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The reaction between differently substituted borasiloxanes and 2,5-bis(3-pyridylethynyl)thiophene provided the first example of luminescent borasiloxane-based chiral helices held together by N-B bonds. The starting building blocks and the helices were fully characterized, and the nature of the N-B bond rationalized by means of theoretical calculations.

The structure and molecular order in the thermotropic ionic liquid crystal (ILC), [choline][geranate(H)octanoate], an analogue of Choline And GEranate (CAGE), which has potential for use as a broad-spectrum antimicrobial and transdermal and oral delivery agent, were investigated by magic-angle spinning (MAS) nuclear magnetic resonance (NMR), polarizing optical microscopy, small-angle X-ray scattering (SAXS), and mass spectrometry. Mass spectrometry and the 1H NMR chemical shift reveal that CAGE-oct is a dynamic system, with metathesis (the exchange of interacting ions) and hydrogen exchange occurring between hydrogen-bonded/ionic complexes such as [(choline)(geranate)(H)(octanoate)], [(choline)(octanoate)2(H)], and [(choline)(geranate)2(H)]. These clusters, which are shown by mass spectrometry to be significantly more stable than expected for typical electrostatic ion clusters, involve hydrogen bonding between the carboxylic acid, carboxylate, and hydroxyl groups, with rapid hydrogen bond breaking and re-formation observed to average the 1H chemical shifts. The formation of a partial bilayer liquid crystal (LC) phase was identified by SAXS and polarizing optical microscopy at temperatures below ∼293 K. The occurrence of this transition close to room temperature could be utilized as a potential temperature-induced “switch” of the anisotropic properties for particular applications. The presence of an isotropic component of approximately 23% was observed to coexist with the LC phase, as detected by polarizing optical microscopy and quantified by both 1H–13C dipolar-chemical shift correlation (DIPSHIFT) and 1H double-quantum (DQ) MAS NMR experiments. At temperatures above the LC-to-isotropic transition, intermediate-range order (clustering of polar and nonpolar domains), a feature of many ILs, persists. Site-specific order parameters for the LC phase of CAGE-oct were obtained from the MAS NMR measurement of the partially averaged 13C–1H dipolar couplings (DCH) by cross-polarization (CP) build-up curves and DIPSHIFT experiments, and 1H–1H dipolar couplings (DHH) by double-quantum (DQ) build-up curves. The corresponding order parameters, SCH and SHH, are in the range 0–0.2 and are lower compared to those for smectic (i.e., layered) phases of conventional nonionic liquid crystals, resembling those of lamellar phases formed by lyotropic surfactant–solvent systems.\ud \ud

The behaviour of two molecular rotors, one charged – 3,3′-diethylthiacarbocyanine iodide (Cy3) and one neutral – 8-[4-decyloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY-C10), have been studied in various ionic liquids. The fluorescent decay lifetime has been used to elucidate the structure of the immediate region around the rotor. The neutral BODIPY-C10 was found to prefer the non-polar alkyl chain environment, leading to two trends in the lifetime of the dye: one when it was fully partitioned into the non-polar domain, and one when it also sampled polar moieties. The positively charged Cy3 dye showed a complex relationship between the bulk viscosity of the ionic liquid and lifetime of the molecular rotor. This was attributed to a combination of polarity related spectral changes, changes in anion cages around the dye, and temperature dependent fluorescent lifetimes alongside the dependence of the rotor upon the viscosity.

A comparison of chlorido-gallium functionalized alkoxides as precursors for aerosol-assisted chemical vapor deposition (AACVD) was carried out. Variable-temperature (VT)-NMR studies were used to probe the fluxional behavior of these alkoxides in solution, and hence their utility as precursors. The synthesis involved the initial isolation of the dimer [GaCl(NMe2)2]2 via a salt metathesis route from GaCl3 and 2 equiv of LiNMe2. This dimer was then reacted with 4 equiv of HOCH2CH2CH2NEt2, resulting in the formation of Ga[μ-(OCH2CH2CH2NEt2)2GaCl2]3 (1). Mass spectrometry and VT-NMR confirmed the oligomeric structure of 1. Tuning of the ligand properties, namely, the chain length and substituents on N, resulted in formation of the monomers [GaCl(OR)2] (R = CH2CH2NEt2, (2); CH2CH2CH2NMe2, (3)). VT-NMR studies, supported by density functional theory calculations, confirmed that the ligands in both 2 and 3 possess a hemilabile coordination to the gallium center, owing to either a shorter carbon backbone (2) or less steric hindrance (3). Both 2 and 3 were selected for use as precursors for AACVD: deposition at 450 °C gave thin films of amorphous Ga2O3, which were subsequently annealed at 1000 °C to afford crystalline Ga2O3 material. The films were fully characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV–visible spectroscopy, and energy dispersive X-ray analysis., A comparison of chlorido-gallium functionalized alkoxides for use as precursors toward gallium oxide (Ga2O3) via aerosol-assisted chemical vapor deposition was carried out. Variable-temperature NMR studies were used to probe the fluxionality of these alkoxides in solution, combined with computational modeling of their dynamic behavior and hence their utility as precursors. Thin films of gallium oxide were deposited, and full characterization of the films was carried out.

A tetracarboxylic acid with a methyl-substituted siloxane core (L-H4) has been prepared and applied in the construction of water stable MOFs with low water affinity. L-H4 itself crystallizes as an interpenetrated 3D hydrogen-bonded network. Reaction of L-H4 with ZrIV/HfIV gave IMP-32-Zr/Hf – both 3D MOFs of scu topology.

The identification of specific design concepts for the in silico design of ionic liquids (ILs) has been accomplished using theoretical methods. Molecular building blocks, such as interchangeable functional groups, are used to design a priori new ILs which have subsequently been experimentally investigated. The conformational design concepts are developed by separately and systematically changing the central (imide), bridging (sulfonyl) and end (trifluoromethyl) group of the bis(trifluoromethanesulfonyl)imide [N(Tf)2]− anion and examining the resultant potential energy surfaces. It is shown that these design concepts can be used to tune separately the minimum energy geometry, transition state barrier height and relative stability of different conformers. The insights obtained have been used to design two novel anions for ILs, trifluoroacetyl(methylsulfonyl)imide [N(Ms)(TFA)]− and acetyl(trifluoromethanesulfonyl)imide [N(Tf)(Ac)]−. The computationally predicted structures show excellent agreement with experimental structures obtained from X-ray crystallography. [C4C1im][N(Tf)(Ac)] and [C4C1im][N(Ms)(TFA)] ILs have been synthesised and ion diffusion coefficients examined using pulsed field gradient stimulated echo NMR spectroscopy. Significantly increased diffusion was observed for the more flexible [N(Tf)(Ac)]− compared with the more rigid [N(Ms)(TFA)]− analogue. Furthermore, a pronounced impact on the fluidity was observed. The viscosity of the IL with the rigid anion was found to be twice as high as the viscosity of the IL with the flexible anion. The design concepts presented in this work will enable researchers in academia and industry to tailor anions to provide ILs with specific desired properties.

Terrorists frequently use explosives and they represent an imminent threat to national and global security. Recent events highlight the necessity of explosive detection, demonstrating the need for developing and applying new sensors for explosive gas detection. Semiconducting metal oxide gas sensors can be incorporated into electronic noses, which provide a cheap, portable and highly sensitive device. Using unmodified, admixed and 2-layered sensors consisting of WO3 and chromium titanium oxide (CTO), an array of seven heterojunction semiconducting metal oxide sensors was produced. All seven sensors were tested against four gases associated with explosive materials. The sensitivity was improved by using 2-layered sensors in response to ethanol, ammonia and nitromethane, whereas the admixed sensors showed high sensitivity when exposed to nitrogen dioxide. The selectivity of the array of sensors was tested using machine-learning techniques with a support vector machine. The technique produced good data classification when classifying the gases used within the study.

Eight imidazolium-based salts with the weakly-coordinating anions [BArF]− and [Al(OtC4F9)4]− ([BArF]− = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) have been synthesized. Characterization by 1H NMR spectroscopy shows that the salts are fully dissociated in solution. Six examples have been further characterized by X-ray crystallography, revealing that weak hydrogen bonds do occur in the solid phase between the imidazolium cations and weakly coordinating anions. Comparison with the bulky [IDiPPH] imidazolium cation (IDiPPH = 1,3-bis{2,6-bis(diisopropyl)phenyl}imidazolium) shows that large steric bulk close to the imidazolium protons can preclude hydrogen bonds from forming. Differential scanning calorimetry of the salts reveal that all are thermally stable up to 200 °C which renders them as potentially suitable background electrolytes for electrochemical processes which take place at elevated temperatures.

We report results for the electrochemistry of the germanium(II) tri-halide anions, [GeCl3]?, [GeBr3]? and [GeI3]?, in supercritical difluoromethane containing 60?mm [NnBu4][BF4] at 19.1?MPa and 358?K. The voltammetry shows mass-transport-limited currents for reduction to germanium at gold on the first scan. There is no evidence of a germanium stripping peak and, on subsequent scans, the electrode slowly passivates with the deposition of approximately 0.4??m of material. The redox potentials for the reduction of the three tri-halides are in the order [GeCl3]?

For the first time, a versatile electrolyte bath is described that can be used to electrodeposit a wide range of p-block elements from supercritical difluoromethane (scCH2 F2 ). The bath comprises the tetrabutylammonium chlorometallate complex of the element in an electrolyte of 50×10(-3) mol dm(-3) tetrabutylammonium chloride at 17.2 MPa and 358 K. Through the use of anionic ([GaCl4 ](-) , [InCl4 ](-) , [GeCl3 ](-) , [SnCl3 ](-) , [SbCl4 ](-) , and [BiCl4 ](-) ) and dianionic ([SeCl6 ](2-) and [TeCl6 ](2-) ) chlorometallate salts, the deposition of elemental Ga, In, Ge, Sn, Sb, Bi, Se, and Te is demonstrated. In all cases, with the exception of gallium, which is a liquid under the deposition conditions, the resulting deposits are characterised by SEM, energy-dispersive X-ray analysis, XRD and Raman spectroscopy. An advantage of this electrolyte system is that the reagents are all crystalline solids, reasonably easy to handle and not highly water or oxygen sensitive. The results presented herein significantly broaden the range of materials accessible by electrodeposition from supercritical fluid and open up the future possibility of utilising the full scope of these unique fluids to electrodeposit functional binary or ternary alloys and compounds of these elements.

A series of indium doped ZnO (IZO) materials were fabricated, characterised and tested for their gas sensing properties. ZnO was synthesised with indium doping levels of 0.2, 0.5, 1 and 3 mol%. These were fabricated into gas sensors. Production took place using a commercially available screen printer, a 3 × 3 mm alumina substrate containing interdigitated electrodes and a platinum heater track. Materials were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Electrical conductivity of all samples was also calculated. Sensors were exposed to ethanol, methanol, n-butanol and acetone at concentrations between 5 and 80 ppm. Low levels of indium doping were found to increase the responsiveness of the sensors. However, higher levels of doping were found to inhibit conductivity and responsiveness to gases of IZO sensors. Sensors with low levels of indium doping were found to show minimal response to other gases, demonstrating a lack of cross sensitivity. These sensors show potential for inclusion into an electronic nose for with the aim of selective alcohol detection.

We report the electrodeposition of germanium from supercritical difluoromethane (sc-CH2F2) at 19 MPa and 358 K using [NnBu4][GeCl3]. Voltammetry shows a classic nucleation loop on the first anodic scan with a high nucleation overpotential for germanium on TiN. In all cases the deposition appears to be kinetically limited by a coupled, potential independent, chemical step. Films of germanium were deposited at a range of potentials. At high overpotentials the films were dendritic and poorly adherent. At lower overpotentials, below ?2 V vs. Ag|LaF3, the films are smoother and more homogeneous. Analysis of the films by energy dispersive X-ray (EDX) spectroscopy shows the presence of germanium with some chloride impurity. Raman spectroscopy confirms the deposition of amorphous germanium. Plating by pulsing to ?1.9 V vs. Ag|LaF3 for 100 ms and then growth at ?1.5 V vs. Ag|LaF3, was found to produce the best films. On annealing at 700°C under an Ar atmosphere for 1 hour the as-deposited amorphous germanium film is converted into crystalline germanium, as determined by X-ray diffraction (XRD) and Raman spectroscopy.

[GeCl2(dioxane)] reacts with the neutral aza-macrocyclic ligands L, L = Me3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane), Me4cyclen (1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) or Me4cyclam (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and two mol. equiv. of Me3SiO3SCF3 in thf solution to yield the unusual and hydrolytically very sensitive [Ge(L)][O3SCF3]2 as white solids in moderate yield. Using shorter reaction times [Ge(Me3tacn)]Cl2 and [Ge(Me3tacn)]Cl[O3SCF3] were also isolated; the preparation of [Ge(Me4cyclen)][GeCl3]2 is also described. The structures of the Me3tacn complexes show κ(3)-coordination of the macrocycle, with the anions interacting only weakly to produce very distorted five- or six-coordination at germanium. In contrast, the structure of [Ge(Me4cyclen)][O3SCF3]2 shows no anion interactions, and a distorted square planar geometry at germanium from coordination to the tetra-aza macrocycle. Crystal structures of the Si(iv) complexes, [SiCl3(Me3tacn)]Y (Y = O3SCF3, BAr(F); [B{3,5-(CF3)2C6H3}4]) and [SiHCl2(Me3tacn)][BAr(F)], obtained from reaction of SiCl4 or SiHCl3 with Me3tacn, followed by addition of either Me3SiO3SCF3 or Na[BAr(F)], contain distorted octahedral cations, with facialκ(3)-coordinated Me3tacn. The open-chain triamine, Me2NCH2CH2N(Me)CH2CH2NMe2 (pmdta), forms [SiCl3(pmdta)][BAr(F)] and [SiBr3(pmdta)][BAr(F)] under similar conditions, containing mer-octahedral cations.

The illicit manufacture of drugs in the 21st century presents a danger to first responders, bystanders and the environment, making its detection important. Electronic noses based on metal oxide semiconducting (MOS) sensors present a potential technology to create devices for such purposes. An array of four thick film MOS gas sensors was fabricated, based on zinc oxide inks. Production took place using a commercially available screen printer, a 3 × 3 mm alumina substrate containing interdigitated electrodes and a platinum heater track. ZnO inks were modified using zeolite β, zeolite Y and mordenite admixtures. The sensors were exposed to four gases commonly found in the clandestine laboratory environment; these were nitrogen dioxide, ethanol, acetone and ammonia. Zeolite modification was found to increase the sensitivity of the sensor, compared to unmodified ZnO sensors, all of which showed strong responses to low ppm concentrations of acetone, ammonia and ethanol and to ppb concentrations of nitrogen dioxide. Machine learning techniques were incorporated to test the selectivity of the sensors. A high level of accuracy was achieved in determining the class of gas observed.

We present investigations into a variety of supporting electrolytes and supercritical fluids probing the phase and conductivity behaviour of these systems and show that they not only provide sufficient electrical conductivity for an electrodeposition bath, but match the requirements imposed by the different precursors and process parameters, e.g. increased temperature, for potential deposition experiments. The two supercritical fluids that have been explored in this study are difluoromethane (CH2F2) and 1,1-difluoroethane (CHF2CH3). For CH2F2, the phase behaviour and electrical conductivity of eight ionic compounds have been studied. Each compound consists of a cation and an anion from the selected candidates i.e. tetramethylammonium ([N(CH3)4](+)), tetrabutylammonium ([N((n)C4H9)4](+)), 1-ethyl-3-methylimidazolium ([EMIM](+)) and 1-butyl-3-methylimidazolium ([BMIM](+)) for cations, and tetrakis(perfluoro-tert-butoxy)aluminate ([Al(OC(CF3)3)4](-)), chloride (Cl(-)), trifluoromethyl sulfonimide ([NTf2](-)) and tris(pentafluoroethyl)trifluorophosphate ([FAP](-)) for anions. For CHF2CH3, [N((n)C4H9)4][BF4] and [N((n)C4H9)4][B{3,5-C6H3(CF3)2}4] have been investigated for comparison with the previously measured solubility and conductivity in CH2F2. We have found that [N((n)C4H9)4][Al(OC(CF3)3)4], [N((n)C4H9)4][FAP] and [N(CH3)4][FAP] have much higher molar conductivity in scCH2F2 at similar conditions than [N((n)C4H9)4][BF4], a widely used commercial electrolyte. Additionally, scCHF2CH3 shows potential for use as the solvent for supercritical fluid electrodeposition, especially at high temperatures since high density of this fluid can be achieved at lower operating pressures than similar fluids that can be used to produce electrochemical baths with comparable conductivity.

A new route to cationic complexes of Mg, Ca, Sr and Ba with 18-membered ring O4S2, O4Se2 and O2S4 donor macrocycles from metal acetonitrile complexes with weakly coordinating [BAr(F)](-) anions is described. The precursors used were [M(MeCN)x][BAr(F)]2 (M = Mg, x = 6; M = Ca, x = 8) and [M'(acacH)(MeCN)5][BAr(F)]2 (M' = Sr or Ba). Reaction of these with the heterocrowns, [18]aneO4S2 (1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane), [18]aneO4Se2 (1,4,10,13-tetraoxa-7,16-diselenacyclooctadecane) or [18]aneO2S4 (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane) in anhydrous CH2Cl2 solution gave [M(heterocrown)(MeCN)2][BAr(F)]2 for M = Mg, Ca or Sr, whilst the larger Ba forms [Ba(heterocrown)(acacH)(MeCN)][BAr(F)]2. The complexes have been characterised by microanalysis, IR, (1)H and (13)C{(1)H} NMR spectroscopy. X-ray crystal structures are reported for [Ca([18]aneO2S4)(MeCN)2][BAr(F)]2, [Ca([18]aneO4Se2)(MeCN)2][BAr(F)]2, [Sr([18]aneO4S2)(MeCN)2][BAr(F)]2, and [Sr([18]aneO4Se2)(MeCN)2][BAr(F)]2 which contain 8-coordinate metal centres with trans-nitrile ligands and κ(6)-heterocrowns, and for the 9-coordinate [Ba([18]aneO4Se2)(acacH)(MeCN)][BAr(F)]2. Adventitious hydrolysis of the magnesium complexes in solution results in six-coordinate complexes, [Mg(κ(3)-[18]aneO4Se2)(OH2)2(MeCN)][BAr(F)]2 and [Mg(κ(3)-[18]aneO4S2)(OH2)2(MeCN)][BAr(F)]2, whose structures were determined. X-ray crystal structures are also reported for [Mg(MeCN)6][BAr(F)]2, [M(MeCN)8][BAr(F)]2 (M = Ca, Sr) and [Ca(18-crown-6)(MeCN)2][BAr(F)]2.

In2O3 and In2O3:M (M = Ti or Ta) thin films were deposited on glass substrates via aerosol-assisted chemical deposition (AACVD) at 450 °C. The resulting films were characterized by a range of techniques including glancing-angle X-ray diffraction, scanning electron microscopy, wavelength dispersive analysis of X-rays, and optical transmission/reflectance studies to investigate the effect of doping on the films. The In2O3:M thin films were found to contain 6.5 and 2.3 at.% of Ti and Ta, respectively. The gas sensing properties were investigated on films deposited onto gas sensing substrates via AACVD. Tantalum doped indium oxide (In2O3:Ta) thin films showed a superior response, compared to In2O3, to a number of reducing gases (ethanol, CO, ammonia) and also the oxidizing gas NO2. Considerable selectivity to ethanol was observed; the greatest gas response (R/R0) was 16.95 to 100 ppm ethanol.

A novel homoleptic bismuth(III) β-diketonate (dibenzoylmethane – dbm) complex [Bi(dbm)3]2 has been used as a precursor to thin films of crystalline β-Bi2O3, and hexachloroplatinic acid (H2PtCl6·6H2O) has been demonstrated as a suitable precursor for deposition of platinum nanoparticles, both deposited via aerosol-assisted chemical vapour deposition (AACVD). Thin films of Pt–Bi2O3 were co-deposited from a mixture of [Bi(dbm)3]2 and H2PtCl6·6H2O; the introduction of Pt particles into β-Bi2O3 causes hydrogen to be evolved during photolysis of water over the composite material, a property not found for Pt particles or β-Bi2O3 alone.

Gallium and indium oxide thin films have received much attention in recent years for their wide range of applications. This review summarises the literature concerning single-source precursors and the methods employed to deposit gallium and indium oxide thin films using these compounds. An update of the literature outlining compounds which are potential single-source precursors to these materials is also included.

Aerosol-assisted chemical vapour deposition (AACVD) of a suspension of [In(thd)(3)] (thd = 2,2,6,6-tetramethylheptane-3,5-dionate) in CH2Cl2 at 450 degrees C afforded thin crystalline films of indium oxide. The films were analyzed by scanning electron microscopy (SEM), glancing angle X-ray diffraction (XRD) and energy dispersive analysis of X-rays (EDX). Efforts to grow thicker films were hampered by the poor solubility of [In(thd)(3)], so the synthesis of heteroleptic compounds of the type [M(bdk)(2)X] (M = Ga, In; bdk = beta-diketonate; X = chloride, hydride, methyl) was attempted such that the solubility could be improved by tuning the ligands surrounding the metal centre. Reaction of stoichiometric amounts of beta-diketones [Hthd and 2,4-pentanedione (acetylacetone, Hacac)] with Lewis base-stabilized adducts of GaH3 resulted only in the isolation of the homoleptic gallium tris(beta-diketonate) compounds [Ga(bdk)(3)], instead of the expected heteroleptic gallium bis(beta-diketonate) hydride, [GaH(bdk)(2)]. An unexpected reduction of Hthd to 2,2,6,6-tetramethylheptane-3,5-diol was also observed. Other attempted syntheses of gallium bis(beta-diketonate) compounds also resulted in the isolation of homoleptic [Ga(bdk)(3)] complexes and similar results were obtained for indium. The compounds were characterised by H-1 NMR spectroscopy, mass spectrometry and elemental analysis and the structures of [In(thd)(3)] and 2,2,6,6-tetramethylheptane-3,5-diol were determined by X-ray crystallography.

The compounds tert-butylarsenium(III) tri-μ-chlorido-bis[trichloridotitanium(IV)], (C(4)H(12)As)[Ti(2)Cl(9)] or [(t)BuAsH(3)][Ti(2)(μ-Cl)(3)Cl(6)], (II), and bis[bromidotriphenylarsenium(V)] di-μ-bromido-μ-oxido-bis[tribromidotitanium(IV)], (C(18)H(15)AsBr)(2)[Ti(2)Br(8)O] or [Ph(3)AsBr](2)[Ti(2)(μ-O)(μ-Br)(2)Br(6)], (III), were obtained unexpectedly from the reaction of simple arsane ligands with Ti(IV) halides, with (II) lying on a mirror plane in the unit cell of the space group Pbcm. Both compounds contain a completely novel ion, with [(t)BuAsH(3)](+) constituting the first structurally characterized example of a primary arsenium cation. The oxide-bridged titanium-containing [Ti(2)(μ-O)(μ-Br)(2)Br(6)](2-) dianion in (III) is also novel, while the bromidotriphenylarsenium(V) cation is structurally characterized for only the second time.

The group 13 monoalkoxometallanes [Me 2 Ga(OC(CH 3 ) 2 CH 2 OMe)] 2 (1) and [Me 2 In(OCH(CH 3 )CH 2 OMe)] 2 (2), incorporating donor functionalised alkoxides, were synthesised from the reaction of GaMe 3 or InMe 3 with ROH (R=C(CH 3 ) 2 CH 2 OMe (1); R=CH(CH 3 )CH 2 OMe (2)) in toluene. X-ray crystallography showed that both compounds adopt dimeric structures with a planar M 2 O 2 ring, and each group 13 atom is coordinated in a distorted trigonal bipyramidal geometry. The AACVD reaction of GaMe 3 and ROH (R =C(CH 3 ) 2 CH 2 OMe, CH 2 CH 2 OMe, CH 2 CH 2 NMe 2 ) resulted in the formation of thin films of Ga 2 O 3 on glass substrates at 450°C. The gallium oxide films were analyzed by scanning electron microscopy, X-ray powder diffraction, energy dispersive analysis of X-rays, wavelength dispersive analysis of X-rays and X-ray photoelectron spectroscopy. This CVD technique offers a rapid, convenient route to Ga 2 O 3 , which involves the in situ formation of dimethylgallium alkoxides, of the type [Me 2 Ga(μ-OR)] 2 similar to compound 1. © 2010 - IOS Press and the authors. All rights reserved.

The new imidazolium salts functionalised with the trimethylsilyl ester group 1a–c, were easily obtained by quaternisation of alkyl- or aryl-imidazoles with trimethylsilyl bromoacetate. Salt 1a was isolated and fully characterised. It reacted with mesityl copper (Cu5Mes5) under trimethylsilyl abstraction to form the complex 2. Methanolysis of 1a–c gave good yields of the carboxylic acid functionalised imidazolium salts 3a–c. Deprotonation of the latter in liquid ammonia led to the zwitterionic imidazolium carboxylates 4a–c. Reaction of 4a with (Cu5Mes5) gave solutions from which the insoluble polymeric 5a crystallised slowly. Generation of the carboxylate-functionalised NHC in situ followed by reaction with Pd(OOCCH3)2 gave the new complex 6a in which the NHC-carboxylate ligand is chelate bidentate.

Some new N,N‘-bis(aryl)imidazolinium salts (3a−h), in which the N-aryl groups have one unsubstituted ortho position and alkyl (Me, Pri) or alkoxy (OMe, OPri) substitution at the other ortho and/or para positions, have been prepared. They were used for the synthesis of N-heterocyclic carbene complexes of palladium in which the N-heterocyclic carbene is attached to cyclometalated or electron-rich aromatic rings (4, 5, 11d,e). The reaction of Pd(tmed)(CH3)2 with the N-heterocyclic carbene generated from 3b and base gave the dimethyl complex 6, which quantitatively eliminated ethane to form the Pd(0) complex 7. The latter was converted to a new type of “pincer” complex (8) by facile cyclometalation of both aromatic groups of the N-heterocyclic carbene ligand. The activities of the new complexes 4 and 9d,e in the Heck reaction of aryl halides were compared. At higher temperatures the complexes 9d,e show low activity in the coupling of aryl chlorides.

Dimethylindenyl-functionalized N-heterocyclic carbene complexes of titanium(IV), titanium(III), zirconium(IV), and vanadium(III) were prepared from potassium indenylcarbenes by salt elimination reactions. X-ray diffraction studies revealed that in the complexes the ligand adopts a bidentate coordination mode. Alkanolysis of a dimethylindene-functionalized imidazolium salt with Y(CH2SiMe3)3(THF)2 gave rise to a dimeric yttrium bromo alkyl in which the ligand adopts a bidentate coodination mode. Aminolysis of the fluorene-functionalized imidazolium salts with {[Cr(N(SiMe3)2)2(THF)2} led to chromium(II) complexes in which the ligand adopts a monodentate binding mode via the N-heterocyclic carbene end with dangling fluorene groups.

The coordination and organometallic chemistry of linear, rigid, tridentate ligands, which incorporate at least one N-heterocyclic carbene and other ‘classical’ donors, is reviewed across the periodic table with emphasis on unique features due to the presence of the N-heterocyclic carbene donor.

The complexes [M(L)][BAr(F)] (BAr(F) = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), L = [18]aneO4S2 (1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane): M = Li-Cs; L = [18]aneO2S4 (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane): M = Li, Na, K; L = [18]aneO4Se2 (1,4,10,13-tetraoxa-7,16-diselenacyclooctadecane): M = Na, K, as well as [Na(18-crown-6)][BAr(F)], are obtained in good yield as crystalline solids by reaction of M[BAr(F)] with the appropriate macrocycle in dry CH2Cl2. X-ray crystallographic analyses of [Li([18]aneO4S2)][BAr(F)] and [Li([18]aneO2S4)][BAr(F)] show discrete distorted octahedral cations with hexadentate coordination to the macrocycle. The heavier alkali metal complexes all contain hexadentate coordination of the heterocrown, supplemented by MF interactions via the anions, producing extended structures with higher coordination numbers; Na: CN = 7 or 8; K: CN = 8; Rb: CN = 9; Cs: CN = 8 or 10. Notably, all of the structures exhibit significant M-S/Se coordination. The crystal structures of the potassium and rubidium complexes show two distinct [M(heterocrown)](+) cations, one with MF interactions to two mutually cis [BAr(F)](-) anions, and the other with mutually trans [BAr(F)](-) anions, giving 1D chain polymers. Solution multinuclear ((1)H, (13)C, (7)Li, (23)Na, (133)Cs) NMR data show that the macrocyclic coordination is retained in CH2Cl2 solution.

The Group 1 complexes, [M(Me6[18]aneN6)][BAr(F)] (M = Li-Cs; Me6[18]aneN6 = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane; BAr(F) = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), are obtained in high yield by reaction of the macrocycle with M[BAr(F)] in anhydrous CH2Cl2 solution, and characterised spectroscopically ((1)H, (13)C{(1)H}, (7)Li, (23)Na, and (133)Cs NMR), by microanalysis and, for M = Li, K, and Rb, by single crystal X-ray analysis. The structures show N6-coordination to the metal ion; the small ionic radius for Li(+) leads to a puckered conformation. In contrast, the K(+) ion fits well into the N6 plane, with the [BAr(F)](-) anions above and below, leading to two K(+) species in the asymmetric unit (a hexagonal planar [K(Me6[18]aneN6)](+) cation and a '[K(Me6[18]aneN6)(κ(1)-BAr(F))2](-) anion', with long axial KF interactions). The Rb(+) ion sits above the N6 plane, with two long axial RbF interactions in one cation and two long, mutually cis RbF interactions in the other. The unusual sandwich cations, [M(Me3tacn)2](+) (M = Na, K; distorted octahedral, N6 donor set) and half-sandwich cations [Li(Me3tacn)(thf)](+) (distorted tetrahedron, N3O donor set), [Li(Me4cyclen)(OH2)](+), and [Na(Me4cyclen)(thf)](+) (both distorted square pyramids with N4O donor sets) were also prepared (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, Me4cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). Density functional theory (DFT) calculations, using the BP86 and B3LYP functionals, show that the accessibility of the [M(Me3tacn)2](+) sandwich cations depends strongly on the M(+) ionic radius, such that it is sufficiently large to avoid steric clashing between the Me groups of the two rings, and small enough to avoid very acute N-M-N chelate angles. The calculations also show that coordination to the Group 1 cation involves significant donation of electron density from the p-orbitals on the N atoms of the macrocycle, rather than purely electrostatic interactions.

Unprecedented homoleptic octathioether macrocyclic coordination to Na(+) in [Na([24]aneS8)](+) has been achieved by using Na[B{3,5-(CF3)2-C6H3}4] as a source of "naked" Na(+) ions and confirmed crystallographically, with d(Na-S) = 2.9561(15)-3.0524(15) Å. Density functional theory calculations show that there is electron transfer from the S 3p and C 2p valence orbitals of the ligand to the 3s and 3p orbitals of the Na(+) ion upon complexation.

The complexes [(C-N-C)MX(n)(thf)(m)] with the 'pincer' 2,6-bis(imidazolylidene)pyridine, (C-N-C) = 2,6-bis(arylimidazol-2-ylidene)pyridine, aryl = 2,6-Pr(i)2C6H3, M = V, X = Cl, n = 2, m = 1 1a; M = Cr, X = Cl, n = 2, m = 0, 2a, X = Br, 2b; M = Mn, X = Br, n = 2, m = 0, 3; M = Nb, X = Cl, n = 3, m = 0, 4; and M = U, X = Cl, n = 4, m = 0, 5, were synthesised by (a) substitution of labile tmed (1a), thf (2a, 3, 5) or dme (4) by free (C-N-C) or by (b) reaction of the bisimidazolium salt (CH-N-CH)Br2 with {Cr[N(SiMe3)2]2(thf)2} followed by amine elimination (2b). Attempted alkylation of 1a, 2, 3a and 4 with Grignard or alkyl lithiums gave intractable mixtures, and in one case [reaction of 1a with (mesityl)MgBr] resulted in exchange of Cl by Br (1b). Oxidation of 1a or [(C-N-C)VCl3] with 4-methylmorpholine N-oxide afforded the trans-V(C-N-C)(=O)Cl2, 6, which by reaction with AgBF4 in MeCN gave trans-[V(C-N-C)(=O)(MeCN)2][BF4]2, 7. Reaction of 1a with p-tolyl azide gave trans-V(C-N-C)(=N-p-tolyl)Cl2 8. The complex trans-Ti(C-N-C)(=NBu(t))Cl2, 9, was prepared by substitution of the pyridine ligands in Ti(NBu(t))Cl2(py)3 by C-N-C.

The factors that affect the dispersion of exfoliated organically modified montmorillonite in a solution of poly(methyl methacrylate) in methyl methacrylate are explored. Exfoliation of montmorillonite in the solution is achieved with the assistance of ultrasound, and rheological measurements indicate a very significant increase in the viscosity, a dramatic shear thinning behavior, and a finite yield stress, all of which are direct consequences of the exfoliated state of the clay platelets. A number of factors, including the sonication power, clay loading, use of a swelling agent, and moisture content of the modified montmorillonite, are found to influence the exfoliation process. The effect of addition of a range of titanate coupling agents (LICA-01, 12, 38, 44, and 97) on the viscosity of the nanoclay dispersions was investigated. It was found that LICA-44 had the effect of reducing the viscosity of the exfoliated montmorillonite dispersion without apparently influencing the extent of the exfoliation. Molecular modeling, UV-visible and Fourier transform infrared spectrometry were used to investigate the possible reasons for efficacy of this LICA. The LICA appears to act through a combination of steric effects and the presence of certain charges on the organic molecule. The magnitude of the negative charges on elements of the LICA appears to influence its ability to bind to the clay and also its ability to reduce the viscosity of the nanoclay. This article indicates how the apparently conflicting requirements of achieving a highly exfoliated state and also maintaining a viscosity low enough for processing can be effectively addressed.

The new binary mixed-valence fluoride of germanium, Ge3F8, has been obtained by heating GeF4 with powdered Ge in an autoclave (390 K/4 bar/48 h). The structure contains pyramidal Ge(II)F3 and octahedral Ge(IV)F6 units, linked by fluoride bridges. The new compound is the missing member of the series (GeF2)n·GeF4 (n = 2, 4, or 6). Sublimation of (GeF2)n·GeF4in vacuo provides a convenient source of GeF2 in ca. 30% overall yield.

Highly unusual Na(+) complexes with neutral tri- and tetra-amines are isolable in good yield from the reaction of NaBAr(F) with the amine in organic media. Structural characterisation reveals primary Na-N bonding, including an unusual sandwich cation [Na(Me3tacn)2](+), derived from homoleptic N6-coordination via two Me3-tacn ligands, and the distorted 5-coordinate [Na(thf)(Me4cyclam)](+).

Bis-β-ketoimine ligands of the form [(CH2 )n {N(H)C(Me)CHC(Me)O}2 ] (L(n) H2 , n=2, 3 and 4) were employed in the formation of a range of gallium complexes [Ga(L(n) )X] (X=Cl, Me, H), which were characterised by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction analysis. The β-ketoimine ligands have also been used for the stabilisation of rare gallium hydride species [Ga(L(n) )H] (n=2 (7); n=3 (8)), which have been structurally characterised for the first time, confirming the formation of five-coordinate, monomeric species. The stability of these hydrides has been probed through thermal analysis, revealing stability at temperatures in excess of 200 °C. The efficacy of all the gallium β-ketoiminate complexes as molecular precursors for the deposition of gallium oxide thin films by chemical vapour deposition (CVD) has been investigated through thermogravimetric analysis and deposition studies, with the best results being found for a bimetallic gallium methyl complex [L(3) {GaMe2 }2 ] (5) and the hydride [Ga(L(3) )H] (8). The resulting films (F5 and F8, respectively) were amorphous as-deposited and thus were characterised primarily by XPS, EDXA and SEM techniques, which showed the formation of stoichiometric (F5) and oxygen-deficient (F8) Ga2 O3 thin films.

Reflection second harmonic generation is employed to examine the surfaces of epitaxial layers of CdxHg1-xTe (CMT) grown on vicinal GaAs (100) substrates. Different vicinal tilts, with respect to the GaAs substrates, are observed in the epitaxial CMT layers. We also report here on the measurement of the second-order nonlinear coefficient (d36) of CMT. Because CMT is strongly absorbing at the 1.06 µm wavelength, this measurement was performed by comparing the second harmonic intensity reflected from the CMT surface to that measured for a quartz sample in transmission. Directly comparable expressions for the reflected and transmitted second harmonic intensities are derived from which a value of d36 = 365±15 pm V-1 is obtained. This value is much larger than those reported for similar zinc-blende-type materials and is attributed to an electronic resonance enhancement.

The effects of a series of small structural changes to (S)-5-nitro-N-(1-phenylethyl)pyridin-2-amine on its solid state non-linear optical properties, including the phenomenon of rotating dielectric axes, have been investigated. Installation of a methyl group in the 3-position of the heterocyclic ring or at the amino nitrogen atom gave the most promising materials, though neither of these materials showed rotating dielectric axes. Details of the crystal structure analyses of a family of these compounds illustrate the delicate interplay between molecular conformation and intermolecular interactions in determining the packing arrangements.

The second order nonlinear coefficient (d36) of the narrow band gap semiconductor, mercury cadmium telluride (MCT), is measured. Because MCT is strongly absorbing at a 1.06 μm wavelength, the measurement was performed by comparing the second harmonic intensity reflected from the material surface to the second harmonic intensity measured for a quartz sample in transmission. The analysis depends on the derivation of comparable expressions for the reflected and transmitted intensities. Using this approach a value of d36=350±40 pm/V is obtained, a value much larger than those reported for similar zinc-blende type materials. The large magnitude of the MCT d36 is attributed to an electronic resonance enhancement.

The organic crystal (S)-3-methyl-5-nitro-N-(1 -phenylethyl)-2-pyridinamine has been previously identified by the powder technique as a promising nonlinear optical material. Large single crystals (3 x 3 x 2 cm(3)) of this material have been grown by temperature lowering of a seeded supersaturated solution in acetone, Refined refractive indices were obtained from the predicted angles of incidence of the phase-matched second harmonic signals. Second-order nonlinear optical coefficients, d(ij), as measured by the Maker fringe technique, are 11, 9, and 7 pm V-1 for d(14), d(25), and d(36). respectively. The results are compared with calculations based on the oriented gas model.

In-situ measurements of ellipsometry and second harmonic generation (SHG) were carried out to monitor the electrochemical growth of native anodic oxide films on Hg1−xCdxTe (MCT). Growth of the anodic oxide was performed using two different methods viz., by linear sweep voltammetry and by applying a constant current density. The influence of scan rate and the magnitude of the applied current density on the properties of the growing films were examined. From the ellipsometry data, we have shown that the measured refractive index value of 2.19 for the oxide film remains unchanged for moderate and high oxide growth rates. Only at very slow growth rates were significant increases in the refractive index observed (n=2.4), indicating an increase in the compactness of the layer. For film thicknesses in excess of ∼1200 A, a non-zero value for the extinction coefficient was found, indicating the incorporation of HgTe particles within the anodic oxide film. SHG rotational anisotropy measurements, performed on the MCT with and without an anodic oxide film showed only the four-fold symmetry associated with the MCT and so confirmed that the oxide was centrosymmetric. However, an increase in the SH intensity was observed in the presence of the oxide and this has been attributed to multiple reflections in the thin oxide film and also to the increase in the χ(2) non-linear susceptibility tensor as a result of charge accumulation at the MCT/anodic oxide interface.

Rotation anisotropy by second harmonic generation (SHG) is carried out on epitaxial Hg1−xCdxTe (MCT) and oxide- and sulphide-covered MCT surfaces and shows the fourfold symmetry pattern expected from the {100} surface (C4v symmetry). The uneven nature of the four peaks confirm the vicinal surface obtained from the growth of the MCT on GaAs {100} substrate orientated 4° toward the 〈110〉 direction. The increase in the SH intensity observed for the oxide-covered MCT surface is associated with charge accumulation at the MCT/oxide interface since the oxide is centrosymmetric and cannot generate SH. The CdS layer on the other hand is strongly nonlinear active and generation here comes from a composite of one noncentrosymmetric layer on top of another. This leads to interactions in the observed SH arising from the coupling depths (∼40 nm) at the two interfaces and from the coherence length (∼1200 nm) in the CdS layer. The in-situ SHG measurements during the growth of the anodic oxide and sulphide layers would suggest that a species, most likely HgTe is embedded in the anodic layer during the initial stages and absorbs the SH radiation at 532 nm. The rotational anisotropy of the sulphide-covered MCT surface confirms that the CdS layer formed maintains the cubic closed pack symmetry of the underlying MCT.

A morphological prediction of the polar crystal morphology of the molecular ionic solid sodium chlorate is presented. This prediction uses interatomic potential calculations that employ surface-specific attachment energy calculations associated with an ab initio calculation of surface charges via a Hartree−Fock calculation using periodic boundary conditions. The data predicts assignment of the absolute polarity of the crystal with respect to the published crystal structure (Burke-Laing, M. E.; Trueblood, K. N. Acta Crystallogr. 1977, B33, 2698), which reveals the chlorate-rich {−1 −1 −1} to be the observed form rather than its sodium-rich Freidel opposite, {111}. The predicted crystal morphology is in reasonable agreement with observed morphologies, although there is an underestimation of the dominant {200} form. The latter is rationalized with experimental data in terms of a face-specific solvent binding model.

Ab initio calculations of the structure and binding energies of K+[Solv]n clusters are reported for water, methanol, and acetonitrile solvents, for n = 1−6. It has been shown that the results obtained at the RHF/DZP//RHF/DZP level of calculation, with no basis set superposition or correlation correction, compare well, in the case of water, with other accurate treatments in the literature. A comparison of the binding energies and structures of the clusters in the three solvents is made. The enthalpies and entropies of formation of the clusters are calculated and compared with the results of experimental measurements on gas-phase clusters. An analysis of the contributions of the ion−solvent and solvent−solvent interactions to the binding energies is also presented.

An abinitio computational study of the formation of complexes of the potassium ion with the crown ether 15-crown-5 in three solvents, water, methanol and acetonitrile, is reported. The binding energy of the complexes has been analysed to identify contributions from structural changes and pair-wise interactions. The importance of the variation of the ion/solvent contribution to the binding energy in different solvents has been established. Reaction schemes have been investigated in which ion/solvent clusters interact with the crown ether to form complexes containing one crown ether molecule or sandwich complexes with two crown ether molecules. The relative importance of the two kinds of complex in the three solvents has been studied. New spectroscopic (IR and 13C NMR) data has been obtained on the acetonitrile solutions which can be interpreted within the general scheme of the theoretical calculations.

The title compounds 2,6-dibromo-3,5-dimethylpyridine, C7H7Br2N, (I), and 2,6-diiodo-3,5-dimethylpyridine, C7H7I2N, (II), constitute the first structurally characterized examples of 2,6-dihalo-3,5-dimethylpyridines. Compound (I) crystallizes as a racemic twin with two symmetry-independent molecules in the asymmetric unit, while (II) is non-planar with the pyridine ring slightly deformed into a saddle shape, and exhibits crystallographically imposed twofold symmetry. Both (I) and (II) exhibit aromatic face-to-face pi-stacking in the solid state, although there are no other long-range interactions. In (I), alternate molecules are oriented at 90 degrees, resulting in X-shaped columns, while in (II), molecules pack in a parallel fashion, leading to a zigzag array.

Ab initio studies of the binding of Na + with a series of 4-substituted monobenzo 15-crown-5 ligands are reported and compared with experimental data. The substituent effect on the cation binding is small and almost negligible for methyl and amino groups but a difference of ca. 12% in the binding energy is found between the 4-methyl and 4-nitro derivatives. The substituent effect is related to the basicity of the aromatic ether oxygens as demonstrated by the correlation found by plotting binding energy (ΔE) vs. average charge of aromatic ether oxygens. A Hammett correlation is found by plotting ΔE vs. σ p - +σ m . Ab initio studies of the binding of Na + and K + with 3n-crown-n (n=4–7) ligands are reported and the effect of a change in the ring size on the cation selectivity is evaluated. Both Na + and K + bind to 18-crown-6 ether more strongly than any other 3n-crown-n ether studied here. The ring-size effect on the cation selectivity is found to depend not only on the hole-size concept, but also on the number of available donor atoms that can effectively participate.

The formation of alkali-metal ion complexes with the crown ethers, 18-crown-6(18c6), benzo-18c6 and dibenzo-18c6 has been investigated. Theoretical studies of structural changes on complexation, binding energies and changes in electron distribution have been carried out using ab initio quantum theoretical methods. A complementary study of the NMR chemical shifts and coupling constants has also been used to obtain information on complexation and structural changes. The overall views of the structural changes and their relation to ion selectivity as determined by the theoretical and NMR investigations are in agreement. In most cases the structural parameters found bear a close relation to those obtained in crystallographic work on the complexes, where such results are available. An attempt has been made to include solvent effects in aqueous solution by computing the energy of the reaction in which some water molecules in the coordination shell of the metal ion are replaced by the crown ether. When this is done, the ion selectivity sequence predicted from the theoretical work is in conformity with existing (incomplete) experimental data.

The reaction of SiX4 (X = Cl or Br) with PMe3 in anhydrous CH2Cl2 forms trans-[SiX4(PMe3)2], while the diphosphines, Me2P(CH2)2PMe2, Et2P(CH2)2PEt2, and o-C6H4(PMe2)2 form cis-[SiX4(diphosphine)], all containing six-coordinate silicon centers. With Me2PCH2PMe2 the product was trans-[SiCl4(κ(1)-Me2PCH2PMe2)2]. The complexes have been characterized by X-ray crystallography, microanalysis, IR, and multinuclear ((1)H, (13)C{(1)H}, and (31)P{(1)H}) NMR spectroscopies. The complexes are stable solids and not significantly dissociated in nondonor solvents, although they are very moisture and oxygen sensitive. This stability conflicts with the predictions of recent density functional theory (DFT) calculations (Wilson et al. Inorg. Chem. 2012, 51, 7657-7668) which suggested six-coordinate silicon phosphines would be unstable, and also contrasts with the failure to isolate complexes with SiF4 (George et al. Dalton Trans. 2011, 40, 1584-1593). No reaction occurred between phosphines and SiI4, or with SiX4 and arsine ligands including AsMe3 and o-C6H4(AsMe2)2. Attempts to make five-coordinate [SiX4(PR3)] using the sterically bulky phosphines, P(t)Bu3, P(i)Pr3, or PCy3 failed, with no apparent reaction occurring, consistent with predictions (Wilson et al. Inorg. Chem. 2012, 51, 7657-7668) that such compounds would be very endothermic, while the large cone angles of the phosphines presumably preclude formation of six-coordination at the small silicon center. The reaction of Si2Cl6 with PMe3 or the diphosphines in CH2Cl2 results in instant disproportionation to the SiCl4 adducts and polychlorosilanes, but from hexane solution very unstable white [Si2Cl6(PMe3)2] and [Si2Cl6(diphosphine)] (diphosphine = Me2P(CH2)2PMe2 or o-C6H4(PMe2)2) precipitate. The reactions of SiHCl3 with PMe3 and Me2P(CH2)2PMe2 also produce the SiCl4 adducts, but using Et2P(CH2)2PEt2, colorless [SiHCl3{Et2P(CH2)2PEt2}] was isolated, which was characterized by an X-ray structure which showed a pseudo-octahedral complex with the Si-H trans to P. Attempts to reduce the silicon(IV) phosphine complexes to silicon(II) were unsuccessful, contrasting with the isolation of stable N-heterocyclic carbene adducts of Si(II).

Tribenzylphosphane, PBz3(C21H21P), crystallizes in a notably different unit cell to its Group 15 analogues NBz3and SbBz3. The packing is dominated by face–edge π-interactions which result in infinite columns of molecules parallel to thebaxis; these columns are linked by further face–edge π-interactions into sheets of columns parallel to the [101] direction. Its hydrochloride salt, tribenzylphosphonium hydrogen dichloride–tribenzylphosphane (1/1), lies on a threefold axis within a trigonal crystal system. It exists in the solid state as a hydrogen-bridged dimer with the composition [H(PBz3)2]+[HCl2]−(C42H43P2+·HCl2−). The cation is the first structurally authenticated example of a phosphane acting as a hydrogen-bond acceptor to a phosphonium group and the cations are linked into a three-dimensional network through intermolecular face–edge π-interactions.

This chapter describes precursor complexes that have been utilized to deposit thin films of main-group metal oxides. An overview of the wide range of precursors that have been reported for the growth of these oxides, which includes metal alkoxides and β-diketonates, is presented including synthetic details. A number of techniques have been used to deposit the metal oxide films, such as chemical vapor deposition (CVD), atomic layer deposition (ALD), and sol–gel, and the technique employed is described. The focus of the chapter is on the chemistry of precursors to the thin films, although mention has also been made of techniques (such as ALD), which tend to utilize simple, commercially available precursors in combination with a secondary oxygen source. The first section describes precursors for the deposition of aluminum oxide, gallium oxide, and indium oxide. Group 13 oxides have a fascinating range of chemistry and find application as components of high-temperature superconductors, transparent conducting oxides (TCOs), and gas sensors. These applications tend to use doped-group 13 metal oxides, and precursors to these materials have been highlighted at the end of the section. The second section describes the range of precursors that have been used for the formation of group 14 oxide thin films. These materials find application in everyday life from silicon dioxide, or silica, which is widely used in electronics manufacturing, to tin dioxide that is commonly used for gas sensors as well as TCO applications. These oxides have been deposited using a variety of methods that can alter the final properties of the films. In most cases, commercially available precursors have been employed, for example, tin halides and organotin precursors for SnO 2 , with the addition of an oxygen source (usually H 2 O, H 2 O 2 , O 2 , and O 3 ); however, there are a few reported examples of more sophisticated precursors which are described as well as a brief overview of doped-group 14 metal oxides. The last section gives an overview of the precursors developed for the deposition of group 15 and 16 metal oxides – including antimony oxide, bismuth oxide, and tellurium oxide. Thin films of the binary group 15 and 16 oxides have limited applications in comparison to the corresponding group 13 and 14 oxides, for example, antimony oxide finds use in catalysis and gas sensor devices and bismuth oxide are of interest in high T c superconductors and potentially for fuel cells.