Axial Chlorine Atoms Research Articles

A semiempirical quantum chemical testing of thermodynamic and molecular properties of arsenic compounds

By the PM3 methods, standard values of entropy, heats and Gibbs energies of formation, first ionization potentials and dipole moments of the molecules have been computed for 65 inorganic and organic arsenic compounds. Linear dependences Pexper=bPtheor (where P is any of the mentioned properties) have been stated, allowing a priori evaluation of thermodynamic and molecular characteristics of As-containing substances. It has been shown that for arsine the PM3 method overestimates gaseous-phase proton affinity not more than by 10%. Triphenylarsinedichloride existence in benzene solution in the form of trigonal bipyramid with two axial chlorine atoms has been concluded.

First paddlewheel complex with a doubly-bonded Ir26+ core

Reaction of IrCl3 with Hhpp in refluxing ethanol (Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyrimidine) yields Ir2(hpp)4Cl2, the first paddlewheel complex of IrIII, with a short Ir–Ir distance of 2.495(1) A, an average Ir–Cl distance of 2.643[6] A, an Ir26+ core bridged by four hpp ligands with two axial chlorine atoms, and a double bond between the Ir atoms.

Dinuclear complexes of first transition series metals with 4,4′-dipyrazolylmethane: characterisation, DNA binding and anticancer properties

New complexes with the bridging ligand 4,4′-dipyrazolymethanne (dpzm) are reported. This ligand gives two types of complex with first transition series viz. [MCl 2dpzm] n (M=Zn, Cu) and [MCl 2dpzm 2] n (M=Mn, Fe, Co, Ni, Cu). X-ray powder diffraction shows the [MCl 2dpzm 2] n series to be isostructural. DNA binding of MCl 2dzpm 2] n (M=Cu, Mn) and of (MCl 2dzpm 2] n (M=Zn) has been studied and the anticancer properties of [MCl 2dpzm 2] n (M=Zn, Cu) and (MCl 2dzpm 2] n (M=Cu, Mn, Fe, Ni) investigated using an in vivo screen against P388 murine leukemia. The structure of CuCl 2dpzm 2·2dmf (dmf = dimethylformide) has been determined from single crystal X-ray consits of linear polymeric chains of CuCl 2dpzm 2 molecules bridged through the N atoms of the ligand. The four equatorial N's give an average CuN distance 2.017(2) Å and the two axial chlorine atoms are at 2.799(1) Ä from the copper atom, giving on overall distored oxtahedral structure. Following loss of the 2dmf of solvation the copper complex is isomorphous with the analogous first transition series complexes and a polymeric structure is considered likely.

Crown ether complexation of scandium(III). Formation and spectroscopic characterisation of ScCl2+–oxacrown species and crystal structures of two scandium dibenzocrowns

The reaction systems ScCl3–SbCl5–MeCN–crown ether(L), where L = 6,7,9,10,17,18,20,21 -octa-hydrodibenzo[b,k][1,4,7,10,13,16] hexaoxacyclooctadecine (dibenzo-18-crown-6), 6,7,9,10,12,13,20,21,23,24,26,27 -dodecahydrodibenzo [b,n][1,4,7,10,13,16,19,22] octaoxacyclotetracosine (dibenzo-24-crown-8) and 6,7,9,10,12,13,15,16,23,24,26,27,29,30,32,33-hexadecahydrodibenzo [b,q][1,4,7,10,13,16,19,22,25,28] decaoxacyclotriacontine (dibenzo-30-crown-10), have been investigated. Halide abstraction generates the ScCl2+ cation in situ which can be stabilised by macrocyclic complexation with the appropriate cyclic ether. The compound [ScCl2(dibenzo-18-crown-6)][SbCl6] was isolated as a white solid and characterised as the hexachloroantimonate (V) salt from microanalytical and spectroscopic (IR, 1H and 13C NMR) data. Entrapment of a trans-ScCl2 unit within the ring cavity involving five-co-ordination of the ring oxygen atoms is seen as the most likely arrangement. Removal of a further chloride ion from this compound, effected by the addition of SbCl5(three equivalents), provides [ScCl(dibenzo-18-crown-6)(MeCN)][SbCl6]2 as established by microanalytical and spectroscopic data, and similar cavity entrapment of a trans-ScCl(MeCN) unit has been discussed. Solution studies, as monitored by 1H NMR spectroscopy, indicate that complete removal of chloride ion from [ScCl(dibenzo-18-crown-6)(MeCN)][SbCl6]2 can be effected but only with a heavy excess (10 equivalents) of SbCl5. The compound [ScCl2(dibenzo-24-crown-8)(H2O)][SbCl6]·2MeCN 1 was isolated as red crystals and structurally characterised by X-ray diffraction studies. Crystals are monoclinic, space group P21/n, Z= 4 and R 0.0638. The structure consists of [ScCl2(dibenzo-24-crown-8)(H2O)]+ cations and [SbCl6]– anions with two solvent (MeCN) molecules trapped in the lattice. For the cation the ScIII co-ordination geometry is essentially pentagonal bipyramidal involving two axial chlorine atoms [Sc–Cl 2.387(4) and 2.397(4)A, Cl–Sc–Cl 173.8(2)°] and five equatorial oxygen atoms comprising four from the crown ether with Sc–O distances in the range 2.184(7)–2.297(7)(mean 2.25 A) and one from a co-ordinated water molecule [Sc–Owater 2.130(8)A]. The threaded ScCl2+ unit is located within the ring cavity but in an ‘off-centre’ position. Intracavity hydrogen bonding of the type Sc–OH2⋯ Oring is present with Owater⋯ Oring 2.65 and 2.75 A. The compound [ScCl2(dibenzo-30-crown-10)(H2O)2][SbCl6]· MeCN·H2O 2 was isolated as yellow needle crystals and characterised crystallographically as the hexachloroantimonate (V) salt. Crystals are triclinic, space group P, Z= 2 and R= 0.0639. There are two solvent molecules (MeCN and H2O) trapped in the lattice. In the [ScCl2(dibenzo-30-crown-10)(H2O)2]+ cations the ScIII ion is seven-co-ordinate, involving bonds to three oxygens from the crown ether, two chlorine atoms and two water molecules, and shows distorted pentagonal-bipyramidal geometry. The trans-ScCl2 unit [Sc–Cl 2.411 (3) and 2.419(3)A, Cl–Sc–Cl 169.3(2)°] is located in an annexe section of the ring with Sc–Oring bond distances ranging between 2.208(8) and 2.280(8)(mean 2.25 A), Sc–Owater 2.148(9) and 2.160(8)A. Both of the co-ordinated water molecules are involved in a complex pattern of intracavity hydrogen bonding of the type Sc–OH2⋯ Oring with one molecule forming three Owater⋯ Oring close contracts in the range 2.83–2.98 A and the other forming four such contracts in the range 2.75–3.00 A.

Electronic structure of Ag2+ impurities in halide lattices

The composition of electronic levels as well as optical transitions associated with AgCl64- and AgF64- complexes have been studied through MS-X alpha and SCCEH calculations performed as a function of equatorial (Req) and axial (Rax) metal-ligand distances. The scheme and composition of levels for AgCl64- is rather different from that for AgF64- and other more ionic systems. The first transition for KCl:Ag2+ (observed at 12 500 cm-1) is assigned to a jump involving the 5a1g orbital which is mainly built (about 70%) from 3p orbitals of axial chlorine atoms. Aside from explaining reasonably the five optical bands experimentally observed for KCl:Ag2+, the present work indicates that the first allowed charge-transfer transition of AgF64- would lie in the ultraviolet region and confirms that the unpaired electron in AgCl64$spends a little more time on equatorial ligands than on the central ion. All these results are consistent with a high value ( chi =2.8) for the optical electronegativity of Ag2+. The dependence of electronic transitions (and also of unpaired spin densities fsigma and fs) on Req and Rax is found to be rather similar for both AgF64- and AgCl64- complexes. The relation between such a dependence and the band widths of optical transitions is outlined.

π-Cyclizations of α-methoxycarbonyl oxycarbenium ions; synthesis of oxacyclic carboxylic esters

Acid-mediated cyclization reactions are described of seven methyl 2-acetoxy-2-(3-alken-1-oxy)acetates with different chain substitution. The major product of the tin tetrachloride-induced cyclization reaction is in most cases a tetrahydropyran containing an equatorial carbomethoxy function at C2 and an axial chlorine atom at C4. The mechanism of its formation involves a net cis-addition of the intermediate α-ester oxycarbenium ion to the carbon-carbon double bond, most likely caused by a quasi axial orientation of the ester function in a chair-like transition state. The results are interpreted by invoking (1) the occurrence of a 2-oxonia-Cope rearrangement and (2) the participation of the ester function in the mechanism of cyclization by trapping the cyclic cationic intermediate. The cyclizations of two methyl 2-acetoxy-2-(4-alken-1-oxy)acetates and two methyl 2-acetoxy-2-(alkynoxy)acetates are also described.

Organic pesticides modify lipid-lipid and lipid-protein domains in model membranes. A laser Raman study

The effect of hexachlorocyclohexane (all isomers) on the thermal transition properties of phospholipid liposomes was determined by Raman spectroscopy. Raman spectra of liposomes with and without the presence of hexachlorocyclohexanes were recorded in the C-H stretching region which shows three major bands around 2850, 2880 and 2930 cm −1. Thermal transition properties were estimated from plots of I 2880 I 2850 and or I 2930 I 2850 vs. temperature, where I represents the intensity of the respective band. Our data on phospholipid liposomes reveal that δ- and γ-hexachlorocyclohexanes drastically reduce and broaden the main thermal transitions of phospholipids at toxic level concentrations. These effects are more pronounced in liposomes containing 18 or more carbon atom long acyl chains. α- and β-isomers at similar concentrations show a minimum effect on the thermal transition properties of phospholipids. Raman analysis of phospholipid liposomes containing melittin, interestingly, reveal that the δ-isomer unlike the γ-isomer strongly alters the transition properties of boundary lipids. These data suggest that the effect of hexachlorocyclohexanes on the thermal transition properties of membranes is stereo specific and that the δ-isomer preferably disrupts the lipid-protein domains. Results are explained on the basis of the dynamic flexibility owing to the equatorial and axial chlorine atoms of various hexachlorocyclohexane isomers.

The EFG Asymmetry Parameters at 35 Cl Nuclei and the Electronic Effects in Chlorine-Containing Organic and Complex Compounds of Group IVA and VA Elements

Abstract The 35 CL NQR method and, in particular, the EFG asymmetry parameters at 35 Cl nuclei were used for the solution of a number of principal problems of theoretical organic and organometallic chemistry, such as the mechanism of non-induction influence of the heteroatom M on the atom Y in the non-linear Y-Z-M or Y-Z = M group, M-Cl bond multiplicity in planar molecular fragments and the asymmetry of halogen atom electron distribution in organic and organometallic molecules. In tetrahedral molecules this distribution is nearly axially symmetric for different M. This symmetry is also characteristic for axial chlorine atoms in trigonal-bipyramidal and octahedral molecules, independently of M. The deviation of the electron distribution of equatorial chlorine atoms from axial symmetry in the two latter cases depends essentially upon M and does not depend much on the peculiarity of the formation of these polyhedra and the character and number of substituents.

Synthesis and reactions of 1,6-bis(2-butyltellurophenyl)-2,5-diazahexa-1,5-diene and related compounds. The crystal and molecular structures of 2-(butyldichlorotelluro)benzaldehyde and bis[2-(hydroxyiminomethyl)phenyl] ditelluride

The synthesis of 1,6-bis(2-butyltellurophenyl)-2,5-diazahexa-1,5-diene and related compounds is reported. Reaction with halogenating reagents leads to rupture of the Te–Bu bond and the isolation of new organyltellurium mono- and tri-halides stabilised via co-ordination to the imino-nitrogen atom. Reduction of the trihalides with sodium metabisulphite stops at the monohalide stage and no ditelluride is produced. Reduction of the tri- or mono-halides with hydrazine hydrate gives, depending on the molar ratio of reactants, either N-amino or N-hydroxo-compounds and in this case ditellurides are formed. Reduction of the trihalides with NaBH4 affords a poly- or oligo-merit tritelluride stabilised by co-ordination of tellurium with the imino-nitrogen atom. By contrast the reaction of 2-(butyltelluro) benzaldehyde with chlorinating agents gives 2-(butyldichloro-telluro) benzaldehyde in which the Te–Bu linkage survives intact. Spectroscopic data, particularly 13C n.m.r., are presented and briefly discussed. The crystal and molecular structures of bis[2-(hydroxyiminomethyl)phenyl] ditelluride and of 2-(butyldichlorotelluro) benzaldehyde have been determined. The ditelluride has Te–Te 2.746(1)A with C–Te–Te angles of 100.0(2) and 100.3(2)°; Te–N distances of 2.822(5)A and 2.876(5)A indicate a weak interaction. In the benzaldehyde derivative the tellurium is bonded to two carbon atoms and two chlorine atoms; a weak Te ⋯ O interaction [2.839(4)A(mean for two independent molecules)] and a lone pair of electrons complete a distorted pseudo-octahedral co-ordination. The molecule, apart from the two axial chlorine atoms, is essentially planar.

The Crystal and Molecular Structure of Aquachloro (meso-tetraphenylporphyrinato)cobalt(III)

Abstract The crystal and molecular structure of the title compounds, [CoIIICl(tpp)(H2O)], has been determined by means of X-ray diffraction techniques. The compound crystallizes in the monoclinic system; space group P21⁄c. The unit cell has a=13.542(2), b=25.760(2), c=10.423(1) Å, β=99.33(2)°, and Z=4. The cobalt atom is coordinated by four porphyrinato nitrogen atoms, one chlorine atom, and one oxygen atom of water, and is displaced by 0.039(2) Å from the mean plane defined by the four porphyrinato nitrogen atoms towards the axial chlorine atom. The average Co–N(tpp) distance is 1.955(2) Å. The Co–Cl distance is 2.216(1), and the Co–O(water) distance, 1.979(3) Å. The porphyrinato core is significantly ruffled and has an approximate \bar4 symmetry. The [CoIIICl(tpp)(H2O)] molecules are stacked along the c axis by O–H···Cl hydrogen bonds.

Conversion of dimolybdenum tetraacetate to Mo 2Cl 4(Ph 2Ppy) 2 and Mo 2(O 2CCH 3) 2(Ph 2Ppy) 2Cl 2 [Ph 2Ppy = 2-(diphenylphosphino)pyridine

Dimolybdenum tetraacetate reacts with (CH 3) 3SiCl and Ph 2Ppy [2-(diphenylphosphino)pyridine] to give green Mo 2Cl 4(Ph 2Ppy) 2 which was too insoluble to crystallize or characterize. The reaction of Mo 2Cl 4(Ph 2Ppy) 2 with acetic acid has been investigated. Mo 2(O 2CCH 3) 4 and Mo 2(O 2CCH 3) 2(Ph 2Ppy) 2Cl 2 are the products resulting from total and partial ligand substitution reactions. The molecular structure of Mo 2(O 2CCH 3) 2(Ph 2Ppy) 2Cl 2 has been investigated by X-ray crystallography. The crystallographic data are as follows: triclinic space group P 1 , a = 10.789(2), b = 12.414 (3), c = 9.888(2) Å, α = 110.48(2)°, β = 113.86(2)°, γ = 67.36(3)°, V= 1088(1) Å 3 and Z = 1. The molecule has two trans bridging acetate groups, two trans 2-diphenylphosphinopyridine ligands arranged in a head-to-tail fashion, and two axial chlorine atoms. The length of the quadruple bond between the molybdenum atoms is 2.1900(3) Å, which makes it the longest one known.

Coordination compounds of ethylhydrazine and 2,2,2-Trifluoroethylhydrazine; crystal and molecular structure of dichlorotetrakis(2,2,2-Trifluoroethylhydrazine) nickel(II)

Ethylhydrazine (EH) forms the complexes MX 2(EH) 2 (M = Co, Ni; X = Cl; M = Co, X = Br), NiBr 2(EH) 2(H 2O) and MX 2(EH) (M = Zn, Cd; X = Cl; M = Zn, X = Br). Spectroscopic evidence suggests that these all contain bridging hydrazine ligands, the cobalt and nickel complexes containing six coordinated metal atoms while the zinc and cadmium complexes are tetrahedral. 2,2,2-Trifluoroethylhydrazine (TFEH) in contrast, forms six coordinate complexes of the type MX 2(TFEH) 4 (M = Co, Zn, X = Br; M = Co, Ni, X = NCS; M = Ni, X = Cl) for which spectroscopic evidence points to unidentate coordination by the hydrazine. An X-ray crystal structure determination on NiCl 2(TFEH) 4 confirms that the hydrazine bonds to nickel through the NH 2 nitrogen only, in a tetragonal structure with axial chlorine atoms. One bis(TFEH) complex ZnBr 2(TFEH) 2 and one hexakis (TFEH) complex, NiBr 2(TFEH) 6, have also been isolated.

Synthesis, spectroscopic studies (Mössbauer and infrared), and the crystal and molecular structure of the organotin(IV)-pyrazine adducts [Sn(CH 3) 2Cl 2] 2pyz and [Sn(CH 3) 2Br 2pyz

Two adducts [Sn(CH 3) 2Cl 2] 2pyz ( Ia) and Sn- (CH 3) 2Br 2pyz] ( Ib) (pyz = pyrazine) have been synthesized and characterized in the solid state. Infrared and Mössbauer spectroscopies suggest a five- coordinated species for the Ia complex with an angular CSnC bond and a six-coordinated compound with a linear CSnC bond for the Ib complex. X-ray diffraction studies confirm a distorted trigonal bipyramidal geometry with N, Cl axial atoms and Cl and methyls in the equatorial plane for Ia where the Cl axSnN bond angle is the lowest one reported to date and the Cl eqSn bond distance the longest one with regard to similar complexes. This molecule has a short contact of 3.47 Å between the tin and the axial chlorine atoms. The molecular structure of complex Ib points out all equivalent bonds in the trans position arising from a polymeric chain with bridged pyrazine ligand. The complex Ib is centro- symmetric at the tin atom.

(CH3)3CCOOSbCl4: Structure Determination by Zeeman Perturbed NQR

A single crystal of tetrachloro(0,0-pivaloylato)antimony(V) has been studied at 77 K, by Zeeman perturbed 35Cl NQR, using a FT-NQR pulsed spectrometer. The four lines at zero-field, ν1 = 27.6468, ν2 = 27.3070, ν 3 = 25.7341 and ν 4 = 25.3438 MHz yield eight EFG tensors in the magnetic field, related by a twofold symmetry element in the crystal. The corresponding asymmetry parameters are η1, = 0.134, η2 = 0.13, η 3 = 0.07, and η4 = 0.09. The molecular structure deduced from the relative orientations of the principal Z-axes of the EFG tensors confirms that the higher quadrupole coupling constants are associated with the chlorine atoms in equatorial positions, relative to the plane of the organic ligand, as predicted from NQR powder studies. It is concluded that the crystal structure is monoclinic with two (class m or 2) or four (class 2/m) molecules per unit cell. The molecular packing is such that the planes formed by equatorial or axial chlorine atoms are approximately at right angles to their symmetry related images.

Nuclear Quadrupole Resonance Studies of Chelated Antimony Complexes. Part III. The Carboxylates: RCO2SbCl4

The 35Cl, 121Sb and 123Sb resonance frequencies for seventeen tetrachloro(carboxylato)antimony V compounds, RCO2SbCl4, are reported. The results confirm the difference in the effects of the substituent on the equatorial chlorine atoms and the axial chlorine atoms of the SbCl4 group, previously remarked in Parts I and II of this series, and this effect has been put on a more quantitative basis by correlating the observed frequencies with the pK’s of the corresponding acids. The compounds with R = isopropyl and R = cyclopropyl both show a phase change in the region of 140 K which may correspond to reorientation of the substituent about the R - CO2 axis.

NMR study of molecules in anisotropic systems. III—Structure and orientation of 1a,2a,3e,4e,5e,6a‐hexachlorocyclohexane in a nematic liquid crystal determined from low‐temperature experiments

Abstract1H NMR spectra of 1a,2a,3e,4e,5e,6a‐hexachlorocyclohexane (γ‐BHC) have been measured in a nematic solution of ZLI2081 at low temperatures to prevent exchange broadening. The spectra were analysed and direct couplings determined. The six‐membered ring is most favourably oriented parallel to the solvent molecule. The principal axes of the order matrix differ from those of the moment of inertia, and the difference is explained as being due to the steric effect of the three axial chlorine atoms. The molecular structure of γ‐BHC in nematic solution is found to differ from that calculated from the MNDO MO method, but resembles that in the crystal determined by x‐ray spectrometry.

Nuclear quadrupole resonance studies of chelated antimony complexes. Part 2. The crystal structure and the35Cl and121,123Sb resonance frequencies of tetrachloro(acetylacetonato)antimony(V) and related compounds

35 Cl and 121,123Sb nuclear quadrupole resonance (n.q.r.) spectra of tetrachloro (acetylacetonato)antimony(v), (1), and ten related compounds have been observed and measured in the range 77–300 K. The crystal structures of (1) and of tetrachloro(benzoylbenzophenato)antimony (5) are also reported. The n.q.r. spectrum of the latter compound indicates the occurrence of a second-order phase-change in the neighbourhood of 135 K; this is confirmed by thermal analysis. Comparison of the crystal structure and n.q.r. spectrum of (1) indicates that a similar phase-change takes place here below 77 K. The distinction between the 35Cl resonance frequencies of the axial and equatorial chlorine atoms of these compounds, already suggested in Part 1, is confirmed.

Asymmetry parameters of the electric field gradient at the 35Cl nuclei of (3-chloropropyl)trichlorostannane

Asymmetry parameters for the electric field gradient at the 35 Cl nuclei of polycrystalline Cl(CH 2 ) 3 SnCl 3 have been measured at 77 K. They are in agreement with a trigonal-bipyramidal structure for the molecule. The electron distribution of the axial chlorine atom in the SnCl 3 group is almost axially symmetric whereas that of the two equatorial atoms and the chlorine atom in the Cl(CH 2 ) 3 group deviate noticeably from the axial symmetry. The deviation is mainly due to the interaction of the lone electron pair of the corresponding chlorine atom with the central tin atom.

NMR Study of Molecules in Anisotropic Systems. II. 1a,2a,3e,4e,5e,6e- and 1e,2e,3e,4e,5e,6e-Hexachlorocyclohexanes Dissolved in Nematic Liquid Crystals

Abstract NMR spectra of the titled compounds (α- and β-BHC) have been measured in nematic solvents and analyzed. Vibrational corrections were important for the full interpretation of the observed direct couplings. The order parameters showed that the BHC molecules orient most preferably with their six-membered rings parallel to the optic axis of the nematic solvents. Molecular structure of α-BHC derived from the direct couplings corresponds well with those determined by the X-ray method on a crystal and calculated by the MNDO MO method. For β-BHC, however, discrepancies are found with the crystallographic structure, suggesting molecular deformations in the crystal state. Principal axes have been determined for the order matrix and compared with those for the moment of inertia. The difference between the two principal axis systems in α-BHC is interpreted as due to a steric repulsive effect between the two axial chlorine atoms and the solvent molecules.

The chlorine-35 and antimony-121 and -123 nuclear quadrupole resonance spectra of five-membered ring chelate derivatives of antimony pentachloride

The 35Cl and 121,123Sb quadrupole resonance spectra of several five-membered ring chelate derivatives of antimony pentachloride are reported. Four of these are of known structure: the singly chelated derivatives of tropolone, N-methyloxamide, and NN′-dimethyloxadiamide, and the doubly chelated derivative of oxalic acid. The doubly chelated derivative of NN′-dimethyloxadiamide, of unknown crystal structure, has also been measured. The 35Cl resonance frequencies of the axial and equatorial chlorine atoms are quite distinct and, for the tropolone complex, imply a 10% difference between the ionicity of the axial and equatorial groups, and are affected to a different extent by the nature of the chelate group. The large value of the 121Sb asymmetry parameter of the oxalate complex is satisfactorily explained by the observed small angular deformations of the geometry from that of a regular octahedron.