ChemInform Abstract: Structure Prediction of Binary Pernitride MN2 Compounds (M: Ca,Sr, Ba,La, and Ti)

Based on ab initio calculations at various pressures meta(stable) modifications of CaN₂, LaN₂, and TiN₂ are predicted.     

Electronic Structure,Chemical Bonding,and Solid‐State NMR Spectroscopy of the Digallides of Ca,Sr, and Ba

Delving into digallides : The characteristics of the chemical bonding of the digallides of the alkaline‐earth metals (see figure) have been studied by application of experimental methods, such as single‐crystal X‐ray diffraction and solid‐state NMR spectroscopy, in combination with quantum mechanical calculations.

     

Chemical Twinning of Salt and Metal in the Subnitridometalates Ba23Na11(MN4)4 with M=V,Nb, Ta

The subnitridometalates Ba₂₃Na₁₁(MN₄)₄ (M=V, Nb, Ta) crystallize in a new structure type, which shows ionic ortho‐nitridometalate anions and motifs from simple (inter)metallic packings: Na‐centered [Na₈] cubes as cutouts of the bcc structure of elemental Na and Na‐centered [Ba₁₀Na₂] icosahedra as found in Laves phases, for example. Single‐crystal and powder X‐ray diffraction studies in combination with quantum‐chemical calculations of the electronic structure and Raman spectroscopy support the characterization of the subnitridometalates as “chemical twins”. They consist of independent building units with locally prevalent ionic or metallic bonding in an overall metallic compound.     

The Periodate‐Based Double Perovskites M2NaIO6 (M = Ca,Sr, and Ba)

The crystal structures of the M₂NaIO₆ series (M = Ca, Sr, Ba), prepared at 650 °C by ceramic methods, were determined from conventional laboratory X‐ray powder diffraction data. Synthesis and crystal growth were made by oxidizing I^– with O₂^(air) to I⁷⁺ followed by crystal growth in the presence of NaF as mineralizator, or by the reaction of the alkali‐metal periodate with the alkaline‐earth metal hydroxide. All three compounds are insoluble and stable in water. The barium compound crystallizes in the cubic space group Fm3m (no. 225) with lattice parameters of a = 8.3384(1) Å, whereas the strontium and calcium compounds crystallize in the monoclinic space group P2₁/c (no. 14) with a = 5.7600(1) Å, b = 5.7759(1) Å, c = 9.9742(1) Å, β = 125.362(1)° and a = 5.5376(1) Å, b = 5.7911(1) Å, c = 9.6055(1) Å, β = 124.300(1)°, respectively. The crystal structure consists of either symmetric (for Ba) or distorted (for Sr and Ca) perovskite superstructures. Ba₂NaIO₆ contains the first perfectly octahedral [IO₆]^5– unit reported. The compounds of the ortho‐periodates are stable up to 800 °C. Spectroscopic measurements as well as DFT calculations show a reasonable agreement between calculated and observed IR‐ and Raman‐active vibrations.     

Primary Fragmentation Pathways of Gas Phase [M(Uracil−H)(Uracil)]+ Complexes (M=Zn,Cu, Ni,Co, Fe,Mn, Cd,Pd , Mg,Ca, Sr,Ba, and Pb): Loss of Uracil versus HNCO

Complexes formed between metal dications, the conjugate base of uracil, and uracil are investigated by sustained off‐resonance irradiation collision‐induced dissociation (SORI‐CID) in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Positive‐ion electrospray spectra show that [M(Ura?H)(Ura)]⁺ (M=Zn, Cu, Ni, Co, Fe, Mn, Cd, Pd, Mg, Ca, Sr, Ba, or Pb) is the most abundant ion even at low concentrations of uracil. SORI‐CID experiments show that the main primary decomposition pathway for all [M(Ura?H)(Ura)]⁺, except where M=Ca, Sr, Ba, or Pb, is the loss of HNCO. Under the same SORI‐CID conditions, when M is Ca, Sr, Ba, or Pb, [M(Ura?H)(Ura)]⁺ are shown to lose a molecule of uracil. Similar results were observed under infrared multiple‐photon dissociation excitation conditions, except that [Ca(Ura?H)(Ura)]⁺ was found to lose HNCO as the primary fragmentation product. The binding energies between neutral uracil and [M(Ura?H)]⁺ (M=Zn, Cu, Ni, Fe, Cd, Pd ,Mg, Ca, Sr Ba, or Pb) are calculated by means of electronic‐structure calculations. The differences in the uracil binding energies between complexes which lose uracil and those which lose HNCO are consistent with the experimentally observed differences in fragmentation pathways. A size dependence in the binding energies suggests that the interaction between uracil and [M(Ura?H)]⁺ is ion–dipole complexation and the experimental evidence presented supports this.     

Synthesis,Structure and Bonding,Optical Properties of Ba4MTrQ6 (M=Cu,Ag; Tr=Ga,In; Q=S,Se)

Four new quaternary chalcogenides, Ba₄AgGaS₆ ( 1 ), Ba₄AgGaSe₆ ( 2 ), Ba₄CuInS₆ ( 3 ), and Ba₄AgInS₆ ( 4 ), were synthesized by solid‐state reactions and their structures were characterized through single‐crystal X‐ray diffraction. In spite of their similar chemical compositions, the flexible arrangement between the transition metals and the triel atoms leads to subtle differences in their polyanion structures. All structures feature similar [MTrQ₆]^8? 1D polyanionic chains (M=Cu, Ag; Tr=Ga, In; Q=S, Se), which are constructed from corner‐sharing MQ₄ or TrQ₄ tetrahedra. However, the transition metals and triels are mixed in 1 , 2 , and 3 , but they occupy independent crystallographic sites in 4 . As a result, compounds 1 – 3 belong to the known Ba₂CoS₃ (Pnma No. 62) or Ba₂MnS₃ (Pnma No. 62) class, whereas 4 crystallizes in its own structural type within the monoclinic P2₁/c (No. 14) space group. The structural relationship among these new phases was also studied with the aid of DFT calculations and related optical properties are presented as well.     

Novel superalkali superhalogen compounds (Li3)+(SH)- (SH=LiF2, BeF3, and BF4) with aromaticity: new electrides and alkalides.

Optimized structures, with all real frequencies, of superalkali superhalides (Li(3))(+)(SH)(-) (SH=LiF(2), BeF(3), and BF(4)), are obtained, for the first time, at the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ computational levels. These superalkali superhalides possess three characteristics that are significantly different from normal alkali halides. 1) They have a variety of structures, which come from five bonding mode types: edge-face, edge-edge, face-face, face-edge, and staggered face-edge. We find that the bonding mode type closely correlates with the Li(3)-SH bond energy. 2) The valence electrons on the Li(3) ring are pushed out by the (SH)(-) anion, and become excess electrons, conferring alkalide or electride characteristics on these Li(3)-SH species, depending on the bonding mode type. 3) The highest occupied molecular orbital of each Li(3)-SH species is a doubly occupied delocalized sigma bonding orbital on the Li(3) ring, which indicates its aromaticity. It is noticeable that the maximum negative nucleus-independent chemical shift value (about -10 ppm) moves out from the center of the Li(3) ring, owing to repulsion by the SH(-) anion. We find that these superalkali superhalides are not only complicated "supermolecules", but are also a new type of alkalide or electride, with aromaticity.     

Electronic Structures of LixV2O5 (x=0.5 and 1): A Theoretical Study

The electronic properties of α‐Li_xV₂O₅ (x=0.5 and 1) are investigated using first principle calculations based on density functional theory with local density approximation. Different intercalation sites for Li in the V₂O₅ lattices are considered, showing different influences on the electronic structures of Li_xV₂O₅. The lowest total energy is found when Li is only intercalated along the c axis between two bridging oxygen ions of sequential V₂O₅ layers. The intercalation of Li into V₂O₅ does not change the electron transition property of V₂O₅, which is an indirect band gap semiconductor, but leads to a reduction of vanadium ions and an increase of the Fermi level of Li_xV₂O₅ arising from the electron transfer from the Li 2 s orbital to the initially empty conduction band of the V₂O₅ host.     

Calculation of EPR g tensors for transition-metal complexes based on multiconfigurational perturbation theory (CASPT2).

The computation of the electronic g tensor by two multireference methods is presented and applied to a selection of molecules including CN, BO, AlO, GaO, InO, ZnH, ZnF, O(2), H(2)O(+), O(3) (-), and H(2)CO(+) (group A) as well as TiF(3), CuCl(4) (2-), Cu(NH(3))(4) (2+), and a series of d(1)-MOX(4) (n-) compounds, with M=V, Cr, Mo, Tc, W, Re and X=F, Cl, Br (group B). Two approaches are considered, namely, one in which spin-orbit coupling and the Zeeman effect are included using second-order perturbation theory and another one in which the Zeeman effect is added through first-order degenerate perturbation theory within the ground-state Kramers doublet. The two methods have been implemented into the MOLCAS quantum chemistry software package. The results obtained for the molecules in group A are in good agreement with experiment and with previously reported calculated g values. The results for the molecules in group B vary. While the g values for the d(1) systems are superior to previous theoretical results, those obtained for the d(9) systems are too large compared to the experimental values.     

Structure and bonding in cyclic isomers of BAl2Hnm (n=3-6, m=-2 to +1): preference for planar tetracoordination, pyramidal tricoordination, and divalency

The structure and energetics of cyclic BAl2Hnm (n=3-6, m=-2 to +1), calculated at the B3LYP/6-311+G** and QCISD(T)/6-311++G** levels, are compared with their corresponding homocyclic boron and aluminium analogues. Structures in which the boron and aluminium atoms have coordination numbers of up to six are found to be minima. There is a parallel between structure and bonding in isomers of BAl2H(3)2- and BSi2H3. The number of structures that contain hydrogens out of the BAl2 ring plane is found to increase from BAl2H3(2-) to BAl2H6+. Double bridging at one bond is common in BAl2H5 and BAl2H6+. Similarly, species with lone pairs on the divalent boron and aluminium atoms are found to be minima on the potential energy surface of BAl2H(3)2-. BAl2H4- (2 b) is the first example of a structure with planar tetracoordinate boron and aluminium atoms in the same structure. Bridging hydrogen atoms on the B--Al bond prefer not to be in the BAl2 plane so that the pi MO is stabilised by pi-sigma mixing. This stabilisation increases with increasing number of bridging hydrogen atoms. The order of stability of the individual structures is decided by optimising the preference for lower coordination at aluminium, a higher coordination at boron and more bridging hydrogen atoms between B--Al bonds. The relative stabilisation energy (RSE) for the minimum energy structures of BAl2Hnm that contain pi-delocalisation are compared with the corresponding homocyclic aluminium and boron analogues.     

A kinetic stability study of MN (MBe,Mg, Ca,Sr, and Ba)

This work describes a structure and kinetic stability study of some complexes with the general formula MN, where M are the alkaline earth metal atoms, Be, Mg, Ca, Sr, and Ba. A complex (A) with two points of attachment to the N₅ ring is the most energetically favored for all metals considered here. Except for Be, structure (B) containing a mono‐coordinated metal atom is a transition state corresponding to the metal atom transfer around the N₅ ring. Pyramidal structure (C) is kinetically unstable with the low isomerization barrier height, ranging from 0.9 to 6.7 kcal/mol. The dissociation barrier heights for the lowest energy isomers (A) are predicted to be 1.2–18.7 kcal/mol (Be to Ba), indicating that kinetic stability increases from lighter to heavier metal atoms. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Benchmark Study of the Performance of Density Functional Theory for Bond Activations with (Ni,Pd)-Based Transition-Metal Catalysts

The performance of 23 density functionals, including one LDA, four GGAs, three meta-GGAs, three hybrid GGAs, eight hybrid meta-GGAs, and ten double-hybrid functionals, was investigated for the computation of activation energies of various covalent main-group single bonds by four catalysts: Pd, PdCl⁻, PdCl₂, and Ni (all in the singlet state). A reactant complex, the barrier, and reaction energy were considered, leading to 164 energy data points for statistical analysis. Extended Gaussian AO basis sets were used in all calculations. The best functional for the complete benchmark set relative to estimated CCSD(T)/CBS reference data is PBE0-D3, with an MAD value of 1.1 kcal mol⁻¹ followed by PW6B95-D3, the double hybrid PWPB95-D3, and B3LYP-D3 (1.9 kcal mol⁻¹ each). The other tested hybrid meta-GGAs perform less well (M06-HF: 7.0 kcal mol⁻¹; M06-2X: 6.3 kcal mol⁻¹; M06: 4.9 kcal mol⁻¹) for the investigated reactions. In the Ni case, some double hybrids show larger errors due to partial breakdown of the perturbative treatment for the correlation energy in cases with difficult electronic structures (partial multi-reference character). Only double hybrids either with very low amounts of perturbative correlation (e.g., PBE0-DH) or that use the opposite-spin correlation component only (e.g., PWPB95) seem to be more robust. We also investigated the effect of the D3 dispersion correction. While the barriers are not affected by this correction, significant and mostly positive results were observed for reaction energies. Furthermore, six very recently proposed double-hybrid functionals were analyzed regarding the influence of the amount of Fock exchange as well as the type of perturbative correlation treatment. According to these results, double hybrids with <50–60 % of exact exchange and ∼30 % perturbative correlation perform best.     

Potential of AMnO3 (A=Ca,Sr, Ba,La) as Active Layer in Inorganic Perovskite Solar Cells

Inorganic perovskite CaMnO was proposed as a substitution for the TiO anatase in electron transport layers of solar cells containing the hybrid perovskite CH NH PbI based on increased mobility of electrons and better optical matching. Due to a suitable band gap concerning the absorption of sunlight, we investigate the potential of CaMnO and similar manganite perovskites, where Ca is replaced by either Sr, Ba or La, as an absorber layer in inorganic perovskite solar cells. In this study, we have used optical measurements on the synthesized AMnO (A=Ca, Sr, Ba, La) samples to aid density functional theory calculations (DFT) in order to accurately simulate the electronic and optical properties of AMnO compounds and gauge their potential for the role of absorber layer. Both experimental measurements and theoretical calculations show suitable band gap of 1.1-1.5 eV, depending on the compound, and absorption coefficients of the order of cm in the visible part of the spectrum.     

Study of the Light‐Induced Spin Crossover Process of the [FeII(bpy)3]2+ Complex

Ab initio calculations have been performed on [Fe^II(bpy)₃]²⁺ (bpy=bipyridine) to establish the variation of the energy of the electronic states relevant to light‐induced excited‐state spin trapping as a function of the Fe? ligand distance. Light‐induced spin crossover takes place after excitation into the singlet metal‐to‐ligand charge‐transfer (MLCT) band. We found that the corresponding electronic states have their energy minimum in the same region as the low‐spin (LS) state and that the energy dependence of the triplet MLCT states are nearly identical to the ¹MLCT states. The high‐spin (HS) state is found to cross the MLCT band near the equilibrium geometry of the MLCT states. These findings give additional support to the hypothesis of a fast singlet–triplet interconversion in the MLCT manifold, followed by a ³MLCT–HS (⁵T₂) conversion accompanied by an elongation of the Fe? N distance.     

Crystal Structure of [M(NH3)5Cl]2[IrCl6]Cl2 (M = Co, Rh, Ir) Binary Complex Salts

Binary complex salts of M(NH₃)₅Cl]₂[IrCl₆]Cl₂ composition, where M = Co(III), Rh(III), or Ir(III), have been studied. All phases are isostructural with [M(NH₃)₅Cl]₂[PtCl₆]Cl₂ complexes [M = Rh(III) and Ir(III)]; Xray structural and crystallochemical analysis have been performed.