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1.
The rotational spectrum of the weakly bound complex pentafluoropyridine⋅⋅⋅formaldehyde has been investigated using Fourier transform microwave spectroscopy. From the analysis of the rotational parameters of the parent species and of the 13C and 15N isotopologues, the structural arrangement of the adduct has been unambiguously established. The full ring fluorination of pyridine has a dramatic effect on its binding properties: It alters the electron density distribution at the π-cloud of pyridine creating a π-hole and changing its electron donor-acceptor capabilities. In the complex, formaldehyde lies above the aromatic ring with one of the oxygen lone pairs, as conventionally envisaged, pointing toward its centre. This lone pair⋅⋅⋅π-hole interaction, reinforced by a weak C−H⋅⋅⋅N interaction, indicates an exchange of the electron-acceptor roles of both molecules when compared to the pyridine⋅⋅⋅formaldehyde adduct. Tunnelling doublets due to the internal rotation of formaldehyde have also been observed and analysed leading to a discussion on the competition between lone pair⋅⋅⋅π-hole and π⋅⋅⋅π stacking interactions.  相似文献   

2.
Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the λ4Te dichloro derivative. Its crystal structure demonstrates that the heterocycle retains its ability to autoassociate by chalcogen bonding (ChB) forming macrocyclic tetramers. The corresponding Te⋅⋅⋅O ChB distances are 2.062 Å, the shortest observed to date in aggregates of this type. DFT−D3 calculations indicate that while the halogenated molecule is stronger as a ChB donor it also is a weaker ChB acceptor; the overall effect is that the ChBs in the chlorinated homotetramer are not significantly stronger. However, partial halogenation or scrambling selectively yield the 2 : 2 heterotetramer with alternating λ4Te and λ2Te centers, which calculations identified as the thermodynamically preferred arrangement.  相似文献   

3.
The halogen bond is a powerful tool for the molecular design and pushing the limits of its strength is of major interest. Bearing the most potent halogen-bond donor atom, astatine monoiodide (AtI) was recently successfully probed [Nat. Chem. 2018 , 10, 428–434]. In this work, we continue the exploration of adducts between AtI and Lewis bases with the tributylphosphine oxide (Bu3PO) ligand, revealing the unexpected experimental occurrence of two distinct chemical species with 1:1 and 2:1 stoichiometries. The 1:1 Bu3PO⋅⋅⋅AtI complex is found to exhibit the strongest astatine-mediated halogen bond so far (with a formation constant of 10(4.24±0.35)). Quantum chemical calculations unveil the intriguing nature of the 2:1 2Bu3PO⋅⋅⋅AtI adduct, involving a halogen bond between AtI and one Bu3PO molecular unit plus CH⋅⋅⋅O hydrogen bonds chelating the second Bu3PO unit.  相似文献   

4.
Chalcogen-bonded silicon phosphinidenes LSi(E)−P−MecAAC (E=S ( 1 ); Se ( 2 ); Te ( 3 ); L=PhC(NtBu)2; MecAAC=C(CH2)(CMe2)2N-2,6-iPr2C6H3)) were synthesized from the reactions of silylene–phosphinidene LSi−P−MecAAC ( A ) with elemental chalcogens. All the compounds reported herein have been characterized by multinuclear NMR, elemental analyses, LIFDI-MS, and single-crystal X-ray diffraction techniques. Furthermore, the regeneration of silylene–phosphinidene ( A ) was achieved from the reactions of 2 – 3 with L′Al (L′=HC{(CMe)(2,6-iPr2C6H3N)}2). Theoretical studies on chalcogen-bonded silicon phosphinidenes indicate that the Si−E (E=S, Se, Te) bond can be best represented as charge-separated electron-sharing σ-bonding interaction between [LSi−P−MecAAC]+ and E. The partial double-bond character of Si−E is attributed to significant hyperconjugative donation from the lone pair on E to the Si−N and Si−P σ*-molecular orbitals.  相似文献   

5.
The interpretation of 36 charge neutral ‘contact pairs’ from the IsoStar database was supported by DFT calculations of model molecules 1 – 12 , and bimolecular adducts thereof. The ‘central groups’ are σ-hole donors (H2O and aromatic C−I), π-hole donors (R−C(O)Me, R−NO2 and R−C6F5) and for comparison R−C6H5 (R=any group or atom). The ‘contact groups’ are hydrogen bond donors X−H (X=N, O, S, or R2C, or R3C) and lone-pair containing fragments (R3C−F, R−C≡N and R2C=O). Nearly all the IsoStar distributions follow expectations based on the electrostatic potential of the ‘central-’ and ‘contact group’. Interaction energies (ΔEBSSE) are dominated by electrostatics (particularly between two polarized molecules) or dispersion (especially in case of large contact area). Orbital interactions never dominate, but could be significant (∼30 %) and of the n/π→σ*/π* kind. The largest degree of directionality in the IsoStar plots was typically observed for adducts more stable than ΔEBSSE≈−4 kcal⋅mol−1, which can be seen as a benchmark-value for the utility of an interaction in crystal engineering. This benchmark could be met with all the σ- and π-hole donors studied.  相似文献   

6.
The reaction of trifluormethyl dichlorophosphine (CF3PCl2) with sodium telluride Na2Te or bis(trimethylsilyl) telluride (Me3Si)2Te results in the formation of four new phosphorus tellurium heterocycles ( 1–4 ) with the electron withdrawing CF3 substituent bonded to phosphorus. The telluratriphosphetane (CF3P)3Te ( 1 ), telluratetraphospholane (CF3P)4Te ( 2 ), telluradiphosphirane (CF3P)2Te ( 3 ) and ditelluratriphospholane (CF3P)3Te2 ( 4 ) are characterized by multinuclear (31P, 19F and 125Te) NMR spectroscopy. A full analysis of the 19F NMR spectrum of telluratriphosphetane (CF3P)3Te is presented. The new heterocycles are remarkably stable in solution and eliminate only slowly tellurium to form cyclophosphines (CF3P)n (n = 3–5).  相似文献   

7.
The structure of the title compound, [TeCl4(C5H10N2S)2] or C10H20Cl4N4S2Te, has been solved in order to study the stereochemical activity of the lone pair of electrons on TeIV. The two crystallographically independent mol­ecules in the asymmetric unit both show a distorted octahedral coordination of the Te atom. The two Te—S bonds are trans to each other in both mol­ecules and are greatly asymmetric, with bond lengths of 2.5686 (7) versus 2.8557 (8) Å and 2.5859 (7) versus 2.8165 (9) Å. The Te—Cl bond lengths lie in the range 2.5236 (7)–2.5589 (8) Å. The asymmetric Te—S bonds and a large S—Te—Cl angle of ca 97° involving the long Te—S bonds indicate stereochemical activity of the lone pair of electrons on Te.  相似文献   

8.
9.
The aryltellurenyl cation [2-(tBuNCH)C6H4Te]+, a Lewis super acid, and the weakly coordinating carborane anion [CB11H12], an extremely weak Brønsted acid (pKa=131.0 in MeCN), form an isolable ion pair complex [2-(tBuNCH)C6H4Te][CB11H12], in which the Brønsted acidity (pKa 7.4 in MeCN) of the formally hydridic B−H bonds is dramatically increased by more than 120 orders of magnitude. The electrophilic activation of B−H bonds in the carborane moiety gives rise to a proton transfer from boron to nitrogen at slightly elevated temperatures, as rationalized by the isolation of a mixture of the zwitterionic isomers 12- and 7-[2-(tBuN{H}CH)C6H4Te(CB11H11)] in ratios ranging from 62 : 38 to 80 : 20.  相似文献   

10.
Ab initio calculation at the MP2/aug-cc-pVTZ level has been performed on the π-hole based NSi tetrel bonded complexes between substituted pyridines and H2SiO. The primary aim of the study is to find out the effect of substitution on the strength and nature of this tetrel bond, and its similarity/difference with the NC tetrel bond. Correlation between the strength of the NSi bond and several molecular properties of the Lewis acid (H2SiO) and base (pyridines) are explored. The properties of the tetrel bond are analyzed using AIM, NBO, and symmetry-adapted perturbation theory calculations. The complexes are characterized with short NSi intermolecular distances and high binding energies ranging between −142.72 and −115.37 kJ/mol. The high value of deformation energy indicates significant geometrical distortion of the monomer units. The AIM and NBO analysis reveal significant coordinate covalent bond character of the N⋅⋅⋅Si π-hole bond. Sharp differences are also noticed in the orbital interactions present in the N⋅⋅⋅Si and N⋅⋅⋅C tetrel bonds.  相似文献   

11.
We have synthesised and characterised 21 new ternary Pb(II) bromides with 16 different pyridine-based organic cations by single crystal XRD measurements. The dominating composition is APbBr3 with 10 representatives, but also 6 examples for APb2Br5 were found. The systematic variation of topological aspects of the organic cations allowed conclusions on the influence of N−H⋅⋅⋅Br hydrogen bridges on the connectivity and bonding situation of the Pb−Br polyhedra. Additionally, it turned out, that further weak ionic interactions can have an influence, if the formation of N−H⋅⋅⋅Br hydrogen bridges is hindered by steric effects. In general, the high versatility of the dominating PbBr6 octahedra, and in some cases higher or lower coordination numbers, allows conclusions on the parameters that influence pattern and extent of the N−H⋅⋅⋅Br bridges as the strongest structure-determining factor. Type and extent of N−H⋅⋅⋅Br bridges have also an impact on the distortion of the PbBr6 octahedra ranging from nearly regular PbBr6 octahedra to 2+2+2 and 1+2+2+1 patterns with significant lone pair activity. Finally, the connectivity mode of the octahedra relates to formation and strength of hydrogen bonds.  相似文献   

12.
The primary geometry about the TeIV atom in the title compound, [TeCl2(C8H6Cl)(C3H5O)] or C11H11Cl3OTe, is a pseudo‐trigonal‐bipyramidal arrangement, with two Cl atoms in apical positions, and the lone pair of electrons and C atoms in the equatorial plane. The TeIV atom is involved in three secondary interactions, two intramolecular [Te?O = 2.842 (3) Å and Te?Cl3 = 3.209 (1) Å] and one intermolecular [Te?Cl = 3.637 (1) Å], the latter giving rise to a helical chain. These helices are linked by C—H?O interchain interactions.  相似文献   

13.
Trifluoromethyl-bearing 5-membered rings are prevalent in bioactive molecules, but modular approaches to these compounds by functionalization of robust C(sp3)−H bonds in a direct and selective manner are extremely challenging. Herein we report the rhodium-catalyzed α-CF3-α-alkyl carbene insertion into C(sp3)−H bonds of a broad range of substrates to access 7 types of CF3-bearing saturated 5-membered carbo- and heterocycles. The reaction is particularly effective for benzylic C−H insertion exerting good site-, diastereo- and enantiocontrol, and applicable to the synthesis of chiral CF3 analogues of bioactive molecules. Ruthenium α-CF3-α-alkyl carbene complexes underwent stoichiometric reactions to give C−H insertion products, lending evidence for the involvement of metal α-CF3-α-alkyl carbene species in the catalytic cycle. DFT calculations revealed that the π⋅⋅⋅π attraction and intra-carbene C−H⋅⋅⋅F hydrogen bond elucidate the origin of selectivity of the benzylic C−H insertion reactions.  相似文献   

14.
Inspection of the X-ray structures of the newly prepared trans-[MII(CNXyl)2(DAPT)2]Cl(BF4) (M=Pd, Pt; Xyl=2,6-Me2C6H3; DAPT=4,6-diaminopyrimidine-2(1H)-thione) complexes and the appropriate Hirshfeld molecular surface analysis allowed the recognition of the previously unknown π-hole⋅⋅⋅metal interactions between a ligated isocyano group (acting as a π-hole donor) and the positively charged d8-PtII and d8-PdII metal centers (acting as nucleophiles); this is the first identification of π-hole⋅⋅⋅metal interactions with triple-bond species. Results of DFT calculations followed by the topological analysis of the electron density distribution within the framework of Bader's theory (quantum theory of atoms in molecules, QTAIM) confirmed the presence of these contacts. The electrostatic surface potential calculations indicated that π-hole⋅⋅⋅metal contacts are formed upon interaction between the electrophilic isocyano C atom (π-hole donor) and the nucleophilic d orbital of the metal centers, which act as π-hole acceptors. Available CCDC data were processed from the perspective of the π-hole⋅⋅⋅metal interactions with isocyanide ligands, and their analysis disclosed the role of metal nucleophilicity in the corresponding π-hole acceptor ability.  相似文献   

15.
Quantum calculations at the MP2/cc-pVTZ have been used to examine 1:1 and 1:2 complexes between O2NX (X = Cl, Br) with HCN and HNC moieties. The interaction of the lone pair of the HCN(HNC) with the σ-hole and π-hole of O2NX molecules and hydrogen bonding between lone pairs of X and O of O2NX with H of HCN and HNC have been considered in 1:1 complexes. The 1:1 complexes can easily be differentiated using the stretching frequency of the N–X bond. Thus, those complexes with σ-hole and H···O2NX interactions show a blue shift of the N-X bond stretching while a red shift is observed in the complexes along the π-hole and H···XNO2 interactions. In the 1:2 complexes, the cooperative and diminutive energetic effects have been analyzed using the many-body interaction energies. The nature of the interactions has been characterized with the Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) methodologies. Stabilization energies of 1:1 and 1:2 complexes including the variation of the zero-point vibrational energy (ΔZPVE) are in the range 3–9 kJ mol?1 and 21–40 kJ mol?1, respectively.  相似文献   

16.
Single‐crystal X‐ray analysis of the β‐heptakis(trifluoromethyl)‐meso ‐tetrakis(p ‐fluorophenyl)porphyrin, H2[(CF3)7TpFPP], has revealed the first example of a stable cis tautomer of a free‐base porphyrin, the long‐postulated intermediate of porphyrin tautomerism. The stability of the unique molecule appears to reflect a dual origin: a strongly saddled porphyrin skeleton, which alleviates electrostatic repulsion between the two NH protons, and two polarization‐enhanced, transannular N−H⋅⋅⋅O−H⋅⋅⋅N hydrogen bond chains, each involving a molecule of water. DFT calculations suggest that the observed tautomer has a lower energy than the alternative, doubly hydrated trans tautomer by some 8.3 kcal mol−1. A fascinating prospect thus exists that H2[(CF3)7TpFPP]⋅2 H2O and cognate structures may act as supramolecular synthons, which, given their chirality, may even be amenable to resolution into optically pure enantiomers.  相似文献   

17.
The geometry around the Te atom in the anion in C13H22N+·C3H3Cl4OTe? is distorted pseudo‐octahedral with three Cl atoms and the O atom forming the equatorial plane, and the C atom lying opposite the tellurium lone pair. Distances and angles are: Te—O 2.0120 (18), Te—C 2.072 (2), Te—Cl 2.5239 (7), 2.5283 (7) and 2.5577 (7) Å; O—Te—C 81.61 (9), O—Te—Cl 90.69 (6), 90.99 (6) and 168.13 (5), C—Te—Cl 87.13 (8), 86.64 (8) and 86.59 (8), and Cl—Te—Cl 87.02 (2), 90.00 (3) and 173.24 (3)°. The anions are arranged in an infinite zigzag chain parallel to the a axis through a secondary Te?Cl bond [3.8391 (8) Å].  相似文献   

18.
Summary.  Single crystals of K2Ag12Te7 (a = 11.460(2), c = 4.660(1) ?; V = 530.01 ?3; space group: P63/m; Z = 1) were synthesized under hydrothermal conditions at 250°C in concentrated aqueous KOH solution from elementary silver and tellurium. The crystal structure is characterized by trigonal prismatic KTe6 polyhedra, connected via two common faces to KTe3 rods parallel to [001]. These rods are combined by two crystallographically independent Ag atoms, each coordinated to four Te and three Ag atoms (Ag–Te and Ag–Ag < 3.1 ?) to a framework of the formula (K2Ag12Te6)2 +  and with channels parallel to the sixfold axis. These channels are statistically occupied by one further Te atom per unit cell, distributed over two independent positions. Received May 17, 2001. Accepted (revised) July 3, 2001  相似文献   

19.
We have measured the second acid dissociation constant, K 2a , at several ionic strengths for hydrogen telluride (H2Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe and Te2−. Since it is produced in our solutions, we have also determined the spectra of Te2 2− both in the uv and in the visible regions. At 25 C, K 2a = (1.28 ± 0.02) × 10−12 by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm-3 was estimated to be (8.7 ± 0.2) × 10−12. The solution thermodynamics of these species are also discussed and comparisons are made to related acids.  相似文献   

20.
Syntheses and NMR Spectroscopic Ivestigations of Salts containing the Novel Anions [PtXn(CF3)6‐n]2— (n = 0 ‐ 5, X = F, OH, Cl, CN) and Crystal Structure of K2[(CF3)2F2Pt(μ‐OH)2PtF2(CF3)2]·2H2O The first syntheses of trifluoromethyl‐complexes of platinum through fluorination of cyanoplatinates are reported. The fluorination of tetracyanoplatinates(II), K2[Pt(CN)4], and hexacyanoplatinates(IV), K2[Pt(CN)6], with ClF in anhydrous HF leads after working up of the products to K2[(CF3)2F2Pt(μ‐OH)2PtF2(CF3)2]·2H2O. The structure of the salt is determined by a X‐ray structure analysis, P21/c (Nr. 14), a = 11.391(2), b = 11.565(2), c = 13.391(3)Å, β = 90.32(3)°, Z = 4, R1 = 0.0326 (I > 2σ(I)). The reaction of [Bu4N]2[Pt(CN)4] with ClF in CH2Cl2 generates mainly cis‐[Bu4N]2[PtCl2(CF3)4] and fac‐[Bu4N]2[PtCl3(CF3)3], but in contrast that of [Bu4N]2[Pt(CN)6] with ClF in CH2Cl2 results cis‐[Bu4N]2[PtX2(CF3)4], [Bu4N]2[PtX(CF3)5] (X = F, Cl) and [Bu4N]2[Pt(CF3)6]. In the products [Bu4N]2[PtXn(CF3)6‐n] (X = F, Cl, n = 0—3) it is possibel to exchange the fluoro‐ligands into chloro‐ and cyano‐ligands by treatment with (CH3)3SiCl und (CH3)3SiCN at 50 °C. With continuing warming the trifluoromethyl‐ligands are exchanged by chloro‐ and cyano‐ligands, while as intermediates CF2Cl and CF2CN ligands are formed. The identity of the new trifluoromethyl‐platinates is proved by 195Pt‐ and 19F‐NMR‐spectroscopy.  相似文献   

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