Studies of the substituent effect in aromatic systems by 35 Cl-NQR. Chloroacetanilides ClxC6H5−x NHCOCH3−y Cly

The ³⁵Cl-NQR spectra of 45 chlorosubsitituted acetanilides, Cl_xC₆H_5?xNHCOCH_3?yCl_y, were investigated and the temperature dependence of some spectra, especially of monochloroacetic acid derivatives, was measured. A preliminary assignment of the NQR frequencies is given. A correlation between NQR frequencies and substituent parameters permits the study of the substituent effect of the acetamido group, ? NHCOCH_3?yCl_y. The chloro-substitution in the side chain of the acetanilides seems to have no noticeable influence on the ³⁵Cl-NQR frequencies of the chlorine atoms at the benzene ring. The NQR frequencies of the chlorine atoms in the chloroacetamido group are, on the other hand, insensitive to substitutions at the benzene nucleus. The possibility of steric influences on the NQR spectrum of ortho-chloro-substituted acetanilides is discussed. The investigation further confirms that a crystal field effect of about ±500 kHz must be considered in the interpretation of NQR spectra of chlorobenzene derivatives.     

35Cl NQR spectra, structure, and mutual influence of substituents in the series of chlorine-containing organic compounds of pentavalent phosphorus

Regularities of transmission of the effect of equatorial and axial substituents were established for a number of chlorine-containing organic compounds of pentatalent phosphorus using³⁵Cl NQR spectra. The field constants of³⁵Cl NQR frequencies of the chlorine atoms participating in the P−Cl bond were estimated for a series of tetrahedral phosphorus ions. The³⁵Cl NQR frequencies of chlorine atoms in tetracoordinated ions of pentavalent phosphorus and in analogous isoelectronic silicon compounds are related by a linear dependence. Deceased Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 915–922, May, 1999.     

35Cl NQR spectra of organyltrichlorogermanes containing theCl_3 Ge - \mathop C\limits_|^| - \mathop N\limits_| - C(O)X fragment

³⁵C1 NQR spectra of compounds containing the fragment C1₃Ge-C-N-C(O)X, which were acquired at 77 K, indicate that in most of the investigated compounds the germanium atom is pentacoordinated owing to the intramolecular interaction Ge ← 0. The³⁵C1 NQR frequencies in these compounds satisfactorily correlate with the bond length of the corresponding Ge-C1 bond. The relationship between the length of the axial Ge-C1 bond and the Ge...O spacing is described by an exponential function. The charge on the chlorine atoms in the investigated models was estimated from the experimental NQR frequencies.     

ab initio calculations of complexes of group IVA tetrachlorides: I. Dynamics of complex formation of SiCl4 with pyridine

Quantum-chemical calculations of a trans-octahedral complex of SiCl₄ with pyridine involving complete optimization of its geometry and variation of the coordinate of the complex-formation reaction were fulfilled by the RHF/6-31G(d) method. The calculated electron distributions of chlorine atoms in the complex were confirmed by experimental ³⁵Cl NQR data. As the components of the system SiCl₄←2NC₅H₅ come closer together, the electron density on N atoms increases and on the Si atom decreases as a result of polarization of these components. On further mutual approach of the components, the electron density is transferred from the ligand to chlorine atoms (mainly on their p orbitals).     

Assessment of substituent effects on the parameters of 35Cl nuclear quadrupole resonance in para‐substituted benzene‐sulphenyl chloride via quantum chemical calculations

In this research, substituent effects on the parameters of ³⁵Cl nuclear quadrupole resonance (NQR) in para‐substituted benzene‐sulphenyl chloride were studied at M062X/6‐311G(d,p) theory level. The ³⁵Cl NQR parameters of the quadrupole coupling constant (QCC) and electric‐field gradient (EFG) tensor, as well as an asymmetric parameter, were shown to be correlated with Hammett constant following their calculations. The frontier orbital energy levels, HOMO‐LUMO gaps, hardness, electrophilicity, and chemical potential values of these molecules were calculated as well. natural bond orbital (NBO) analysis was applied for calculating natural populations at chlorine atoms.     

Quantum-chemical study of chlorophosphoranes: I. Structure of the (C<Subscript>6</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>PCl<Subscript>3</Subscript> molecule in gaseous and crystalline states

The quantum-chemical calculations of the (C₆H₅)₂PCl₃ molecule were performed by the methods RHF/6-31G(d) and MP2/6-31G(d) with complete and partial optimization of its geometry. The results of calculations were used for evaluating the NQR frequencies of ³⁵Cl and the parameters of asymmetry of the of electric field gradient on the ³⁵Cl nuclei of this molecule. According to the results of calculations with the partial optimization of geometry and to the experimental data of ³⁵Cl NQR the bond lengths were found of central atom P in the solid state of this compound. The mutual influence of its axial and equatorial bonds was studied. It is shown that in chlorophosphoranes the ³⁵Cl NQR frequencies of the axial and equatorial chlorine atoms decrease with the decrease in the bond lengths of phosphorus atom.     

Quantum-chemical study of chlorophosphoranes: II. Structure of molecules of (Cl2)aP(ClnX3?n)e series, and mutual influence of axial and equatorial substituents

The quantum-chemical calculations of the (C₆H₅)₂PCl₃ molecule were performed by the methods RHF/6-31G(d) and MP2/6-31G(d) with complete and partial optimization of its geometry. The results of calculations were used for evaluating the NQR frequencies of ³⁵Cl and the parameters of asymmetry of the of electric field gradient on the ³⁵Cl nuclei of this molecule. According to the results of calculations with the partial optimization of geometry and to the experimental data of ³⁵Cl NQR the bond lengths were found of central atom P in the solid state of this compound. The mutual influence of its axial and equatorial bonds was studied. It is shown that in chlorophosphoranes the ³⁵Cl NQR frequencies of the axial and equatorial chlorine atoms decrease with the decrease in the bond lengths of phosphorus atom.     

The effects of fluorine substitution on the 35Cl NQR spectra of fluoroaromatic compounds containing element-chlorine bonds

The ³⁵Cl NQR spectra of pentafluorosubstituted derivatives of benzene C₆F₅X (X = NPCl₃, CONPCl₃, SO₂NPCl₃, NCCl₂, SCl, COCl, SO₂NCl₂, CONCl₂, PCl₂, SO₂Cl) and phosphazocompounds (dimers, [RNPCl₃]₂; R = C₆F₅, C₆H₅, 2,3,5,6-tetrafluoropyridyl) have been recorded and interpreted. On passing from phenyl to pentafluorophenyl derivatives, the ³⁵Cl NQR frequencies increased. The influence of the relative numbers and positions of the fluorine atoms in the benzene ring on the ³⁵Cl NQR frequencies of fluoro-containing benzoyl chlorides has been discussed. The results are explained in terms of charge alteration on chlorine under the influence of the aromatic fluorine atoms. A linear correlation has been found between ³⁵Cl NQR frequencies of pentafluorophenyl derivatives and those of their hydrocarbon analogues. A relationship between elecronegativity of the element and the ionic character of the element-chlorine bond has been revealed. The reactivities of pentafluorophenyl and phenyl derivatives containing element-chlorine bonds have been predicted using the ν_Cl values.     

Mutual influence of axial and equatorial P-Cl bonds in the molecular forms of pentachlorophosphorane,their lengths in gaseous and crystalline states

The quantum-chemical calculations by RHF/6-31G(d), MR2/6-31G(d) and MP2/6-31+G(d) methods of molecular forms of pentachlorophosphorane with the complete geometry optimization at the different lengths of P-Cl bonds are performed. The results of the calculations are used for estimation of respective ³⁵Cl NQR frequencies. The lengths of axial (2.05 Å) and equatorial (2.01 Å) P-Cl bonds are found, when the calculated NQR frequencies of Cl atoms practically coincide with the obtained experimentally at 77 K. These bonds are a little shorter than in the gaseous state of the matter. In contrast to the ratio of the lengths of the experimental P-Cl bonds and NQR frequencies of respective Cl atoms, at the use of increased lengths of these bonds in the quantum-chemical calculations of the molecule, the ³⁵Cl NQR frequencies of Cl atoms calculated from the results of these calculations, increase. Therewith, the change in the length of the equatorial P-Cl bonds with unchanged length of axial bonds leads to a significantly greater change in the NQR frequencies of axial chloroine atoms than of the equatorial, and vice versa.     

Molecular structure and electronic effects of chlorophosphorane from mndo calculations and35Cl NQR data

The molecular geometries of eleven compounds of pentacoordinated phosphorus are optimized and charges on the central phosphorus atom and on the ligands are calculated by the semiempirical MNDO method. In cases of chlorine atoms as ligands, correlations between the chlorine-35 NQR frequencies and charges on the chlorine atoms of P-Cl bonds, on the one hand, and these bond lengths, on the other, are established. Parameters of the corresponding correlation equations are obtained and discussed. The efficiency of this calculation procedure and NQR method for analyzing the geometrical structure and electron distributions in chlorophosphorane molecules is shown. Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 6, pp. 1074–1082, November–December, 1997.     

35Cl, 93Nb, 181Ta,and 121Sb NQR in Cl5MV · OPCl3 (MV = Nb,Ta, Sb,or P) Complexes

The behavior of ³⁵Cl NQR spectra in Cl₅M · OPCl₃ complexes is affected by the nature of the metal center and the distortion of its surrounding geometry. In all cases considered, the ³⁵Cl NQR frequencies in the OPCl₃ fragment shift toward higher frequencies upon complex formation, whereas the frequencies of axial chlorine atoms in the Cl₅M group in the phosphorus and antimony complexes lie below those for the equatorial atoms, and in the niobium and tantalum complexes, the frequencies of the axial atoms are higher than those of the equatorial ones.     

A Study of Transition‐Metal Organometallic Complexes Combining 35Cl Solid‐State NMR Spectroscopy and 35Cl NQR Spectroscopy and First‐Principles DFT Calculations

A series of transition‐metal organometallic complexes with commonly occurring metal? chlorine bonding motifs were characterized using ³⁵Cl solid‐state NMR (SSNMR) spectroscopy, ³⁵Cl nuclear quadrupole resonance (NQR) spectroscopy, and first‐principles density functional theory (DFT) calculations of NMR interaction tensors. Static ³⁵Cl ultra‐wideline NMR spectra were acquired in a piecewise manner at standard (9.4 T) and high (21.1 T) magnetic field strengths using the WURST‐QCPMG pulse sequence. The ³⁵Cl electric field gradient (EFG) and chemical shielding (CS) tensor parameters were readily extracted from analytical simulations of the spectra; in particular, the quadrupolar parameters are shown to be very sensitive to structural differences, and can easily differentiate between chlorine atoms in bridging and terminal bonding environments. ³⁵Cl NQR spectra were acquired for many of the complexes, which aided in resolving structurally similar, yet crystallographically distinct and magnetically inequivalent chlorine sites, and with the interpretation and assignment of ³⁵Cl SSNMR spectra. ³⁵Cl EFG tensors obtained from first‐principles DFT calculations are consistently in good agreement with experiment, highlighting the importance of using a combined approach of theoretical and experimental methods for structural characterization. Finally, a preliminary example of a ³⁵Cl SSNMR spectrum of a transition‐metal species (TiCl₄) diluted and supported on non‐porous silica is presented. The combination of ³⁵Cl SSNMR and ³⁵Cl NQR spectroscopy and DFT calculations is shown to be a promising and simple methodology for the characterization of all manner of chlorine‐containing transition‐metal complexes, in pure, impure bulk and supported forms.     

35Cl NQR spectra of osmium and iridium chlorochalcogen complexes

Conclusions A study was carried out on the NQR spectra of the chlorine atoms in Os(IV) and Ir(III) complexes with sulfur, selenium, and tellurium chlorides as ligands. The ECl₃ group coordinates as the ligand in the osmium compounds studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1409–1411, June, 1986.     

Structure of the 3-ClC<Subscript>6</Subscript>H<Subscript>4</Subscript>COCl · SnCl<Subscript>4</Subscript> complex according to <Superscript>35</Superscript>Сl NQR data and ab initio calculations

Calculations of two structures of the 3-ClC₆H₄COCl · SnCl₄ complex have been performed by the MP2/LANL2DZ method, and computational results have been compared with the experimental ³⁵Сl NQR data. It has been found that, in contrast to earlier assumptions, the complex has a common arrangement of chlorine atoms and the ligand in a strongly distorted trigonal-bipyramidal coordination sphere of the tin atom. Untypical experimental ³⁵Сl NQR data for this complex are caused by specific features of its crystal structure.     

Electronic and Steric Structure of ClAsX<Subscript>2</Subscript> Molecules: Evaluation by <Superscript>35</Superscript>Cl NQR and Quantum-Chemical Calculations

Molecules of the series ClAsX₂ [X = C₂H₅, N(CH₃)₂, OCH₃] were studied by RHF/6-31G(d) and MP2/6-31G(d) calculations. Their ³⁵Cl NQR frequencies were calculated from the populations of the 3p constituents of the chlorine valence p orbitals. The features of interaction of the geminal atoms in the molecules and the effect of this interaction on the electron distribution in them were analyzed.     

Features of the molecular structure of compounds of (Cl3PNAr)2 series (Ar = C6H4Z, Z = H, Cl) by quantum-chemical calculations and the data of 35Cl nuclear quadrupole resonance

A series of dimeric molecules (Cl₃PNAr)₂ where Ar = C₆H₄Z, Z = H or Cl in 2–4 positions, was calculated by the RHF/6-31G* method with the full geometry optimization. A specific nature of the intramolecular steric orientation of aryl groups was revealed, therewith in the case Ar = C₆H₄Cl-2 short nonvalent contacts were founf between the ortho-chlorine atom and PCl₃ group manifested in the peculiarity of geometric parameters and NQR spectroscopy data of this compound. The correlation of the ³⁵Cl NQR frequencies of P-Cl bonds with the values of the charges on the chlorine atoms obtained by quantum-chemical calculations of the molecules was analyzed.     

Electronic and Spatial Structure of Piperidine and Its Substituted Derivatives from the Results of ab initio Calculations

The results of non empirical quantum-chemical calculations using the RHF/6-31G(d) and MP2/6-31G(d) methods do not agree with proposals for the axial position of the H atom on the N atom in the piperidine molecule. According to RHF/6-31G(d) calculations for the N-methylpiperidine molecule and its chloro-substituted derivatives an equatorially placed methyl group is energetically more favored than an axial. The axial C-Cl and C-H bonds in these molecules are longer than the equatorial. The ³⁵ Cl NQR frequencies for the axial Cl atoms are lower than the equatorial. The ³⁵ Cl NQR frequency of the axial chlorine atom in 2-chloro-1-methylpiperidine is anomalously low. This is chiefly due to the high population density of its p σ-orbital and this is a result of the polarization of the C-Cl bond via the N atom unshared electron pair directly through the field. The effect of a similar unshared electron pair on the parameters of the C-Cl bond in the ClCH₂NH₂ molecule has been studied by the RHF/6-31(g) method for different angles of rotation of the ClCH₂ group around the C-N bond. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1044–1052, July, 2005.     

Special Features of the Geometry of the 2,2,2,4,4,4-Hexachloro-1,3-dimethyl-1,3-diaza-2,4-diphosphetane Molecule and Its Electron Distribution According to Data of ab initio Calculations

The results of a nonempirical calculation of the 2,2,2,4,4,4-hexachloro-1,3-dimethyl-1,3-diaza-2,4-diphosphetane (Cl₃PNCH₃)₂ molecule by the RHF 6-31G(d) method are in agreement with the data of X-ray structural analysis of this compound. Calculated ³⁵Cl NQR frequencies for axial and equatorial chlorine atoms are close to the experimental values. The population of the orbitals of the lone electron pairs and the p orbitals of the equatorial Cl atoms were significantly lower than those of the axial atoms. Among the MO there was no MO corresponding to a three-center bond involving a P atom and axial Cl and N atoms.     

Ligand effect on chlorine electron density distribution in titanium tetrachloride complexes

C1 Kα line shifts and ³⁵Cl NQR frequencies have been measured for series of titanium tetrachloride complexes. Nonempirical calculations of corresponding free ligands have been carried out on the MP2/6‐31G* level. Dependencies of the experimental data obtained on experimental and calculated parameters of ligand donor ability have been analyzed. It is shown that the electron density on acceptor chlorine atoms and the electric field gradient on their nuclei are determined at first by the polarizing effect of the ligand. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:177–181, 2000     

<Superscript>35</Superscript>Cl NQR for the SbCl<Subscript>3</Subscript> complex with aniline,SbCl<Subscript>3</Subscript>·NH<Subscript>2</Subscript>C<Subscript>6</Subscript>H<Subscript>5</Subscript>

The temperature dependence of the ³⁵Cl NQR frequencies and spin-lattice relaxation times has been investigated for a trigonal-bipyramidal vn complex SbCl₃·NH₂C₆H₅. Thermally activated motion of chlorine atoms (pseudorotation) was not revealed in the complex, in contrast to the vπ complexes of SbCl₃ with related molecular structures. The high potential barrier of pseudorotation in the aniline complex is likely to be due to the unusually high nonequivalence of Sb-Cl chemical bonds.