Gérard Jugie

VOCl3: Crystallization, crystal structure, and structural relationships: A joint X-ray and 35Cl-NQR investigation

Abstract Cooling of VOCl 3 below its melting point (196 K) yields an amorphous phase, which transforms into the crystalline state upon further cooling. The crystallization is accompanied by a remarkable change in color from pale yellow to deep orange. A single crystal has been grown from the amorphous phase. VOCl 3 crystallizes in the orthorhombic system, space group Pnma , with lattice parameters a = 4.963(1), b = 9.140(4), c = 11.221(5)A at 133 K; Z = 4. The 35 Cl-NQR experiments show two signals at approximately 11.4 MHz of intensity 2:1, which implies two different crystallographic sites for chlorine atoms, in agreement with the centrosymmetric space group Pnma . The crystal structure exhibits isolated tetrahedral molecules VOCl 3 lying on a mirror plane and stacked with their VO axis along [100] to form trigonal prismatic columns. A close relationship exists with the structure of AsBr 3 , in which the lone pair occupies the position corresponding to the oxygen atoms.

Etude par resonance magnetique nucleaire de la structure de quelques composes d'addition formes par des aminophosphines avec le borine et le monoethylborane

Abstract Four equimolecular adducts between aminophosphines [(CH3)2NP(CH3)2 and [(CH3)2N)3P] and boron hydrides [BH3 and B(C2H5)H2] have been prepared and characterised. From a study of their NMR (1H, 11B and 31P) spectra it is concluded that, in spite of the presence of two different donor atoms, the actual dative bond is a phosphorus-boron one.

Quadrupole resonance studies of hydrogen bonding in alkylammonium halides under high pressure

The temperature and pressure dependence of the 79Br and 127I quadrupole resonance frequencies have been studied in the salts [MeNH3]+Br–, [MeNH3]+I–, [EtNH3]+Br–, and [EtNH3]+I–, and their N-deuterated derivatives. The observed pressure coefficients of the quadrupole coupling constant can be large, as much as 11 kHz (MPa)–1 for 127I resonance in [MeNH3]+I–. The effects of rise in temperature and deuteration are explained mainly in terms of an anisotropic expansion of the hydrogen bonds between the cation and the bromide or iodide ions; pressure appears both to compress the hydrogen bonds and to change their angular configuration at the halide ion.

New NQR and electrochemical observations on a series of quadruply bonded dimolybdenum complexes of arsines

SummaryNew coordination complexes of the type Mo2X4(AsEt3)4 and Mo2(O2CCF3)4(AsR3)2 where X=Cl, Br, NCS and R= Et or Ph, have been prepared. These compounds, identified and characterized by their Raman, infrared, u.v.-visible, and1 H n.m.r. have been studied by75As n.q.r. spectroscopy. In the case of the two fluoroacetate complexes, n.q.r. and other spectroscopic data indicate that the two arsenic ligands are weakly coordinated at the axial position of the Mo24+ unit. Rotating-disk electrode polarography and voltammetry show that Mo2Cl4(AsEt3)4 and Mo2Br4(AsEt3)4 can be oxidized through a reversible transfer of a single electron while interestingly Mo2(NCS)4(AsEt3)4 exhibits a two-step oxidation which leads successively to a paramagnetic cation [Mo2(NCS)4(AsEt3)4]+ and to a diamagnetic one [Mo2(NCS)4(AsEt3)4]2+.

A joint variable temperature 35-Cl nor and x-ray investigation of phase transitions in tetrachloro-o-benzoquinone

Abstract The phase transitions exhibited by tetrachioro-o-benzoquinone have been followed by a joint study of the temperature dependences of the 35-Cl NQR spectra and of the crystal structures. In going from 77 to 330 K three phase changes have been detected and the corresponding transition temperatures determined: T α→β = 213 K, T γ→δ = 210 K, and T δ→α = 303 K. The drastic modifications in NQR line multiplicities which reflects the crystalline state evolution are discussed and mechanisms which lead these transformations (loss of symmetry, rotation of the molecules) are proposed.

Competition between different nucleophilic sites belonging to the same Lewis bases. Part 3. The basicity of arsenic and phosphorus sites relative to borane

After establishing some structural characteristics of a few simple AsR3·BH3 adducts (R = Me, Et, or Ph) by n.m.r. spectroscopy, the reaction of BH3 with a ligand (L) containing both phosphorus and arsenic donor sites (Ph2PCH2CH2AsPh2) has been studied. The superior basicity of phosphorus as compared to arsenic in these adducts is shown by displacement reactions and a calorimetric study. Enthalpic data (in kJ mol–1) obtained for the gas-liquid reactions (i) and (ii) are ΔH1=–160.4 and ΔH2, =–153.4 for M = P, and ΔH1=–76.1 and ΔH2=–111.3 2MPh3(sol)+ B2H6(g) [graphic omitted] 2MPh3·BH3(sol)(i), MPh3(sol)+ BH3(g) [graphic omitted] MPh3·BH3(sol)(ii) for M = As. In the case of L, two stages of compiexation may be separated and the corresponding enthalpies (kJ mol–1) are ΔH1=–165.3 (2L + B2H6) and ΔH2=–155.6 (L + BH3) corresponding to complexation of the phosphorus site, and ΔH1=–60.7 (2L·BH3+ B2H6) and ΔH2=–103.3 (L·BH3+ BH3) corresponding to complexation of the arsenic site.

Nuclear quadrupole resonance in the chloranil–hexamethylbenzene complex at high pressure

The 35Cl quadrupole resonance frequencies in chloranil and its hexamethylbenzene complex have been studied at pressures up to 750 MPa and temperatures of 254 and 273 K. An analysis of the relative frequency shifts suggests that under these conditions the 35Cl frequency moves upwards on complex formation by nearly 100 kHz.

Competition between different nucleophilic sites belonging to the same Lewis bases. Part I. Aminophosphines towards borane

The nature of the donor–acceptor interactions in aminophosphine–borane adducts has been investigated by means of the chemical behaviour of the borane group and 1H, 11B, and 31P n.m.r. spectra. The phosphorus atom appears to be a better acceptor than nitrogen towards BH3 when these two donor atoms are linked together, such as in Me2NPMe2 and (Me2N)2PMe. However, when these two atoms are separated by a methylene bridge, as in (Et2NCH2)3P, borane co-ordinates with nitrogen rather than with phosphorus. The results are explicable in terms of multiple bond behaviours and steric hindrance.

Nuclear quadrupole resonance of several copper(I) complexes with heterocyclic thioamido ligands. Crystal structure of chlorobis[tetrahydro-1H-pyrimidine-2-thione]copper(I)

The 63Cu and 65Cu n.q.r. spectra of the copper(I)–chloride and –bromide complexes of imidazolidine-2-thione (izt) and tetrahydro-1H-pyrimidine-2-thione (tpt), and the crystal structure of the complex [Cu(tpt)2Cl] are reported. The n.q.r. data indicate that there is no phase change in the 77–300 K temperature interval. The compound [Cu(tpt)2Cl] crystallizes in space group P41212 with a=b= 7.803(2), c= 22.093(7)A, and Z= 4. The structure has been solved by standard methods with a final R of 0.047. The complex is mononuclear and contains only one kind of CuI atom which is trigonally co-ordinated by two tpt molecules (Cu–S 2.206 A) and one chlorine atom (Cu–Cl 2.317 A). The conformation of the complex molecule is influenced by two intramolecular N–H ⋯ Cl hydrogen bonds.

Etude par resonance quadripolaire des noyaux 63-Cu et 75-As de complexes tetrameres de la triethylarsine avec des halogenures de cuivre(I)

Abstract 63-Cu and 75-As quadrupole resonance results have been obtained for the tetrameric triethylarsine copper(I) halides (Cl, Br and I). Unusual behaviours of the temperature dependence of the 63-Cu and 75-As quadrupole resonance lines have been observed simultaneously. Between 77 and 300 K, the chlorine derivative undergoes two structural phase changes at 93 and 173 K, while phase transformations occur at 152 and 86 K respectively for the bromine and iodine derivatives.