Molecular precursors to gallium oxide thin films

The donor-functionalised alkoxides [Et(2)Ga(OR)](2)(R = CH(2)CH(2)NMe(2)(1), CH(CH(2)NMe(2))(2)(2), CH(2)CH(2)OMe (3), CH(CH(3))CH(2)NMe(2)(4), C(CH(3))(2)CH(2)OMe (5)) were synthesised by the 1:1 reaction of Et(3)Ga with ROH in hexane or dichloromethane at room temperature. Reaction of Et(3)Ga with excess ROH in refluxing toluene resulted in the isolation of a 1:1 mixture of [Et(2)Ga(OR)](2) and the ethylgallium bisalkoxide [EtGa(OR)(2)](R = CH(2)CH(2)NMe(2)(6) or CH(CH(3))CH(2)NMe(2)(7)). X-ray crystallography showed that compound 6 is monomeric and this complex represents the first structurally characterised monomeric gallium bisalkoxide. Homoleptic gallium trisalkoxides [Ga(OR)(3)](2) were prepared by the 1:6 reaction of [Ga(NMe(2))(3)](2) with ROH (R = CH(2)CH(2)NMe(2)(8), CH(CH(3))CH(2)NMe(2)(9), C(CH(3))(2)CH(2)OMe (10)). The decomposition of compounds 1, 4, 5 and 8 were studied by thermal gravimetric analysis. Low pressure CVD of 1 and 5 resulted in the formation of thin films of crystalline Ga(2)O(3).     

Single-source precursors to gallium and indium oxide thin films

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.     

Silylated gallium and indium chalcogenide ring systems as potential precursors to ME (E=O, S) materials

The reaction of R₃M (M=Ga, In) with HESiR′₃ (E=O, S; R′₃=Ph₃, ⁱPr₃, Et₃, ^tBuMe₂) leads to the formation of (Me₂GaOSiPh₃)₂ (1); (Me₂GaOSi^tBuMe₂)₂ (2); (Me₂GaOSiEt₃)₂ (3); (Me₂InOSiPh₃)₂ (4); (Me₂InOSi^tBuMe₂)₂ (5); (Me₂InOSiEt₃)₂ (6); (Me₂GaSSiPh₃)₂ (7); (Et₂GaSSiPh₃)₂ (8); (Me₂GaSSiⁱPr₃)₂ (9); (Et₂GaSSiⁱPr₃)₂ (10); (Me₂InSSiPh₃)₃ (11); (Me₂InSSiⁱPr₃)_n (12), in high yields at room temperature. The compounds have been characterized by multinuclear NMR and in most cases by X-ray crystallography. The molecular structures of (1), (4), (7) and (8) have been determined. Compounds (3), (6) and (10) are liquids at room temperature. In the solid state, (1), (4), (7) and (9) are dimers with central core of the dimer being composed of a M₂E₂ four-membered ring. VT-NMR studies of (7) show facile redistribution between four- and six-membered rings in solution. The thermal decomposition of (1)–(12) was examined by TGA and range from 200 to 350°C. Bulk pyrolysis of (1) and (2) led to the formation of Ga₂O₃; (4) and (5) In metal; (7)–(10) GaS and (11)–(12) InS powders, respectively.      

Dimethyl selenide complexes of copper,gallium and indium halides as potential precursors for selenium-containing chalcopyrite semiconducting materials

The coordination chemistry of copper, gallium and indium halides with the simplest possible selenoether i.e. Me₂Se was investigated with the aim to use the resulting complexes as precursors for selenium-containing chalcopyrite semiconducting materials. An optimized general procedure for the high yield synthesis is described and the influence of a halide ion on the structure and solubility of these metal halide dimethyl selenide complexes are discussed. These complexes were characterized by the elemental analysis, FT-IR and ¹H NMR spectroscopy as well as single crystal X-ray structures, the later study showing them to be monomeric for gallium halides, mono- or dimeric for indium halides and either an ion-pairs or 2-D extended structure in the case of copper halides.     

Strategies for the construction of supramolecular assemblies from poly-NHC ligand precursors

The field of supramolecular assemblies has developed rapidly in the last few decades, thanks in a large part to their diverse applications. These assemblies have been mostly based on Werner-type coordination motifs in which metal centres are coordinated by nitrogen or oxygen donors. Recently, N-heterocyclic carbene(NHC) ligands have been employed as carbon donors not only because of their appealing structures but also due to the extensive applications in catalysis, biomedicine and material science of the resulting assemblies. During the last decade, NHC-based supramolecular assemblies have witnessed rapid growth and extensive application in molecular recognition, luminescent materials and catalysis. For different topological systems, a diverse selection of poly-NHC precursors and synthetic strategies is crucial to precisely control the synthesis of supramolecular architectures. Several synthetic strategies have been developed to synthesise two-dimensional(2D) molecular metallacycles and three-dimensional(3D) metallacages from a wide range of poly-NHC precursors, including a straightforward one-pot strategy,supramolecular transmetalation, stepwise synthesis, an improved one-pot strategy involving self-sorting behaviour of 3D metallacages and a subtle variation strategy of poly-NHC ligand precursors. This review offers a summary of the synthetic strategies applied for the construction of different poly-NHC-based supramolecular assemblies, particularly emphasizes recent progress in the synthesis of large and complex supramolecular assemblies from poly-NHC precursors, and further attention is given to their application in postsynthetic modifications(PSMs), host-guest chemistry, luminescent properties and biomedical applications.     

Heteroleptic [1]zirconametalloarenophanes: potential precursors to metal-enriched metallopolymers

[1]Zirconametalloarenophanes [Cr(η(5)-C(5)H(4))ZrCp'(2)(η(7)-C(7)H(6))] and [Mn(η(5)-C(5)H(4))ZrCp'(2)(η(6)-C(6)H(5))] (Cp' = C(5)H(4)(t)Bu) have been isolated for the first time. These species represent potential precursors en route to metal-enriched metallopolymers by ROP. The electronic structure was assessed by means of UV-visible spectroscopy and TD-DFT calculations.     

Synthetic approach to potential precursors of sclerophytin A

A direct approach to simple bicyclic analogues of the antitumor natural diterpene, sclerophytin A, is described. The readily available bicyclic ketone 8 (prepared from furan and trichloroacetone) was enantioselectively methylated to give the optically active ketone 11. Regioselective allylation using Negishi's method afforded the α,α-dialkyl ketone 12, which was converted to the chloroacetate 15 by hydroboration-oxidation and protection. Regioselective Baeyer-Villiger oxidation afforded the lactone 7a which could be transformed into the silyl ether 7b. Tebbe olefination furnished a mixture of two enol ethers in which the desired product 17 was the minor isomer. Several attempts to use the major endocyclic enol ether 18 to give the tricyclic analogues of sclerophytin proved unsuccessful. Opening of the lactone of 18 and selective protection of the diol afforded the primary alcohol 24 which was oxidized to the keto aldehyde 25. Unfortunately pinacol coupling of 25 did not give any cyclic product. The diene 27 was also prepared from 25 but all attempts at ring-closing metathesis of 27 met with the same fate. The failure of these various cyclization methods underscores the difficulty in forming medium-sized ring systems, especially those cis-fused at the 2- and 5-positions of a tetrahydrofuran ring.     

Oligonuclear gallium nitrogen cage compounds: molecular intermediates on the way from gallium hydrazides to gallium nitride

Gallium hydrazides are potentially applicable as facile starting compounds for the generation of GaN by thermolysis. The decomposition pathways are, however, complicated and depend strongly on the substituents attached to the gallium atoms and the hydrazido groups. This paper describes some systematic investigations into the thermolysis of the gallium hydrazine adduct Bu(t)(3)Ga←NH(2)-NHMe (1a) and the dimeric gallium hydrazides [R(2)Ga(N(2)H(2)R')](2) (2b, R = Bu(t), R' = Bu(t); 2c, R = Pr(i), R' = Ph; 2d, R = Me, R' = Bu(t)) which have four- or five-membered heterocycles in their molecular cores. Heating of the adduct 1a to 170 °C gave the heterocyclic compound Bu(t)(2)Ga(μ-NH(2))[μ-N(Me)-N(=CH(2))]GaBu(t)(2) (3) by cleavage of N-N bonds and rearrangement. 3 was further converted at 400 °C into the tetrameric gallium cyanide (Bu(t)(2)GaCN)(4) (4). The thermolysis of the hydrazide (Bu(t)(2)Ga)(2)(NH-NHBu(t))(2) (2b) at temperatures between 270 and 420 °C resulted in cleavage of all N-N bonds and the formation of an octanuclear gallium imide, (Bu(t)GaNH)(8) (6). The trimeric dialkylgallium amide (Bu(t)(2)GaNH(2))(3) (5) was isolated as an intermediate. Thermolysis of the hydrazides (Pr(i)(2)Ga)(2)(NH-NHPh)(NH(2)-NPh) (2c) and (Me(2)Ga)(2)(NH-NHBu(t))(2) (2d) proceeded in contrast with retention of the N-N bonds and afforded a variety of novel gallium hydrazido cage compounds with four gallium atoms and up to four hydrazido groups in a single molecule: (Pr(i)Ga)(4)(NH-NPh)(3)NH (7), (MeGa)(4)(NH-NBu(t))(4) (8), (MeGa)(4)(NH-NBu(t))(3)NBu(t) (9), and (MeGa)(4)(NHNBu(t))(3)NH (10). Partial hydrolysis gave reproducibly the unique octanuclear mixed hydrazido oxo compound (MeGa)(8)(NHNBu(t))(4)O(4) (11).     

Rare examples of transition-metal-main-group metal heterometallic metal-organic frameworks from gallium and indium dipyrrinato complexes and silver salts: synthesis and framework variability

New main-group metal dipyrrinato complexes [M(4-pyrdpm)3], where M = Ga3+ or In3+ and 4-pyrdpm is the anion of 5-(4-pyridyl)dipyrrin (4-pyrdpmH), have been synthesized and incorporated into metal-organic frameworks (MOFs) by reacting the dipyrrinato complexes with silver(I) salts. MOFs formed with AgOTf (OTf = O3SCF3) and AgSbF6 gave frameworks with three-dimensional (10,3) and two-dimensional (6,3) topologies, respectively. In contrast, AgPF6 produced both (10,3) and (6,3) network topologies, suggesting that the PF6 anion has little preference for templating (10,3) versus (6,3) frameworks within this system. These findings update an earlier MOF study that examined the role of these anions in templating related heterometallic MOFs which used [Fe(4-pyrdpm)3] and [Co(4-pyrdpm)3] metalloligands. All of the dipyrrin compounds reported here have been characterized by single-crystal X-ray crystallography, including the first crystallographically characterized example of a 1,2,3-unsubstituted free-base dipyrrin, 4-pyrdpmH.     

Peculiarities of the synthesis and thermolysis of heterometallic coordination compounds used as precursors for nickelates of rare-earth elements

The influence of the solvent on the composition of solid products is investigated using the example of the interaction of rare-earth element (REE) nitrates, Ln(NO₃)₃, with square-planar complexes of nickel and Schiff bases, Ni(SB). The composition of solid products is determined by X-ray fluorescence analysis and elemental analysis. It is shown that from the labile Ln(NO₃)₃-Ni(SB) systems, individual heterometallic compounds can be obtained, moreover, if in systems there are complexes with more dentate Ni(mosalen) ligands, only binuclear heterocomplexes can be produced. In case of Ni(salen) ligand, the formation of trinuclear complexes is achieved by selecting the optimal solvent. Among the considered compounds, binuclear complexes are of special interest due to the possibility of their use as precursors of REE nickelates.     

Shell cross-linked polymer micelles: stabilized assemblies with great versatility and potential

Shell cross-linked polymer micelles have been introduced within the past 3 years, and they have already demonstrated great promise as robust nanostructured core-shell nanospheres. The formation of cross-links throughout the shell of polymer micelles offers stability to the nanostructured assemblies, by providing reinforcement to the weak interactions that facilitate polymer micelle existence. Cross-linking can be accomplished by direct reaction between the chain segments located within the polymer micelle shell, or via addition of multi-functional cross-linking reagents. The dimensions, composition, and properties of each of the domains of the polymer micelles can be controlled by selection of diblock copolymer composition, conditions for polymer micelle assembly, and chemistry used for cross-linking. An overview of each of the examples of SCK nanospheres currently known is presented here.     

CdSe sensitized thin aqueous films: probing the potential distribution inside multilayer assemblies

Ultrathin polypeptide multilayer films are assembled by the sequential electrostatic adsorption of monolayers of poly-l-lysine and poly-l-glutamic acid onto carboxylic acid terminated alkanethiol-modified gold surfaces. The polypeptide multilayer films are hydrophilic, can incorporate electroactive species such as ferri/ferrocyanide, and are stable when immersed in organic solvents such as 1,2-dichloroethane. Cadmium selenide quantum dots stabilized by negatively charged citrate groups are electrostatically attached to the multilayer film assembly in order to act as photoactive species. Photocurrent responses originating from the CdSe sensitized ultrathin multilayer film are investigated as functions of the applied potential, the thickness of the film and the presence of quenchers in the organic phase. A theoretical model is proposed in order to analyze the kinetics of the photoinduced electron-transfer reactions and to probe the potential distribution within the film.     

Hexacyanometallate anions as precursors of two new trinuclear heterobimetallic assemblies: Syntheses,structures and cryomagnetic properties

Two new cyano bridged Cu–Co and Cu–Fe trinuclear bimetallic assemblies, [(CuL)[Co(CN)₆](CuL)]ClO₄ · 3.5H₂O (1) and [(CuL)[Fe(CN)₆](CuL)] · 13H₂O (2) where [L = (3E,5E)-N¹,N⁴-bis((pyridin-2-yl)methylene)butane-1,4-diamine] have been prepared using cyanometallates as anion precursors and characterised by elemental analyses, spectroscopic studies, single crystal X-ray diffraction and cryomagnetic susceptibility measurements. Magneto-structural correlations have been drawn from cryomagnetic susceptibility measurements over a wide temperature range (2–300 K) under 0.5 T magnetic fields. Weak antiferromagnetic interactions with J = −0.81 and −0.73 cm⁻¹ are found for 1 and 2, respectively, showing a very weak coupling, as expected from the diamagnetic long chain –NC–Co–CN–CN– and –NC–Fe–CN–CN– bridges revealed from the single crystal X-ray diffraction studies.     

Identifying bryostatins and potential precursors from the bryozoan Bugula neritina

The bryozoan species Bugula neritina contains the anticancer agent bryostatin. Bryostatin has been extracted from these sessile marine invertebrates since the late 1960s from the Gulf of California, Gulf of Mexico, as well as various locations on the eastern and western rims of the Pacific Ocean. In this work we are focusing on animals harvested in the Gulf of Mexico near Alligator Point (Florida). Using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) we measure the concentration of 70 elements in B. neritina, a sea squirt, and the sediment from the point of harvesting. This data has helped us generate an extraction process for marine natural products. Combining UV/VIS absorbance measurements with Matrix Assisted Laser Desorption Ionization-Time of Flight-Mass Spectrometer (MALDI-TOF-MS), we demonstrated that the specific form of bryostatin extracted is a function of the solvent. A 9.4T Fourier Transform-Ion Cyclotron Resonance (FT-ICR) mass spectrometer, whose sensitivity, mass accuracy, and resolving power allowed the exact empirical formulas of potential precursors of bryostatin to be identified, was employed. Finally we examine extracts of 14 marine species of the Gulf of Mexico, from the sand trout (Cynoscion arenarius) to chicken liver sponge (Chrondrilla nucula), all recently collected, which had shown some medicinal activity thirty years ago in a National Cancer Institute study. By the MALDI-TOF-MS, we were able to identify mass spectral features that correspond to different variations of the basic bryostatin structure, which raises the question if the bryozoans are the original source of bryostatin.     

Synthesis of inorganic polymers as glass precursors and for other uses: Pre-ceramic block or graft copolymers as potential precursors to composite materials

Pre-ceramic block or graft copolymers may offer entrée into nanocomposite ceramics provided the two homopolymers are immiscible and one can carefully control the size of the blocks or grafts. We are exploring the possibility of making copolymers from methylsilsesquioxane, ? [MeSi(O)_1.5]_x? , (SiO), a precursor to ‘black glass’ and the polysilazane, ? [MeHSiNH]_x? , (SiMe), a precursor to silicon carbide nitride. Our initial effors have been directed towards delineating the chemical transformations that SiO, prepared by room-temperature catalytic redistribution of ? [MeHSiO]_x? using Cp₂ TiMe₂ as the catalyst (0.1 wt %), undergoes as it is heated to 900 °C in nitrogen. We find that, although Cp₂ TiMe₂ will not catalyze the redistribution of SiMe at room temperature, in the presence of even small amounts of ? [MeHSiO]_x? it is an active catalyst precursor and a copolymer can be formed. Spectra and chemical composition studies on the pyrolysis products of the copolymers and SiO are described.     

S,C-sulfonium ylides from thiophenes: potential carbene precursors

Photolysis of S,C-sulfonium ylides derived from thioanisol, thiophene, benzothiophene, or dibenzothiophene provides products deriving from dicarbomethoxycarbene. In methanol, no rearrangement of the carbene to the ketene derivative is observed. Formation of dibenzothiophene and benzothiophene is quantitative. For the thiophene-based ylide, insertion of the carbene into the alpha-CH bond of thiophene is observed. Evidence is presented that supports formation of both singlet and triplet carbene.     

A new polyoxometalate-based 3d-4f heterometallic aggregate: a model for the design and synthesis of new heterometallic clusters

A new polytungstoarsenate-based 3d-4f heterometallic aggregate has been synthesized, consisting of three {alpha-AsW10 O 38} fragments bridged by three {Fe-(mu3-O)3-Ce} heterometallic clusters.     

Acyclic congener of cucurbituril: synthesis and recognition properties

The cucurbit[n]uril (CB[n]) family of macrocycles occupies a prominent role in molecular recognition and self-assembly studies despite the current inability to access specific cucurbit[n]uril homologues, derivatives, and analogues by straightforward tailor-made synthetic procedures. In this paper, we explore an approach that circumvents the challenges posed by the tailor-made synthesis of macrocyclic CB[n] by preparing 1, which functions as an acyclic CB[6] congener. The o-xylylene connections to the glycoluril rings preorganize 1 into the (a,a,a,a)-1 conformation required for binding and reduce its tendency to undergo self-association. We surveyed the binding properties of 1 toward 16 amines (K(a) 相似文献