Formation of cyclo- and polystannanes by dehydrogenative stannane coupling catalyzed by platinum(II) complexes

Reaction of (PhMe₂P)₂PtMe₂ or [(κ²-P,N)-Ph₂PC₂H₄NMe₂]PtMe₂ with an excess of H₂SnBu₂ or H₂SnPh₂ resulted in the catalytic formation of cyclo-, oligo- and/or polystannanes. In the reaction of (PhMe₂P)₂PtMe₂ with H₂SnBu₂, linear oligomeric species H(SnBu₂)_nH were observed in the initial stage of the reaction, which eventually converted into cyclostannanes. Only polystannanes were observed in the reaction of [(κ²-P,N)-Ph₂PC₂H₄NMe₂]PtMe₂ with H₂SnBu₂. The reactions of H₂SnPh₂ were similar, but more difficult to analyze due to redistribution reactions and the formation of insoluble products. The mechanism of the reactions is clearly different to that previously observed for HSnR₃ because metal complexes indicative of oxidative addition/reductive elimination reactions were only observed as minor products.     

A 31P1H NMR study of the reactions of [Rh2(μ-Cl)2(cod)2] with unsymmetrical,bidentate ligands and hydrogen

[Rh₂(μ-Cl)₂(cod)₂] reacts with Ph₂PCH₂CH₂OMe (PC₂O), Ph₂P(CH₂)₃NMe₂ (PC₃N), PBuⁿPh₂ or PPh₃ to give [Rh(cod)L₂]Cl (L = PC₂O, PC₃N, PBuⁿPh₂, PPh₃). In the presence of hydrogen, [Rh(cod)L₂]Cl is converted to [RhClH₂L₃]. In contrast, [Rh(cod)(PC₂O)₂]BPh₄ reacts with H₂ to give [RhH₂(PC₂O)₂S₂]BPh₄ (S = solvent). With Ph₂PCH₂CH₂NMe₂ (PC₂N) or Ph₂PCH₂CH₂SMe (PC₂S), [Rh₂(μ-Cl)₂(cod)₂] reacts to form the chelate complexes cis- [Rh(PC₂N)₂]⁺ or cis-[Rh(PC₂S)₂]⁺, neither of which reacts with hydrogen under ambient conditions. The products of the reactions are characterized in situ by ³¹P¹H NMR spectroscopy.     

Extending the coordination chemistry of cobalt with the metalloligand [Pt2(μ-S)2(PPh3)4]: Synthesis of the first cobalt(III) derivatives

The coordination chemistry of the metalloligand [Pt₂(μ-S)₂(PPh₃)₄] towards cobalt(II) and cobalt(III) centres has been explored using an electrospray ionisation mass spectrometry (ESI MS)-directed methodology. Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with CoCl₂·6H₂O in methanol gave a green-yellow suspension of the known adduct [Pt₂(μ-S)₂(PPh₃)₄CoCl₂], and the CoBr₂ adduct could be similarly prepared. When in situ-generated [Pt₂(μ-S)₂(PPh₃)₄CoCl₂] is reacted with 8-hydroxyquinoline (HQ) and base, the initial product is the cobalt(II) adduct [Pt₂(μ-S)₂(PPh₃)₄CoQ]⁺, which is then converted in air to the cobalt(III) adduct [Pt₂(μ-S)₂(PPh₃)₄CoQ₂]⁺, isolated as its hexafluorophosphate salt. The corresponding picolinate (Pic) derivative [Pt₂(μ-S)₂(PPh₃)₄Co(Pic)₂]⁺ was similarly prepared, however reaction of [Pt₂(μ-S)₂(PPh₃)₄], CoCl₂·6H₂O and 8-(tosylamino)quinoline (HTQ) produced only the cobalt(II) adduct [Pt₂(μ-S)₂(PPh₃)₄CoTQ]⁺. Reactions of [Pt₂(μ-S)₂(PPh₃)₄], CoCl₂·6H₂O and dithiocarbamates gave cobalt(III) complexes [Pt₂(μ-S)₂(PPh₃)₄Co(S₂CNR₂)₂]⁺ [R = Et or R₂ = (CH₂)₄], and proceeded much more rapidly, consistent with the known ability of the dithiocarbamate ligand to stabilize cobalt in higher oxidation states. A study of the fragmentation of cobalt(III) adducts by positive-ion ESI mass spectrometry indicated that [Pt₂(μ-S)₂(PPh₃)₄CoQ₂]⁺ fragments to form the radical cation [Pt₂(μ-S)₂(PPh₃)₄]⁺, which could also be generated by ESI MS analysis of [Pt₂(μ-S)₂(PPh₃)₄] in methanol-NaOH solution. In contrast, the corresponding indium(III) derivative [Pt₂(μ-S)₂(PPh₃)₄InQ₂]⁺, and the cobalt(III) dithiocarbamate [Pt₂(μ-S)₂(PPh₃)₄Co(S₂CN(CH₂)₄)₂]⁺ are much more reluctant to fragment under analogous conditions, and the differences are discussed in terms of cobalt(III) redox chemistry.     

Syntheses and michael additions to vinylidene diphosphine complexes of type [M(CO)4{(Ph2P)2CCH2}] (MCr,Mo or W)

Treatment of [M(CO)₄Ph₂PCHPPh₂]⁻ with CH₃- OCH₂Cl at 20 °C gave the methoxymethyl derivations [M(CO)₄{Ph₂PCH(CH₂OCH₃)PPh₂}] (MCr or W), but a similar treatment at 80 °C gave derivatives of a vinylidene diphosphine [M(CO)₄(Ph₂P)₂C CH₂]. Treatment of [M(CO)₄Ph₂PCHPPh₂]⁻with CH₃CHClOCH₃ at 20 or 80 °C gave only [M(CO)₄- (Ph₂P)₂CHCH(CH₃)OCH₃] (MCr or W). The vinylidene diphosphine complexes [M(CO)₄(Ph₂P)2- CCH₂] (MCr, Mo or W) were even more easily prepared by treating [M(CO)₆] with (Ph₂P)₂CCH₂ (vdpp) in hot solvents such as CH₃OCH₂CH₂OCH₂- CH₂OCH₃.Treatment of [W(CO)₄vdpp] with LiBuⁿ followed by methanol gave [W(CO)₄(Ph₂P)₂CHCH₂Buⁿ] (1c), i.e. conjugate addition to the CCH₂ occurs. 1c was also made by treating [W(CO)₄(Ph₂P)₂CH]⁻ with n-pentyl-iodide. Similarly LiMe was added to [W(CO)₄(Ph₂P)₂CCH₂]. Treatment of [M(CO)₄- vdpp] with NaCH(COOEt)₂ gave [M(CO)₄(Ph₂- P)₂CHCH₂CH(COOEt)₂] (MW or Mo). Pyrrolidine added to the CCH₂ bonds of [M(CO)₄vddp] to give [M(CO)₄(Ph₂P)₂CHCH₂NC₄H₈]. ³¹p and ¹H NMR and IR data are given.     

An electrospray mass spectrometry-directed survey of the coordination chemistry of the metalloligand [Pt2(μ-S)2(PPh3)4] with platinum(II) and palladium(II) chloride substrates: influence of metal-ligand lability on product type

The reactivity of the metalloligand [Pt₂(μ-S)₂(PPh₃)₄] towards a wide range of platinum(II) and palladium(II) chloride complex substrates [L₂MCl₂] has been explored, using the technique of electrospray ionisation mass spectrometry to directly analyse reaction solutions. In the majority of cases, products are formed by addition of the ML₂²⁺ fragment to the {Pt₂S₂} core, giving trinuclear species [Pt₂(μ-S)₂(PPh₃)₄ML₂]²⁺. The adducts with Pt(diene) [diene=cyclo-octa-1,5-diene (cod), norbornadiene], Pd(cod), Pd(bipy) (bipy=2,2^′-bipyridine), Pt(PMe₃)₂ and Pt(PTA)₂ (PTA=phosphatriaza-adamantane) moieties were synthesised and characterised on the macroscopic scale, with [Pt₂(μ-S)₂(PPh₃)₄Pt(cod)] (BF₄)₂ and [Pt₂(μ-S)₂(PPh₃)₄Pd(bipy)] (PF₆)₂ also characterised by X-ray diffraction studies. No metal scrambling was found to occur, as has been observed in some previous cases involving the related complexes [Pt₂(μ-Se)₂(PPh₃)₄] and [Pt₂(μ-S)₂(dppe)₂] (dppe=Ph₂PCH₂CH₂PPh₂). With cis-[PtCl₂(SOMe₂)₂] the species [Pt₂(μ-S)₂(PPh₃)₄PtCl(SOMe₂)]⁺ was formed, as a result of the lability of the SOMe₂ ligand. With palladium(II)-phosphine systems, the observed product species is dependent on the phosphine; the bulky PPh₃ ligand in [PdCl₂(PPh₃)₂] leads primarily to the analogous known species [Pt₂(μ-S)₂(PPh₃)₄PdCl(PPh₃)]⁺, and a small amount of the metal-scrambled species [PtPd₂S₂(PPh₃)₅Cl]⁺. In contrast, [PdCl₂(PTA)₂], containing the small PTA ligand gave [Pt₂(μ-S)₂(PPh₃)₄Pd(PTA)₂]²⁺.     

Kinetic studies on the reactions of HCl with trans-[MoL(CNPh)(Ph2PCH2CH2PPh2)2] (L=N2, H2 or CO)

The kinetics of the reactions between anhydrous HCl and trans-[MoL(CNPh)(Ph₂PCH₂CH₂PPh₂)₂] (L=CO, N₂ or H₂) have been studied in thf at 25.0 °C. When L=CO, the product is [MoH(CO)(CNPh)(Ph₂PCH₂CH₂PPh₂)₂]⁺, and when L=H₂ or N₂ the product is trans-[MoCl(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]. Using stopped-flow spectrophotometry reveals that the protonation chemistry of trans-[MoL(CNPh)(Ph₂PCH₂CH₂PPh₂)₂] is complicated. It is proposed that in all cases protonation occurs initially at the nitrogen atom of the isonitrile ligand to form trans-[MoL(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]⁺. Only when L=N₂ is this single protonation sufficient to labilise L to dissociation, and subsequent binding of Cl⁻ gives trans-[MoCl(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]. At high concentrations of HCl a second protonation occurs which inhibits the substitution. It is proposed that this second proton binds to the dinitrogen ligand. When L=CO or H₂, a second protonation is also observed but in these cases the second protonation is proposed to occur at the carbon atom of the aminocarbyne ligand, generating trans-[MoL(CHNHPh)(Ph₂PCH₂CH₂PPh₂)₂]²⁺. Addition of the second proton labilises the trans-H₂ to dissociation, and subsequent rapid binding of Cl⁻ and dissociation of a proton yields the product trans-[MoCl(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]. Dissociation of L=CO does not occur from trans-[Mo(CO)(CHNHPh)(Ph₂PCH₂CH₂PPh₂)₂]²⁺, but rather migration of the proton from carbon to molybdenum, and dissociation of the other proton produces [MoH(CO)(CNPh)(Ph₂PCH₂CH₂PPh₂)₂]⁺.     

Reactivity of tricarbonyl(η5-cyclopentadienyl)(dimethyldithiocarbamato)tungsten towards coordinatively unsaturated species

Visible light irradiation of solutions containing [(η⁵-C₅H₅)(CO)₃ WSC(S)NMe₂] (1) and Fe₂(CO)₉ or Mn₂(CO)₁₀ leads to a transmetallation type of reaction and formation of Fe(S₂CNMe₂)₂ and Mn(CO)₄(S₂CNMe₂) respectively. However, the reaction or 1 with M(PPh₃)₄, M = Pt, or Pd, leads to conversion to the dicarbonyl chelate complex [(η⁵C₂H₅(CO)₂ W(S₂CNMe₂)].     

A series of inorganic-organic hybrid compounds constructed from bis(undecatungstophosphate) lanthanates and copper-organic units

A series of inorganic-organic hybrid compounds built from bis(undecatungstophosphate) lanthanates and copper-complexes, namely, H₈[Cu(en)₂H₂O]₄[Cu(en)₂]{[Cu(en)₂][La(PW₁₁O₃₉)₂]}₂·18H₂O (1), H₆[Na₂(en)₂(H₂O)₅][Cu(en)₂H₂O]₄[Cu(en)₂]{[Cu(en)₂][Ce(PW₁₁O₃₉)₂]}₂·16H₂O (2), H₆[Na₂(en)₂(H₂O)₅][Cu(en)₂H₂O]₄[Cu(en)₂]{[Cu(en)₂][Pr(PW₁₁O₃₉)₂]}₂·18H₂O (3), H₆[Na₂(en)₂(H₂O)₄][Cu(en)₂H₂O]₄[Cu(en)₂]{[Cu(en)₂][Nd(PW₁₁O₃₉)₂]}₂·14H₂O (4), H₆[Na₂(en)₂(H₂O)₅][Cu(en)₂H₂O]₄[Cu(en)₂]{[Cu(en)₂][Sm(PW₁₁O₃₉)₂]}₂·20H₂O (5), and H₇[Cu(en)₂]₂[Sm(PW₁₁O₃₉)₂]·10H₂O (6) (where en = 1,2-ethylenediamine), have been prepared. In these compounds, two lacunary [PW₁₁O₃₉]⁷⁻ anions sandwich an eight-coordinated Ln(III) cation to yield [Ln(PW₁₁O₃₉)₂]¹¹⁻ anion in a twisted square anti-prismatic geometry, which is further bridged by [Cu(en)₂]²⁺ fragments to generate a 1D zigzag-like chain. In 1-6, the coordination bond interactions and weak interactions between adjacent 1D chains play an important role in the zigzagging distances and angles of different 1D chains. The magnetic studies indicate that antiferromagnetic interactions exist in compounds 1, 2 and 4.     

Organic derivatives of aluminium. Part I. Reactions of alkanolamines with aluminium isopropoxide

Reactions of alkanolamines [R₁R₂NXOH; R₁ = H, CH₃, C₂H₅; R₂ = H, CH₃, C₂H₅ and X = -CH₂CH₂-, -CH₂CH₂CH₂-, -CH₂CHCH₃, -C₆H₄CH₂CH₂-] with aluminium isopropoxide in different molar ratios (1 to 3) yield compounds of the type Al(OPrⁱ)_3?n(OXNR₁R₂)_n, where ‘n’ can be 1, 2 and 3. Most of the derivatives are distillable liquids, soluble in common organic solvents and susceptible to hydrolysis even by atmospheric moisture. The new derivatives are characterized by elemental analysis, IR and ¹H NMR spectra. Molecular weight measurements of Al(OPrⁱ)_3?n(OXNR₁R₂)_n reveal them to be tetrameric in nature.     

New energetic materials: Synthesis and characterization of copper 5-nitriminotetrazolates

The energetic compounds 5-nitriminotetrazole (H₂AtNO₂, 1), 1-methyl-5-nitriminotetrazole (1MeHAtNO₂, 2) and 2-methyl-5-nitraminotetrazole (2MeHAtNO₂, 3), were reacted with Cu(NO₃)₂ · 3H₂O and CuCl₂ · 2H₂O, respectively, in water as well as in aqueous ammonia solution. The syntheses yielded the complexes [Cu(HAtNO₂)₂(H₂O)₄] (4), [Cu(AtNO₂)(NH₃)₃]₂ (5), (NH₄)₂[Cu(AtNO₂)₂(H₂O)₂] (6), [Cu(1MeAtNO₂)₂(NH₃)₂] (7), [Cu(2-MeAtNO₂)₂(2-MeHAtNO₂)₂] (8), [Cu(2MeAtNO₂)₂]_∞ (9), [Cu(2-MeAtNO₂)₂(NH₃)₂] (10), and [Cu(2MeAtNO₂)₂(NH₃)₄] · H₂O (11). All complexes were characterized using low temperature single crystal X-ray diffraction, IR spectroscopy, elemental analysis, and differential scanning calorimetry. The magnetic properties of six of the complexes were investigated. Due to the energetic characters, the sensitivities towards impact and friction were investigated using the BAM drophammer and friction tester. The values range from “very sensitive”, comparable to primary explosives, to “insensitive” depending on the amount of water or ammonia coordinated. Since Cu(II) salts can be used for colorants in pyrotechnics, the combustions and flame colors were discovered to be intensively green.     

The encapsulated lithium effect on the first hyperpolarizability of C<Subscript>60</Subscript>Cl<Subscript>2</Subscript> and C<Subscript>60</Subscript>F<Subscript>2</Subscript>

In this paper, we report a study on the structure and first hyperpolarizability of C₆₀Cl₂ and C₆₀F₂. The calculation results show that the first hyperpolarizabilities of C₆₀Cl₂ and C₆₀F₂ were 172 au and 249 au, respectively. Compared with the fullerenes, the first hyperpolarizability of C₆₀Cl₂ increased from 0 au to 172 au, while the first hyperpolarizability of C₆₀F₂ increased from 0 au to 249 au. In order to further increase the first hyperpolarizability of C₆₀Cl₂ and C₆₀F₂, Li@C₆₀Cl₂ and Li@C₆₀F₂ were obtained by introducing a lithium atom to C₆₀Cl₂ and C₆₀F₂. The first hyperpolarizabilities of Li@C₆₀Cl₂ and Li@C₆₀F₂ were 2589 au and 985 au, representing a 15-fold and 3.9-fold increase, respectively, over those of C₆₀Cl₂ and C₆₀F₂. The transition energies of four molecules (C₆₀Cl₂, Li@C₆₀Cl₂, C₆₀F₂, Li@C₆₀F₂) were calculated, and were found to be 0.17866 au, 0.05229 au, 0.18385 au, and 0.05212 au, respectively. A two-level model explains why the first hyperpolarizability increases for Li@C₆₀Cl₂ and Li@C₆₀F₂.     

Decarbonylation of As2Co2(CO)6, a binuclear cobalt carbonyl derivative of diarsenic

The structures and relative energies of the As₂Co₂(CO)_n (n = 6, 5, 4) derivatives are predicted by density functional theory to be analogous to those of the corresponding H₂C₂Co₂(CO)_n derivatives. Thus As₂Co₂(CO)₆ is predicted to have three carbonyls on one cobalt atom eclipsed relative to the three carbonyls on the other cobalt atom. The corresponding As₂Co₂(CO)₆ structure with a staggered rather than eclipsed arrangement of the Co(CO)₃ units is a transition state rather than a genuine minimum. For As₂Co₂(CO)₅ the structure in which an equatorial group is removed from the As₂Co₂(CO)₆ structure and a singly bridged As₂Co₂(CO)₄(μ-CO) structure are predicted to have essentially the same energies, within <2 kcal/mol. A higher energy As₂Co₂(CO)₅ structure by 9 ± 2 kcal/mol is derived from the As₂Co₂(CO)₆ structure by removal of an axial carbonyl group. The two unbridged As₂Co₂(CO)₅ structures correspond to those observed experimentally in the photolysis of As₂Co₂(CO)₆ in Nujol matrices at low temperatures. In such photolysis experiments the higher energy isomer is produced initially and then converted to the lower energy isomer upon annealing. A singly bridged structure was found for As₂Co₂(CO)₄. The analogous structure was not observed in the previous work with H₂C₂Co₂(CO)₄. However, such a H₂C₂Co(CO)₃(μ-CO) structure is found here for the acetylene complex. This singly bridged structure is predicted to lie 1.9 kcal/mol below the H₂C₂Co₂(CO)₄4-1S structure by the BP86 method but 3.5 kcal/mol above the latter by the B3LYP method. In addition to the singly bridged As₂Co₂(CO)₄ structure, the same six unbridged structures were located for As₂Co₂(CO)₄ that were previously found for H₂C₂Co₂(CO)₆.     

Adaptation of Nitrogen Fixation by Intact Soybean Nodules to Altered Rhizosphere pO(2)

The N₂-fixing legume nodule requires O₂ for ATP production; however, the O₂ sensitivity of nitrogenase dictates a requirement for a low pO₂ inside the nodule. The effects of long term exposures to various pO₂s on N₂[C₂H₂] fixation were evaluated with intact soybean (Glycine max [L.] Merr., var. Wye) plants. Continuous exposure of their rhizosphere to a pO₂ of 0.06 atmospheres initially reduced nitrogenase activity by 37 to 45% with restoration of original activity in 4 to 24 hours and with no further change in tests up to 95 hours; continuous exposure to 0.02 atmosphere of O₂ initially reduced nitrogenase activity 72%, with only partial recovery by 95 hours. Similar exposures to a pO₂ of 0.32 atmospheres had little effect on N₂[C₂H₂] fixation; a pO₂ of 0.89 atmospheres initially reduced nitrogenase activity by 98% with restoration to only 14 to 24% of that of the ambient O₂ controls by 95 hours. Re-exposure to ambient pO₂ of plants adapted to nonambient pO₂s reduced N₂[C₂H₂] fixation to similar magnitudes as the reductions which occurred upon initial exposure to variant pO₂ conditions, and a time period was required to readapt to ambient O₂. It is concluded that the N₂[C₂H₂]-fixing system of intact soybean plants is able to adapt to a wide range of external pO₂s as probably occur in soil. We postulate that this occurs through an undefined mechanism which enables the nodule to maintain an internal pO₂ optimal for nitrogenase activity.     

Density functional theory study on the mechanism and thermochemistry of olefins addition to nickel dithiolenes

We investigated the reaction mechanism and thermochemical property of conjugated dienes or mono-olefins with nickel dithiolenes (Ni(S₂C₂R₂)₂) using density functional theory. The reactions between conjugated dienes and nickel dithiolenes are concerted reactions. The thermochemical property study shows that the introduction of electron-withdrawing groups (–CF₃ or –CN) to nickel dithiolene (Ni(S₂C₂H₂)₂) not only significantly lowers the activation energy barrier but also strongly stabilises the products. The introduction of electron-donating group (–CH₃) to butadiene has the same effect. So, we conclude that the reactions between nickel dithiolenes and conjugated dienes are electrophilic cycloaddition. Mono-olefins can add to nickel dithiolenes through interligand pathway, which is a two-step process or through intraligand pathway, which is a one-step process. The thermochemical property study shows that the activation enthalpy for the reaction of butadiene with Ni(S₂C₂(CF₃)₂)₂ is much lower than those of C4 mono-olefins with Ni(S₂C₂(CF₃)₂)₂ for both interligand addition and intraligand addition. The Gibbs free energy for the reaction of butadiene with Ni(S₂C₂(CF₃)₂)₂ is also more favourable than those of C4 mono-olefins with Ni(S₂C₂(CF₃)₂)₂. It is the very preferential pathway for Ni(S₂C₂(CF₃)₂)₂ to bind butadiene than C4 mono-olefins.     

Post-proline Dipeptidyl Amino-peptidase from Flavobacterium

Nitrogenase catalyzes not only the reduction of N₂ to NH₃ but also the reduction of C₂H₂ to C₂H₄ and H⁺ ion to H₂ gas, etc. The detailed mechanism of the nitrogenase reaction is not clear. We have prepared monoclonal antibodies against Component I nitrogenase of A. vinelandii and examined the effects of antibodies on the nitrogenase reactions. A monoclonal antibody designated MA-1 inhibited C₂H₂ reduction activity strongly but did not inhibit H₂ evolution activity. MA-2, on the contrary, inhibited only H₂ evolution activity. MA-8 inhibited both C₂H₂ reduction and H₂ evolution activity to the same extent.     

Preparations and properties of tripodal and linear tetradentate N,S-Donor ligands and their complexes containing the MoO22+core

New linear and tripodal tetradentate ligands, LH₂, are reported and their syntheses are described. The new linear ligands L = HSCH₂CH₂SCH₂CH₂NRCH₂CR₂SH, R = H, CH₃) and the new tripodal ligands N(CH₂CH₂SH)₂CH₂Z, Z = CH₂NH₂, CH₂N(CH₃)₂, CH₂N(C₂H₅)₂, CH₂SCH₃ and CO₂^- were synthesized. The known linear ligands HSCH₂CH₂NCH₃(CH₂)_nNCH₃CH₂CH₂SH (n = 2, 3) and HSCR₂CH₂NHCH₂CH₂NHCH₂CR₂SH (R = H, CH₃) were also utilized. These ligands react with MoO₂(acac)₂ in CH₃OH to yield MoO₂L complexes in high yield. Infra-red and ¹H nmr spectra provide evidence to supplement X-ray crystallographic results reported elsewhere for selected numbers of the series. Octahedral structures with cis MoO₂²⁺ groupings are assigned. Solution ¹H nmr studies are consistent with a trans placement of the two thiolate donors in agreement with the X-ray studies.     

Antibacterial effect of hydrogen peroxide-titanium dioxide suspensions in the decontamination of rough titanium surfaces

The chemical decontamination of infected dental implants is essential for the successful treatment of peri-implantitis. The aim of this study was to assess the antibacterial effect of a hydrogen peroxide-titanium dioxide (H₂O₂–TiO₂) suspension against Staphylococcus epidermidis biofilms. Titanium (Ti) coins were inoculated with a bioluminescent S. epidermidis strain for 8 h and subsequently exposed to H₂O₂ with and without TiO₂ nanoparticles or chlorhexidine (CHX). Bacterial regrowth, bacterial load and viability after decontamination were analyzed by continuous luminescence monitoring, live/dead staining and scanning electron microscopy. Bacterial regrowth was delayed on surfaces treated with H₂O₂–TiO₂ compared to H₂O₂. H₂O₂-based treatments resulted in a lower bacterial load compared to CHX. Few viable bacteria were found on surfaces treated with H₂O₂ and H₂O₂–TiO₂, which contrasted with a uniform layer of dead bacteria for surfaces treated with CHX. H₂O₂–TiO₂ suspensions could therefore be considered an alternative approach in the decontamination of dental implants.     

Hydrothermal syntheses and structures of vanadium oxyfluorides templated by organic and metal organic cations

The hydrothermal reactions of V₂O₅, HF and an organodiphosphonic acid, in the presence of appropriate templating organoammonium or metal-organic complex cations provided three new oxyfluorovanadate compounds. The V(IV) species [H₃N(CH₂)₂NH₂(CH₂)₂NH₂(CH₂)₂NH₃][V₃O₃F₂(H₂O){O₃PCH₂PO₃}₂]·2H₂O (1·2H₂O) exhibits a three-dimensional anionic framework constructed from {VO(O₃PCH₂PO₃)}_n²ⁿ⁻ chains and {VF₂O₄} octahedra. The molecular structure of [N(CH₂CH₂NH₃)₃]₂[NH₄][V₃O₂F₆(O₃PCH₂PO₃)₂]·2H₂O (2·2H₂O) is characterized by the presence of unique {V₃O₂F₆(O₃PCH₂PO₃)₂}⁷⁻ clusters. The bimetallic phase [{Cu(ophen)}VOF{HO₃P(CH₂)₅PO₃}] (3) is one-dimensional with {Cu₂V₂O₂F₂(HO₃PR)₂(O₃PR)₂} cluster building blocks.     

The chemical reactivity of tetraisobutyldialuminum towards ethers,nitrogen lewis bases,aluminumtrimethyl, borontrichloride and ethylene

Treatment of Al₂ⁱBu₄ with THF and Et₂O results in partial decomposition to afford Al metal while reaction with γ-picoline products a bis-adduct of limited stability. Reactions with AlMe₃ and BCl₃, separately, involves ligand exchange with accompanying disproportionation to yield Al metal. Dimethylamine induces disproportionation to afford AlⁱBu₃·HNMe₂ and an intemediate trialuminum species. The latter undergoes AlAl bond cleavage with formation of H₂, _iBu₂AlNMe₂, and [Me₂N- (ⁱBu)AlAlⁱBu₂]₂· Al₂iBu₄ eliminates Me₂CCH₂ in solution at 80 °C, and the catenated AlH intermediate reacts with ethylene to afford AlEt and AlCH₂CH₂CH₂CH₃ moieties.     

High-spin binuclear cyclopentadienyliron chlorides: a density functional theory study

Theoretical studies on the cyclopentadienyliron chlorides Cp₂Fe₂Cl _n (n?=?6???1) with iron in the formal oxidation states from +1 to +4 indicate that all the high-spin species are predicted to be the lowest energy structures and they are paramagnetic complexes with magnetic moments between 2.8μ _B and 5.9μ _B. The mixed oxidation state derivatives with odd number of chloride atoms have larger magnetic moments than other species. In addition to Cp₂Fe₂Cl, which has the largest magnetic moment, these high-spin species have terminal Cp rings and bridging Cl atoms up to a maximum of two bridges. The Cp₂Fe₂Cl₄, Cp₂Fe₂Cl₃ and Cp₂Fe₂Cl₂ derivatives are predicted to be thermodynamically stable molecules with respect to exothermic reactions for the loss of one Cl atom from Cp₂Fe₂Cl _n . Moreover, the lowest energy Cp₂Fe₂Cl _n (n?=?3, 4) derivatives can be derived by the oxidative addition reactions of Cp₂Fe₂Cl _n?2 + Cl₂ → Cp₂Fe₂Cl _n .