One-dimensional BeH2 polymers: infrared spectra and theoretical calculations

Laser-ablated beryllium atoms react with H2 upon co-condensation in excess hydrogen and neon to form BeH2 and (BeH2)2, which are identified through isotopic substitution and DFT calculations. Unreacted Be atoms isolated in solid neon or hydrogen are excited to the 1P0 state and react further with H2 to enhance the BeH2 and (BeH2)2 concentrations and produce (BeH2)n polymers. The series of strong infrared-active parallel Be-H-Be bridge-bond stretching modes observed for (BeH2)n polymers suggests one-dimensional structures, and this conclusion is supported by DFT calculations. The computed polymerization energy per BeH2 unit is about 33 kcal/mol.     

Full configuration interaction calculation of the low lying valence and Rydberg states of BeH

The all-electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and quadrupole moments have also been calculated. The results provide a set of benchmark values for energies, wave functions, properties, and transition properties for the five electron BeH molecule. Most of the states have large multiconfigurational character in spite of their essentially single excited nature and a number of them present an important Rydberg-valence mixing that is achieved through the mixed nature of the particle MO of the single excitations.     

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.     

BeH2与HX(X=F,Cl, Br,I)形成的二氢键复合物的结构特征与本质

对BeH2与HX(X=F, Cl, Br, I)形成的二氢键复合物的结构特征及本质进行了探讨. 在MP2/6-311++G(3d,3p)水平优化、频率验证, 得到复合物的分子结构, 用分子间距离及电子密度拓扑理论确认BeH2与卤化氢已形成了二氢键型复合物. 在MP2/6-311++G(3d, 3p)水平下进行基函数重叠误差(BSSE)校正后的结合能在-14.468 kJ·mol-1到-5.464 kJ·mol-1之间.用对称匹配微扰理论(SAPT)对复合物的结合能进行分解, 结果表明, BeH2…HX二氢键复合物中静电能对总吸引能的贡献都是最主要的, 但交换排斥能、诱导能、色散能对总结合能的贡献也很重要. 从BeH2…HF到BeH2…HI, 诱导能对总吸引能的贡献从37.8%逐渐减小到24.0%. 而色散能对总吸引能的贡献从BeH2…HF体系中的16.0%逐渐增加到BeH2…HI体系中的33.8%.     

Full configuration interaction calculation of BeH adiabatic states

An all-electron full configuration interaction (FCI) calculation of the adiabatic potential energy curves of some of the lower states of BeH molecule is presented. A moderately large ANO basis set of atomic natural orbitals (ANO) augmented with Rydberg functions has been used in order to describe the valence and Rydberg states and their interactions. The Rydberg set of ANOs has been placed on the Be at all bond distances. So, the basis set can be described as 4s3p2d1f3s2p1d(BeH)+4s4p2d(Be). The dipole moments of several states and transition dipole strengths from the ground state are also reported as a function of the R(Be-H) distance. The position and the number of states involved in several avoided crossings present in this system have been discussed. Spectroscopic parameters have been calculated from a number of the vibrational states that result from the adiabatic curves except for some states in which this would be completely nonsense, as it is the case for the very distorted curves of the 3s and 3p (2)Sigma(+) states or the double-well potential of the 4p (2)Pi state. The so-called "D complex" at 54 050 cm(-1) (185.0 nm) is resolved into the three 3d substates ((2)Sigma(+),(2)Pi,(2)Delta). A diexcited valence state is calculated as the lowest state of (2)Sigma(-) symmetry and its spectroscopic parameters are reported, as well as those of the 2 (2)Delta (4d) state The adiabatic curve of the 4 (2)Sigma(+) state shows a swallow well at large distances (around 4.1 A) as a result of an avoided crossing with the 3 (2)Sigma(+) state. The probability that some vibrational levels of this well could be populated is discussed within an approached Landau-Zerner model and is found to be high. No evidence is found of the E(4ssigma) (2)Sigma(+) state in the region of the "D complex". Instead, the spectroscopic properties obtained from the (4ssigma) 6 (2)Sigma(+) adiabatic curve of the present work seem to agree with those of the experimental F(4psigma) (2)Sigma(+) state. The FCI calculations provide benchmark results for other correlation models for the open-shell BeH system and evidence both the limitations and capabilities of the basis set.     

The ab initio ground-state potential energy function of beryllium monohydride, BeH

The accurate ground-state potential energy function of beryllium monohydride, BeH, has been determined from large-scale ab initio calculations using the multi-reference averaged coupled-pair functional (MR-ACPF) method in conjunction with the correlation-consistent core-valence basis sets up to septuple-zeta quality. The effects of electron correlation beyond the MR-ACPF level of approximation were taken into account. The scalar relativistic and adiabatic (the diagonal correction) effects, as well as some of the nonadiabatic effects, were also discussed. The vibration-rotation energy levels of three isotopologues, BeH, BeD, and BeT, were predicted to sub-cm(-1) accuracy.     

The ionization potential of the BeH molecule

The ionization potential of the BeH molecule is derived from a few Rydberg states observed in the absorption spectrum and from “ab initio” calculations of the energies of the ground states of the BeH and BeH⁺ molecules at their equilibrium distances. The values are in agreement and yield PI(BeH, X²Σ⁺) = 66 100 ± 500 cm^?1.     

An accurate ab initio potential energy surface and calculated spectroscopic constants for BeH2, BeD2, and BeHD

A three-dimensional potential energy surface for the ground electronic state of BeH(2) has been determined by three-dimensional spline interpolation over 6864 symmetry-unique ab initio points calculated at the icMRCI/aug-cc-pV5Z level and corrected for core-electron correlation computed at the MR-ACPF/cc-pCV5Z level. Calculated spectroscopic constants of BeH(2) and BeD(2) are in excellent agreement with recent experimental results: for 11 bands of BeH(2) and 5 bands of BeD(2) the root mean square (rms) band origin discrepancies were only 0.15(+/-0.09) and 0.46(+/-0.19) cm(-1), respectively, and the rms relative discrepancies in the inertial rotational constants (B([v])) were only 0.028% and 0.023%, respectively. Spectral constants for BeHD were predicted using the same potential surface. The effect of different interpolation methods on predicted potential function values and on the calculated level energies and spectroscopic constants has been examined.     

Theoretical study of changes in pi-electron delocalization in the analogues of an ortho-hydroxy schiff base when the proton is replaced with Li+ or BeH+

Molecular geometries of ortho-hydroxy Schiff base in keto-enamine and enol-imine tautomeric forms, its anion, and their derivatives in which H+ was replaced with Li+ or BeH+ were optimized at the B3LYP/6-311+G level of theory. Isodesmic reactions for estimating delocalization due to H-bonding or cation chelating were calculated. Geometry-based aromaticity index HOMA and magnetism-based NICS1(zz) index were used to estimate pi-electron delocalization. Keto-enamine tautomer exhibits low aromaticity in the ring and a relatively high pi-electron delocalization in the quasi-ring. The reverse was found for enol-imine tautomer. The Li+ and BeH+ derivatives showed a relatively high pi-electron delocalization in the ring and in the quasi-ring. This may be interpreted by an extension of the electron delocalization path in the pi-electron system through low-lying unoccupied p-type orbitals of Li+ and BeH+ cations.     

Pauli repulsion in the open shell species BeH and Co+

Using the natural bond orbital method, one may associate the valence bond configuration and Lewis structure concepts to wave functions consisting of molecular orbitals and thus gain intuitive insight into the molecular potential energy curves. Natural bond orbital analysis of the restricted open shell Hartree–Fock and unrestricted Hartree–Fock wave functions for the BeH ground state provides an intuitive model to help understand the nature of the bonding in this open shell species. The contrasting behavior of the bonding orbitals for different spins can be attributed to differences in the Pauli repulsive interactions with the lonepair orbitals. Such behavior occurs in BeH(²Σ) but does not in CO⁺(²Π) because the Pauli repulsion depends on the orbital overlap.     

High-pressure Brillouin scattering of amorphous BeH2

High-pressure micro-Brillouin scattering is employed to investigate the pressure dependence of the sound velocity, refractive index, equation of state, and mechanical properties of amorphous BeH2. The refractive index n has been determined by using two scattering geometries (70 degrees and 180 degrees). The equation of state is deduced from the pressure dependences of the sound velocity. The bulk modulus is 14.2 (+/-3.0) GPa and its pressure derivative is 5.3 (+/-0.5). The polarizability is calculated from the refractive index and the density of the material. It increases with pressure while Poisson's ratio decreases with pressure.     

Binding of the two-valence-electron metal ions Sc(+), Ti(2+), and V(3+) to the second-row hydrides BeH(2), BH(3), NH(3), OH(2), and FH: a computational study

We report results from a computational study of the binding in complexes formed from one of the transition-metal ions Sc(+), Ti(2+), or V(3+), each of which has two valence electrons outside an argon core, and one of the second-row hydrides FH, OH(2), NH(3), BH(3), or BeH(2). The complexes that involve the electron-rich ligands FH, OH(2), and NH(3) have strong ion-dipole components to their binding. There are large stabilization energies for sigma-interactions that transfer charge from occupied lone-pair natural bond orbitals on the F, O, or N atom of the (idealized) Lewis structure into empty non-Lewis orbitals on the metal ions; these interactions effectively increase electron density in the bonding region between the metal ion and liganded atom, and the metal ions in these complexes act in the capacity of Lewis acids. The complexes formed from the electron-poor hydrides BH(3) and BeH(2) consistently incorporate bridging hydrogen atoms to support binding, and there are large stabilization energies for interactions that transfer charge from the Be-H or B-H bonds into the region between the metal ion and liganded atom. The metal ions in Sc(+)-BeH(2), Ti(2+)-BeH(2), Ti(2+)-BH(3), and V(3+)-BH(3) act in the capacity of Lewis acids, whereas the scandium ion in Sc(+)-BH(3) acts as a Lewis base.     

Theoretical study on the small clusters of LiH, NaH, BeH(2), and MgH(2)

High-level ab initio molecular orbital theory is used to calculate the geometries, vibrational frequencies, atomic charges, and binding energies of the small clusters (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) (n = 1-4). For (LiH)(n) and (NaH)(n), there are planar cyclic structures when n = 2, 3. We have found the cubic structure T(d) in addition to the planar cyclic D(4)(h) when n = 4. The D(4)(h) is less stable than the T(d) geometry. For (BeH(2))(n) and (MgH(2))(n), when n = 3, there are three kinds of structures: chain C(2)(v), planar cyclic D(3)(h), and hat-like C(2)(v). The C(2)(v) geometry is more stable than the others. When n = 4, there are four kinds of structures: chain D(2)(h), cubic T(d), string-like C(2), and cubic transformation C(1). The most stable compounds in the families of (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) are cubic T(d), cubic T(d), chain D(2)(h), and string-like C(2) geometries, respectively, when n = 4. Calculated binding energies range from -24 to -37 kcal/mol for (LiH)(n) and --19 to -30 kcal/mol for (NaH)(n), (BeH(2))(n), and (MgH(2))(n). The hydrogen atoms in hydride clusters always have negative charges. The atomic charges of planar cyclic structures are weaker than those of cubic structures, and there is a tendency of reducing along with the increase of the cluster size. The vibrational frequencies of planar cyclic structures have consistent tendency, too. It indicates that the bond distance increases with the ionic character of the bond.     

Fluorescence "Turn-On" chemosensor for the selective detection of beryllium

A new fluorogenic method for selective and sensitive determination of beryllium using 2,6-diphenyl-4-benzo-9-crown-3-pyrane (DBCP) was developed. The proposed fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to beryllium ions in MeOH/H(2)O (70:30, v/v) solution. The fluorescence enhancement of DBCP is attributed to a 1:1 complex formation between DBCP and Be(2+) ion, which has been utilized as the basis for selective detection of Be(2+) ion. With the optimum condition described, the fluorescence enhancement at 531 nm was linear to the concentration of beryllium in the range of 1.6×10(-8)-1.6×10(-7) M and a detection limit of 1.5×10(-9) M. The fluorescent probe exhibits high selectivity for Be(2+) ion over the other common mono, di- and trivalent cations.     

Ab initio studies of the electronic structure and density of states of metallic beryllium

Hartree–Fock–Roothaan studies are reported for low-lying electronic states of metallic beryllium as modeled by a moiety of 135 beryllium atoms. The system corresponds to 16 coordination shells of a central Be with internuclear separations derived from the lattice constants of the bulk metal. The calculations become tractable by use of the full D_3h symmetry of the system at both the integrals and self-consistent-field stages and by employing ab initio effective potentials for the 1s electrons of each beryllium atom. Ionization potentials, binding energies, orbital energies, electric field gradients, nuclear-electrostatic potentials, diamagnetic shielding constants, second moments, and Mulliken populations are calculated for selected electronic states. The calculated ionization potential for the lowest state agrees to within 10% of the experimental bulk work function. A density-of-states analysis for that state is reported and compared with band structure calculations.     

Planar tetracoordinate carbon species involving beryllium substituents

Planar tetracoordinate carbon (ptC) arrangements can be achieved by employing multiple substituents based on beryllium, despite its rather weak pi-acceptor ability. A variety of ptC-containing examples, some with more than one ptC, have been designed computationally by elaborating the planar C(BeH) 4 (2-) prototype at B3LYP/6-311++G(3df,2p) and MP2/6-311++G(3df,2p) levels of theory for some small ptC representatives. The prototype prefers a D(2h) paramagnetic triplet ground state due to Hund's rule, rather than a singlet. The highly polarized C-Be bonding weakens the rigidity of the tetrahedral carbon in T(d)C(BeH) 4 enormously, and the enhancement of both C-Be and Be 4 peripheral covalent bonding exerted by the extra electrons stabilizes the ptC eventually. The delocalization of the two p pi electrons is only modest, but their density on the most electronegative carbon atom helps stabilize the ptC arrangement. This is in contrast to the conventional strategy to delocalize p(pi) lone pairs for stabilizing the ptC arrangement. Various strategies to achieve neutral derivatives with ptCs are demonstrated.     

Beryllium(II) complexes of the Kläui tripodal ligand cyclopentadienyltris(diethylphosphito-p)cobaltate(-)

The interactions of the beryllium(II) ion with the cyclopentadienyltris(diethylphosphito-P)cobaltate monoanion, L(-), have been investigated, in aqueous solution, by synthetic methods, potentiometry, ESMS, and (1)H, (31)P, and (9)Be NMR spectroscopy. L(-) has been found able to displace either two or three water molecules in the beryllium(II) coordination sphere, to form mononuclear, dinuclear, and trinuclear derivatives, in which the metal ion is pseudotetrahedrally coordinated. The species [BeL(H(2)O)](+) and [Be(2)L(2)(mu-OH)](+) have been identified in solution while complexes of formula BeL(2) and [Be(3)L(4)](ClO(4))(2) have been isolated as solid materials. The species [BeL(OPPh(2))](+), closely related to [BeL(H(2)O)](+), has been characterized in acetone solution and isolated as tetraphenylborate salt. The structure of the unusual trimeric complex [Be(3)L(4)](2+) has been elucidated by an unprecedented 2D (9)Be-(31)P NMR correlation spectrum showing the presence of a single central beryllium nucleus and two equivalent terminal beryllium nuclei. The three beryllium centers are held together by four cobaltate ligands, which display two different bonding modes: two ligands are terminally linked with all the three oxygen donors to one terminal beryllium, and the other two bridge two metal centers, sharing the oxygen donors between central and terminal beryllium atoms.     

α,β‐Unsaturated and Saturated Derivatives of Be,Mg, and Ca: Are They Carbon or Metal Acids in the Gas Phase?

The gas-phase acidity of R--XH (R=H, CH(3), CH(2)CH(3), CH==CH(2), C[triple chemical bond]CH; X=Be, Mg, Ca) alkaline-earth-metal derivatives has been investigated through the use of high-level CCSD(T) calculations by using a 6-311+G(3df,2p) basis set. BeH(2) is a stronger acid than BH(3) and CH(4) for two concomitant reasons: 1) the dissociation energy of the Be--H bond is smaller than the dissociation energies of the B--H and C--H bonds, and 2) the electron affinity of BeH(.) is larger in absolute value than those of BH(2) (.) and CH(3) (.). The acidity also increases on going from BeH(2) to MgH(2) due to these two same factors. Quite importantly, despite the fact that the X--H bonds in the R--XH (X=Mg, Ca) derivatives exhibit the expected X(delta+)--H(delta-) polarity, they behave as metal acids in the gas phase and only Be derivatives behave as carbon acids in the gas phase. The ethylberyllium hydride exhibits an unexpected high acidity compared with the methyl derivative because deprotonation of the system is accompanied by a cyclization that stabilizes the anion. Similarly to that found for derivatives that contain heteroatoms from groups 14, 15, and 16, the unsaturated compounds are stronger acids than the saturated counterparts, with the only exception of the Ca-vinyl derivative. Most importantly, among ethyl, vinyl, and ethynyl derivatives containing a heteroatom of the main group of the Periodic Table, those containing Be, Mg, and Ca are among the strongest gas-phase acids.     

Exponentially and pre-exponentially correlated Gaussians for atomic quantum calculations

Explicitly correlated, n-electron, one-center s Gaussian (ECG) functions that depend on the interelectron distances in the exponent are combined with s ECGs which also depend on the interelectron separations through pre-exponential r(ij)(2) multipliers. The pre-exponentially r(ij)(2)-dependent ECGs are included in the basis to better describe the interelectron correlation and the interelectron cusps. The basis set is tested in the calculations of the ground state of the beryllium atom ((9)Be).     

HD isotope effect on the dihydrogen bond of NH+4...BeH2 by ab initio path integral molecular dynamics simulation

In order to investigate the HD isotope effect on a dihydrogen bonded cation system, we have studied NH+4...BeH2 and its isotopomers by ab initio path integral molecular dynamics. It is found that the dihydrogen bond can be exchanged by NH+(4) rotation. The deuterated isotopomer (ND+(4)...BeD(2); DD) can exchange the dihydrogen bond more easily than other isotopomers such as (NH+4...BeH2; HH). This unusual isotope effect is ascribed to the "quantum localization" which occurs when the effective energy barrier for the rotational mode becomes higher by the zero point energy of other modes. We also found that the binding energy of dihydrogen bonds for DD species is the smallest among the isotopomers.