Showing papers in "Polyhedron in 1997"

Abstract: The organosulfur compounds present in fossil fuels vary widely in their reactivities in catalytic hydrodesulfurization. In naphtha, thiophene is so much less reactive than the thiols, sulfides, and disulfides that the latter can be considered to be virtually infinitely reactive in practical high-conversion processes. Similarly, in gas oils and petroleum residua, the reactivities of (alkyl-substituted) 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene are much less than those of other sulfur-containing compounds. Consequently, in deep hydrodesulfurization, the conversion of these key substituted dibenzothiophenes largely determines the required conditions. Because of the growing technological importance of deep desulfurization of heavy feedstocks, we infer that 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene are the most appropriate compounds for investigations of candidate catalysts and reaction mechanisms.

Abstract: Recent legislation directed at reducing sulfur levels in petroleum-based fuels has led to numerous studies of commercial hydrotreating, the process whereby sulfur, nitrogen, and oxygen are removed from organic compounds in petroleum feedstocks. The goal of this overview is to highlight organometallic and clean surface model studies that offer realistic ways of understanding details of hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodeoxygenation (HDO) reactions as they occur on heterogeneous hydrotreating catalysts.

Abstract: 1. 2. C O N T E N T S INTRODUCTION . . . . . . . . . . CONVENTIONAL LIGANDS . . . . . . . . . . . . . . 2.1. Group 14 : donor ligands . . . . . . . . . . . . . . . 2.2. Group 15 : nitrogen ligands . . . . . . . . . . . . 2.3. Group 15 : phosphorous ligands . . . . . . . . . . . . 2.4. Group 16: oxygen ligands . . . . . . . . . . . . . . . 2.5. Group 16: sulfur and selenium ligands . . . . . . . . . . . . 2.6. Miscellaneous . . . . . . . . . . . . . . . . . 551 551 551 552 555 556 557 559 3. MACROCYCLIC LIGANDS . . . . . . . . . . . . . . . . . . 559 3.1. Nitrogen donor macrocyclic ligands . . . . . . . . . . . . . 559 3.2. Nitrogen/oxygen mixed donor macrocyclic ligands . . . . . . . 560 3.3. Nitrogen/sulfur mixed donor macrocyclic ligands . . . . . . . . . . . . 564 3.4. Oxygen donor macrocyclic ligands . . . . . . . . . . . . . . 564 4. CONCLUSION . . . . . . . . . . . . . . . . . . . . . 564

Abstract: The sandwich-like bis(phthalocyaninato)lanthanide(III) complexes Ln[Pc′(R) 8 ] 2 (Ln = Eu, Gd; Pc′ = 2,3,9,10,16,17,23,24-octasubstituted phthalocyaninate; R = H, n-C 7 H 15 , OC 5 H 11 ) have been prepared by treating Ln(acac) 3 ·nH 2 O (Ln = Eu, Gd; acac = acetylacetonate) with dilithium phthalocyaninate or with the corresponding disubstituted phthalonitriles in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The spectroscopic and electrochemical properties of the substituted sandwich complexes have been investigated and compared with those of the unsubstituted analogues. The matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) and electrospray ionisation mass spectrometry (ESI-MS) have also been employed to unambiguously characterise this novel class of compounds for the first time.

Abstract: The study of the H+ −CrO42− system in 3.0 M KCl as ionic medium at 25°C by means of emf (glass electrode) and direct calorimetric measurements, in the total CrVI concentration (B), average number of H+ bounds per central group CrO42− (Z), and pH ranges: 25 ⩽ B ⩽ 100 mM, 0 ⩽ Z ⩽ 1.16 and 1 ⩽ pH ⩽ 8, respectively, indicates the formation of the following complexes Hp(CrO4)q(p−2q), stability constants (logβpq(± 3σ)) and partial molar enthalpies (ΔHpq(±3 σ) kcal.mol−1): HCrO4−, 5.888(4), −0.6(1); Cr2O72−, 13.900(3), −5.7(1); H2CrO4, 7.004(7), 1.8(2) and HCr2O7−, 15.007(5), −5.0(1), respectively, according to the general reaction: pH+ + qCrO42− ⇄ Hp(CrO4)q(p−2q). The results previously obtained by Raman spectroscopy for this system are better adjusted when the HCrO4− species is included. The energies and optimized structures from ab initio calculations for the CrO42−, HCrO4−, Cr2O72−, H2CrO4 and HCr2O7− species have also been obtained. For the HCrO4− species the values of bond lengths and angles theoretically calculated are in good agreement with the experimental data of the anion in the crystal structure of the compound (PPh4)[CrVIO3(OH)]. Finally, correlations between thermodynamic experimental and structural theoretical parameters are discussed.

Abstract: Deca- and dodeca-silsesquioxane cages were prepared by partial rearrangement of octa-silsesquioxanes, R8(SiO1.5)8 (1), to give species of the type R10(SiO1.5)10 (II) and D2d-R12(SiO1.5)12 (III) . This rearrangement is catalysed by sodium acetate, sodium cyanate, sodium sulfite, sodium hydroxide and potassium carbonate in acetone as solvent. The mixture of [Cl-(CH2)3]8(SiO1.5)8 (Ic), [Cl-(CH2)3]10(SiO1.5)10 (IIc) and D2d-[Cl-(CH2)3]12-(SiO1.5)12 (IIIc) can be separated by NP-HPLC. The reaction was also studied in acetonitrile using sodium fluoride, sodium or potassium hexafluorosilicate and 18-crown-6 as catalysts. Simulataneous reaction of (Ic) and [NCS-(CH2)3]8(SiO1.5)8 (If) with sodium acetate in acetone leads to a maxture of octa-, deca- and dodeca-silsesquioxanes with a statistical distribution of the Cl(CH2)3- and NCS(CH2)3-side groups. The 29Si NMR data of the synthesized silsesquioxanes have been collected. The shift data can be calculated following simple additivity rules.

Abstract: Starting from 1,10-phenanthroline, a series of novel ligands(L), imidazo[f]1,10-phenanthroline (IP), 2-phenylimidazo[f]1,10-phenanthroline (PIP) and the derivatives, and their complexes [Ru(bpy) 2 L] 2+ have been synthesized and characterized. The effects of different electron donor and acceptor groups on the 1 H NMR, electronic absorption and emission spectra were studied. Time-resolved luminescence studies revealed that the addition of calf thymus DNA into the complex solution results in increases for both the emissive intensities and excited state lifetimes, and indicates that the electron group on L has no significant effect on the intercalation binding mode between DNA and the complexes.

Abstract: New copper(II) complexes [Cu(H2L)(H2O)n]Cl2·xH2O (n = 0 or 2) with linear and tripodal tetradentate ligands have been synthesized and characterized using elemental analysis, molar conductance, IR spectra, magnetic measurements, electronic and ESR spectra. The spectral studies support the binding of linear ligands with two N and two O donor sites to copper(II) ion, providing a square planar geometry and show also that tripodal ligands were coordinated to the metal ion by oly one nitrogen atom, giving an arrangement of NO3 donor groups, the other axial sites being occupied by the solvent. The ESR data indicate that the covalent character of the metal-ligand bonding in the copper(II) complexes increases with increasing electron donating effect of the ligand substituents R. From the results of cyclic voltammetry, it is shown that chelate structure and ligand geometry, steric bulk and electron donating effects of the ligand substituents are among the factors influencing the redox potentials of the complexes.

Abstract: Copper(II) and nickel(II) complexes of 2,3-butanedione bis(N(3)-methyl-, bis(N(3)-dimethyl-, bis(pyridyl- and bis(hexamethyleneiminylthiosemicarbazone), (H2Bu3M, H2Bu3DM, H2Bupip and H2Buhexim, respectively) have been prepared and studied spectroscopically. The four thiosemicarbazones have been characterized by their melting points, as well as IR, electronic and NMR (1H, 13C) spectra. The four coordinate copper(II) complexes have been studied by EPR spectroscopy and the copper(II) and nickel(II) complexes by a number of the spectroscopic techniques mentioned above. Upon formation of these complexes, loss of the N(2)H hydrogens occurs and the ligands coordinate to the metal centers as dianionic, tetradentate N2S2 ligands. The crystal structures of H2Bupip and the nickel(II) complex of 2,3-butanedione N3-methyl-phenylthiosemicarbazone, [Ni(Bu3MPh)], have been solved.

Abstract: N(1)-Alkyl-2(arylazo)imidazoles p-C6H4N NC3H2H N(1)R′, RaaiR′ R′ =Me(2), Et (3);R=H(a), Me(b), OMe(c), Cl(d), NO2(e) yield catonicbis-related with both copper(I) (4,5) and silver(I) (6,7). These were isolated as perchlorate salts and the composition is supported by elemental analyses. The complexes are 1:1 electrolytes in methanol. The N N stretch in copper(I) complexes shows a large shift to lower frequency (ca 1335 cm−1) from the free ligand value (ca 1400 cm−1) due to d(Cu) → π* (RaaiR′) back bonding. This effect is much less pronounced in silver(I) complexes indicating a negligible dπ-π* (RaaiR′) interaction. The complexes show highly resolved symmetrical1H NMR spectra. The copper(I) complexes exhibit intense MLCT transitions in the visible region. In methanol the Cu(RaaiR′)2+ couple has E1/2 ca 0.45V vs SCE at 298 K. The high positive potential may be due to the distortion in the geometry of Cu(RaaiR)2+.

Abstract: Three complexes of the formula [Zn(2,2′-biny)(CCl3CO2)2(H2O)] (1). [Zn (1,10-phen) (CCl3CO2)2(H2O)] (1a) and [Zn(μ-4,4′-bipy)(4-4′-bipy)2(CCl3CO2)2(H2O)4]n (2) have been synthesized and characterized by elemental analysis, IR spectra, thermal analysis and single-crystal X-ray diffraction for 1 and 2 and X-ray powder pattern for 1a. The metal coordination in complex 1 is distorted trigonal bipyramidal with N(1), O(2) and O(5) defining the basal plane, O(3) and N(2) being in apical positions. The X-ray crystal structure of 2 reveals that the local coordination round the ZnII ion is a distorted octahedron, in which Zn(H2O)4 coordination planes are bridged by 4,4′-bipyridine to form an infinite chain structure. Two 4,4′-bipyridine molecules and two trichloroacetate anions exist in the lattice linked by intermolecular hydrogen bonds to coordinated water molecule. Complexes 1 and 1a have a similar pattern of bonding and showed identical TGA curve and almost similar X-ray powder diffractograms.

Abstract: One-dimensional coordination polymers of [Cd(4,4′-bipy) 3 (H 2 O) 2 ](ClO 4 ) 2 · 2H 2 O ( 1 ) and [{Cd(4,4′-bipy)(H 2 O) 2 (ClO 4 ) 2 }(4,4′-bipy)] ( 2 ) were synthesized, respectively, in EtOH/H 2 O solution through a self-assembly process or by the ethanothermal reaction in a sealed tube. In the presence of NLO-active organic chromophore 2-nitroaniline or N-methyl-2-nitroaniline, the solution self-assembly reaction gave two-dimensional inclusion compounds of [{Cd(4,4′-bipy) 2 (H 2 O) 2 }( o -NAN) 2 ](ClO 4 ) 2 · H 2 O where o -NAN = 2-nitroaniline ( 3 ) and [{Cd(4,4′-bipy) 2 (ClO 4 ) 2 }( o -MENAN) 2 ] where o -MENAN = N-methyl-2-nitroanlinie ( 4 ), respectively. The four compounds were characterized by FT-IR, diffuse reflectance UV/VIS, X-ray powder diffraction and single crystal X-ray analysis.

Abstract: The title compound was prepared from 1-methyl-2(3H)-inidazolinethione and triphenyltin(IV) hydroxide, and its crystal structure was determined by X-ray diffraction. The crystal consists of discrete molecules with the tin atom coordinated to one carbon atom of each of the three phenyl groups and to the sulfur atom of the deprotonated ligand. An SnN interaction [2.920(3) A] slightly distorts the tin coordination geometry from that of a perfect tetrahedron. NMR spectroscopy was used to study the hydrolysis of this compound in CDC13.

Abstract: From the reactions of SnCl4 with organotin(IV) chlorides (RSnCl3, R2SnCl2 and R3SnCl, where R = Bu, Me and Ph) with N-(2-hydroxybenzaldehyde)-1-amino-2-phenyleneimine, N-(2-hydroxyl-1-naphthaldehyde)-1-amino-2-phenyleneimine, N,N′-bis(2-hydroxybenzaldehyde)-1,2-phenylenediimine and N,N′-bis(2-hydroxy-1-naphthaldehyde)-1,2-phenylenediimine a series of complexes have been synthesized and characterized, respectively, by microanalytical, IR, and 1H NMR spectroscopic methods. The Ph2SnCl2 reacted with N-(2-hydroxy-1-naphthaldehyde)-1-amino-2-phenyleneimine giving Ph2Sn(NAPPDI) [where NAPPDI = deprotonated N,N′-bis(2-hydroxy-1-naphthaldehyde)-1,2-phenylenediimine], wherein the former Schiff base exhibit a facile intramolecular CN bond cleavage and intermolecular CN bond formation.

Abstract: A new series of copper(II) complexes derived from 4-(2-thienyl-methylidene amino) antipyrine (TAAP) and 4-furfurylidene amino antipyrine (FAAP) have been synthesized. The complexes are formulated as [(TAAP)Cu](ClO 4 ) 2 , [(FAAP) 2 Cu](ClO 4 ) 2 , [(FAAP)Cu(OH)Br], [L 2 CUX 2 ]· n H 2 O and [L 2 Cu(NO 3 ) 2 ], L  TAAP or FAAP, X  Cl or Br and n = 2 or 1, based on their elemental analyses and infrared spectral data. The infrared data indicate the bidentate nature of both ligands in all complexes except in [(TAAP) Cu](ClO 4 ) 2 where the ligand acts as a tridentate chelating agent. The electronic and EPR spectral data are used to interpret the nature of bonding of the ligands with the copper(II) ion, ground state and ligand field strength. The room temperature magnetic moments indicate polymeric structure for [(TAAP)CUX 2 ]· n H 2 O, [(TAAP)Cu](ClO 4 ) 2 , and [(FAAP)Cu(OH)Br] and monomeric structure for the rest of the complexes. The biological activity studies of the complexes and the free ligands towards three gram-positive, seven gramnegative bacteria and three fungal species have been studied and the potential is related to the nature and structure of the complexes.

Abstract: A series of N(4)-substituted thiosemicarbazones of isatin were synthesized and their copper(II) complexes prepared from copper(II) chloride X-ray crystal structures of two of the thiosemicarbazones, isatin 3-(hexamethylenimylthiosemicarbazone) and isatin 3-(N(4)-ethylthiosemicarbazone), have been solved and are compared with a previously published structure of isatin 3-(N(4)- p -tolythiosemicarbazone) The coordination chemistry of the copper(II) complexes of these and other isatin thiosemicarbazones is reported and discussed

Abstract: Some new palladium(II) complexes of 2-acetylpyridine N(4)-propyl- and N(4)dipropyl- and 3-hexamethyleneiminylthiosemicarbazones with potentially interesting biological activity were described. The thiosemicarbazones and their palladium(II) complexes have been characterized by spectroscopic, and electrochemical techniques. The protonation constants of HAc4P Ka1 and Ka2, were determined by spectrophotometry and the pK1a and pKa2 values are equal to 12.23 ±0.02 and 4.11 ±0.02. The antifungal properties and the effect selected compounds on DNA synthesis of P388 and L1210 cell cultures is reported.

Abstract: Hydrodenitrogenation (HDN) catalysis is the process of removing nitrogen from petroleum feed-stocks in the form of NH3 to provide more processable and environmentally compatible liquid fuels. In practice, HDN is carried out simultaneously with other catalytic hydrotreating reactions such as hydrodesulfurization (HDS), yet HDN is significantly less well-studied than HDS. This contribution provides an overview of the heterogeneous HDN process, then outlines various homogeneous models for hydrodenitrogenation catalysis including binding modes of HDN substrates, catalytic hydrogenation processes and recent CN bond cleavage reactions of nitrogen heterocycles. Emphasis is placed on aryloxide and alkoxide complexes of the early metals that afford some of the best homogeneous models for hydrodenitrogenation catalysis to date.

Abstract: Novel cyclic tetranuclear manganese(III) complexes with Schiff base ligands, N,N′-substituted-salicylidene-1,3-diaminobenzene (X = H, 5-Br), X-salmphenH2, MnIII4(X-salmphen)6 have been prepared and characterized by spectroscopies, magnetic susceptibility, electrochemical measurements and X-ray crystallography. Two manganese ions of the tetranuclear complexes are bridged by two X-salmphen ligands and consist of a dimer unit, [Mn2(X-salmphen)2]2+. The residual two X-salmphen ligands bridge these dimer units. The resulting tetranuclear complexes constitute a dimer of the two dimetric structures that contains a intramolecular and intermolecular π-π stacking, between phenylene rings of X-salmphen ligands. The physicochemical properties of the tetranuclear complexes having a N3O3 donor set are found to be analogous to those observed for tris(N-dodecyl-salicylidenaminato)manganese(III) complexes, MnIII(N-Dod-sal)3. The structure of this complex is also determined by X-ray crystallography. The magnetic properties of the tetranuclear complexes indicate that there is little or no interaction among these central manganese ions.

Abstract: Structural features and physical properties of dmphen (2,9-dimethyl-1,10-phenanthroline) complexes with d10 metals ZnII, Ni0 and AgI were determined. These, together with the more well-known CuI compounds, constitute a rare example of an Ni0, CuI, ZnII isoelectric, isostructural series. The first homoleptic zinc dmphen compounds [ZnNO3(dmphen)2]NO3 (1) and Zn(dmphen)2(BF4)2 (2) were prepared. Their structures were determined by X-ray crystallography. Compound 1 is five-coordinate, with one nitrate ion coordinated. Compound 2, of the same stoichiometry as 1, exhibits the pseudotetrahedral, four-coordinate Zn(dmphen)22+ cation, which is isoelectronic and isostructural with the more well known Cu(dmphen)2+ cation. Ni(dmphen)2 (4) was prepared for the first time. Reaction of Ni0(cyclooctadiene)2 with dmphen in ethanol or tetrahydrofuran gave crystals of dark blue Ni0(dmphen)2 (4). NMR experiments show that 4 is diamagnetic, with chemically equivalent dmphen ligands. From this species, by reaction with dichloromethane, Ni2(dmphen)2Cl4 (5) was obtained. In this compound each nickel atom bears one terminal chloride ligand and the two nickel atoms are connected by two μ-chlorine atoms. Finally, Ag(dmphen)2BF4 (6) was prepared, which now extends the isostructural series described above to a second-row transition metal. The structure of this compound was determined by X-ray crystallography.

Abstract: New nickel(II) complexes of general formula, [Ni(NNS)2] (NNS− = uninegatively charged tridentate ligands formed by condensation of 6-methyl-2-formylpyridine with S-methyl- and S-benzyldithiocarbazates) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic evidence support a distorted octahedral structure for these complexes. The crystal and molecular structure of the bis{S-methyl-β-N-(6-methylpyrid-2-yl)methylenedithiocarbazato}nickel(II) complex has been determined by X-ray diffraction studies. The complex has a distorted octahedral structure with the ligands coordinated to the nickel(II) ion as uninegatively charged tridentate chelating agents via the pyridine nitrogen, the azomethine nitrogen and the mercaptide sulphur atoms. The distortion from the regular octahedral geometry is ascribed to the stereochemical limitations imposed by the planar tridentate ligands.

Abstract: Oxovanadium(IV) complexes of aroyl hydrazone Schiff bases, viz. salicyloyl, nicotinoyl and benzoyl hydrazones, have been synthesized and characterized by elemental analysis, spectroscopy (IR and UV-vis) methods, magnetic susceptibility, EPR measurements, molar conductance and cyclic voltammetry studies. The room-temperature magnetic moments of the complexes are in the range 0.97–1.03 B.M. and are indicative of the presence of anti-ferromagnetic exchange. A binuclear structure has been proposed for the complexes.

Abstract: Fundamental studies of desulfurization chemistry induced by single-crystal transition-metal surfaces are reviewed with emphasis on recent work. Specifically, the chemistry associated with clean, modified and multimetallic systems is addressed. A brief of our experimental approach, including the use of systematic variation in CS bond enthalpies for mechanistic studies, is discussed. Studies of thiol reactions on Mo(110) have shown that desulfurization occurs via homolytic CS bond dissociation in the thiolate intermediate. Furthermore, the relative rates of desulfurization can be correlated with CS bond strengths. The product distributions for molecules that form radical or cation intermediates and undergo various rearrangement reactions are used to elucidate reaction mechanisms. Adsorbates like oxygen and sulfur passivate the surface toward CS and CH bond scission in most cases. However, oxygen substitution also occurs when thiols react on some oxygen-covered surfaces. No synergistic reactivity was observed for thiol chemistry on bimetallic CoMo surfaces.

Abstract: Removal of the nitrogen atom from aromatic nitrogen-containing molecules takes place via hydrogenation of the aromatic rings, CN bond cleavage of the resulting saturated amines by NH 3 elimination, and alkene (de)hydrogenation. The separate reaction steps cannot be combined into one kinetic equation, because every reaction takes place on a different catalytic site which differs in its ability to bind reactants, intermediates and products. A multi-site Langmuir-Hinshelwood rate model has to be used in the kinetic modeling. Depending on the type of molecule, aniline or pyridine-like, the rate determining step is phenyl hydrogenation or ring opening elimination, respectively. The HDN behaviour of polycyclic aromatic N-containing molecules is based on a combination of the HDN reactions of aniline and pyridine-like molecules. The catalyst components influence the rate as well as the adsorption constants. Ni has a positive effect on all reaction steps for all reactant molecules, while the effect of phosphorus depends on the type of rate determining reaction, and thus on the reactant. Hydrogenation reactions are promoted by P (aniline and alkene), and elimination reactions are negatively influenced (piperidine and decahydroquinoline). The reverse is true for H 2 S, suggesting that phosphorus increases the number of sulfur vacancies which are considered to be the catalytic sites for (de)hydrotreating reactions.

Abstract: N,N′-Di( p -tolylformamidine), HDTolF, reacts with an ether solution of methyl lithium to give Li 2 (μ-DTolF) 2 (Et 2 O) 2 ( I ), while N,N′-diphenylformamidine, HDPhF, reacts with a THF solution of MeMgCl to give the bioctahedral molecule (DPhF)(THF)Mg(μ-THF)(μ-Cl) 2 Mg(THF)(DPhF) ( II ), in which one of the THF molecules is bonded to both Mg atoms. Crystal structures of I, II , as well as the neutral molecule HDTolF ( III ) and the salt [H 2 DTolF][BF 4 ] ( IV ) are presented. The neutral molecule shows distinct amine and imine CN distances, while the ionic species show identical CN distances.

Abstract: The reactive 16 e − metal fragment [C 5 Me 5 )Rh(PMe 3 )] inserts into a wide variety of thiophene CS bonds. The structures of the thiophene, benzothiophene and dibenzothiophene insertition complexes have been determined. While the thiophene complex adopts a planar six-membered ring structure the other metallacycles are bent and all molecules posses localized diene structures. The mechanism of CS cleavage was found to proceed by way of initial sulfur coordination. 2-Methylbenzothiophene gives a kinetic product resulting from cleavage of the sulfur-vinyl bond, but then rearranges to cleave the sulfur-aryl bond. A number of substituted dibenzothiophenes were examined, showing little electronic effect of substituents, but showing a large steric effect of substituents at the 4 and 6 positions. 4,6-Dimethyldibenzothiophene does not undergo cleavage, but instead forms an S-bond complex. Reactions of a cobalt analog, (C 5 Me 5 )Co(C 2 H 4 ) 2 with thiophenes also lead to CS cleaved products and the use of a dinuclear iridium system produces a butadiene complex in which both CS bonds have been cleaved.

Abstract: The reactions of 1-(4-fluorophenyl)-1,2-dicarbadodecaborane(12) 1 and 1-(4-fluorophenyl)-1,7-dicarbadodecaborane(12) 2 with tetrabutylammonium fluoride hydrate in tetrahydrofuran or acetonitrile have been monitored by 19F and 11B NMR. No carborane intermediates were observed prior to formation of the nido- anions 7-(4-FC6H4)-7,8-C2B9H11− 3 and 7-(4-FC6H4)-7,9-C2B9H11− 4 which each required two molecular proportions of fluoride and, by inference, one of water for complete reaction. The spectra of the initial anionic monoboron product of both reactions showed it to be the new fluoroborate HOBHF2− 5. The B-attached hydrogen atom of the fluoroborate 5 is derived from the starting carborane, since it was retained when Bu4NF·(D2O)n was used, but the nido-anions 3 and 4 bonded deuterium at the open face in this experiment. The 1H, 11B, 19F and 13C NMR spectra of carboranes 1–4 have been recorded and assigned.

Abstract: Reaction of [VO(acac)2] with S-methyl 3-(2-hydroxyphenyl) methylenedithiocarbazate (H2L1) and its nitro- (H2L2) and bromo derivatives (H2L3) as tridentate heterodonor (ONS)2− ligands offers a basic VO(ONS) core. In the presence of bidentate (N,N′) donor ancillar ligands, various mono- and dinuclear oxovanadium(IV) complexes [VOL(2,2′-bipy)] (1–3), [VOL(Phen)] (4, 5) and [LOV(μ-4,4′-bipy)VOL] (4, 5) and [LOV(μ-4,4′-bipy)VOL] (6–8) were obtained. The compounds have been characterized by EPR, electronic and FAB mass spectroscopic studies. The X-ray crystal structure of a representative compound [VOL2(2,2′-bipy)] (2) is reported and shows the presence of the tridentate ONS ligand occupying the meridional sites leading to distorted octahedral geometry. The nitrogen donor, occupying an apical position has a trans-labilizing influence, resulting in elongation of the VO terminal bond. Magnetic susceptibility and EPR spectral studies indicate non-interacting nature (vbJ vb ≈ 0) of the vanadium(IV) unpaired electrons in the dinuclear complexes (6–8).

Abstract: Pyrazine forms 1:1 complexes with cadmium(II) halides, CdX 2 · pyrazine (X = Cl, Br, I). The structures of all three members of this series have been determined by single-crystal X-ray diffraction. All of the complexes crystallize as infinite CdX 2 chains in which cadmium atoms are doubly bridged by pairs of halide atoms; pyrazine ligands complete the pseudo-octahedral coordination of the cadmium atoms and link the CdX 2 chains to form extended two-dimensional layers. While this type of coordination is fairly common for chloro and bromo derivatives, the iodo compound represents, to the best of our knowledge, the first example of an iodo derivative with this coordination. In each case the layers stack along the crystallographic a -axis to complete the structure. In the bromo and iodo complexes, which are isomorphous, the pyrazine ring planes are perpendicular to the plane of the layer. The chloro derivative has a very similar structure; however, the pyrazine rings are rotated by 19.3° away from perpendicular, bringing the ortho -CH groups into close proximity [2.89 (2) A] to a chloride atom.