35Cl NQR Spectra Research Articles

Noncovalent interactions in perchlorinated sulfonium and ammonium derivatives of closo-decaborate anion: 35Cl NQR and crystal structure

Three salts of perchlorinated sulfonium and ammonium derivatives of tetrabuthylammonium nonachloro-closo-decaborate, (n-Bu4N)2[2-B10Cl9-cyclo-S(CH2)4S-B10Cl9] (1), (n-Bu4N)[2-B10Cl9-cyclo-S(C2H4)2O] (2) and (n-Bu4N)[1-B10Cl9N(n-Pr3)] (3) are synthesized and characterized using IR, 11B, 1H, 13C NMR, X-Ray and 35Cl NQR-spectroscopy. The noncovalent interactions involving chlorine atoms were identified by 35Cl NQR spectra. The results were discussed in comparison with those of X-ray diffraction analysis which are based on measuring contacts shorter than the sum of van der Waals (vdW) radii of atoms. It has been found that the crystal lattice of 2 exhibits dynamic properties strongly different from those of 1 and 3. Whereas the 35Cl NQR spectra of the latters were extremely wide (up to 1200 kHz), the spectrum of 2 demonstrated a narrowing of almost an order of magnitude (up to 120 kHz) which indicated a significant weakening of the tendency for the formation of intermolecular bonds by chlorine atoms of this cluster.

Noncovalent Interactions in Compounds Based on Perchlorinated Boron Cluster as Monitored by 35Cl NQR (Review)

The article surveys the first 35Cl NQR results on detecting and characterizing noncovalent interactions in systems assembling [B10Cl10]2− clusters via halogen atoms. A number of compounds of decachloro-closo-decaborates with alkali metal or organic cations as well as with silver(I), copper(II) and iron(II) complexes were studied using 35Cl NQR and X-ray diffraction. The main interest of this survey is a capability of chlorine atoms to participate in noncovalent interactions with organic cations, ligand and solvent molecules without touching upon issues of synthesis. Whereas X-ray diffraction establishes the noncovalent interactions relying on the sum of vdW radii which serves as the basic and sometimes the only experimental criterion for identifying such interactions, the 35Cl NQR technique registers subtle perturbations in electron density distribution on the chlorine site caused by secondary interactions Cl···X. They adequately split the 35Cl NQR spectra thus selecting from the entire set of interatomic contacts those actually induced by noncovalent interactions.

Secondary interactions as defined by 35Cl NQR spectra in cesium decachloro-closo-decaborates prepared in non-aqueous solutions

Two solvates of cesium decachloro-closo-decaborate, Cs2[B10Cl10]·2CH3CN and Cs2[B10Cl10]·4DMF, are synthesized and characterized by IR-, 11B NMR, and 35Cl NQR-spectroscopies as well as X-ray diffraction and powder diffraction analyses. The weak secondary interactions involving chlorine atoms were selected by the 35Cl NQR spectra of the full set of interatomic contacts characterized by X-ray diffraction. It has been found that the chlorine atoms form numerous secondary interactions with solvate molecules (B−Cl…H and B−Cl…C interactions with methyl groups and p…π with CN groups), whereas no noticeable perturbation of the chlorine electron density distribution, which could result in the splitting of the 35Cl NQR spectra, has been found due to the cesium cations or Cl…Cl interactions.

Secondary interactions in decachloro-closo-decaborates of alkali metals M2[B10Cl10] (M = K+ and Cs+): 35Cl NQR and X-ray studies

New salts containing bulky decachloro-closo-decaborate dianion of composition M2[B10Cl10] (M=K+ and Cs+) were synthesized and characterized using the IR, 11B NMR and 35Cl NQR spectroscopies, powder and single crystal X-ray diffractions. The potassium salt was obtained as solvate K2[B10Cl10]·3H2O, and cesium salt – as solvates Cs2[B10Cl10]·H2O and Cs2[B10Cl10]·2H2O. Using 35Cl NQR, the interatomic contacts, caused by secondary interactions, were selected of all the totality of interatomic contacts, measured by X-ray diffraction. The B–Cl…H secondary bonds were identified in all the compounds, whereas no contributions to the electric field gradient on the appropriate chlorine atoms were registered from cations M (M=K or Cs). The high coordination numbers of alkali ions screened the effective positive charge on them leading to insignificant perturbation of the chlorine electron density distribution which resulted in negligibly small splitting of the 35Cl NQR spectra due to the alkali cations.

Secondary interactions in decachloro-closo-decaborates R2[B10Cl10] (R = Et3NH+, Ph4P+, and [Ag(NH3)2]+): 35Cl NQR, PW-DFT, and X-ray studies

Three new salts R2[B10Cl10] (R=Et3NH+, Ph4P+, [Ag(NH3)2]+, 1–3) containing bulky decachloro-closo-decaborate dianion have been synthesized and characterized using the IR, 11B NMR, and 35Cl NQR spectroscopy. Neither IR nor 11B NMR spectra have shown distinctions between compounds 1–3, whereas 35Cl NQR spectra of all the compounds have been split evidencing for crystallographic non-equivalence of chlorine atoms caused by secondary interactions. Crystal structures of 2 and 3 have been studied using X-ray diffraction and periodic DFT calculations, whereas unit cell parameters and space group of 1 have been estimated using powder X-ray diffraction. The 35Cl NQR data supported by analysis of calculated electron density functions within the framework of Bader’s Quantum Theory of Atoms in Molecules (QTAIM) showed that both cation and solvent molecules take part in N–H…Cl and C–H…Cl bonding as strong as 2.5 and 2.1kcal/mol, respectively. The QTAIM study has revealed in 2 a number of p…π interactions between lone pairs of chlorine atoms and delocalized electron density of phenyl rings or CN groups of acetonitrile molecules, and the strongest of them (0.9kcal/mol) has been reflected in the 35Cl NQR spectrum. The results have shown that the halogen-substituted boron clusters can act as tags sensitive to H…Hal and p…π bonding, which can be identified by the NQR spectra even in the absence of structural data.

35Cl NQR spectra of certain chlorine-containing chromium compounds

The coordination of chlorobenzene to Cr(CO)3 and ClC6H5Cr+ fragments is shown to result in a considerable rise in the NQR frequency of chlorine atoms. The field constant in (chlorobenzene)chromium tricarbonyl was found to grow markedly, relative to pure chlorobenzene.

Stereoelectronic structure of 1-methyl-3-(trichlorogermyl)propionic acid as found by Ab initio calculations

Calculations of three structures of the 1-methyl-3-(trichlorogermyl)propionic acid molecule and its dimers were performed at the RHF/6-31G(d) level with the full geometry optimization. According to the calculations, in this molecule in a gaseous state the Ge atom is most likely pentacoordinated due to the Ge←O coordination interaction. The dimerization does not diminish, but slightly increases the strength of Ge←O coordination bond. At the formation of the Ge←O bond the electron density on the oxygen atom increases and on the Ge atom decreases. The comparison of the results of calculations with X-ray diffraction data and with the 35Cl NQR spectrum shows that stereoelectronic structure of this compound in the crystalline and gaseous states are quite different.

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.

NQR study of neutral–ionic phase transition and quantum paraelectric state in organic charge-transfer complexes

NQR measurements were performed for the charge-transfer complexes DMTTF–QBr n Cl n −4 under ambient and hydrostatic pressures in order to understand the neutral–ionic phase transition and the quantum critical behavior. The 35Cl NQR spectrum of DMTTF–QCl 4 showed a splitting and a shift below T c, indicating the occurrence of dimerization and charge transfer. The spin-lattice relaxation rate 1/ T 1 showed a peak anomaly around T c, reflecting the critical slowing down. The quantum paraelectric states in DMTTF–2,6-QBr 2Cl 2 and pressured DMTTF–QBr 4 were studied by the 79Br NQR. We found the microscopic evidence for the evolution of the critical fluctuations at low temperatures in the temperature dependence of spin-lattice relaxation rate.

Silver dichloroacetate: A compound with weak Ag–Cl bonding interactions and an extraordinary range of 35Cl NQR frequencies

Silver complexes of halocarbons and silver salts of halogenated organic acids (for example, silver chloroacetate) often show secondary Ag⋯X bonding interactions and unusually low 35Cl NQR frequencies, due to secondary bonding of chlorines to silver atoms. The crystal structure of silver dichloroacetate has been determined at 100 K and shows six crystallographically-inequivalent chlorines. The structure is built from Ag 2(OOCCHCl 2) 2 dimers, similar to those found in silver chloroacetate; in both compounds the dimers are linked by additional Ag–O and Ag–Cl bonds. In the structure of silver dichloroacetate, two distinct conformations of the dichloromethyl groups are present. Two chlorines have no silver neighbors closer than 3.50 Å; two bridge to one Ag atom each, at Ag⋯Cl secondary bond distances of 2.8203(4) and 3.0196(4) Å, and two are apical, coordinating to at least two Ag neighbors each, at longer bond distances of 3.1401 (3)–3.3704(4) Å. Such very long distances are nevertheless shorter than the sum of the van der Waals radii of silver and chlorine, ca. 3.45 Å. The 35Cl NQR spectrum of silver dichloroacetate at 77 K shows six signals scattered over the broad range from 35.600 to 38.498 MHz. Their EFG asymmetry parameters η were measured by the Fourier analysis of the slow beats in the spin echo envelope of the NQR signal of polycrystalline samples. The two highest-frequency chlorines have relatively low η values, 0.075 and 0.106, as befits Cl atoms not coordinated to Ag, and are placed by their conformations far from the carboxylate plane. The two middle-frequency chlorines have higher η values, 0.167 and 0.168, as expected for bridging Cl atoms. The two low-frequency chlorines have lower η values of 0.114 and 0.129, as expected for apical Cl atoms. For purposes of comparison, η values for Ag 2(OOCCH 2Cl) 2, Na(OOCCH 2Cl), and Ca(OOCCH 2Cl) 2 · H 2O were also recorded. So far, we have not observed any significant effect on the 35Cl NQR parameters of halogenated organic anions coordinated to hard-acid metal ions (K +, Rb +, Ca 2+). The effects of the different conformations of the Cl 2CH groups on the broad NQR frequency range are also discussed.

Effect of Substitution on the Molecular Geometry of N-(2/3/4-Substituted-phenyl)-2,2-dichloro-acetamides, 2/3/4-XC6H4NH-CO-CHCl2 (X = CH3 or Cl)

2MPDCA The effect of ring substitution on the molecular geometry of amides of the type 2/3/4-XC6H4NHCO- CHCl2 (X = CH3 or Cl) has been studied by determining the crystal structures of the compounds N-(2-methylphenyl)-2,2-dichloro-acetamide, 2-CH3C6H4NH-CO-CHCl2 (); N-(3-methylphenyl)- 2,2-dichloro-acetamide, 3-CH3C6H4NH-CO-CHCl2 (3MPDCA) and N-(3-chlorophenyl)- 2,2-dichloro-acetamide, 3-ClC6H4NH-CO-CHCl2 (3CPDCA). The results are analyzed along with our earlier crystal structures of the amides N-(phenyl)-2,2-dichloro-acetamide, C6H5NH-COCHCl2 (PDCA); N-chloro-N-(phenyl)-2,2-dichloro-acetamide, C6H5NCl-CO-CHCl2 (NCPDCA); N-(4-methylphenyl)-2,2-dichloro-acetamide, 4-CH3C6H4NH-CO-CHCl2 (4MPDCA); N-(2-chlorophenyl)- 2,2-dichloro-acetamide, 2-ClC6H4NH-CO-CHCl2 (2CPDCA); N-(4-chlorophenyl)-2,2-dichloro- acetamide, 4-ClC6H4NH-CO-CHCl2 (4CPDCA). The results have also been compared and correlated with the crystal structure data of trichloro-acetamide analogues of the type 2/3/4- XC6H4NH-CO-CCl3 (X = CH3 or Cl): N-(phenyl)-2,2,2-trichloro-acetamide, N-(2-methylphenyl)- 2,2,2-trichloro-acetamide, N-(3-methylphenyl)-2,2,2-trichloro-acetamide, N-(4-methylphenyl)- 2,2,2-trichloro-acetamide, N-(2-chlorophenyl)-2,2,2-trichloro-acetamide, N-(3-chlorophenyl)-2,2,2- trichloro-acetamide, N-(4-chlorophenyl)-2,2,2-trichloro-acetamide, N-chloro-N-(phenyl)-2,2,2-trichloro- acetamide and N-(phenyl)-acetamide. The crystal system, space group, formula units and lattice constants in Å of the new structures are: 2MPDCA: monoclinic, P21/n, Z = 4, a = 4.7059(5), b = 11.600(1), c = 18.918(2), β = 94.702(9)° ; 3MPDCA: orthorhombic, P212121, Z = 4, a = 4.759(1), b = 10.543(3), c = 20.205(5); 3CPDCA: orthorhombic, Pnma, Z = 4, a = 9.935(1), b = 6.997(1), c = 14.140(2). 2MPDCA, 3MPDCA and 3CPDCA show a molecule each in their asymmetric units, in agreement with the observed 35Cl NQR spectra of the compounds

Critical Dynamics in BCPS at the N-IC Phase Transition

New experimental NMR data show that the unusual behavior, observed recently in the 35Cl NQR spectra, does not occur in 35Cl NMR measurements on BCPS. The results of the analysis of the 35Cl NMR line shape and the critical dynamics fit well with the predictions of the standard theory for IC systems.

Critical Dynamics in BCPS at the N-IC Phase Transition*

New experimental NMR data show that the unusual behavior, observed recently in the 35 Cl NQR spectra, does not occur in 35 Cl NMR measurements on BCPS. The results of the analysis of the 35 Cl NMR line shape and the critical dynamics fit well with the predictions of the standard theory for IC systems. *Paper originally presented at 10th European Meeting on Ferroelectricity, Cambridge, U.K., August 3–10 2003.

35Cl NQR Spectra of Arylsulphonamides, N-Chloro and N,N-Dichloro Arylsulphonamides

The effect of substitution in the phenyl ring on the γ (35Cl NQR) of N-Cl bonds of the N-chloroand N,N-dichloro-arylsulphonamides has been studied and correlated. The correlation of 35Cl NQR spectra of both the N-chloro and N,N-dichloro-arylsulphonamides is exceedingly good, although there was no systematic variation in the frequencies with substituents in the phenyl ring. The effect of substitution on the C-35Cl NQR of the phenyl ring has also been correlated. The deviation here is also not systematic due to the fact that the chemically equivalent chlorine atoms may exhibit different NQR frequencies due to crystal field effect. Finally, γ (C - 35Cl NQR) of all the 4-chloro-1-substitutedbenzenes have been correlated through the line diagram.

35Cl NQR spectra of phosphorus chlorides and their molecular conformations in crystals. Part 2. Steric effects in ArPCl2 and RPCl2 molecules

The MNDO, HF and MP2 calculations showed that in the molecules of both types, RPCl2(R=CH3,ClCH2,CF3,CC13) and ArPCl2 increasing of steric interactions between R and Ar radicals and chlorine atoms of the PCl2 group leads to enhancement of s-character of LP2 orbital of the chlorine atoms. In the series RPCl2, in contradistinction to the series ArPCl2, increasing of steric interactions leads to decreasing of percentage of s-character of LP3 hybrid orbital of the chlorine atoms and increasing of LP3 donor–acceptor interactions with antibonding orbital of the P–C bond. The difference in coefficients of linear dependencies between 35Cl NQR frequencies of the chlorine atoms of PCl2 group and atomic charges on these atoms in the series RPCl2 and ArPCl2 are explained by the above mentioned distinctions. 35Cl NQR spectrum at 77K of CCl3PCl2 have been obtained: ν(C–Cl)=38.853(2),39.469(1)MHz, ν(P–Cl)=27.306MHz.

Structural Studies on Substituted N-(phenyl)-2,2-DichIoroacetamides, 2/4-XC6H4 NHCO CHCI2 (X = H, Cl or CH3)

Abstract The effect of substitution in the phenyl ring on the crystal systems of amides of the type, 2/4-XC6H4-NHCO-CHCl2 (X = H, Cl or CH3), has been studied by determining the crystal structures of the compounds, iV-(phenyl)-2,2-dichloroacetamide, C6H5-NHCO-CHCl2 (PhDCA); N-(2-chlorophenyl)-2,2-dichloroacetamide, 2-ClC6H4-NHCO-CHCl2 (o-ClPhDCA), jY-(4-chlorophenyl)-2,2-dichloroacetamide, 4-ClC6H4-NHCO-CHCl2 (p-ClPhDCA) and N -(4-methylphenyl)-2,2-dichloroacetamide, 4-CH3C6H4-NHCO-CHCl2 (p-CH3PhDCA) and analysed the data along with our earlier crystal structures of the compounds, N-(phenyl)-2,2,2-trichloro-acetamide (PhTCA), N-(2-chlorophenyl)-2,2,2-trichloroacetamide (o-ClPhTCA), N -(4-chloro-phenyl)-2,2,2-trichloroacetamide (p-ClPhTCA), N-(4-methylphenyl)-2,2,2-trichloroacetamide (p-CH3PhTCA); N-chloro-N-(phenyl)-2,2-dichloroacetamide (NClPhDCA), N-chloro-N-(phenyl)-2,2,2-trichloroacetamide (NClPhTCA) and N-(phenyl) acetamide (PhA). The crystal type, space group, formula units and lattice constants in A of the new structures are; PhDCA: monoclinic, P 21/c, Z = 4, a = 8.785(3), b = 11.139(4), c = 9.521(3), ß = 97.47(2)°; o-CIPhDCA: monoclinic, P 21/c, Z = 4, a = 4.711(2), b = 11.234(6), c = 19.191(8), ß = 98.12(2)°; p-CIPhDCA: monoclinic, P 21/c, Z = 8, a = 18.627(5), b = 11.533(3), c = 9.583(3), ß = 102.43(2)°, and /?-CH3PhDCA: orthorhombic, Pbca, Z = 8, a = 9.464(3), b = 9.894(3), c = 21.973(7). The compound p-ClPhDCA shows two molecules in its asymmetric unit. This is in agreement with the multiple lines observed in the 35Cl NQR spectra of the compound. The crystal systems of the chlorosubstituted and methyl substituted chloroacetamides get interchanged on replacement of the side chain -CHCl2 by -CCl3. C(i)-C(j) ring distances show no significant variations with the substitution either at the side chain or in the phenyl ring. C(ring)-N and C (0)-N bond distances are also not much affected by either ring or side chain substitution, but are affected by N-chlorination, while the C -0 bond length is slightly shortened by the replacement of the -CH3 group by -CCl3, the introduction of electron withdrawing group into the phenyl ring or by N-chlorination. Deviations of C2(ring)-Cl(ring)-N, C6(ring)-Cl(ring)-N and C (ring)-N-C(0) bond angles from 120° narrow down on substitution either in the phenyl ring or in the side chain, but the latter increases on W-chlorination of the compounds.

Conformational Isomerism and Chlorotropy Mechanisms of Chloromethyl- and Trichloromethyldichlorophosphines

35Cl NQR spectroscopy and MP2//RHF/6-31++G(d,p) and MNDO-PM3 calculations were used to study the conformational and chlorotropic isomerism of chlorodimethyldichlorophosphine (I) and trichloromethyldichlorophosphine (II). The experimental 35Cl NQR spectrum is in complete accord with the staggered conformation of phosphine II obtained using an RHF/6-31++G(d,p) calculation. The rotational barrier of the CCl3 group is 38.1 kJ/mol. On the other hand, the spectrum of phosphine I is in accord with a gauche conformation, which agrees with experiment only upon taking account of electron correlation (MP2). The ylide and phosphinic chlorotropic isomers for I and II are thermodynamically stable with greater stability found for II. The chlorotropic phosphine–ylide conversion in system I proceeds exclusively through a sigmatropic transition state in qualitative accord with nonempirical and semiempirical calculations. Such a conversion is theoretically possible in system II by means of dissociation of the P+—C− ylide bond.

35Cl NQR Spectra and ab initio Calculations of gem-Substituted 1-Chlorocyclohexane Derivatives

The 35Cl NQR spectra of gem-substiutted 1-chlorocyclohexane derivatives C6H10XCl (X = H, CH3, CH3O, Cl) at 77 K were measured. Ab initio RHF/6-31G(d) calculations of their conformers, and also of conformers of monosubstituted cyclohexanes were performed. Based on the calculation results, the NQR lines were assigned and the conformational energies of the substituents were evaluated. The relative conformational energies of the Cl atom and CH3O group disagree with previous data.

Molecular structure of pentafluorophenyltetrachloro- and bis(pentafluorophenyl)trichlorophosphoranes

The 35Cl NQR spectra and ab initioquantum-chemical calculations show that chlorophosphoranes C6F5PCl4 and (C6F5)2PCl3 have a trigonal bipyramidal structure with the equatorial location of the pentafluorophenyl groups. This conclusion agrees with the rule of location of substituents in the molecule taking into account their electronegativity and refutes the existing concepts concerning the structure of the above mentioned chlorophosphoranes.

35Cl NQR spectra of phosphorus chlorides and their molecular conformations in crystals. Part 1. Phosphorus (III) chlorides RPCl2

For the phosphorus chlorides RPCl2 (R=Cl, Me, ClCH2, CF3, Et, i−Pr, Me2C=CH, PhCH=CH, Me2N, Et2N, Pr2N, MeO, PhO) and R′PCl2 (R′=Ar, 2-thienyl) two linear correlations between the 35Cl NQR frequencies and charges on the chlorine atoms of the PCl2 groups calculated by the MNDO procedure have been found. It was shown that the 35Cl NQR spectra and the relative magnitudes of the charges on the chlorine atoms of the PCl2 groups can be used to determine conformation of the RPCl2 molecules in crystal. Ab initio (RHF/6-31 G∗ and MP2/6-31 G∗) calculations showed that the gauche conformation of Me2NPCl2 molecule is more stable than trans conformation. In light of ab initio calculations electron diffraction results (Vilkov L.V., Khaikin L.S., Dokl. Akad. Nauk SSSR, 168 (1966) 810) are erroneous. The NBO analysis confirmed the presence of donor–acceptor interactions between the lone pair orbital of the nitrogen atom and the antibonding orbitals of the P–Cl bonds.