not well understood. In this work, we use density functional theory to systematically investigate the bulk trapping and storage capabilities of the transition metal carbides. We specifically examine how trapping and storage changes with the transition metal, from the group IVB to group VIB, carbon concentration, and structure. Our results demonstrate a strong correlation between the trap energy and the number of valence electrons in the transition metal, suggesting that the group IVB transition metal carbides are the best carbides for trapping and storage. Hydrogen preferentially sits at octahedral interstices, e.g., the carbon vacancies, in the structure except in certain cases near the Me2C concentration when tetrahedral interstices, devoid of nearest neighbor carbon, can become more favorable. Our results further demonstrate that the lower the carbon concentration, the more hydrogen the transition metal carbide can store. These results demonstrate which carbides will act as the best traps for hydrogen.

Experimental and theoretical study on electronic structure and mechanical property of TaxHf1−xC

TaxHf1−xC can withstand extreme environments, but the challenges in their densification prevent them from being used for many applications. In this paper, a method to prepare dense homogeneous TaxHf1−xC solid solutions with a cubic structure is prosed. Moreover, mechanical properties of TaxHf1−xC are characterized, including the elastic modulus and Poisson ratio. The hardness and Debye temperature are estimated by using empirical equation. The properties related to the electronic structures of TaxHf1−xC (x = 0, 0.25, 0.5, 0.75, 1), including the density of states and Mulliken populations, are systematically calculated by using the first-principles method. From the calculation, we found that all TaxHf1−xC are thermodynamically stable at room temperature. Moreover, Ta0.5Hf0.5C has a higher Young's modulus and shear modulus comparing to Ta0.75Hf0.25C and Ta0.25Hf0.75C. Ta0.75Hf0.25C possesses the highest bulk modulus, suggesting that it has greater comprehensive mechanical properties than the others. In addition, the compositions of their chemical bonds are discussed according to their density of states, population analysis and Debye temperature. We found that the number of valence electrons of transition metals significantly affects their mechanical properties. Finally, the relation between the mechanical properties of TaxHf1−xC (x = 0, 0.25, 0.5, 0.75, 1) and the chemical bonds are summarized.

Ground and excited states analysis of alkali metal ethylenediamine and crown ether complexes.

High-level electronic structure calculations are carried out to obtain optimized geometries and excitation energies of neutral lithium, sodium, and potassium complexes with two ethylenediamine and one or two crown ether molecules. Three different sizes of crowns are employed (12-crown-4, 15-crown-5, 18-crown-6). The ground state of all complexes contains an electron in an s-type orbital. For the mono-crown ether complexes, this orbital is the polarized valence s-orbital of the metal, but for the other systems this orbital is a peripheral diffuse orbital. The nature of the low-lying electronic states is found to be different for each of these species. Specifically, the metal ethylenediamine complexes follow the previously discovered shell model of metal ammonia complexes (1s, 1p, 1d, 2s, 1f), but both mono- and sandwich di-crown ether complexes bear a different shell model partially due to their lower (cylindrical) symmetry and the stabilization of the 2s-type orbital. Li(15-crown-5) is the only complex with the metal in the middle of the crown ether and adopts closely the shell model of metal ammonia complexes. Our findings suggest that the electronic band structure of electrides (metal crown ether sandwich aggregates) and expanded metals (metal ammonia aggregates) should be different despite the similar nature of these systems (bearing diffuse electrons around a metal complex).

Single-Electron Lanthanide-Lanthanide Bonds Inside Fullerenes toward Robust Redox-Active Molecular Magnets.

ConspectusA characteristic phenomenon of lanthanide–fullerene interactions is the transfer of metal valence electrons to the carbon cage. With early lanthanides such as La, a complete transfer of six valence electrons takes place for the metal dimers encapsulated in the fullerene cage. However, the low energy of the σ-type Ln–Ln bonding orbital in the second half of the lanthanide row limits the Ln2 → fullerene transfer to only five electrons. One electron remains in the Ln–Ln bonding orbital, whereas the fullerene cage with a formal charge of −5 is left electron-deficient. Such Ln2@C80 molecules are unstable in the neutral form but can be stabilized by substitution of one carbon atom by nitrogen to give azafullerenes Ln2@C79N or by quenching the unpaired electron on the fullerene cage by reacting it with a chemical such as benzyl bromide, transforming one sp2 carbon into an sp3 carbon and yielding the monoadduct Ln2@C80(CH2Ph). Because of the presence of the Ln–Ln bonding molecular orbital with one electron, the Ln2@C79N and Ln2@C80(R) molecules feature a unique single-electron Ln–Ln bond and an unconventional +2.5 oxidation state of the lanthanides.In this Account, which brings together metallofullerenes, molecular magnets, and lanthanides in unconventional valence states, we review the progress in the studies of dimetallofullerenes with single-electron Ln–Ln bonds and highlight the consequences of the unpaired electron residing in the Ln–Ln bonding orbital for the magnetic interactions between Ln ions. Usually, Ln···Ln exchange coupling in polynuclear lanthanide compounds is weak because of the core nature of 4f electrons. However, when interactions between Ln centers are mediated by a radical bridge, stronger coupling may be achieved because of the diffuse nature of radical-based orbitals. Ultimately, when the role of a radical bridge is played by a single unpaired electron in the Ln–Ln bonding orbital, the strength of the exchange coupling is increased dramatically. Giant exchange coupling in endohedral Ln2 dimers is combined with a rather strong axial ligand field exerted on the lanthanide ions by the fullerene cage and the excess electron density localized between two Ln ions. As a result, Ln2@C79N and Ln2@C80(CH2Ph) compounds exhibit slow relaxation of magnetization and exceptionally high blocking temperatures for Ln = Dy and Tb. At low temperatures, the [Ln3+–e–Ln3+] fragment behaves as a single giant spin. Furthermore, the Ln–Ln bonding orbital in dimetallofullerenes is redox-active, which allows its population to be changed by electrochemical reactions, thus changing the magnetic properties because the change in the number of electrons residing in the Ln–Ln orbital affects the magnetic structure of the molecule.

Insight into the nature of M-C bonding in the lanthanide/actinide-biscarbene complexes: a theoretical perspective.

We have investigated M-C bonds in lanthanide and actinide complexes ML2 (M = Ce, Th, U, Np and Pu; L = C(PPh2NMes)2) using scalar-relativistic theory. The M-C bonds possess typical σ and π bonding character, except for the nearly π-only Th-C bonds. The metal valence electrons significantly reside in the valence d and f orbitals for CeL2, UL2, NpL2 and PuL2, while for ThL2 most electron population is in 6d orbitals. The contribution of 6d orbitals to the An-C bonds decreases and that of 5f orbitals increases across the actinide series. QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) analyses confirm that the M-C bonds possess significant covalent character. This work provides insights into the contributions of d and f valence orbitals to M-C bonding. And inclusion of Np and Pu in this evaluation extends understanding to later actinides.

Structural diversity of homobinuclear transition metal complexes of the phenazine ligand: theoretical investigation

DFT/BP86 calculations have been carried out on a series of hypothetical binuclear compounds of general formula (L3M)2(C12N2H8) (M = Sc–Ni, L3 = (CO)3, (PH3)3 and Cp−, and C12N2H8 = phenazine ligand-denoted Phn). The various structures with syn and anti configurations have been investigated, in order to determine the phenazine’s coordination to first-row transition metals of various spin states with syn and anti conformations. The lowest energy structures depend on the nature of the metal, the spin state, and the molecular symmetry. This study has shown that the electronic communication between the metal centers depends on their oxidation state and the attached ligands. The tricarbonyl and the triphosphine ligands gave rise to comparable results in terms of stability order of isomers, metal-metal bond distances, and the coordination modes. Metal-metal multiple bonding has been evidenced for Sc, Ti, and V complexes to compensate the electronic deficiency. The Cr, Mn, Fe, Co, and Ni-rich metals prefer the anti conformation due to the enhancement of the metal valence electron count. The spin density values calculated for the triplet and quintet spin structures point out that the unpaired electrons are localized generally on the metal centers. The Wiberg bond indices are used to evaluate the metal-metal bonding. Furthermore, calculations using the BP86-D functional which take into account the attractive part of the van der Waals type interaction potential between atoms and molecules that are not directly connected to each other gave comparable results to those obtained by BP86 functional in terms of coordination modes, HOMO-LUMO gaps, metal-metal bond orders, and the stability order between isomers, but with slight deviation of M–C, M–N, and M–M bond distances not exceeding 3%.

Интенсивность контактного взаимодействия и перенос материалов при шлифовании и микроцарапании тугоплавких металлов

Peculiarities in the contact surfaces formation and material transfer at micro-scratching and grinding of refractory metals are investigated. There is shown a connection of metal quantity transferred to the area of crystal wear, a degree of ground surface charging with silicon carbide crystals and wear of an abrasive tool with the electron structure of atoms in refractory metals. It is defined, that the intensity of metal transfer in a crystal surface layer decreases with the increase of a principle quantum number of metal valence electrons. According to the intensity of the interaction silicon carbide during grinding and micro-cutting the refractory metals are classified into adhesion-active metals of IVB, VB sub-groups and inert metals of VIB subgroup of the Periodic Table.

Elastic properties of amorphous T0.75Y0.75B14 (T = Sc, Ti, V, Y, Zr, Nb) and the effect of O incorporation on bonding, density and elasticity (T′ = Ti, Zr)

We have systematically studied the effect of transition metal valence electron concentration (VEC) of amorphous T0.75Y0.75B14 (a-T0.75Y0.75B14, T = Sc, Ti, V, Y, Zr, Nb) on the elastic properties, bonding, density and electronic structure using ab initio molecular dynamics. As the transition metal VEC is increased in both periods, the bulk modulus increases linearly with molar- and mass density. This trend can be understood by a concomitant decrease in cohesive energy. T′ = Ti and Zr were selected to validate the predicted data experimentally. A-Ti0.74Y0.80B14 and a-Zr0.75Y0.75B14 thin films were synthesized by high power pulsed magnetron sputtering. Chemical composition analysis revealed the presence of up to 5 at.% impurities, with O being the largest fraction. The measured Young’s modulus values for a-Ti0.74Y0.80B14 (301 ± 8 GPa) and a-Zr0.75Y0.75B14 (306 ± 9 GPa) are more than 20% smaller than the predicted ones. The influence of O incorporation on the elastic properties for these selected systems was theoretically studied, exemplarily in a-Ti0.75Y0.75B12.75O1.25. Based on ab initio data, we suggest that a-Ti0.75Y0.75B14 exhibits a very dense B network, which is partly severed in a-Ti0.75Y0.75B12.75O1.25. Upon O incorporation, the average coordination number of B and the molar density decrease by 9% and 8%, respectively. Based on these data the more than 20% reduced Young’s modulus obtained experimentally for films containing impurities compared to the calculated Young’s modulus for a-Ti0.75Y0.75B14 (without incorporated oxygen) can be rationalized. The presence of oxygen impurities disrupts the strong B network causing a concomitant decrease in molar density and Young’s modulus. Very good agreement between the measured and calculated Young’s modulus values is obtained if the presence of impurities is considered in the calculations. The implications of these findings are that prediction efforts regarding the elastic properties of amorphous borides containing oxygen impurities on the at.% level are flawed without taking the presence of impurities into account.

Method of Equilibrium Density Matrix. Energy of Interacting Valence Electrons in Metal

In this article we apply the method of density matrices for the description of the equilibrium system of interacting electrons. Variational principle of the density matrices is used in the framework of the mean field method for research of systems of valence electrons in metals. We obtained the model Hamiltonian describing the behavior of interacting electrons, which describes all the properties of superconductors. Note that was using the Coulomb potential that acts between two electrons in the coordinate space.

General Trends in Electronic Structure, Stability, Chemical Bonding and Mechanical Properties of Ultrahigh Temperature Ceramics TMB2 (TM = transition metal)

The electronic structure, stability, chemical bonding and mechanical properties of 3d, 4d and 5d transition metal diboride TMB2 were investigated using first-principles calculations based on density functional theory. All the primary chemical bonds, i.e., metallic, ionic and covalent have contributions to the bonding of TMB2. The number of valence electrons of transition metals or the valence electron concentration (VEC) of TMB2 has strong effects on the lattice parameters, stability and mechanical properties of TMB2. Both lattice constants a and c decrease with VEC, but c decreases faster than a, which is attributed to the enhanced TM d–B p (sp2) bonding. Bulk modulus B of TMB2 increases continuously with VEC due to the enhanced TM d–B p (sp2) and TM dd bonding. Shear modulus G increases with VEC, reaching a maximum at VEC = 3.33, and then decreases with further increase of VEC. YB2 and MnB2 have low Young's modulus and are predicted to have good thermal shock resistance. According to Pugh's criterion (G/B < 0.571), MnB2, MoB2 and WB2 are predicted as ductile or damage tolerant ultrahigh temperature ceramics (UHTCs).

Stability, elastic properties and fracture toughness of Al0.75X0.75B14 (X=Sc, Ti, V, Cr, Y, Zr, Nb, Mo) investigated using ab initio calculations

The effect of the transition metal valence electron concentration on the energy of formation, effective charge of B icosahedra, elastic properties, surface energy and fracture toughness was calculated using density functional theory for icosahedral transition metal borides of AlXB14 (X=Sc, Ti, V, Cr, Y, Zr, Nb, Mo). Consistent with previous work on AlYB14 (Kölpin et al 2009 J. Phys.: Condens. Matter 21 355006) it is shown that phase stability is generally dependent on the effective charge of the icosahedral transition metal borides. Also, ionization potential and electronegativity are identified as parameters affecting the effective charge of B icosahedra suitable for use in predicting the phase stability. Al0.75Y0.75B14, Al0.75Sc0.75B14 and Al0.75Zr0.75B14 have been identified as promising phases for application as protective coatings as they exhibit high phase stability and stiffness combined with a comparatively high fracture toughness.

Structural, Spectroscopic, and Electronic Properties of Cubic G0-Rb2KTiOF5 Oxyfluoride

The G0-Rb2KTiOF5 single crystals with dimensions up to nearly a centimeter in size have been prepared by slow solidification method. The elpasolite-related crystal structure of G0-Rb2KTiOF5 has been refined by Rietveld method at T = 298 K (space group Fm3̅m, Z = 4, a = 8.880(1) Å, V = 700.16(2) Å3; RB = 2.66%). The wide optical transparency range of 0.25–9 μm and forbidden band gap of Eg = 3.87 eV have been obtained for the G0-Rb2KTiOF5 crystal. Dominating photoluminescence bands at 3.36 and 2.33 eV are related to free and self-trapped excitons, respectively. The electronic structure of G0-Rb2KTiOF5 has been evaluated by X-ray photoelectron spectroscopy and calculated with the first-principles methods. A good agreement between theoretical and experimental results has been achieved. Chemical bonding effects have been discussed for all metal ions using binding energy difference parameters and a wide comparison with related oxides and fluorides. The competition between O2– and F– ions for metal valence electrons has been found.

Theoretical study of elastic properties and phase stability of M0.5Al0.5N1−xOx (M = Sc, Ti, V, Cr)

The influence of oxygen content and transition metal valence electron concentration on the phase stability and elastic properties of cubic M0.5Al0.5N1−xOx (M = Sc, Ti, V, Cr; x = 0 – 0.5) was studied using ab initio calculations. The negative value of enthalpy of mixing was observed for all phases indicating full miscibility of M0.5Al0.5N with the hypothetical M0.5Al0.5O. Bulk moduli are decreased as x in M0.5Al0.5N1−xOx is increased. This can be understood based on the electronic structure. As N is substituted by O, there are no noticeable changes in the chemical bonding nature. However, O is more electronegative than N, giving rise to an increase in the ionic character of the overall bonding. In spite of that, the M – O bond in M0.5Al0.5N1−xOx is longer than the corresponding M–N bond, which implies that this bond becomes weaker. Hence, we propose that the decrease of bulk moduli upon O incorporation into M0.5Al0.5N1−xOx is caused by weaker M–O bonds.

ChemInform Abstract: Oxidation by Hydrogen in the Chemistry and Physics of the Rare‐Earth Metals

AbstractReview: 29 refs.

Synthesis, Structural, Magnetic, and Electronic Properties of Cubic CsMnMoO3F3 Oxyfluoride

A powder sample of CsMnMoO3F3 oxyfluoride has been prepared by solid state synthesis. The pyrochlore-related crystal structure of CsMnMoO3F3 has been refined by the Rietveld method at T = 298 K (space group Fd-3m, a = 10.59141(4) A, V = 1188.123(8) A3; RB = 3.44%). The stability of the cubic phase has been obtained over the temperature range T = 110–293 K by heat capacity measurements. Magnetic properties have been measured over the range of T = 2–300 K. The electronic structure of CsMnMoO3F3 has been evaluated by X-ray photoelectron spectroscopy. Chemical bonding effects have been discussed for all metal ions using binding energy difference parameters and wide comparison with related oxides and fluorides. The competition between O2– and F– ions for metal valence electrons has been found.

Oxidation by Hydrogen in the Chemistry and Physics of the Rare‐Earth Metals

Rare-earth metals (RE) easily react with hydrogen. For decades the bonding of hydrogen has been discussed controversially in terms of either the "proton model" or the "anion model". Detailed investigations of metal-rich compounds of the rare-earth metals provide clear evidence for the incorporation of hydrogen as a hydride anion. Several categories of compounds can be distinguished regarding their behavior towards hydrogen. Low-valence compounds with metal-metal bonding frequently provide their excess electrons to form hydride ions as found with the halide hydrides REXH(n). However, there are exceptions, such as, LaI which does not react with hydrogen as a result of special electronic and electrostatic conditions. The opposite is true with La(2)C(3) although this compound does not provide excess metal valence electrons. An amorphous phase La(2)C(3)H(1.5) forms at very low temperature, around 450 K. The presence of hydrogen strongly influences the electrical and magnetic properties, for example, spin-glass formation and colossal magneto resistance arising in the presence of 4f(n) cores with the lanthanoid elements.