BN-Substituted fullerenes C60−2x (BN) x : a computational 11B and 15N NMR study

Density functional theory has been used to investigate the ¹⁵N and ¹¹B NMR parameters of heterofullerenes C_60?2x (BN) _x (x = 1, 2, 3, 6, 9, 12, 15, 18, 21, and 24). Geometry structures of all the BN-substituted fullerenes have been optimized at the B3LYP/6-31+G* level of theory. Afterward, ¹¹B and ¹⁵N chemical shielding isotropy and anisotropy (CSI, CSA) parameters have been calculated at the same level. The obtained results illustrate the electrostatic environment divisions of the nuclei into few layers, which have been then confirmed by calculating natural charges at B and N sites. A good correlation has been seen between the layers of CSI and CSA values and three local structures around boron and nitrogen atoms. The effects of curvature of fullerene structure on chemical shielding (CS) parameters of heterofullerenes have also been investigated by computing CS tensors for curved and relaxed structures of a set of small fragments separated from the heterofullerenes, suggesting high sensitivity of CS parameters to the curvature of fullerene structure.     

Electronic and Structural Properties of Neutral, Anionic, and Cationic Rh x Cu4−x (x = 0–4) Small Clusters: A DFT Study

In this study, electronic structure, stability, and tendency to exchange electron of neutral, anionic, and cationic Rh _x Cu_4?x (x = 0–4) small clusters were investigated by density functional theory calculations. For neutral small clusters, it was found that the most stable structures of Rh₄, Rh₃Cu and Rh₂Cu₂ have distorted tetrahedral shape while the most stable structures of RhCu₃ and Cu₄ have quasi-planer shape. Adding charges to the clusters, caused shapes of the most stable structures undergo variations. Stabilities of the neutral, anionic, and cationic clusters decrease linearly with increasing the copper content. In addition, calculated chemical harnesses indicated that the small cluster with 75 % copper content has the least chemical hardness. Interestingly, prevailing number of electronegative (Rh) and electropositive (Cu) atoms in the anionic and cationic clusters coincides with high dipole moment in these species that occur at 25 and 75 % copper respectively.     

Synthesis, electrical and thermal properties of Bi4V2−xMexO11 (x = 0.0 and 0.02) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xMe_xO₁₁ (Me = Nb, Zr, Y and Cu and x = 0.0 and 0.02) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been analysed by X-ray diffraction method. The dielectric constant, dielectric loss and AC conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy and hence its AC conductivity increases with the increase of temperature. The DC conductivity of material has been measured as a function of temperature from room temperature to 380 °C and its activation energy was calculated using the relation σ = σ ₀exp (?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the heat capacity and heat flow of the compounds. The results are discussed in detail.     

Electrophilicity Scale of Activated Amides: 17O NMR and 15N NMR Chemical Shifts of Acyclic Twisted Amides in N−C(O) Cross-Coupling

The structure and properties of amides are of tremendous interest in organic synthesis and biochemistry. Traditional amides are planar and the carbonyl group non-electrophilic due to n_N→π*_C=O conjugation. In this study, we report electrophilicity scale by exploiting ¹⁷O NMR and ¹⁵N NMR chemical shifts of acyclic twisted and destabilized acyclic amides that have recently received major attention as precursors in N-C(O) cross-coupling by selective oxidative addition as well as precursors in electrophilic activation of N-C(O) bonds. Most crucially, we demonstrate that acyclic twisted amides feature electrophilicity of the carbonyl group that ranges between that of acid anhydrides and acid chlorides. Furthermore, a wide range of electrophilic amides is possible with gradually varying carbonyl electrophilicity by steric and electronic tuning of amide bond properties. Overall, the study quantifies for the first time that steric and electronic destabilization of the amide bond in common acyclic amides renders the amide bond as electrophilic as acid anhydrides and chlorides. These findings should have major implications on the fundamental properties of amide bonds.     

Synthesis and characterization of M(II) (M = Cd,Hg and Pb) complexes with naphthodiaza-crown macrocyclic ligand and study of metal ion recognition by fluorescence, 1H NMR spectroscopy,and DFT calculation

To find metal ion recognition by L (L = O₂N₂-donor naphthodiaza-crown macrocyclic ligand), the complexes [ML]²⁺ (M = Cd, Hg and Pb) were synthesized and characterized by IR, ¹H, ¹³C NMR, and mass spectrometry, as well as elemental microanalysis. Hg(II) showed perceptible enhancement of the fluorescence of L in which ultra-low limit of detection for Hg(II) by L was determined as 1 nM in ethanol and DMSO. L reserved selectivity of Hg(II) in its binary mixtures with metal cations in solution. A 1 : 1 stoichiometry was found for the interaction of Hg(II) with L while Benesi–Hildebrand method was applied to calculate its complexation binding constant (K_BH) employing fluorescence spectrophotometry. The monitoring of the chemical shifts in ¹H NMR spectra of these complexes demonstrated that the central macrocycle of L was tailored for the size of Hg(II). Density functional theory calculations using B₃LYP/6–31G* basis set demonstrated that the macrocycle cavity of L was properly fitted for complex formation with Hg(II) cation, while both Cd(II) and Pb(II) cations did not form strong bonds with L from inadequate cation size. The present study shows detection method of Hg(II) and also possible application of naphthodiaza as an appropriate fluorophore macrocyclic ligand for detecting other metal ions.     

Synthesis,electrical and thermal properties of Bi4V2−xMexO11 (Me=Nb,Zr, Y and Cu with x = 0.0 and 0.06) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xMe_xO₁₁ (Me=Nb, Zr, Y and Cu and x = 0.0 and 0.06) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been analysed by X-ray diffraction method. The dielectric constant, dielectric loss and AC conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy, and hence, its AC conductivity increases with the increase of temperature. The DC conductivity of material has been measured as a function of temperature from room temperature to 723 K and its activation energy was calculated using the relation σ = σ ₀exp (?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the phase transition (heat capacity and heat flow) of the compounds. The results are discussed in detail.     

New N-nicotinyl and N-isonicotinyl, N′,N″-diaryl phosphorictriamides with new Er(III) complex: synthesis, spectroscopic study and crystal structures

Ten new N-nicotinyl and N-isonicotinyl phosphoramidates with formula XP(O)R₂, X?=?Nicotinamide(nia), R?=?NHCH₂Ph (1), N(CH₃)CH₂Ph (2), NHCH(CH₃)Ph (3), NH-CH₂C₄H₃O (4), NHCH₂(C₅H₄N) (5), 3-NH-C₅H₄N (6), and YP(O)R₂, Y?=?isonicotinamide(iso), R?=?NHCH₂Ph (7), N(CH₃)CH₂Ph (8), NHCH(CH₃)Ph (9), NH-CH₂C₄H₃O (10) plus one new Er(III) complex with formula Er(L)₂(NO₃)₃ (11), L?=?(iso)PO(NHCH₂C₄H₃O)₂ (10), were synthesized and characterized by elemental analysis and ¹H, ¹³C, ³¹P NMR, IR, UV?Cvis spectroscopy. Crystal structures of compounds 10 and 11 were also determined by X-ray crystallography. Interestingly, the ¹H NMR spectra of compounds 1, 2, 6, 7, 9 indicated long-range ⁿ J _P,H (n?=?5,6,7) coupling constants, in the range of 1.4?C1.9?Hz, for the splitting of pyridine ring protons with phosphorus atom. IR results showed that the ??(C=O) values of compounds 7?C10 are greater than those of compounds 1?C5 which means that isonicotinyl moiety is more electron withdrawing than nicotinyl group. X-ray outcomes revealed that in complex 11 three phosphoric triamide ligands have been connected to each Er(III); one from N_pyridine and two from P=O donor sites. One of the P=O donor ligands is mono dentate while the other one acts as a bidentate ligand and coordinates to another Er atom via its N_pyridine site. By forming complex 11 the P=O and C?CN_amide bond lengths of ligand is increased in both, mono and bi dentate, ligands while the C=O bond length is decreased to lower values. These variations are in good agreement with IR results. All H-bonds and electrostatic interactions lead to form a three-dimensional polymeric cluster in the crystal lattice of 10 and 11.     

Density functional study on structures, stabilities, and electronic properties of size-selected Pd n Si q (n = 1–7 and q = 0, +1, −1) clusters

The density functional theory (DFT) calculations within the framework of generalized gradient approximation have been employed to systematically investigate the geometrical structures, stabilities, and electronic properties of Pd _n Si ^q (n = 1–7 and q = 0, +1, ?1) clusters and compared them with the pure ${\text{Pd}}_{n + 1}^{q}$ (n = 1–7 and q = 0, +1, ?1) clusters for illustrating the effect of doping Si atom into palladium nanoclusters. The most stable configurations adopt a three-dimensional structure for both pure and Si-doped palladium clusters at n = 3–7. As a result of doping, the Pd _n Si clusters adopt different geometries as compared to that of Pd _n+1. A careful analysis of the binding energies per atom, fragmentation energies, second-order difference of energies, and HOMO–LUMO energy gaps as a function of cluster size shows that the clusters ${\text{Pd}}_{4}^{ + }$ , ${\text{Pd}}_{4}$ , ${\text{Pd}}_{8}^{ - }$ , ${\text{Pd}}_{5} {\text{Si}}^{0, + , - }$ , and ${\text{Pd}}_{7} {\text{Si}}^{0, + , - }$ possess relatively higher stability. There is enhancement in the stabilities of palladium frameworks due to doping with an impurity atom. In addition, the charge transfer has been analyzed to understand the effect of doped atom and compared further.     

Three novel Cu(II), Cd(II) and Cr(III) complexes of 6−Methylpyridine−2−carboxylic acid with thiocyanate: Synthesis,crystal structures,DFT calculations,molecular docking and α-Glucosidase inhibition studies

Novel complexes of 6?methylpyridine?2?carboxylic acid and thiocyanate {[Cu(NCS)(6-mpa)₂], (1); [Cd(NCS)(6-mpa)]_n, (2); [Cr(NCS)(6-mpa)₂·H₂O], (3)} were synthesized, and their structures were characterized by XRD analysis, FT–IR and UV–Vis spectroscopic techniques. The inhibitory activities of the synthesized complexes (1–3) on α-glucosidase were determined by using genistein reference compound. Furthermore, the optimized geometry and vibrational harmonic frequencies for the complexes 1–3 were obtained by DFT/HSEh1PBE/6–311G(d,p)/LanL2DZ level. Electronic spectral properties were examined by using TD-DFT/HSEh1PBE/6–311G(d,p)/LanL2DZ level with CPCM model. Additionally, major contributions to the electronic transitions were determined via Swizard program. The refractive index, linear optical and non?nonlinear optical parameters of the complexes 1–3 were investigated at HSEh1PBE/6–311G(d,p) level. The docking studies of the complexes 1–3 to the binding site of the target protein (the template structure S. cerevisiae isomaltase are fulfilled. Lastly, natural bond orbital analysis was used to investigate inter- and intra-molecular bonding and interaction among bonds.     

Coupled cluster,MP2, and DFT study of structures,stabilities, vibrations,and bonding properties of XXeOH (X = F,Cl, Br,and I)

The optimized geometries, molecular properties, and stabilities of new noble gas molecules, XXeOH (X = F, Cl, Br, and I), were studied using CCSD, MP2, CAM-B3LYP, and WB97XD methods and large basis sets. All XXeOH molecules showed equilibrium structures with Cs symmetry. The results also showed that some bonds in XXeOH could be presented as a typical ionic bond. An alteration in ion-pair character was observed for IXeOH, showing two OH ^? and IXe ⁺ parts, while in other molecules, they could be presented as XeOH ⁺ and X ^? . Two decomposition routes were proposed for these molecules that showed high exothermic reactions. However, despite their low thermodynamic stabilities, their decomposition rate constants were small and all molecules (except BrXeOH) had high kinetic stabilities, indicating the possibility for identification and characterization of these molecules. However, in addition to the calculation of their vibrational frequencies, NBO atomic charges, and hybridizations, the bonding properties of XXeOH molecules were studied by AIM calculations (to calculate electron densities, bond elipticities, and Laplacian of electron densities) and second-order intramolecular perturbation energies using NBO calculations. Moreover, the ease of formations and relative stabilities of XXeOH molecules were compared using heats of formations, Gibbs free energies of formations and isodesmic reactions. These calculations showed that the stability of XXeOH molecules was decreased from F to I.     

Supramolecular Cd(II) complexes with (E)-N,N′-bis(2-pyridyl)iminoisoindoline (2-pyimiso): synthesis,X-ray structures,Hirshfeld surface analyses,and DFT study of [CdX2(2-pyimiso)2] (X = Cl or NCS)*

The paucity of coordination entities bearing (E)-N,N′-bis(heteroaryl)iminoisoindolines has prompted us to investigate coordination modes and supramolecular features of (E)-N,N′-bis(2-pyridyl)iminoisoindoline (2-pyimiso), a versatile iminobis(pyridyl) ligand. In this article we report the synthesis, spectroscopic characterization and crystal structure analysis of two Cd(II) : 2-pyimiso (1?:?2) bis-adducts, [CdX₂(2-pyimiso)₂] [X = Cl (1) or NCS (2)]. Our X-ray structural results reveal that 1 exhibits distorted tetrahedral coordination (four-coordinate geometry index τ₄ = 0.92), whereas 2 displays six-coordinate Cd(II) and two four-membered chelate rings (bite angles = 52.5°), each comprising one Cd–N_py [2.247(2) Å] bond and one Cd?N_imine [2.809(21) Å] secondary interaction. Remarkably, in 2 each 2-pyimiso unit binds to Cd(II) according to an unusual bidentate coordination. The contributions of the Cd–N and Cd–Cl bond valences to the total metal valence for both 1 and 2 have been evaluated to confirm the coordination modes of 2-pyimiso, which can be interpreted in terms of Jørgensen’s principle of symbiosis. X-ray structure and Hirshfeld surface analyses have shown that the crystal structure of 1 is determined by two perpendicular 1-D chains formed by weak hydrogen bonds along the a- and c-axes, whereas the supramolecular architecture of 2 exhibits 2-D sheets parallel to the ab-plane interconnected by C–H?π interactions along the c-axis. A vibrational analysis of both products has been conducted at the DFT B3LYP-D3/LACV3P** level of calculation.     

Solution phase structures of enantiopure and racemic lithium N-benzyl-N-(α-methylbenzyl)amide in THF: low temperature 6Li and 15N NMR spectroscopic studies

The antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide are highly efficient enantiopure ammonia equivalents for the asymmetric synthesis of β-amino acid derivatives via conjugate addition to α,β-unsaturated esters. ⁶Li and ¹⁵N NMR spectroscopic studies of doubly labelled ⁶lithium (S)-¹⁵N-benzyl-¹⁵N-(α-methylbenzyl)amide in THF at low temperature reveal the presence of lithium amide dimers as the only observable species. Either a monomeric or dimeric lithium amide reactive species can be accommodated within the transition state mnemonic for this class of conjugate addition reaction. This enantiopure lithium amide offers unique opportunities over achiral (e.g., lithium dibenzylamide) and C₂-symmetric (e.g., lithium bis-N,N-α-methylbenzylamide) counterparts for further mechanistic study owing to the ready distinction of the various dimers formed.     

Electronic structure and molecular properties of [Re6−x Os x Se8Cl6](4−x)− (x = 0–3) clusters: A study based on time-dependent density functional theory including spin-orbit and solvent effects

Relativistic time-dependent density functional (TDDFT) calculations including spin-orbit interactions via the zero order regular approximation (ZORA) and solvent effects are carried out on the [Re_6?x Os _x Se₈Cl₆]^(4?x)? (x = 0–3) cluster. These calculations indicate that the lowest energy electronic transitions of the MMCT and LMCT type are similar to those observed in strongly luminescent 24-electron hexanuclear rhenium chalcogenide clusters [Re₆Se₈Cl₆]^4?. Thus our calculations predict that [Re_6?x Os _x Se₈Cl₆]^(4?x)? (x = 0–3) clusters could be luminescent.     

Searching new structures of beryllium-doped in small-sized magnesium clusters: Be2MgnQ (Q = 0, −1; n = 1–11) clusters DFT study

Using CALYPSO method to search new structures of neutral and anionic beryllium-doped magnesium clusters followed by density functional theory (DFT) calculations, an extensive study of the structures, electronic and spectral properties of Be₂Mg_n^Q (Q = 0, −1; n = 2–11) clusters is performed. Based on the structural optimization, it is found that the Be₂Mg_n^Q (Q = 0, −1) clusters are shown by tetrahedral-based geometries at n = 2–6 and tower-like-based geometries at n = 7–11. The calculations of stability indicate that Be₂Mg₅^Q=0, Be₂Mg₅^Q=−1, and Be₂Mg₈^Q=−1 clusters are “magic” clusters with high stability. The NCP shows that the charges are transferred from Mg atoms to Be atoms. The s- and p-orbitals interactions of Mg and Be atoms are main responsible for their NEC. In particular, chemical bond analysis including molecular orbitals (MOs) and chemical bonding composition for magic clusters to further study their stability. The results confirmed that the high stability of these clusters is due to the interactions between the Be atom and the Mg₅ or Mg₈ host. Finally, theoretical calculations of infrared and Raman spectra of the ground state of Be₂Mg_n^Q (Q = 0, −1; n = 1–11) clusters were performed, which will be absolutely useful for future experiments to identify these clusters.     

Glass Stability and Glass Forming Ability of Ge25−xSe75Sbx (x = 12, 15, and 18) Chalcogenide Glasses Using Thermal Parameters

In the present communication glass stability (GS) and glass forming ability (GFA) of Ge_25−xSe₇₅Sb_x (x = 12, 15, and 18) chalcogenide glasses have been calculated in terms of certain thermal parameters, i.e., reduced glass transition temperature (T_rg), Hruby number (H), S-parameter (S), and ΔT. The glassy samples have been prepared by quenching of melt technique. For structure characterization, XRD technique has been used. For thermal analysis Differential Scanning Calorimetery (DSC) has been used. DSC scans have been recorded at different heating rates, i.e., 5, 10, 15, and 20 K min⁻¹. Stability of glassy samples has also been confirmed in terms of activation energy of glass transition calculated by Kissinger relation. All these parameters indicate that GS and GFA both decrease with increase of Sb content in Ge_25−xSe₇₅Sb_x (x = 12, 15, and 18) glassy series.     

Do halogen and methyl substituents have electronic effects on the structures of simple disilanes? An experimental and theoretical study of the molecular structures of the series X3SiSiMe3 (X = H, F, Cl and Br)

The gas-phase molecular structures of a series of halogen-substituted disilanes [X₃SiSiMe₃ (X = H, F, Cl and Br)], 1,1,1-trimethyldisilane (H₃SiSiMe₃), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F₃SiSiMe₃), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl₃SiSiMe₃) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br₃SiSiMe₃), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C _3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X₃SiSiXMe₂ (X = F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes.     

Steric and electronic effects of N -coordinated NC − and NCS− on NiS2PN: synthesis,spectral and single crystal X-ray structural studies on N,N ′-di- n -butyldithiocarbamate complexes of nickel(II) with phosphorus and nitrogen donor ligands

Planar nickel(II) complexes involving N,N′-dibutyldithiocarbamate, such as [Ni(bu₂dtc)(PPh₃)(NC)] (1) and [Ni(bu₂dtc)(PPh₃)(NCS)] (2) (where bu₂dtc = N,N′-dibutyldithiocarbamate anion) have been prepared, characterized by electronic, IR and NMR spectra and their structures determined by single crystal X-ray crystallography. Cyclic voltammetric characterizations of the complexes are also reported. IR spectra of the two complexes indicate the isobidentate coordination (ν_c-s ? 1095 cm^?1 without splitting) of the dithiocarbamate moiety. The important stretching mode characteristic of the thioureide bond (ν_C–N) occurs at higher wave numbers compared to that of the parent dithiocarbamate complex [Ni(bu₂dtc)₂]. The electronic spectra of 1 and 2 show signature bands at 426 nm and 478 nm, respectively. NMR spectra show large ³¹P chemical shifts in both compounds and the most important N¹³CS₂ chemical shift appears at 204.86 ppm and 203.23 ppm for 1 and 2, respectively. The CV studies clearly show the presence of reduced electron density on the nickel ions in mixed-ligand complexes 1 and 2 compared to the parent dithiocarbamate. Single crystal X-ray structure studies show that 2 crystallizes as a new triclinic polymorph, whose molecular structure closely resembles that of the previously reported monoclinic form. Both complexes contain a planar NiS₂PN chromophore in keeping with the observed diamagnetism. In both complexes the Ni-S distances are significantly different. The thioureide C–N distances of the complexes are shorter than those observed in the parent [Ni(bu₂dtc)₂]. The two compounds allow comparison of the influence of NCS^? in place of NC^?.     

Synthesis, IR spectra, and solid-state luminescence of triphenylguanidinium salts with the anions B10H 10 2− , B12H 12 2− , B9C2H 12 2− , [Co(C2B9H11)2]−, and [Ni(C2B9H11)2]−

Triphenylguanidinium Ph₃GH⁺ salts with the anions B₁₀H ₁₀ ^2? , B₁₂H ₁₂ ^2? , B₉C₂H ₁₂ ^2? , [Co(C₂B₉H₁₁)₂]^?, and [Ni(C₂B₉H₁₁)₂]^? were synthesized and described by DTA, IR spectroscopy, and solid-state luminescence. By IR spectroscopy, it was shown that intermolecular interactions involving the NH groups of the cation are enhanced in the sequence [Co(C₂B₉H₁₁)₂]^? ～ [Ni(C₂B₉H₁₁)₂]^? < B₉C₂H ₁₂ ^2? < B₁₂H ₁₂ ^2? < B₁₀H ₁₀ ^2? .