Tunable phase transition,band gap and SHG properties by halogen replacement of hybrid perovskites [(thiomorpholinium)PbX3, X = Cl,Br, I]

By the replacement of halogen anion, three new multifunctional organic-inorganic hybrid perovskites (thiomorpholinium)PbX₃ (X = Cl, Br, I) were successfully synthesized and underwent reversible structural transformation above room temperature, accompanied by the anomalous change of dielectric constant. With the adjustment of the halogen anion from Cl to I in the inorganic skeleton, the space group is transformed from centrosymmetric space group P2₁/c ((thiomorpholinium)PbCl₃) to chiral one P2₁2₁2₁ ((thiomorpholinium)PbBr₃, (thiomorpholinium)PbI₃) at room temperature. The ordered-disordered transition of organic cations and the change of hydrogen bonds with the increase of temperature lead to above-room-temperature phase transitions. Ultraviolet absorption and second-harmonic generation (SHG) measurements confirmed that both the band gap and SHG activity of (thiomorpholinium)PbX₃ (X = Cl, Br, I) crystals were tunable. The band gaps reveal a broadening trend with 3.532 eV, 3.410 eV and 3.175 eV along the Cl → Br → I series. This work provides an effective molecular design for multifunctional organic-inorganic perovskites.     

Lattice potential energies and thermochemical properties of triethylammonium halides (Et3NHX) (X = Cl,Br, and I)

A series of triethylammonium halides (Et₃NHCl, Et₃NHBr, and Et₃NHI) was synthesized. The crystal structures of the three compounds were characterized by X-ray crystallography. The lattice potential energies and ionic radius of the common cation of the three compounds were obtained from crystallographic data. Molar enthalpies of dissolution of the compounds at various values of molality were measured in the double-distilled water at T = 298.150 K by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory, the values of molar enthalpies of dissolution at infinite dilution and Pitzer’s parameters of the compounds were obtained. The values of apparent relative molar enthalpies, relative partial molar enthalpies of the solvent and the compounds at different molalities were derived from the experimental values of molar enthalpies of dissolution of the compounds. Finally, hydration enthalpy of the common cation Et₃NH⁺ was calculated to be ΔH₊ = ?(150.386 ± 4.071) kJ · mol^?1 by designing a thermochemical cycle.     

Spectroscopic properties and bond dissociation energies of PbX,PbX±, PbX2 and PbX2± (X ​= ​F,Cl, Br,I)

Ab initio calculations have been performed to investigate some of the spectroscopic properties, like geometry, frequency, electron affinity, ionization potential and finally adiabatic bond dissociation energies (BDEs) of lead monohalides, lead dihalides and their ions viz. PbX, PbX^±, PbX₂, $\mathrm{P}\mathrm{b}{\mathrm{X}}_{\mathrm{2}}^{\pm }$ (X ?= ?F, Cl, Br, I) in their ground state at the QCISD(T)//MP2 level of theory using correlation consistent basis sets. For the validation of MP2 optimized geometry and frequency, we further obtained geometry and frequency of all the neutral and ionic systems using QCISD(T) method with the same basis sets. The BDEs of PbX₂ molecules are calculated using the BDEs of $\mathrm{P}\mathrm{b}{\mathrm{X}}_{\mathrm{2}}^{\pm }$ ions and taking ionization potential and electron affinity of various systems. The calculated values are found in good agreement with the available data. Most of the data for ionic systems are reported first time in literature.     

A first-principle study of the stability and electronic properties of halide inorganic double perovskite Cs2PbX6 (X = Cl,I) for solar cell application

The problem of lead toxicity in perovskites materials that are currently performing with the most efficiency can be partially solved by choosing double perovskites compounds Cs₂PbX₆ (X = Cl,I), which have considerably reduced lead contents. These materials are slightly more stable, and substituting Cl and I with Br in small percentages further improves their mechanical stability and electronic properties. In this study, the properties of these promising materials were investigated in their pure and mixed forms.     

Coupling of terminal alkynes by RuHXL2 (X = Cl or N(SiMe3)2, L = PiPr3)

The compounds RuL₂HX, where L = PⁱPr₃ and X = Cl or N(SiMe₃)₂, are catalyst precursors for dimerization of terminal alkynes to enynes and also to cumulenes at 23 °C; selectivity among these products is X-dependent, but not high. Conversion of Ru species onto the catalytic cycle was undetectably small, so alternative approaches to understanding the catalytic mechanism were employed: stoichiometric reactions, independent synthesis of candidate intermediates, and trapping with CO. These show the intermediacy of vinylidenes and vinyl compounds, and reveal conversion of cumulenes to the thermodynamically more stable enynes.     

A systematic computational study on the reactions of dimethyl sulfoxide with XO (X = NO2, Cl, Br and I)

The reactions of dimethyl sulfoxide (DMSO) with XO (X = NO₂, Cl, Br, I) have been studied at CCSD/6-311G(d,p)//B3LYP/6-311G(d,p) level. Two reaction channels have been considered: (1) the oxygen-atom transfer (OAT) from XO (X = NO₂, Cl, Br, I) to DMSO and (2) the hydrogen-abstraction by XO (X = NO₂, Cl, Br, I). The reaction mechanisms of DMSO with NO₃, ClO and BrO are similar: the OAT channel is the dominant channel and DMSO₂ is the primary product; the hydrogen-abstraction channel is not likely to be competitive with the OAT channel. The DMSO + IO reaction, because two reaction channels have the overall negative reaction activation energies and Gibbs free energies, the reaction could occur on both reaction channels. Furthermore, the formation of the stable complex may vary the yield rate of DMSO₂.     

Electronic structure and molecular properties of the [Mo6X8L6]; X = Cl, Br, I; L = F, Cl, Br, I clusters

Relativistic TDDFT calculations including spin orbit interactions via the ZORA approximation and solvent effects were carried out on the [Mo₆X₈L₆]²⁻ X = Cl, Br, I ; L = F, Cl, Br, I clusters. These calculations indicate that the closely spaced lowest excited states are largely centered on the cubic [Mo₆X₈]⁴⁺ core. Thus, our calculations and the electronic similarities with the strongly luminescent [Mo₆Cl₈Cl₆]²⁻, [Mo₆Br₈Br₆]²⁻ and [Mo₆I₈I₆]²⁻ clusters, suggest that the clusters [Mo₆Cl₈F₆]²⁻, [Mo₆Br₈F₆]²⁻, [Mo₆I₈F₆]²⁻, [Mo₆I₈Cl₆]²⁻ and [Mo₆I₈Br₆]²⁻ studied here might be also luminescent. The calculated bond energies and reactivity indexes indicate that the most labile clusters are those with axial iodide ligands.     

ns2np4 (n = 4, 5) lone pair triplets whirling in M*F2E3 (M* = Kr,Xe): Stereochemistry and ab initio analyses

The stereochemistry of ns²np⁴ (n = 4, 5) lone pair LP characterizing noble gas Kr and Xe (labeled M*) in M*F₂ difluorides is examined within coherent crystal chemistry and ab initio visualizations. M*²⁺ in such oxidation state brings three lone pairs (E) and difluorides are formulated M*F₂E₃. The analyses use electron localization function (ELF) obtained within density functional theory calculations showing the development of the LP triplets whirling {E₃} quantified in the relevant chemical systems. Detailed ELF data analyses allowed showing that in α KrF₂E₃ and isostructural XeF₂E₃ difluorides the three E electronic clouds merge or hybridize into a torus and adopt a perfect gyration circle with an elliptical section, while in β KrF₂ the network architecture deforms the whole torus into an ellipsoid shape. Original precise metrics are provided for the torus in the different compounds under study. In KrF₂ the geometric changes upon β → α phase transition is schematized and mechanisms for the transformation with temperature or pressure are proposed. The results are further highlighted by electronic band structure calculations which show similar features of equal band gaps of 3 eV in both α and β KrF₂ and a reorganization of frontier orbitals due to the different orientations of the F-Kr-F linear molecule in the two tetragonal structures.     

Ab initio prediction of the low-temperature phase diagrams in the systems CsX–LiX (X = F, Cl, Br, I)

We have calculated the low-temperature phase diagrams for the ternary alkali halides CsX–LiX (X = F, Cl, Br, I) at an ab initio level without any recourse to experimental information. The starting point of our general approach is the global exploration of the enthalpy landscapes for many different compositions in these systems. Candidates for both ordered stoichiometric modifications and crystalline solid-solution phases are identified, and their free enthalpies are computed at an ab initio level. From this the low-temperature phase diagrams are derived. We find that in all systems under investigation only crystalline ordered phases should be present, in agreement with available experimental data. Furthermore, we predict several new thermodynamically stable and metastable phases in these systems.     

Isomerism in tetrahedral rhenium cluster complexes [Re4Q4(PMe2Ph)4X8]·nCH2Cl2 (Q = Se, X = Br; Q = Te, X = Cl, Br)

Three new tetrahedral rhenium cluster compounds [Re₄Se₄(PMe₂Ph)₄Br₈]·1.5CH₂Cl₂ (1), [Re₄Te₄(PMe₂Ph)₄Br₈]·CH₂Cl₂ (2), and [Re₄Te₄(PMe₂Ph)₄Cl₈]·CH₂Cl₂ (3) have been synthesized by the reaction of the corresponding precursor chalcohalide complexes [Re₄Q₄(TeX₂)₄X₈] (X = Br, Q = Se (for 1), Te (for 2); X = Cl, Q = Te (for 3)) with dimethylphenylphosphine in CH₂Cl₂. All compounds have been characterized by X-ray single-crystal diffraction and elemental analyses, IR and ³¹P NMR spectroscopy. ³¹P NMR spectroscopy indicates the formation of isomers in solution, confirmed by single-crystal X-ray analysis.     

Crystal structure and magnetic properties of the new cobalt tellurite halide Co5(TeO3)4X2 (X = Cl,Br)

Two new cobalt tellurite halides Co₅(TeO₃)₄Cl₂ and Co₅(TeO₃)₄Br₂ have been synthesized and found to be iso-structural with Ni₅(TeO₃)₄X₂ (X = Cl, Br). Co₅(TeO₃)₄X₂ crystallizes in the monoclinic system space group C2/c, and the Br-phase has the lattice parameters a = 20.440(1) Å, b = 5.2760(2) Å, c = 16.4710(7) Å, β = 124.790(5)°, and Z = 4. The crystal structures were solved from single-crystal X-ray data, R1 = 1.90 and 1.77, respectively, for the Cl- and Br-phases. The crystal structure is layered with only weak van der Waals' interactions in between the layers. The layers are built by large [Co₅O₁₆X₂] groups consisting of five edge- and face-sharing Co-octahedra. Each group is connected to adjacent groups via corner sharing through common oxygen atoms as well as through [TeO₃E] groups. Magnetic susceptibility measurements on oriented single crystals reveal pronounced anisotropy in a broad temperature range and clear signs of antiferromagnetic ordering at low temperatures. Anisotropic susceptibility of an iso-structural Ni-based compound was also studied and compared with the corresponding results of Co₅(TeO₃)₄X₂. Magnetic anisotropy is discussed in framework of single-ion anisotropy effects.     

DFT studies on nonlinear optical properties of neutral nest-shaped heterothiometallic [MOS3Py5Cu3X] (M = Mo, W; X = F, Cl, Br, I) clusters

Theoretical calculations were carried out on some neutral nest-shaped heterothiometallic cluster compounds [MOS₃Py₅Cu₃X] (M = Mo, W; X = F, Cl, Br, I) with the high first static hyperpolarizabilities β values. The geometries of these cluster compounds were optimized by the restricted DFT method at B3LYP level with LanL2DZ base set without any constrains. In order to understand the relationship between the first static hyperpolarizabilities and the compositions of these clusters, the frontier orbital compositions and energy gaps between the HOMO and LUMO orbitals were calculated and analysed. In these clusters the HOMO orbitals are mainly composed of halogen atoms and the first static hyperpolarizability increases from F to I atom. The LUMO orbitals of clusters [MoOS₃Py₅Cu₃X] are comprised of Mo, O and S atoms while the LUMO orbitals of clusters [WOS₃Py₅Cu₃X] composed of W atom and pyridine ring. The energy gaps between the HOMO and LUMO orbitals of the clusters [MoOS₃Py₅Cu₃X] are smaller than those of the clusters [WOS₃Py₅Cu₃X]. As a result the first static hyperpolarizability values of the clusters [MoOS₃Py₅Cu₃X] are higher than those of the clusters [WOS₃Py₅Cu₃X].     

An experimental and theoretical investigation on hypervalent organoselenium(II) halides: Case study of [2-(Et2NCH2)C6H4]SeX (X = Cl,Br, I)

Cleavage of the Se–Se bond in [2-(Et₂NCH₂)C₆H₄]₂Se₂ (1) with SO₂Cl₂ (1:1 molar ratio) yielded the organoselenium(II) chloride [2-(Et₂NCH₂)C₆H₄]SeCl (2). Treatment of 2 with excess of KX yielded the organoselenium(II) halides [2-(Et₂NCH₂)C₆H₄]SeX [X = Br (3), I (4)]. The new compounds 2–4 were characterized by solution NMR spectroscopy (¹H, ¹³C, ⁷⁷Se, 2D experiments). The solid-state molecular structures of 2, 2·HCl and 3 were established by single crystal X-ray diffraction. Distorted T-shaped coordination geometries of type (C,N)SeX (X = Cl, Br) and CSeCl₂ were found for the neutral halides 2 and 3, and the zwitterionic species [2-{Et₂N⁺(H)CH₂}C₆H₄]SeCl₂￣ (2·HCl), respectively. DFT calculations were performed on 2–4 and the related tellurium compounds [2-(Et₂NCH₂)C₆H₄]TeX [X = Cl (5), Br (6) and I (7)] in order to elucidate the bond nature and FT-Raman features of this class of organochalcogen(II) derivatives.     

Self-assembly of two novel bisupporting Keggin-polyoxometalate derivatives: Hydrothermal synthesis and structure characterization of (X = P, m = 1; X = Si, m = 2)

Two novel organic–inorganic hybrid polyoxometalates, (X = P, m = 1 1; X = Si, m = 2 2; 2,2′-bpy = 2,2′-bpyridine), have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. They are isostructural, possessing orthorhombic, and the parameters of unit cells for compound 1 are space group Pbca, a = 17.317(4) Å, b = 17.092(3) Å, c = 20.587(4) Å, V = 6445(2) Å³, Z = 4; for compound 2 are space group Pcab, a = 17.181(3) Å, b = 18.198(4) Å, c = 20.672(4) Å, V = 6463(2) Å³, Z = 4. The two compounds show a layer framework constructed from Keggin-polyoxoanion clusters and [Cu (2, 2′-bpy)₂]²⁺ coordination polymer fragments via weak covalent interactions, resulting in a 3D network via supramolecular interactions. Their electrochemical properties are studied in detail.     

Photodynamic action of bis(tertiary arsine (diars)) metal(III) complexes trans-[M(diars)2X2] (X = Cl, Br, I); M = Co, Cr, Rh: Optical and EPR spin-trapping studies

Photodynamic properties of series of metal complexes having the general formula [M(diars)₂X₂]ClO₄ or BF₄ where M = Co³⁺, Cr³⁺, Rh³⁺; X = Cl, Br, I, diars = o-phenylene bis(dimethylarsine) are studied. Photogeneration of singlet oxygen is monitored by both optical and EPR methods. In comparison with rose bengal ((¹O₂) for RB = 0.76), singlet oxygen generating efficiencies of these complexes are determined. Rate of N,N-dimethyl-4-nitrosoaniline (RNO) bleaching is found to be retarded by specific ¹O₂ quencher NaN₃, confirming the involvement of ¹O₂ as an active intermediate. Photolysis of these complexes in the presence of spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) generates 12-line EPR spectra, characteristic of O₂⁻ adduct. Photogeneration of O₂⁻ is also monitored by optical spectroscopy using superoxide dismutase (SOD) inhibitable cytochrome c reduction assay. The results indicate that the [Co(diars)₂Br₂]ClO₄ complex possesses high ability to generate reactive oxygen species (ROS). Both Type I and II paths are involved in the photosensitisation of the metal complexes. The antimicrobial activity of the complexes against selected bacteria is estimated. The relationship between the enzymatic production of ROS and antimicrobial activity of the complexes is examined and a good correlation between two factors is found. The [CoBr₂(diars)₂]ClO₄ complex investigated in this study effect photo cleavage of the plasmid DNA (pUC18).     

Dissociation mechanism of electronically excited CH2X2 (X = Cl, Br) formed by near-resonant neutralization using charge-inversion mass spectrometry

The dissociation mechanism of excited CH₂X₂ (X = Cl, Br) was investigated using charge-inversion mass spectrometry, in which positive ions collide with an alkali metal target to generate neutral fragments, and the negative ions formed from the neutral fragments are mass analyzed. Different relative abundances of the negative ions were observed in the charge-inversion spectra for CH₂Cl₂ and CH₂Br₂. The kinetic energy release values calculated from analysis of the peak associated with in the charge-inversion mass spectrum of the parent ion indicate that the excited CH₂Cl₂ formed by neutralization dissociates spontaneously into CHCl₂ + H.     

Binding energies and bonding nature of MX(CO)(PH3)2(C60) (M = Rh or Ir; X = H or Cl): Theoretical study

IrH(CO)(PH₃)₂(C₆₀), IrCl(CO)(PH₃)₂(C₆₀), and RhH(CO)(PH₃)₂(C₆₀) were theoretically investigated with DFT and MP2 to MP4(SDQ) methods.  Because the DFT method considerably underestimates the binding energy compared to the MP2 method, their binding energies were evaluated by the ONIOM(MP4(SDQ):UFF) method.  The binding energy decreases in the order IrH(CO)(PH₃)₂(C₆₀) (59.4) > RhH(CO)(PH₃)₂(C₆₀) (48.2) > Pt(PH₃)₂(C₆₀) (47.2) > IrCl(CO)(PH₃)₂(C₆₀) (43.0), where in parentheses are the binding energy (in kcal/mol) calculated with the ONIOM(MP4(SDQ):UFF) method and that of Pt(PH₃)₂(C₆₀) was calculated with the same method and the same basis sets in our previous work.  This decreasing order is interpreted in terms of the d_π orbital energy, the d orbital expansion, the presence of the empty d_σ orbital, and the distortion energy of the metal fragment induced by the complexation; for instance, the d_π orbital is at higher energy and more expands in IrH(CO)(PH₃)₂ than in the Rh analogue, which leads to the larger binding energy of IrH(CO)(PH₃)₂(C₆₀) than that of the Rh analogue. IrCl(CO)(PH₃)₂ is less favorable than IrH(CO)(PH₃)₂ because of the lower energy of d_π orbital.  Although the π-back donation is stronger in IrCl(CO)(PH₃)₂(C₆₀) than in RhH(CO)(PH₃)₂(C₆₀), the binding energy of IrCl(CO)(PH₃)₂(C₆₀) is smaller than that of RhH(CO)(PH₃)₂(C₆₀) due to the larger distortion energy of the IrCl-(CO)(PH₃)₂ moiety.  Although the d_π orbital of Pt(PH₃)₂ is at higher energy than that of IrH-(CO)(PH₃)₂, the binding energy of IrH(CO)(PH₃)₂(C₆₀) is larger than that of Pt(PH₃)₂(C₆₀) because the distortion energy is large and the d_σ orbital is doubly occupied in Pt(PH₃)₂(C₆₀).  It is also noted that these binding energies are much larger than those of the ethylene analogues like those of the Pt(0) complexes, which is reasonably interpreted in terms that the LUMO of C₆₀ is at much lower energy than those of ethylene.     

Topological characterization of HXO2 (X = Cl, Br, I) isomerization

The isomerization reactions of HOOX --> HOXO --> HXO2 (X = Cl, Br, I) have been studied by using the density functional theory. The breakage and formation of the chemical bonds of the titled reactions have been discussed by the topological analysis method of electronic density. The calculated results show that there is a transitional structure of a three-membered ring on each of the isomerization reaction paths. The "energy transition state (ETS)" and the "structure transition state (STS)" in all of the studied reactions have been found. In all these reactions, the position of the structure transition state and the scope of the structure transition region correlate well with the reaction energy. The STS appears after the ETS in the exothermic reaction but it appears before the ETS in the endothermic reaction. The less reaction energy there is, the wider scope of the structure transition region.     

Synthese,Eigenschaften und Kristallstruktur von Cu3Mo8O23X2 (X = Cl,Br, I)

Synthesis, Properties, and Crystal Structure of Cu₃Mo₈O₂₃X₂ (X = Cl, Br, I) Single crystals of the Cu₃Mo₈O₂₃X₂ compounds were grown by chemical transport reactions at the lower temperature of a gradient 873–823 K without extra transport agent (auto transport). As DTA/TG measurements indicate, the gaseous compounds, necessary for chemical transport reactions, are formed by partial decomposition of Cu₃Mo₈O₂₃X₂ at 873 K. Cu₃Mo₈O₂₃Br₂ crystallizes with the orthorombic space group Pbcm (a = 4.021(1), b = 22.978(2), c = 21.673(2) Å, Z = 4). The crystal structure consists of pentagonal columns ¹_∞[Mo₆O₇O_20/2] linked by additional MoO_6/2 octahedra. All the polyhedra(pentagonal bipyramide, octahedra) are distorted. Infinite chains ¹_∞[Cu₃Br₂] along [100] are arranged in tunnels with s‐like square shape, left open by the pentagonal columns. Cu₃Mo₈O₂₃Cl₂ (a = 4.010(1), b = 22.942(2), c = 21.639(2) Å) and Cu₃Mo₈O₂₃I₂ (a = 4.052(1), b = 23.075(2), c = 21.719(2) Å) are isotypic.