Homometallic glycolates containing hydroxyl functionality for anchoring another metal: synthesis and characterization of heterometallic alkoxide–glycolates of Ti and Zr incorporating Al and Nb

Reaction of Ti(OPrⁱ)₄ with 2-methyl-2,4-pentanediol [HOGOH, where G = CMe₂CH₂CH(Me)] in 1?:?3 M ratio under reflux afforded the monomeric [Ti(OGO)(OGOH)₂] (1), which on further reactions with [Al(OPrⁱ)₃] or [Nb(OPrⁱ)₅] in 1?:?1 and 1?:?2 M ratios afforded heterometallic derivatives, [Ti(OGO)₃{M(OPrⁱ)_n?2}] and [Ti(OGO)₃{M(OPrⁱ)_n?1}₂] [where M = Al (n = 3), Nb (n = 5)], respectively. Similar reactions of Zr(OPrⁱ)₄?PrⁱOH with a number of glycols [HOGOH, where G = CH(Me)CH(Me), CMe₂CMe₂, CMe₂CH₂CH(Me)] yielded dimeric [Zr₂(OGO)₂(OGOH)₄]. [Zr₂(OGO)₆{M(OPrⁱ)_n?2}₂] and [Zr₂(OGO)₄(OGOH)₂M(OPrⁱ)_n?2] [M = Al (n = 3), Ti (n = 4), Nb (n = 5)] were prepared by 1?:?2 and 1?:?1 reactions, respectively, of [Zr₂(OGO)₂(OGOH)₄] with Al(OPrⁱ)₃, Ti(OPrⁱ)₄, or Nb(OPrⁱ)₅. Surprisingly, a 1?:?2 reaction of [VO(OPrⁱ)₃] with 2,2-diethyl-1,3-propanediol in benzene followed a different reaction and produced a neutral tetranuclear derivative [V₄(O)₄(μ-OCH₂CEt₂CH₂O)₂(OCH₂CEt₂CH₂O)₄] (18). All of these derivatives were characterized by elemental analysis, molecular weight measurements, FT-IR, and ¹H NMR (and wherever possible, by ²⁷Al or ⁵¹V NMR) spectroscopic studies. The derivatives [Zr₂(OCMe₂CH₂CH(Me)O)₂(OCMe₂CH₂CH(Me)OH)₄] (9 and 18) were additionally characterized by single-crystal X-ray structure analysis.     

Synthesis and Characterization of Some Unique Heterocyclic Derivatives Containing Aluminium(III) Atoms in 4- and 6-Co-Ordination States∶ Reaction of Bis(β-Diketonato) Aluminium (III)-DI-μ-Isopropoxo-DI-Isopropoxo Aluminium(III) with Triphenylsilanol and Diphenylsilanediol

Reactions of bis ( g -diketonato) aluminium(III)-di- w -isopropoxo-di-isopropoxo-aluminium (III), [CH₃COCHCOR)2Al( w -OPrⁱ)₂Al(OPrⁱ) ₂], with triphenylsilanol, Ph₃SiOH, in 1:1 and 1:2 molar ratios and with diphenylsilanediol, Ph₂Si(OH)₂, in a 1:1 molar ratio, have resulted in the synthesis of [(CH₃COCHCOR)₂Al( w -OPrⁱ)₂Al(OSiPh₃)(OPrⁱ)], [(CH₃COCHCOR)₂Al( w -OPrⁱ)₂Al(OSiPh₃)₂] and [(CH₃COCHCOR)₂Al( w -OPrⁱ)₂Al(OSiPh₂O], respectively. These are soluble in a variety of organic solvents ( e.g. , benzene, chloroform and dimethylsulfoxide) and show dinuclear behaviour in chloroform. These derivatives have been characterized by elemental analyses, molecular weight measurements, IR and NMR (¹H, ¹³C and ²⁷Al) studies.     

Synthetic,spectroscopic, thermal,and structural studies of antimony(III) bis(pyrrolidinedithiocarbamato)alkyldithiocarbonates

An account of the synthesis, spectroscopic, thermal and structural behavior of antimony(III) bis(pyrrolidinedithiocarbamato)alkyldithiocarbonates is presented. The reaction of antimony(III) bis(pyrrolidinedithiocarbamate) chloride with potassium organodithiocarbonate in equimolar ratio yielded the corresponding mixed derivatives of the type [(CH₂)₄NCS₂]₂SbS₂COR [where R = Me, Et, Pr ⁿ , Pr ⁱ , Bu ⁿ , and Bu ⁱ ]. These newly synthesized complexes have been characterized by physicochemical [molecular weight determination, melting points, and elemental analysis], spectral [UV, IR, far-IR, NMR (¹H and ¹³C)], thermal [TG, DTA, and FAB⁺ mass], and structural [powder XRD and SEM] studies. Analytical studies leads to purity and structural properties of the synthesized complexes on the other hand powder X-ray diffraction and SEM studies show that multiphase, polycrystalline, and rod-shaped complexes have been formed having nanorange crystallite size and monoclinic crystal system.     

The Synthesis and Spectroscopic Characterization of Heterobimetallic Bu2Sn(IV) Complexes Derived from Some Chelating Ligands

The interaction of Bu₂Sn(OPrⁱ)₂ with a trifunctional tetradentate Schiff base (LH₃) (where H₃L = HOC₆H₄CH═NCH₃C(CH₂OH)₂) yields the precursor complex Bu₂Sn(LH) 1, which, on equimolar reactions with different metal alkoxides [Al(OPrⁱ)₃, Bu₃Sn(OPrⁱ), Ge(OEt)₄]; Al(Medea)(OPrⁱ) (where Medea = CH₃N- (CH₂CH₂O)₂); and Me₃SiCl in the presence of Et₃N], affords, respectively, the complexes Bu₂Sn(L)Al(OPrⁱ)₂ 2, Bu₂Sn(L)Al(Medea) 3, Bu₂Sn(L)Bu₃Sn 4, Bu₂Sn(L)Ge(OEt)₃ 5, and Bu₂Sn(L)SiMe₃ 6. The reactions of 2 with 2,5-dimethyl-2,5-hexanediol in a 1:1 ratio and with acetylacetone (acacH) in a 1:2 molar ratio afforded derivatives Bu₂Sn(L)Al(OC(CH₃)₂CH₂CH₂C(CH₃)₂ O) 7 and Bu₂Sn(L)Al(acac)₂ 8, respectively. All of the derivatives 1– 8 have been characterized by elemental analyses, molecular weight measurements, and spectroscopic [IR and NMR (¹H, ¹¹⁹Sn, ²⁹Si, and ²⁷Al)] studies.     

Aluminum five‐ and six‐coordination in bis(acetylacetonato)aminoalkoxides

Reactions of bis(acetylacetonato)aluminum(III)‐di‐μ‐isopropoxo‐di‐isopropoxo aluminum(III), [(CH₃COCHCOCH₃)₂Al(μ‐OPrⁱ)₂Al(OPrⁱ)₂] with aminoalcohols, (HO R NR¹R²) in 1:1 and 1:2 molar ratios in refluxing anhydrous benzene yielded binuclear complexes of the types [(CH₃COCHCOCH₃)₂Al(μ‐OPrⁱ)₂Al(O R NR¹R²)(OPrⁱ)] and [(CH₃COCHCOCH₃)₂Al(μ‐OPrⁱ)₂Al(O R NR¹R²)₂] (R   (CH₂)₃ , R¹ = R² = H; R =  CH₂C(CH₃)₂ , R¹ = R² = H; R =  (CH₂)₂ , R¹ = H, R² =  CH₃; and R   (CH₂)₂ , R¹ = R² = CH₃), respectively. All these compounds are soluble in common organic solvents and exhibit sharp melting points. Molecular weight determinations reveal their binuclear nature in refluxing benzene. Plausible structures have been proposed on the basis of elemental analysis, molecular weight measurements, IR, NMR (¹H, ¹³C, and ²⁷Al), and FAB mass spectral studies. ²⁷Al NMR spectra show the presence of both five‐ and six‐coordinated aluminum sites. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:518–522, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10184     

Synthesis and characterization of a new class of heteronuclear derivatives of zirconium(IV)

Reactions of Zr{Al(OPrⁱ)₄}₂Cl₂ or Zr{Nb(OPrⁱ)₆}₂Cl₂ with KNb(OPrⁱ)₆/KAl(OPrⁱ)₄ and diethanolamines RN(CH₂CH₂OH)₂ [R=H(L^HH₂), Me(L^MeH₂), and Ph(L^PhH₂)] in the presence of two equivalents of Et₃N yield interesting hetero(bi- and tri-) nuclear derivatives (1)–(8) All of these new derivatives have been characterized by elemental analyses, molecular weight measurements, and spectroscopic studies.Ram C. Mehrotra - Deceased     

Reactivity of Dialumane and “Dialumene” Compounds toward Alkenes

The reactions of dialumane [L(thf)Al? Al(thf)L] ( 1 , L=[{(2,6‐iPr₂C₆H₃)NC(Me)}₂]^2?) with stilbene and styrene afforded the oxidation/insertion products [L(thf)Al(CH(Ph)? CH(Ph))AlL] ( 2 ) and [L(thf)Al(CH(Ph)? CH₂)Al(thf)L] ( 3 ), respectively. In the presence of Na metal, precursor 1 reacted with butadienes, possibly through the reduced “dialumene” or the “carbene‐like” :AlL species, to yield aluminacyclopentenes [LAl(CH₂C(Me)?C(Me)CH₂)Na]_n ( 4 a ) and [Na(dme)₃][LAl(CH₂C(Me)?CHCH₂)] ( 4 b , dme=dimethoxyethane) as [1+4] cycloaddition products, as well as the [2+4] cycloaddition product 1,6‐dialumina‐3,8‐cyclodecadiene, [{Na(dme)}₂][LAl(CH₂C(Me)?C(Me)CH₂)₂AlL] ( 5 ). The possible mechanisms of the cycloaddition reactions were studied by using DFT computations.     

Glycol modified cis -diisopropoxy- bis ( N -phenylsalicylideneiminato)zirconium(IV): syntheses,characterization and low temperature transformation to nanocrystalline zirconia

Zr(OPrⁱ)₄·PrⁱOH reacts with N-phenylsalicylideneimine in anhydrous benzene in 1 : 2 molar ratio to afford [Zr{O(C₆H₄)CH=NPh}₂{OPrⁱ}₂] (1). Further reactions of 1 with various glycols yield heteroleptic complexes of the type [Zr{O(C₆H₄)CH=NPh}₂{O–G–O}] [where–G–= (CH₂)₂ (2), (CH₂CHCH₃) (3), (CH₃CHCHCH₃) (4), (CH₂CHC₂H₅) (5), (CH₂)₃ (6), (CH₂CH₂CHCH₃) (7), and (CH₂)₆ (8)]. All new derivatives have been characterized by elemental analyses, FTIR and NMR (¹H and ¹³C{¹H}) studies. FAB mass spectra of 1 and 7 revealed the monomeric nature of these complexes. Complete hydrolyses and low temperature transformations of 1 and 7 using Sol-Gel technique formed tetragonal phase of ZrO₂ at 700°C, whereas transformation of tetragonal to monoclinic phase occurred at 900°C. SEM observations of these samples indicate formation of agglomerates of nanocrystalline zirconia (Scherer analysis).     

Homo- and hetero-dinuclear derivatives of aluminium containing Schiff-base ligands: synthesis,characterization and antibacterial activity of mononuclear derivative of aluminium

Reactions of Al(OPrⁱ)₃ with LH₂ =?[R′C(NYOH)CHC(R)OH] R=R′=CH₃, Y =?(CH₂)₂ (L¹H₂); R =?CH₃, R′ =?C₆H₅, Y =?(CH₂)₂ (L²H₂); R =?R′ =?CH₃, Y =?(CH₂)₃ (L³H₂); R =?CH₃, R′ =?C₆H₅, Y =?(CH₂)₃ (L⁴H₂), in 1 : 2 molar ratio give mononuclear derivatives of aluminium AlLLH (1a–1d). Equimolar reactions of AlLLH with M(OPrⁱ)₃ (M =?Al and B) yield homo- and hetero-dinuclear derivatives AlLLM(OPrⁱ)₂ (M=Al=2a–2d M=B=3a–3d). Reaction of 2a with L¹H₂ affords AlL¹L¹AlL¹ (4). All these derivatives have been characterized by elemental analysis, molecular weight measurements and plausible structures have been suggested on the basis of IR, NMR [¹H, ¹³C, ²⁷Al and ¹¹B] spectral data and FAB-mass studies of 2b and 3b. Schiff base L¹H₂ and its mononuclear derivative with aluminium (AlL¹L¹H) have been screened for their antibacterial activity against Escherischia coli and Bacillus subtilis.     

Homodinuclear glycolate derivatives of bismuth(V) and arsenic(III): synthesis and spectroscopic studies

Ligand bridged homodinuclear derivatives of bismuth(V) of the type, (1a–1d) [where R =–C(CH₃)₂CH₂CH(CH₃)–(1a),–CH(CH₂CH₃)CH₂–(1b),–CH(CH₃)CH(CH₃)–(1c),–CH(CH₃)CH₂–(1d)] have been synthesized by reactions of equimolar oxobis(triphenylbismuth)dichloride, {[Ph₃Bi]₂O}Cl₂ with glycols, HOROH in the presence of NaOMe. Reactions of sodiumtetraisopropoxoarsonate, NaAs(OPrⁱ)₄ with in 1 : 1 molar ratio yielded homodinuclear alkoxo derivatives of arsenic(III) containing glycols, (2a–2d). All compounds were characterized by elemental analysis, molecular weight determinations, IR and NMR (¹H and ¹³C) spectral studies.     

Synthesis and characterization of heterobimetallic mixed-ligand complexes containing Zr(μ-OPri)2Al bridging units

Interesting varieties of heterobimetallic mixed-ligand complexes [Zr{M(OPrⁱ) _n }₂ (L)] (where M = Al, n = 4, L = OC₆H₄CH = NCH₂CH₂O (1); M = Nb, n = 6, L = OC₆H₄CH = NCH₂CH₂O (2); M = Al, n = 4, L = OC₁₀H₆CH = NCH₂CH₂O (3); M = Nb, n = 6, L = OC₁₀H₆CH = NCH₂CH₂O (4)), [Zr{Al(OPrⁱ)₄}₂Cl(OAr)] (where Ar = C₆H₃Me₂-2,5 (5); Ar = C₆H₂Me-4-Bu₂-2,6 (6), [Zr{Al(OPrⁱ)₄}₂(OAr)₂] (where Ar = C₆H₃Me₂-2,5 (7); Ar = C₆H₂Me-4-Bu₂-2,6 (8), [Zr{Al(OPrⁱ)₄}₃(OAr)] (where Ar = C₆H₃Me₂-2,5 (9); Ar = C₆H₃Me₂-2,6 (10), [ZrAl(OPrⁱ)_7-n (ON=CMe₂) _n ] (where n = 4 (11); n = 7 (12), [ZrAl₂(OPrⁱ)_10-n (ON=CMe₂) _n ] (where n = 4 (13); n = 6 (14); n = 10 (15) and [Zr{Al(OPrⁱ)₄}₂{ON=CMe(R)} _n Cl_2–n] [where n = 1, R = Me (16); n = 2, R = Me (17); n = 1, R = Et (18); n = 2, R = Et (19)] have been prepared either by the salt elimination method or by alkoxide-ligand exchange. All of these heterobimetallic complexes have been characterized by elemental analyses, molecular weight measurements, and spectroscopic (I.r., ¹H-, and ²⁷Al- n.m.r.) studies.     

Synthesis and characterization of a new type of heterometallic derivative of zirconium

ZrCl₄ reacts with the potassium salt of the bifunctional tridentate Schiff base HOC₆H₄C(H)=NCH₂CH(Me)OH (LH₂) in a 1:1 molar ratio in benzene to give a new complex Zr(L)Cl₂ which, on reaction with different potassium isopropoxymetallates [e.g., KAl(OPr ⁱ )₄, KTi(OPr ⁱ )₅, and KNb(OPr ⁱ )₆], yield novel heterobimetallic derivatives. These new homo and heteronuclear coordination compounds have been characterized by elemental (N, Cl, Al, Ti, and Nb) analyses, molecular weight (ebullioscopic) measurements and spectral [i.r., n.m.r. (¹H, ¹³C and ²⁷Al)] studies and probable structures for them have been suggested.     

SYNTHESIS AND NMR CHARACTERIZATION OF P-VINYL SUBSTITUTED PHOSPHAZENE PRECURSORS1

Abstract

The reactions of either PhPCl₂ or PCl₃ with (Me₃Si)₂NLi followed by H₂C[dbnd]CHMgBr were used to prepare the new P-vinyl substituted [bis(trimethylsilyl)amino]phosphines, (Me₃Si)₂NP(R)CH[dbnd]CH₂ [1: R=Ph, 2: CH[dbnd]CH₂, 3: R=Me, and 4: R=N(SiMe₃)₂]. Oxidative bromination of phosphines 3–1 afforded the P-bromo-P-vinyl-N-(trimethylsilyl)phosphoranimines, Me₃SiN[dbnd]P(CH[dbnd]CH₂)(R)Br [5: R=Ph, 6: R=CH[dbnd]CH₂, 7: R=Me], which, upon treatment with CF₃CH₂OH/Et₃N, were subsequently converted to the P-trifluoroethoxy derivatives, Me₃SiN[dbnd]P(CH[dbnd]CH₂)(R)OCH₂CF₃ [8: R=Ph, 9: R=CH[dbnd]CH₂, 10: R=Me]. Compounds 1–10, which are of interest as potential precursors to P-vinyl substituted poly(phosphazenes), were fully characterized by elemental analyses (except for the thermally unstable P-Br derivatives 5–7) and NMR spectroscopy (¹H, ¹³C, and ³¹P) including complete analysis of the vinylic proton splitting patterns via HOM2DJ experiments.     

The First Butyltin(IV) Homo- and Heterobimetallic Diethanolaminates

Equimolar reactions of BuSn(OPrⁱ)₃ with diethanolamines, RN(CH₂CH₂ OH) ₂ (abbreviated as RdeaH₂, where R = H or Me), afford dimeric isopropoxo-bridged six-coordinate butyltin(IV) complexes [{Bu(η³-Rdea)Sn(μ-OPrⁱ)}₂] (R = H ( 1 ), Me ( 2 )). Interactions between BuSn(OPrⁱ)₃ and diethanolamines (RdeaH₂) in a 1:2 molar ratio yield monomeric derivatives of the type [BuSn(Rdea)(RdeaH)] (R = H ( 3 ), R = Me ( 4 )). These homometallic complexes on 1:1 reactions with an appropriate metal alkoxide form monomeric heterobimetallic complexes of the type [BuSn (Rdea)₂ {M(OR′)_n}] (R = H, M = Al, R′ = Prⁱ, n = 2 ( 5 ); R = H, M = Ti, R = Prⁱ, n = 3 ( 6 ); R = H, M = Zr, R′ = Prⁱ, n = 3 ( 7 ); R = Me, M = Al, R′ = Prⁱ, n = 2 ( 8 ); R = Me, M = Ti, R′ = Prⁱ, n = 3 ( 9 ); R = Me, M = Ge, R′ = Et, n = 3 ( 10 )). The driving force behind this work was (i) to explore the utility of homometal complexes ( 1 ) –( 4 ) in assembling a metal alkoxide fragment via a condensation reaction and (ii) to gain insights into the structures of new compounds by NMR spectral data. All of these derivatives have been characterized by elemental analysis, spectroscopic (IR, NMR; ¹H, ²⁷Al, and ¹¹⁹Sn) studies, and molecular weight measurements. ¹¹⁹Sn NMR spectral studies indicate that both the homometallic ( 3 ) and ( 4 ) and heterobimetallic ( 5 ) – ( 9 ) complexes exist in a solution in an equilibrium of six- and five-coordinated tin(IV) species.     

A Sr(II)-Zr(IV)-Cd(II) Alkoxide Cluster: Synthesis and X-Ray Structure of [{Cd(OPri)3}Sr{Zr2(OPri)9}]2

New heterotrimetallic alkoxide [{Cd(OPrⁱ)₃}Sr{Zr₂(OPrⁱ)₉}]₂ (1) is obtained quantitatively in an anion-exchange reaction involving well-characterised iodide heterobimetallic alkoxide ICd{Zr₂(OPrⁱ)₉} and the alkali metal reagent KSr(OPrⁱ)₃. The formation of 1 is accompanied with an exchange of metals (Cd(II) and Sr(II)) between the constituting fragments (‘Cd{Zr₂(OPrⁱ)₉}⁺’ and ‘Sr(OPrⁱ)₃ ^?’) and the chelating Zr₂(OPrⁱ)₉ ^? anion, in 1, coordinates to Sr²⁺ in contrast to the precursor ICdZr₂(OPrⁱ)₉ where it is bound to Cd²⁺. The heterotrimetallic nature of 1 is unambiguously established by multinuclear (¹H, ¹³C and ¹¹³Cd) NMR spectral data and a single crystal X-ray diffraction analysis.     

Reaction of silicon with alcohols in autoclave

A reaction of activated silicon with alcohols in an autoclave at 240—270 °C was studied. It was found that primary alcohols form tetraalkoxysilanes Si(OR)₄ with high selectivity (up to 97%), while the secondary PrⁱOH gave a mixture of compounds HSi(OPrⁱ)₃, Si(OPrⁱ)₄, HSi(OPrⁱ)₂OSi(OPrⁱ)₂H, HSi(OPrⁱ)₂OSi(OPrⁱ)₃, and Si(OPrⁱ)₃OSi(OPrⁱ)₃ with the predominance of trialkoxysilane (up to 67%). Carrying out the reaction under the indicated conditions has the advantage of experimental simplicity, reagent availability, high conversion of silicon, good isolated yields of products.     

Synthesis and Tunable Reactivity of N‐Heterocyclic Germylene

Modifying the β‐diketimine ligand LH 1 (LH=[ArN?C(Me)? CH?C(Me)? NHAr], Ar=2,6‐iPr₂C₆H₃) through replacement of the proton in 3‐position by a benzyl group (Bz) leads to the new ^BzLH ligand 2, which could be isolated in 77 % yield. According to ¹H NMR spectroscopy, 2 is a mixture of the bis(imino) form [(ArN?C(Me)]₂CH(Bz) 2a and its tautomer [ArN?C(Me)? C(Bz)?C(Me)NHAr] 2b. Nevertheless, lithiation of the mixture of 2a and 2b affords solely the N‐lithiated β‐diketiminate [ArN?C(Me)? C(Bz)?C(Me)? NLiAr], ^BzLLi 3. The latter reacts readily with GeCl_2?dioxane to form the chlorogermylene ^BzLGeCl 4, which serves as a precursor for a new zwitterionic germylene by dehydrochlorination with LiN(SiMe₃)₂. This reaction leads to the zwitterionic germylene ^BzL′Ge: 5 (^BzL′=ArNC(?CH₂)C(Bz)?C(Me)NAr) which could be isolated in 83 % yield. The benzyl group has a distinct influence on the reactivity of zwitterionic 5 in comparison to its benzyl‐free analogue, as shown by the reaction of 5 with phenylacetylene, which yields solely the 1,4‐addition product 6, that is, the alkynyl germylene ^BzLGeCCPh. Compounds 2–8 have been fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single‐crystal X‐ray diffraction analyses.     

Effects of substitution and terminal groups for liquid-crystallinity enhanced luminescence of disubstituted polyacetylenes carrying chromophoric terphenyl pendants

Liquid-crystalline and light-emitting poly(2-alkyne)s containing terphenyl cores with hexamethyleneoxy spacers,and cyano or n-propoxy tails -[CH3C=C(CH2)6O-terphenyl-R]n-,where R=CN,CH3PA6CN,R=OCH2CH2CH3,CH3PA6OPr,were synthesized.The effects of the substitution and terminal groups on the properties,especially the mesomorphic and optical properties of the polymers,were investigated.The disubstituted acetylene monomers (CH3A6CN,CH3A6OPr) were pre- pared through multistep reaction routes and were polymerized by WCl6-Ph4Sn in good yields (up to 82%).All the monomers and CH3PA6CN exhibited the enantiotropic SmA phase with a monolayer arrangement at elevated temperatures,whereas CH3PA6OPr formed a bilayer SmAd packing arrangement.Upon excitation at 330 nm,strong UV and blue emission peaks at 362 and 411 nm were observed in CH3PA6OPr and CH3PA6CN,respectively.The luminescent properties of CH3PA6CN and CH3PA6OPr have been improved by introducing the methyl substituted group,and the quantum yield of the polymer with cyano tail CH3PA6CN (φ= 74%) was found to be higher than that of CH3PA6OPr (φ= 60%).Compared to polyacety- lene parents,both CH3PA6OPr and CH3PA6CN showed a narrower energy gap.This demonstrated that the electrical con- ductivities of polyacetylenes could be enhanced by attaching appropriate pendants to the conjugated polyene backbones.     

Glycol modified titanosiloxane as molecular precursor for homogenous titania–silica material: synthesis and characterization

Ti(OPrⁱ)₄ reacts with HOSi(O^tBu)₃ in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy titanosiloxane precursors, [Ti(OPrⁱ)₃{OSi(O^tBu)₃}] (A) and [Ti(OPrⁱ)₂{OSi(O^tBu)₃}₂] (B), respectively. Further reactions of (A) or (B) with glycols in 1:1 molar ratio afforded six complexes of the types [Ti(OPrⁱ)(O–G–O){OSi(O^tBu)₃}] (1A–3A) and [Ti(O–G–O){OSi(O^tBu)₃}₂] (1B–3B), respectively [where G = (CH₂)₂ (1A, 1B); (CH₂)₃ (2A, 2B) and {CH₂CH₂CH(CH₃)} (3A, 3B)]. Both (A) and (B) are liquids while all the other products are viscous liquids which get solidified on ageing. Cryoscopic molecular weight measurements of the fresh products indicate their monomeric nature. FAB mass studies of (A) and (B) also indicate monomeric nature. However, FAB mass spectra of the two representative solids (1A) and (2B) suggest dimeric behavior of the glycolato derivatives. (A) distills at 85 °C/5 mm while other products get decomposed even under reduced pressure. TG analyses of (A), (B), (1A), and (1B) suggest formation of titania–silica materials at 200 °C for (A) and (B) and 350 °C for (1A) and (1B). The products have been characterized by elemental analyses, FTIR and ¹H, ¹³C & ²⁹Si-NMR techniques. All these products are soluble in common organic solvents indicating a homogenous distribution of the components on the molecular scale. The Si/Ti ratio of the oxide may be controlled easily by the composition of the starting precursors. Hydrolysis of the glycol modified derivative, (1A) by the Sol–Gel technique affords the desired homogenous titania–silica material, TiO₂·SiO₂ in nano-size while, the precursor (A) yields a non-stiochiometric silica doped titania material. However, pyrolysis of (A) yields nano-sized crystallites of TiO₂·SiO₂. All these materials were characterized by FTIR, powder XRD patterns, SEM images, and EDX analyses.