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Polyaniline (PANI)/inorganic-nanomaterial based nanocomposites are attractive for gas sensing applications due to the synergistic behavior arising at their interfaces. In this work, HCl doped-PANI-nanofibers/WS2 nanosheet based nanocomposites were prepared by the template-free in situ polymerization of aniline on WS2 nanosheets, which were previously obtained by direct liquid exfoliation. The optimal performance was shown by the PANI/WS2 (w/w 10%) sample and it was characterized extensively using electron microscopy (SEM and TEM), several spectroscopic techniques (UV-Vis, Raman and FTIR), and X-ray diffraction. The nanomaterial was deposited on gold interdigitated electrodes which were then used as chemiresistive transducers for ammonia sensing at room temperature. The device was tested for ammonia concentrations of 50–200 ppm. The resistance of the device was found to increase with the concentration of ammonia vapours and a maximum response of up to 81% was recorded for 200 ppm of ammonia. The long-term stability, selectivity, sensitivity, and repeatability of the device were investigated. Apart from these, the device was also found to perform well under humid conditions. A mechanism based on the synergistic behavior due to the p–n heterogeneous characteristics at the interface of PANI and WS2 is proposed.

High-quality, ultrathin 2D-MoS2 layers with large area were grown on SiO2/Si substrates by using atmospheric pressure chemical vapor deposition (APCVD) at elevated temperatures. The growth precursors (MoO3 and S) were placed separately inside the double-zone furnace to control the growth parameters individually for better flexibility in the growth process. In this study, it was found that the shape and edge structure of the evolved MoS2 flakes were significantly influenced by the chemical potential of the Mo and S precursor concentration. In keeping with the concentration gradient of the Mo precursor (MoO3) on the substrate surface, the shape of MoS2 flakes changed from hexagonal to truncated triangle and then to triangular shapes, owing to the Mo-rich to S-rich conditions. The surface roughness and thickness of the differently shaped MoS2 flakes were studied by using atomic force microscope (AFM). Additionally, Raman and photoluminescence (PL) techniques were employed to characterize the crystalline quality, number of grown layers and optical performance of the as-grown MoS2 layers. Auger electron spectroscopy (AES) analysis and scanning electron microscopy (SEM) confirmed that the equilibrium crystal shape of the MoS2 was hexagonal under Mo-rich conditions. However, the shape of the MoS2 crystal changed to a triangle under S-rich conditions. Furthermore, the influence of chemical potential on the edge structure of the monolayer MoS2 and its effect on the equilibrium shape of the crystal were studied.

In this work, it has been demonstrated that for hydrophilic materials, like SiC, etc., superhydrophobicity can be achieved by coating them with a material like Au/Pd with surface adsorbed organic contaminants, rather than modifying them by fluoropolymers as is usually done. Dense and randomly aligned 3C-SiC nanorods were grown in a cold-wall APCVD reactor using Ni as a catalyst which formed a network of micro/nano air pockets and exhibited superhydrophobic behavior when modified by an Au/Pd metal alloy coating by forming hierarchical nanostructures with surface adsorbed organic contaminants. A high water contact angle (160°), very low sliding angle (

Classical models illustrate the genesis of bottom-up techniques for synthesis of pristine ZnO or Al-doped ZnO nanoparticles via surfactant aided or hydrothermal chemistry, to constitute the fundamental modules of nanotechnology and nanodevices. The present study demonstrates a facile as well as surfactant and catalyst free route for synthesis of morphology controlled Al-doped ZnO nanorods. Morphological evaluation (via FESEM and TEM characterization) clearly verifies the successful synthesis of ZnO and Al-doped ZnO nanorods. Moreover, crystallographic and FTIR studies ratified presence of multiple different planes as well as phases of ZnO and Al-doped ZnO nanostructures, eventually confirming the doping process. Further, the alteration in mode of electronic transition and surface charge of ZnO nanorods post doping with Al was witnessed from its UV–visible or photoluminescence spectra and zeta potential measurements, respectively. Electrical measurements were performed on prepared Al-doped ZnO nanorods which were fabricated as single nanorod devices. Owing to substitutional and interstitial doping, the electrical conductivity of the devices was drastically enhanced after doping. Excellent electrical attribute of the nanorods when fabricated into single nanorod device was indicative of its potential to be deployed as next generation nano-biosensors or piezo-electric devices.

Partially Fe filled multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapor deposition with propane at 850 {\deg}C using a simple mixture of iron (III) acetylacetonate (Fe(acac)3) powder and conventional photoresist. Scanning electron microscopy revealed that catalytic nanoparticles with an average diameter of 70 nm are formed on the Si substrate which governs the diameter of the MWCNTs. Transmission electron microscopy shows that the nanotubes have a multi-walled structure with partial Fe filling. A site-selective growth of partially Fe filled MWCNTs is achieved by a simple photolithographic route., Comment: Filled CNT, CVD, Partial filling, Photolithography

Two different methods of surface modification of cotton fabrics are compared: direct fluorination using elemental fluorine and admicellar polymerization, which uses a surfactant and fluoromonomer system. Sample characterization includes infrared spectroscopy, analysis of mechanical properties, analysis of wetting times, contact angle measurements, scanning electron microscopy, elemental analysis, and atomic force microscopy analysis. Fourier transform infrared spectroscopy and elemental analysis showed the presence of fluorine moieties. For direct fluorinated cotton fabric, the static contact angle was found to be 117°, and for cotton fabric modified by admicellar polymerization, the contact angle was 125°. In all cases, the presence of a very thin fluorocarbon layer on the surface was confirmed, but differences in terms of the amount of fluorochemical formed and in surface structure were also found.

(11bR,11′bR)-4,4′-(1,2-Phenylene)bis[4,5-dihydro-3H-dinaphtho[2,1-c:1′,2′-e]phosphepin] [abbreviated as (R)-BINAPHANE], (3R,3′R,4S,4′S,11bS,11′bS)-4,4′-bis(1,1-dimethylethyl)-4,4′,5,5′-tetrahydro-3,3′-bi-3H-dinaphtho[2,1-c:1′,2′-e]phosphepin [(S)-BINAPINE], (1S,1′S,2R,2′R)-1,1′-bis(1,1-dimethylethyl)-2,2′-biphospholane [(S,S,R,R)-TANGPHOS] and (2R,2′R,5R,5′R)-1,1′-(1,2-phenylene)bis[2,5-bis(1-methylethyl)phospholane] [(R,R)-i-Pr-DUPHOS] are C2-bridged chiral diphosphines that form stable complexes with palladium(II) and platinum(II) containing a five-membered chelate ring. The Pd(II)-BINAPHANE catalyst displayed good to excellent enantioselectivities with ee values as high as 99.0% albeit in low yields for the carbonyl-ene reaction between phenylglyoxal and alkenes. Its Pt(II) counterpart afforded improved yields while retaining satisfactory enantioselectivity. For the carbonyl-ene reaction between ethyl trifluoropyruvate and alkenes, the Pd(II)-BINAPHANE catalyst afforded both good yields and extremely high enantioselectivities with ees as high as 99.6%. A comparative study on the Pd(II) catalysts of the four C2-bridged chiral diphosphines revealed that Pd(II)-BINAPHANE afforded the best enantioselectivity. The ee values derived from Pd(II)-BINAPHANE are much higher than those derived from the other three Pd(II) catalysts. A comparison of the catalyst structures shows that the Pd(II)-BINAPHANE catalyst is the only one that has two bulky (R)-binaphthyl groups close to the reaction site. Hence it creates a deep chiral space that can efficiently control the reaction behavior in the carbonyl-ene reactions resulting in excellent enantioselectivity.

Cubic silicon carbide (beta-SiC)/SiO2 nanowires with uniform and knotted-core structures have been synthesized on nickel-coated Si(111) substrates at 1150 degrees C by using hexamethyldisilane (HMDS) as the source material in a hot wall atmospheric pressure chemical vapor deposition (APCVD) system. The nanowires consist of a single crystalline beta-SiC core wrapped with an amorphous SiO2 shell. The as-prepared SiC nanowires and the deposited Ni films were characterized by field emission scanning electron microscopy, X-ray diffraction, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, micro-Raman spectroscopy, infrared spectroscopy and atomic force microscopy. The results show that the nanowires are random in direction and have diameter ranges from 25 nm to 70 nm. The core of the nanowires has a cubic zinc blend structure and a high density of planar defects is often found. The twin plane defects are suspected to be the main reason for the formation of the knotted-core SiC nanowires. A possible growth mechanism based on vapor-liquid-solid (VLS) by base growth technique is proposed.

Sword-like (diameter ranging from 40 nm to 300 nm) and needle-like zinc oxide (ZnO) nanostructures (average tip diameter ∼40 nm) were synthesized on annealed silver template over silicon substrate and directly on silicon wafer, respectively via thermal evaporation of metallic zinc followed by a thermal annealing in air. The surface morphology, microstructure, chemical analysis and optical properties of the grown samples were investigated by field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, room temperature photoluminescence and Raman spectroscopy. The sword-like ZnO nanostructures grown on annealed silver template are of high optical quality compared to needle-like ZnO nanorods for UV emission and show enhanced Raman scattering.

Many studies have been done on low energy (1–200 keV) and high dose (1016–1017) implantation of Mn in GaAs. This study is an attempt to incorporate Mn ions in GaAs through implantation of 1 MeV Mn+1 ions in semi-insulating GaAs substrates at doses of 3×1015/cm2 and subsequent annealing. This was done to find out if any alloy of Mn–Ga–As, or binary compounds of Mn–Ga or Mn–As form due to annealing of Mn+1 ions implanted in GaAs substrates. High Resolution XRD (HRXRD) performed before annealing shows a possibility of Ga–Mn–As alloy formation, and after annealing at 800°C, except for GaAs main peaks no other phase peaks were detected. Scanning electron microscopy (SEM) shows nanostructures of various dimensions which are thought to be formed due to the defects generated due to implantation. Fourier Transform Infrared (FTIR) study shows the shift in bandgap due to Mn doping. Raman spectroscopy shows the red shift in LO and TO peak positions of GaAs after annealing, which indicates the presence of disorder and damage due to implantation. Resistivity measurement shows a thermally activated semiconductor character of charge conduction with an activation energy of 51 meV and this activation may have occurred through the transitions from impurity band to valence band. Large positive (∼25%) magnetoresistance and a mixture of ferromagnetic and paramagnetic behavior obtained in the magnetization measurement indicate the presence of ferromagnetic MnAs nanoclusters embedded in paramagnetic GaAs:Mn matrix.

Large-scale zinc oxide (ZnO) nanotetrapods have been grown on p-type Si (111) substrate by oxidizing zinc pieces in air by thermal evaporation technique without the presence of any catalyst. The size and morphology of the nanostructures was found to depend on experimental parameters. The grown nanostructures were characterized by X-ray Diffraction (XRD), Photoluminescence (PL), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and analysis of elemental composition was done by Energy Dispersive X-ray analysis (EDX). The EDX spectrum shows that the grown product contains Zn and O only. The X-ray diffraction pattern indicates that the microstructure of the obtained products is typical hexagonal wurtzite ZnO. The optical properties were studied using room temperature PL spectroscopy which indicates that the products are of high optical quality and the near band edge UV transition peak intensity increases with decrease in tetrapod size. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tungsten oxide (WO3) thin films were deposited by a modified hot filament chemical vapor deposition (HFCVD) technique using Si (1 0 0) substrates. The substrate temperature was varied from room temperature to 430 °C at an interval of 100 °C. The influence of the substrate temperature on the structural and optical properties of the WO3 films was studied. X-ray diffraction and Raman spectra show that as substrate temperature increases the film tends to crystallize from the amorphous state and the surface roughness decreases sharply after 230 °C as confirmed from AFM image analysis. Also from the X-ray analysis it is evident that the substrate orientation plays a key role in growth. There is a sharp peak for samples on Si substrate due to texturing. The film thickness also decreases as substrate temperature increases. UV–vis spectra show that as substrate temperature increases the film property changes from metallic to insulating behavior due to changing stoichiometry, which was confirmed by XPS analysis.

Polymer fibers are one of the main substances used for the reinforcement of plastic composites. Surface modification of aramid fiber was performed by direct fluorination. The crystallinity and the decomposition temperature of the modified fiber were increased. Scanning electron microscope shows that the roughness increases in the modified fiber. Composites were prepared by using modified and unmodified fibers. It was shown that the mechanical and thermal properties increase for modified fiber reinforcing composites. To reduce the fiber degradation or breakdown, composites were prepared by solution casting method. POLYM. COMPOS., 28:462–469, 2007. © 2007 Society of Plastics Engineers

Palladium Schottky contacts were fabricated on 3C–SiC heteroepitaxial layers (grown on Si substrates) and characterized by current–voltage measurements. The effects of epitaxial layer thickness and the device configuration on the diode parameters were investigated and analyzed in terms of the interfacial defect density. The influence of operating temperature on the I–V characteristics of the Schottky junctions were studied and the apparent anomalies in temperature dependence of barrier height and ideality factor were explained with the model of localized inhomogeneities of barrier height over the Schottky contact region.

Thermal stability of the Ru/β-silicon carbide (SiC) interfaces up to 800 °C is investigated using secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS) and glancing incidence X-ray diffraction (GIXRD) studies. The objective of this work is to assess the potentiality of ruthenium to be used as a stable gate metal of the Schottky junction gas sensors working at high temperature. The SIMS and RBS studies indicate no significant change in the interface after short-term as well as long-term annealing at 400 °C, the optimum operating temperature of the Ru/β-SiC (epilayer on Si) Schottky junction gas sensors. Glancing incidence X-ray diffraction study does not detect any silicide formation at the Ru/SiC interface after heat treatment at this temperature. However, annealing the junction at a substantially higher temperature (800 °C) results in the formation of ruthenium silicides at the interface over a narrow region along with the oxidation of the top few Ru layers.

The Pd/β-SiC interfaces were studied using secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS). This was done with the intent of clarifying any reaction or inter-diffusion at the interface upon prolonged annealing at different temperatures in air. SIMS study indicates that the interface is stable up to 400 °C for at least 12 h. However, at 800 °C, the interface was completely degraded with significant inter-diffusion of palladium and silicon. The RBS study confirms the SIMS observations.

A complete NMR study involving both 1D and 2D 13C-{103Rh} and 31P-{103Rh} HMQC measurements, on [Rh6C(CO)14(PPh3)]2- are reported and discussed, together with the multiple Rh quantum effects found for resonances associated with edge- and face-bridging CO's. As found in [Rh6C(CO)15]2-, the carbonyl ligands in [Rh6C(CO)14(PPh3)]2- undergo CO-intermolecular exchange with 13CO at different rates; for the edge-bridging CO's, the lower the value of 1J(Rh–CO), the faster the rate of intermolecular exchange with 13CO.

The dissolution of PtO2 in concentrated H2SO4 under an atmosphere of CO results in the formation of hexacarbonyldiplatinum(I), [{Pt(CO)3}2]2+ (1), the first homoleptic, dinuclear, cationic platinum carbonyl complex, of which a prolonged evacuation leads to reversible disproportionation to give cis-[Pt(CO)2]2+(solv) (2) and Pt(0). 1 has been completely characterized by NMR (13C and 195Pt), IR, Raman, and EXAFS spectroscopy. The structure of 1 is rigid on the NMR time scale at room temperature. NMR: δ(13CA) 166.3, δ(13CB) 158.7, δ(195Pt) −211.0 ppm; 1J(Pt−CA) = 1281.5 Hz, 1J(Pt−CB) = 1595.7 Hz, 1J(Pt−Pt‘) = 550.9 Hz. The strongly polarized, sharp Raman band at 165 cm-1 (ρ = ca. 0.25) indicates the presence of a direct Pt−Pt bond. The IR and Raman spectra in the CO stretching region are entirely consistent with the presence of only terminal CO's on a nonbridged Pt−Pt bond with D2d symmetry. ν(CO)IR: 2174 (E), 2187 (B2), and 2218 cm-1 (B2); ν(CO)Raman: 2173 (E), 2194 (B2), 2219 (B2), 2209 (A1) and 2233 cm-...

The progressive addition of hydrazine and the following increasingly substituted hydrazines L (N2H4 Ia, H2NNHMe Ib, H2NNHPh Ie, H2NNMe2 Id, or MeHNNHMe Ic) to [Rh2(CO)4Cl2] resulted in the initial formation of [{Rh(CO)2Cl}2(µ-L)] 1 followed by the formation of cis-[Rh(CO)2L(Cl)] 2; analogous mononuclear complexes were formed directly on addition of the more heavily substituted hydrazines Me2NNMe2 IIf and H2NNPh2 IIg, but addition of 1,2-N2H2Ph2 IIIh to [Rh2(CO)4Cl2] resulted in disproportionation of the hydrazine and formation of cis-[Rh(CO)2(NH2Ph)Cl] 3 and cis-[Rh(CO)2(PhNNPh)Cl] 4. The above complexes have been spectroscopically characterised by IR and 13C/15N NMR measurements. X-Ray structural analysis on [{Rh(CO)2Cl}2(µ-L)] (L = H2NNHMe or MeHNNHMe) confirmed that L adopts a µ-η1∶η1-mode of bonding with a cisoid arrangement of the Rh(CO)2Cl groups about the N–N bond.

The products resulting from the progressive addition of pyridine (py) to a solution of [Rh2(µ-Cl)2(CO)4] 1 have been found to depend both upon the solvent and the atmosphere (CO or N2). In CH2Cl2 under N2, cis-[Rh(CO)2Cl(py)] 2, [Rh(CO)2Cl(py)2] 3 and [Rh2(µ-CO)3Cl2(py)4] 4 were obtained successively; under CO, 4 was converted into 3 and under N2 disproportionation of 4 slowly occurred to give 3 and trans-[Rh(CO)Cl(py)2] 5 which reacted with CO to give 3. In more polar solvents (thf or MeOH), 1 reacted under N2 to give the lightly solvent-stabilised complex [Rh(CO)2Cl(solv)] 6 (solv = thf a or MeOH b) and, in the presence of AgClO4, cis-[Rh(CO)2(solv)2]+ 7 (solv = thf a or MeOH b); additionally, when solv = MeOH there was spectroscopic evidence for the formation of [Rh2(µ-CO)x(MeOH)y]2+ 8 (x = 2, y = 4 or x = 3, y = 6) which reacted with CO to give [Rh(CO)2(MeOH)2]+. Complex 7 reacted with py to give successively cis-[Rh(CO)2(py)2]+ 9 and [Rh(CO)(py)3]+ 10; under CO 10 was converted into 9. The stereochemistry of all the above complexes has been established through a combination of IR and multinuclear (13C, 15N, 103Rh) NMR measurements and X-ray crystallography for 2 and 4. Analogous reactions have been carried out using trans-[Rh2(µ-Cl)2(CO)2(CxHy)2] 11 (CxHy = C2H4 a or C8H14 b) under a nitrogen atmosphere and spectroscopic measurements on the reaction of 11a with pyridine were consistent with the successive formation of [Rh2(µ-Cl)2(CO)2(C2H4)2(py)2] 12, which lost ethylene and rearranged to give [Rh2(µ-CO)2Cl2(py)2] 13. Reaction of 11b with pyridine gave immediately trans-[Rh2(µ-Cl)2(CO)2(py)2] 14 and both 13 and 14 further reacted with pyridine to give 5.

This article reports the formation of Schottky nanocontacts on single crystalline ZnO nanorods (NR) using atomic force microscopy (AFM) with a PtIr-coated Si cantilever in a contact mode. ZnO NRs were synthesized by thermal evaporation of metallic zinc thin film followed by annealing. The NRs are [11 $$ \overline{2} $$ 0] directed (i.e., along a-axis) which is quite unusual for wurtzite ZnO. The appearance of an intense visible emission band in room-temperature photoluminescence indicates the presence of a high density of intrinsic defects confirming n-type ZnO. The PtIr tip/ZnO Schottky nanocontacts with an ultra fine effective contact radius ~0.5 nm on horizontally dispersed NRs show an ideality factor of ~7, turn on voltage of ~1.0 V, Schottky barrier height of ~0.65 eV, breakdown voltage of ~−4.7 V, and ON to OFF current ratio of ~500 at ±2 V. The junction corresponds to a nanoscale Schottky contact with satisfactory properties which is comparable to the other PtIr/ZnO or Pt/ZnO reports at higher loading forces. Single crystallinity and contact on the side faces of the horizontally dispersed NRs are primarily thought to be the key factors for higher device performances.

Reaction of N-acetyl-3-butanoyltetramic acid (Habta)(N-acetyl-3-butanoyl-1,5-dihydro-4-hydroxy-2H-pyrrol-2-one) with [Rh(acac)(CO)2](acac = acetylacetonate) in a 1 : 1 ratio gave [Rh(abta)(CO)2]1 which underwent displacement of CO by either P(OPh)3 or PPh3 to give [Rh(abta)(CO)L][L = P(OPh)3 or 2 PPh34] and [Rh(abta){P(OPh)3}2]3; the reaction of 4 with PPh3 gave the five-co-ordinate complex [Rh(abta)(CO)(PPh3)2]5. The solid-state structure of 3 has been determined by X-ray diffraction. It shows that rhodium adopts a slightly distorted square-planar geometry with the abta enolate ligand adopting an O,O′ mode of co-ordination via the functionalities associated with C4 and the acyl group at C3 in the pyrrolidine ring. Under 13CO, 3 is in equilibrium with 2 and 1 as shown by 13C NMR spectroscopy. No evidence has been found for the formation of five-co-ordinate complexes through the addition of P(OPh)3 to 2.

The synthesis of Ni filled multiwalled carbon nanotubes was performed by atmospheric pressure chemical vapor deposition with propane on Si at 850 C using a simple mixture of Ni(salen), and a conventional photoresist. Analysis of the carbon nanotubes using scanning electron microscopy together with high resolution transmission electron microscopy show that the nanotubes have grown by a tip growth mechanism and exhibit a multi walled structure with partial Ni filling. The high quality of the Ni filled nanotubes is evidenced by Raman spectroscopy. The magnetic properties of Ni filled nanotubes were analyzed using a superconducting quantum interference device which revealed their ferromagnetic behavior with large coercivity. A scalable as well as site selective growth of high quality Ni filled carbon nanotubes is achieved by a simple photolithographic method., Comment: multiwalled carbon nanotubes,chemical vapor deposition,Ni(salen),photoresist,magnetic properties,coercivity

The surface reconstruction of the Fe catalyst films due to high temperature processing in hydrogen prior to nanotube nucleation and its effect on the growth morphologies of partially filled carbon nanotubes (CNTs) synthesized using atmospheric pressure chemical vapor deposition (APCVD) of propane was investigated. Results show that pre-heating of the catalyst film deeply influences the particle size distribution, which governs the growth morphologies of the corresponding CNTs. The distribution of the catalyst particles over the Si substrate was analyzed before and after the heat treatment by atomic force microscopy (AFM) which reveals that heat treatment causes clusters of catalyst to coalesce and form macroscopic islands. The X-ray diffraction (XRD) pattern of the grown material indicates that they are graphitic in nature. Scanning electron microscopy (SEM) analysis suggested that the growth density strongly depends on the pre heat treatment of the Fe catalyst film. Multiwalled CNTs with partial catalyst filling were observed via high-resolution transmission electron microscopy (HRTEM) measurements. The degree of graphitization of the CNTs also depends on the pre heating as demonstrated by Raman analysis. A simple model for the growth of partially catalyst filled nanotubes is proposed., Comment: APCVD; Catalyzed growth; Partially filled CNT; RAMAN Spectroscopy. arXiv admin note: text overlap with arXiv:1908.00391, arXiv:1906.00167

By the use of the INEPT pulse sequence it has been possible to obtain 15N and 103Rh NMR data on [RhH2(PPh3)2(bipy)]Cl (bipy = 2,2′-bipyridyl) containing natural abundance 15N and prove the stereochemistry; 1H and 31P NMR data are also reported for [RhH2(PPh3)2(bipy)]Cl which can be easily prepared in the pure state by the reaction of [RhCl(PPh3)3] or [Rh2Cl2(PPh3)4] with bipy ([Rh]: [bipy] = 1:1) under an H2 atmosphere.

All the intermediates involved in the platinum catalysed methoxycarbonylation of ethene have been characterised by in situ NMR; the low activity of platinum catalysts in this reaction is shown to be due to trapping of the active intermediates by carbon monoxide at every step in the catalytic cycle and to the ready reversibility of the product forming reactions.

Exclusively cis-protonation occurs at axial N-atoms of chair shaped P3N9 ring cores in the protolysis of the lithium salt of hexaanionic cyclotriphosphazenate [(CyN)6P3N3]6− with three equivalents of butan-1-ol and cis-deprotonation takes place at the hexaprotic cyclotriphosphazene (PhNH)6P3N3 with three equivalents of BunLi, respectively, yielding both times lithium salts of cis-trihydrogen cyclotriphosphazenates [(RNH)3(RN)3P3N3]3− .

The reaction of Rh(NO3)3·2H2O with PPh3 and N2H4·H2O in MeOH gave the dinuclear carbopentazane complex [[graphic omitted]H)2CH2}]2+1, which has been characterised by multinuclear NMR measurements and X-ray diffraction. It is a dipositive, dinuclear cation in which the two bis(triphenylphosphine)rhodium units are bridged by the tetradentate carbopentazane ligand. The rhodium atoms have the expected square-planar geometry, with Rh–P and Rh–N distances of 2.225(3)–2.253(3) and 2.130(6)–2.166(6)A respectively. A series of experiments, aimed at elucidating the mechanism of formation of 1, indicated that the formation of the NCH2N linkage occurs via acid-catalysed nucleophilic addition of free N2H4 to the CH2 group of an NH2NCH2 ligand co-ordinated to RhI, and unambiguous multinuclear NMR (13C, 15N and 31P) and mass spectrometric evidence has been obtained for the monomeric complex [[graphic omitted]HNH2)]+, which readily rearranges to form 1. Related experiments have also provided evidence for the formation of [[graphic omitted]HNH2)]+, which also rearranges to give a dinuclear complex, [[graphic omitted]H)2CHMe}]2+.

Dissolution of [RhCl(PPh3)3], Wilkinson's catalyst, in pyridine affords an efficient catalyst for the selective reductive coupling of aldehydes. The reaction requires a close balance of the hydrogenating power and alkyl coupling ability of the catalyst. The species present in the pyridine solution of Wilkinson's catalyst have been studied in order to probe the origin of this selectivity. Pyridine has been found to replace one or more of the phosphine ligands in the precursor complex to give complexes of the type [RhCl(py)x(PPh3)3–x](py = pyridine, x = 1 or 2) and [Rh(py)x,(PPh3)4–x]CI (x = 1, 2 or 3). The reactions of these complexes with hydrogen have been shown to give cis-dihydride complexes viaoxidative addition. The complex trans-[Rh(CO)(py)(PPh3)2] ClO4has been synthesised and characterised spectroscopically and found not to react with H2 at room temperature. Preliminary in situ NMR measurements have shown that under the conditions of the catalysis either phosphine or pyridine can be replaced by a CO ligand. This results in a marked decrease in the activity of the rhodium centre towards oxidative addition of hydrogen and in the stability, with respect to elimination of H2, of the dihydride.

The crystal structure of trans-[Rh(CO)(PPh3)2(OClO3)] has been determined, and it has been established that the perchlorate group is easily displaced by substituted hydrazines to give trans-[Rh(CO)(PPh3)2L]ClO4(L = NH2NH2–xRx; x= 1 or 2; R = Me or Ph). X-Ray crystallography shows that for all these complexes the unsymmetrically substituted hydrazine co-ordinates to rhodium viathe NH2 group.

Results from magnetisation-transfer measurements on [RhCl(PPh3)3] and [RhH2Cl(PPh3)3] have been compared with data for analogous complexes obtained by replacing Cl with ONO2 and NH3. For the chloro- and ammine-rhodium(I) complexes the rate constants for phosphine isomerisation and overall phosphine dissociation are similar and much lower than those observed for the nitrato complex. Nitrogen-15 NMR measurements show that this difference is probably due to the greater substitution lability of ONO2 over Cl and NH3. For the rhodium(III) complexes it was possible to obtain rate constants for phosphine dissociation for both PPh3trans to PPh3 and PPh3trans to H and similar rate constants are found for [RhH2Cl(PPh3)3] and [RhH2(ONO2)(PPh3)3]. These are larger than those for [RhH2(NH3)(PPh3)3]ClO4, and this is consistent with going from a neutral to a cationic complex. In all three cases the rate constant for the fastest phosphine dissociation (trans to H) mirrors the rate of hydride isomerisation. The crystal structure of [Rh(NH3)(PPh3)3]ClO4 has been determined and the structural data are compared with those of other square-planar rhodium(I) complexes.

Refluxing Rh(NO3)3·2H2O with an excess of PPh3 in MeOH or EtOH for over 48 h gives trans-[Rh(CO)(ONO2)(PPh3)2]1 whereas the same reaction at room temperature gives predominantly [Rh(ONO2)(PPh3)3]2. X-Ray structure determinations of 1 and 2 show the nitrate groups to be monodentate in each case although disorder of the CO and NO3 groups in 1 precludes accurate determination of bond lengths and angles. There is no reaction of trans-[Rh(CO)X(PPh3)2](X = Cl, F or ONO2) with H2 at room temperature and 1 atm pressure, whereas there is an immediate reaction of [Rh(ONO2)(PPh3)3] under the same conditions to give [RhH2(ONO2)(PPh3)3]3, which has been characterised by multinuclear NMR spectroscopy. Compound 3 loses PPh3 to give [RhH2(O2NO)(PPh3)2]6a which has been characterised similarly and by X-ray crystallography; although the metal-bound hydrogens were not located the structure is clearly based on an octahedral geometry with trans phosphines and a bidentate nitrate.

Results of infrared spectroscopic studies following the standard procedure are reported for the hydrogen-bonding systems involving phenol–azabenzene and ethanol–azabenzene complexes. The theoretical model proposed by Bader is examined and a theoretical index for an assessment of the relative strength of these hydrogen-bonding bases is proposed.