One-Dimensional BeH2 Polymers: Infrared Spectra and Theoretical Calculations

Hydride and halide abstraction reactions behind the enhanced basicity of Be and Mg clusters with nitrogen bases

In this study, we investigate the protonation effects on the structure, relative stability and basicity of complexes formed by the interaction of monomers and dimers of BeX2 and MgX2 (X = H, F) with NH3, CH2NH, HCN, and NC5H5 bases. Calculations were performed using the M06-2X/aug-cc-pVTZ formalism, along with QTAIM, ELF and NCI methods for electron density analysis and MBIE and LMO-EDA energy decomposition analyses for interaction enthalpies. The protonation of the MH2- and M2H4-Base complexes occurs at the negatively charged hydrogen atoms of the MH2 and M2H4 moieties through typical hydride abstraction reactions, while protonation at the N atom of the base is systematically less exothermic. The preference for the hydride transfer mechanism is directly associated with the significant exothermicity of H2 formation through the interaction between H- and H+, and the high hydride donor ability of these complexes. The basicity of both, MH2 and M2H4 compounds increases enormously upon association with the corresponding bases, with the increase exceeding 40 orders of magnitude in terms of ionization constants. Due to the smaller exothermicity of HF formation, the basicity of fluorides is lower than that of hydrides. In Be complexes, the protonation at the N atom of the base dominates over the fluoride abstraction mechanism. However, for the Mg complexes the fluoride abstraction mechanism is energetically the most favorable process, reflecting the greater facility of Mg complexes to lose F-.

A Holistic View of the Interactions between Electron-Deficient Systems: Clustering of Beryllium and Magnesium Hydrides and Halides

In the search for common bonding patterns in pure and mixed clusters of beryllium and magnesium derivatives, the most stable dimers and trimers involving BeX2 and MgX2 (X = H, F, Cl) have been studied in the gas phase using B3LYP and M06-2X DFT methods and the G4 ab initio composite procedure. To obtain some insight into their structure, stability, and bonding characteristics, we have used two different energy decomposition formalisms, namely MBIE and LMO-EDA, in parallel with the analysis of the electron density with the help of QTAIM, ELF, NCIPLOT, and AdNDP approaches. Some interesting differences are already observed in the dimers, where the stability sequence observed for the hydrides differs entirely from that of the fluorides and chlorides. Trimers also show some peculiarities associated with the presence of compact trigonal cyclic structures that compete in stability with the more conventional hexagonal and linear forms. As observed for dimers, the stability of the trimers changes significantly from hydrides to fluorides or chlorides. Although some of these clusters were previously explored in the literature, the novelty of this work is to provide a holistic approach to the entire series of compounds by using chemical bonding tools, allowing us to understand the stability trends in detail and providing insights for a significant number of new, unexplored structures.

Efficient and Automated Quantum Chemical Calculation of Rovibrational Nonresonant Raman Spectra

An outline of a newly developed program for the simulation of rovibrational nonresonant Raman spectra is presented. This program is an extension of our recently developed code for rovibrational infrared spectra [J. Chem Phys. 152 (2020) 244104] and relies on vibrational wavefunctions from variational configuration interaction theory to allow for an almost fully automated calculation of such spectra in pure ab initio fashion. Due to efficient contraction schemes this program requires modest computational resources and it can be controlled by only a few lines of input. As the required polarizability surfaces are also computed in an automated fashion, this implementation enables the routine application to small molecules. For demonstrating its capabilities, benchmark calculations for water H216O are compared to reference data and spectra for the beryllium dihydride dimer, Be2H4 (D2h), are predicted. The inversion symmetry of the D2h systems lead to complementary infrared and Raman spectra, which are needed both for a comprehensive investigation of this system.

Viable aromatic BenHn stars enclosing a planar hypercoordinate boron or late transition metal

Similar to B_n rings, star-like Be_nH_n rings can serve as the n-electron σ-donors for designing species with planar hypercoordinate atom.

Energetics and reactivity of small beryllium deuterides

Enthalpies and free energies of reaction for small neutral and charged beryllium deuterides BeD, BeD₂, and BeD₃ that have been calculated are reported for a temperature range of 0 K to 1000 K. We discuss probable dissociation channels and possible ways of producing BeD by localizing the relevant transition states and by calculating corresponding rate constants. BeD and BeD⁺ are found to be the most stable ones among the considered compounds. BeD₂ and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\mathrm{BeD}}_2^{+} $$\end{document}BeD2+ are more likely to decompose into Be^0,+ + D₂ than into BeD^0,+ + D. The metastable BeD₃ and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\mathrm{BeD}}_3^{+} $$\end{document}BeD3+ predominantly decompose into BeD^0,+ + D₂. In light of our results on the reaction energetics, we can interpret the pathways for production of BeD via BeD₂ and BeD₃ intermediates observed in molecular dynamics simulations.

Fully Hydrogenated Beryllium Nanoclusters

We present the ground state and energetically low structures of BenH2n nanoclusters as predicted using density functional theory (DFT) and employing the M06 meta-hybrid exchange-correlation functional. Results using the M06 functional are benchmarked against high accuracy coupled-cluster CCSD(T) and found to be in excellent agreement. For small values of n, the linear or polymeric form is the lowest energy geometry, while for sizes larger, n > 9 ring type and link type structures are the energetically lowest configurations. This trend has also been observed through ab initio molecular dynamics (AIMD) simulations at finite temperatures. In addition to the binding energies of the structures we report on polymerization energies, Be-H bond energies with respect to coordination details, hydrogen desorption energies of saturated and oversaturated species, as well as computed infrared spectra of all the ground state and energetically low lying structures presented. Furthermore, we find that the saturated polymeric forms of the nanoclusters cannot retain molecular hydrogen, in contrast to what is expected when zero point energy corrections are not taken into account.

Ab initio theoretical investigation of beryllium and beryllium hydride nanoparticles and nanocrystals with implications for the corresponding infinite systems

Using judicially chosen DFT calculations for Be_n and Be_nH_x nanoparticles we predict correctly the n → ∞ behavior for crystals and polymers.

Exploring dynamical electron theory beyond the Born-Oppenheimer framework: from chemical reactivity to non-adiabatically coupled electronic and nuclear wavepackets on-the-fly under laser field

Chemical theory and its application to dynamical electrons in molecules under intense electromagnetic fields is explored, in which we take an explicit account of nuclear nonadiabatic (kinematic) interactions along with simultaneous coupling with intense optical interactions. All the electronic wavefunctions studied here are necessarily time-dependent, and thereby beyond stationary state quantum chemistry based on the Born-Oppenheimer framework. As a general and tractable alternative framework with which to track the electronic and nuclear simultaneous dynamics, we propose an on-the-fly method to calculate the electron and nuclear wavepackets coupled along the branching non-Born-Oppenheimer paths, through which their bifurcations, strong quantum entanglement between nuclear electronic motions, and coherence and decoherence among the phases associated with them are properly represented. Some illustrative numerical examples are also reported, which are aimed at our final goals; real time tracking of nonadiabatic electronic states, chemical dynamics in densely degenerate electronic states coupled with nuclear motions and manipulation and/or creation of new electronic states in terms of intense lasers, and so on. Other examples are also presented as to how the electron wavepacket dynamics can be used to analyze chemical reactions, shedding a new light on some typical and conventional chemical reactions such as proton transfer followed by tautomerization.

Computationally designed families of flat, tubular, and cage molecules assembled with "starbenzene" building blocks through hydrogen-bridge bonds

Using density functional calculations, we demonstrate that the planarity of the nonclassical planar tetracoordinate carbon (ptC) arrangement can be utilized to construct new families of flat, tubular, and cage molecules which are geometrically akin to graphenes, carbon nanotubes, and fullerenes but have fundamentally different chemical bonds. These molecules are assembled with a single type of hexagonal blocks called starbenzene (D(6h) C(6)Be(6)H(6)) through hydrogen-bridge bonds that have an average bonding energy of 25.4-33.1 kcal mol(-1). Starbenzene is an aromatic molecule with six pi electrons, but its carbon atoms prefer ptC arrangements rather than the planar trigonal sp(2) arrangements like those in benzene. Various stability assessments indicate their excellent stabilities for experimental realization. For example, one starbenzene unit in an infinite two-dimensional molecular sheet lies on average 154.1 kcal mol(-1) below three isolated linear C(2)Be(2)H(2) (global minimum) monomers. This value is close to the energy lowering of 157.4 kcal mol(-1) of benzene relative to three acetylene molecules. The ptC bonding in starbenzene can be extended to give new series of starlike monocyclic aromatic molecules (D(4h) C(4)Be(4)H(4)(2-), D(5h) C(5)Be(5)H(5)(-), D(6h) C(6)Be(6)H(6), D(7h) C(7)Be(7)H(7)(+), D(8h) C(8)Be(8)H(8)(2-), and D(9h) C(9)Be(9)H(9)(-)), known as starenes. The starene isomers with classical trigonal carbon sp(2) bonding are all less stable than the corresponding starlike starenes. Similarly, lithiated C(5)Be(5)H(5) can be assembled into a C(60)-like molecule. The chemical bonding involved in the title molecules includes aromaticity, ptC arrangements, hydrogen-bridge bonds, ionic bonds, and covalent bonds, which, along with their unique geometric features, may result in new applications.

Vibrational dynamics of amorphous beryllium hydride and lithium beryllium hydrides

The vibrational density of states of amorphous beryllium hydride (a-BeH2) and lithium beryllium hydrides have been studied using inelastic neutron scattering, infrared, and Raman spectroscopies. The positions of the symmetrical (120-180 meV) and antisymmetrical (200-260 meV) Be-H stretching modes and those of the H-Be-H bending mode (50-120 meV) have been determined and the results discussed and compared with recent theoretical calculations. With the addition of lithium to the beryllium hydride network, the vibrational bands are shifted to lower energies, indicating a less rigid network.

Sodium Hydride Clusters in Solid Hydrogen and Neon: Infrared Spectra and Theoretical Calculations

Laser-ablated sodium atom reactions with H2 have been investigated in solid molecular hydrogens and neon. The NaH molecule and (NaH)2,3,4 clusters were identified by IR spectra with isotopic substitution (HD and D2) and comparison to frequencies calculated by density functional theory and the MP2 method. The use of para-hydrogen enriched samples provides evidence for a (H2)nNaH subcomplex surrounded by the solid hydrogen matrix cage. The ionic rhombic (NaH)2 dimer is characterized by strong absorptions at 761.7, 759.1, and 757.0 cm(-1), respectively, in solid neon, para-hydrogen, and normal hydrogen matrices. The cyclic sodium hydride trimer and tetramer clusters are also observed. Although the spontaneous reaction of two Li and H2 to form (LiH)2 occurs on annealing in solid H2, the formation of (NaH)2 requires near uv photoexcitation.

Infrared Spectra and Theoretical Calculations of Lithium Hydride Clusters in Solid Hydrogen, Neon, and Argon

A matrix isolation IR study of laser-ablated lithium atom reactions with H2 has been performed in solid para-hydrogen, normal hydrogen, neon, and argon. The LiH molecule and (LiH)(2,3,4) clusters were identified by IR spectra with isotopic substitution (HD, D(2), and H(2) + D(2)) and comparison to frequencies calculated by density functional theory and the MP2 method. The LiH diatomic molecule is highly polarized and associates additional H(2) to form primary (H(2))(2)LiH chemical complexes surrounded by a physical cage of solid hydrogen where the ortho and para spin states form three different primary complexes and play a role in the identification of the bis-dihydrogen complex and in characterization of the matrix cage. The highly ionic rhombic (LiH)(2) dimer, which is trapped in solid matrices, is calculated to be 22 kcal/mol more stable than the inverse hydrogen bonded linear LiH-LiH dimer, which is not observed here. The cyclic lithium hydride trimer and tetramer clusters were also observed. Although the spontaneous reaction of 2 Li and H(2) to form (LiH)(2) occurs on annealing in solid H(2), the formation of higher clusters requires visible irradiation. We observed the simplest possible chemical reduction of dihydrogen using two lithium valence electrons to form the rhombic (LiH)(2) dimer.

Infrared Spectroscopic Observation of the Group 13 Metal Hydroxides, M(OH)1,2,3 (M =Al, Ga, In, and Tl) and HAl(OH)2

Reactions of laser-ablated Al, Ga, In, and Tl atoms with H2O2 and with H2 + O2 mixtures diluted in argon give new absorptions in the O-H and M-O stretching and O-H bending regions, which are assigned to the metal mono-, di-, and trihydroxide molecules. Isotopic substitutions (D2O2, 18O2, 16,18O2, HD, and D2) confirm the assignments, and DFT calculations reproduce the experimental results. Infrared spectra for the Al(OH)(OD) molecule verify the calculated C2v structure. The trihydroxide molecules increase on annealing from the spontaneous reaction with a second H2O2 molecule. Aluminum atom reactions with the H2 + O2 mixtures favor the HAl(OH)2 product, suggesting that AlH3 generated by UV irradiation combines with O2 to form HAl(OH)2.

Infrared Spectra of M(OH)1,2,3 (M = Mn, Fe, Co, Ni) Molecules in Solid Argon and the Character of First Row Transition Metal Hydroxide Bonding

Reactions of laser-ablated Mn, Fe, Co, and Ni atoms with H(2)O(2) and with H(2) + O(2) mixtures in excess argon give new absorptions in the O-H and M-O stretching regions, which are assigned to metal dihydroxide and trihydroxide molecules, M(OH)(2) and M(OH)(3). Isotopic substitutions (D(2)O(2), (18)O(2), (16,18)O(2), D(2)) confirmed the assignments and DFT calculations reproduced the experimental results. The O-H stretching frequencies decreased in the dihydroxides from Sc to Zn. Mulliken and natural charge distributions indicate significant electron transfer from metal d orbitals to OH ligands that decreases from Sc to Zn, suggesting that the early transition metal hydroxides are more ionic and that the later transition metal hydroxides are more covalent.

Ab initio prediction of the potential energy surface and vibration-rotation energy levels of BeH2

The equilibrium structure and potential energy surface of beryllium dihydride BeH(2) in its ground electronic state have been determined from highly accurate ab initio calculations. The vibration-rotation energy levels of three isotopomers BeH(2), BeD(2), and BeHD were predicted using the variational method. The calculated spectroscopic constants are in remarkably good agreement with the existing experimental data (sub-cm(-1) accuracy) and should be useful in a further analysis of high-resolution vibration-rotation spectra of all three isotopomers.