Solution 13C Research Articles

Factors Dictating the Nuclearity/Aggregation and Acetate Coordination Modes of Lutidine-Coordinated Zinc(II) Acetate Complexes

The reactions of Zn(OAc)(2).2H(2)O with various positional isomers of lutidine were explored with a view to understand the factors responsible for the nuclearity/aggregation and acetate coordination modes of the products. The reactions of Zn(OAc)(2).2H(2)O with 3,5-lutidine, 2,3-lutidine, 2,4-lutidine, and 3,4-lutidine in a 1:1 ratio in methanol at ambient temperature afforded three discrete trinuclear complexes [Zn(3)(OAc)(2)(mu(2)-eta(2):eta(1)-OAc)(2)(mu(2)-eta(1):eta(1)-OAc)(2)(H(2)O)(2)(3,5-lutidine)(2)] (1), [Zn(3)(mu(2)-eta(1):eta(1)-OAc)(4)(mu(2)-eta(2):eta(0)-OAc)(2)L(2)] [L = 2,3-lutidine (2) and 2,4-lutidine (3)], and a one-dimensional coordination polymer [Zn(OAc)(mu(2)-eta(1):eta(1)-OAc)(3,4-lutidine)] (4) in 93, 79, 81, and 94% yields, respectively. Complexes 1-4 were characterized by microanalytical, IR, solution ((1)H and (13)C), and solid-state cross-polarization magic angle spinning (13)C NMR spectroscopic techniques and single-crystal X-ray diffraction data. Complex 1 is unique in that it contains three types of acetate coordination modes, namely, monodentate, bridging bidentate, and asymmetric chelating bridging. Variable-temperature (1)H NMR data indicated that complex 1 partially dissociates in solution, and the remaining undissociated 1 undergoes a rapid "carboxylate shift" even at 218 K. The plausible mechanism of formation of complexes 1-4 was explained with the aid of a point zero charge (pzc) model, according to which the nuclearity/aggregation observed in complexes 1-4 depends upon the number and nature of equilibrating species formed upon dissolution of the reactants in methanol, and these in turn depend upon the subtle basic/steric properties of lutidines. Further, noncovalent interactions play a crucial role in determining the nuclearity/aggregation and acetate coordination modes of the products.

Selective synthesis of monomeric or dimeric titanatranes via fine tuning in triethanolateamine ligand

Monomeric titanatrane i-PrOTi(OCMe 2CH 2) 3N ( 1) and dimeric titanatranes [ i-PrOTi(OCH 2CH 2) n N(CH 2CMe 2O) 3− n ] 2 ( n = 1, 2; n = 2, 3) were synthesized by the reaction of Ti(O- i-Pr) 4 with a series of triethanolateamines such as (OCH 2CH 2) n N(CH 2CMe 2O) 3− n 3− ( n = 0, Lig 1 ; n = 1, Lig 2 ; n = 2, Lig 3 ), which vary by the number of CMe 2 groups adjacent to a OH functionality from 3 ( Lig 1H 3 ) to 2 ( Lig 2H 3 ) to 1 ( Lig 3H 3 ). The resultant titanatranes 1– 3 have been characterized by solution 1H and 13C{ 1H} NMR and their solid state structures have been determined by X-ray crystallography. Whereas compound 1 is monomeric in the solid state, compounds 2 and 3 are dimeric, due to the reduction of the steric congestion in the vicinity of the Ti.

Polymeric and polymer-ligated spirobicyclic zwitterionic Janovsky complexes

A novel approach to the synthesis of spirobicyclic Janovsky complexes is described. The complexes were prepared on silica and polystyrene polymeric supports as well as on a solution-borne poly(carbodiimide) polymer with 100% atom economy. A carbon-centered intramolecular de-aromatizing nucleophilic aromatic substitution ipso-cyclization mechanism describes the synthesis of these spirobicyclics. The molecules were characterized by solution and solid-state 1H and 13C NMR, IR, and MS.

Alpha cellulose from industrial and agricultural renewable sources like short flax fibres, ears of corn and wheat-straw and its transformation into cellulose acetates

Cellulose with high content of alpha cellulose (ca. 98%, named CF) was extracted from short flax fibres following a free chloride procedure based on a two-step oxidative approach. The same procedure provided celluloses with alpha cellulose content around 83% from ears of corn (CC) and wheat straw (CW). CF can be used for the preparation of cellulose triacetate (CTA) and diacetate (CA), while both CC and CW can be used for the preparation of CA. The polymerisation degree (DP), dynamic light scattering (DLS) measurements, solution 13C NMR and solid state (CP MAS) 13C NMR spectra were properly used to characterise the extracted celluloses CF, CC, CW as well as their acetylated derivatives CTA and CA. Commercial alpha cellulose and CA samples were characterised in the same way and compared with CF, CC, CW and CTA, CA, respectively. From these comparisons, they all appeared to be cellulose materials suitable for industrial developments.

The nucleophilic chemical reactions of NaX Faujasite zeolite with diisopropyl phosphorofluoridate (diisopropyl fluorophosphate, DFP)

Diisopropyl phosphorofluoridate (commonly known as diisopropyl fluorophosphate and commonly abbreviated DFP) was adsorbed in dry NaX zeolite with and without adsorption of a stoichiometric amount of water. The chemical products from the reaction of zeolite and water with DFP, in relation to residual DFP, were identified and quantified from the quantitative NMR chemical shift values and intensities of solid-state 13C and 31P NMR and solution 13C, 31P, 17O and 1H NMR. In dry zeolite, DFP undergoes an elimination reaction to form propene and a framework bound isopropyl phosphorofluoridate ion. In NaX loaded with a stoichiometric amount of water, DFP undergoes hydrolysis to form isopropanol and isopropyl hydrogen phosphate. Upon addition of water to the DFP exposed zeolite, residual DFP undergoes hydrolysis to form isopropanol and isopropyl hydrogen phosphorofluoridate. Evidently upon addition of water to the dry DFP exposed NaX, the previously formed framework bound isopropyl phosphorofluoridate ion is also hydrolyzed to isopropyl hydrogen phosphate. Addition of water to the zeolite after DFP adsorption increased the hydrolysis reaction from 6.5% to 44.5%. Unlike other reported catalyzed hydrolyses, where hydrolysis of DFP involves water attack on the phosphorous, in NaX zeolite the ester carbon is attacked.

Furanose dynamics in the HhaI methyltransferase target DNA studied by solution and solid-state NMR relaxation.

Both solid-state and solution NMR relaxation measurements are routinely used to quantify the internal dynamics of biomolecules, but in very few cases have these two techniques been applied to the same system, and even fewer attempts have been made so far to describe the results obtained through these two methods through a common theoretical framework. We have previously collected both solution 13C and solid-state 2H relaxation measurements for multiple nuclei within the furanose rings of several nucleotides of the DNA sequence recognized by HhaI methyltransferase. The data demonstrated that the furanose rings within the GCGC recognition sequence are very flexible, with the furanose rings of the cytidine, which is the methylation target, experiencing the most extensive motions. To interpret these experimental results quantitatively, we have developed a dynamic model of furanose rings based on the analysis of solid-state 2H line shapes. The motions are modeled by treating bond reorientations as Brownian excursions within a restoring potential. By applying this model, we are able to reproduce the rates of 2H spin-lattice relaxation in the solid and 13C spin-lattice relaxation in solution using comparable restoring force constants and internal diffusion coefficients. As expected, the 13C relaxation rates in solution are less sensitive to motions that are slower than overall molecular tumbling than to the details of global molecular reorientation, but are somewhat more sensitive to motions in the immediate region of the Larmor frequency. Thus, we conclude that the local internal motions of this DNA oligomer in solution and in the hydrated solid state are virtually the same, and we validate an approach to the conjoint analysis of solution and solid-state NMR relaxation and line shapes data, with wide applicability to many biophysical problems.

Chromonic Liquid Crystal Formation by Edicol Sunset Yellow

The solution and liquid crystalline phases formed by dissolution of the dye Edicol Sunset Yellow (ESY) in water have been examined using optical microscopy, multinuclear NMR (1H, 2H, 13C, 23Na), and X-ray diffraction. From the solution 1H and 13C spectra (particularly 13C), it is clear that the tautomeric form present in all these phases is the hydrazone, NH, structure, not the usually given azo, OH, form. Two chromonic mesophases occur: a nematic (N) phase at approximately 30-40 wt % and a hexagonal (M) phase at approximately 40-45 wt %. X-ray diffraction data show that the aggregates in the mesophases are single molecule stacks, with a typical spacing of approximately 3.5 angstroms, as expected for these systems. The NMR quadrupole splittings (2H2O, 23Na) are similar to those observed for surfactant lyotropic mesophases, suggesting that there are no water molecules or counter ions that are tightly bound to the ESY aggregates. An unusual feature of the X-ray diffraction pattern of the mesophases is the occurrence of diffuse off-axis reflections at approximately 6.8 angstroms. It is proposed that these arise from a head-to-tail packing of the molecules within the stacks.

Studies of Inclusion Complexes of Dichloromethane in Cryptophanes by Exchange Kinetics and 13C NMR in Solution and the Solid State

Cryptophanes are molecular hosts having high binding affinities for small, neutral molecules in weakly polar solvents. We have previously studied dichloromethane as a guest inside the cavity of cryptophane-E (cryptophane-333), in solution as well as in the solid state. Here, we present a solution 13C relaxation study of dichloromethane as the guest molecule complexed in the cavity of two smaller hosts: cryptophane-A (cryptophane-222) and cryptophane-223. 13C relaxation measurements were performed for both guest and host molecules. Exchange kinetics have to be explicitly taken into consideration in order to derive 13C relaxation properties of the bound guest. Rate coefficients were measured using proton 1D-exchange experiments. We have also investigated dichloromethane complexed in the cavity of cryptophane-233 in the solid state, by estimating the motionally averaged 13C−1H dipolar interactions from recoupling experiments under magic angle spinning (MAS) conditions. The measurements for the three cryptoph...

Structural studies of 4,5,6,7-tetrabromobenzimidazole derivatives by means of solid-state 13C, 15N NMR spectroscopy and DFT calculations

Tetrabromobenzimidazole derivatives containing sulfur or nitrogen atom in a five- or six-membered saturated ring were synthesized as potential ligands of casein kinase (CK2). Structural data of these compounds are crucial for understanding their inhibitory activity as inhibitors. Solution and solid-state 13C NMR spectra were recorded for six compounds, and 15N MAS spectra – for two of them. 13C CPMAS spectra were assigned by comparison with solution data and with the aid of dipolar dephasing and variable contact time experiments. The correctness of assignments of 13C and 15N chemical shifts was verified by GIAO DFT calculations of shielding constants. The differences between the solution and solid-state chemical shift values were explained in terms of intermolecular interactions. The doublet resonances occurring in the solid-state 13C and 15N NMR spectra of N 1, N 2-propylene-2-amino-4,5,6,7-tetrabromobenzimidazole indicate the presence of two molecules in crystallographic unit cell. Shielding constants calculated for a dimer with two N1′ H…N3 hydrogen bonds suggest that the association type does not influence carbon shielding. The coexistence of two tautomers with N1′ H and N3 H is less probable.

Syntheses, structures and antimicrobial activities of various metal complexes of hinokitiol

Metal–oxygen bonding complexes (M = Mg II, Mn II, Ni II, Mo VI, W VI, Pd II, Sb III, Bi III, Fe III, Ti IV, K I, Ba II, Zr IV and Hf IV) with a hinokitiol (Hhino; 2-hydroxy-4-isopropylcyclohepta-2,4,6-trienone or β-thujaplicin) ligand, which has two unequivalent oxygen donor atoms, were synthesized and characterized by elemental analysis, TG/DTA, FT-IR and solution ( 1H and 13C) NMR spectroscopy. Single-crystal X-ray structure analysis revealed various molecular structures for the complexes, which were classified into several families of family, i.e. type A [M II(hino) 2(L)] 2 (M = Mg II, Mn II, Ni II; L = EtOH or MeOH), with a dimeric structure consisting of one bridging hino − anion, one chelating hino − anion and one alcohol or water molecule, type B, with the octahedral, cis-dioxo, bis-chelate complexes cis-[M VIO 2(hino) 2] (M = Mo VI, W VI), type C, with square planar complex [M II(hino) 2] (M = Pd II), type D, with tris-chelate, 7-coordinate complexes with one inert electron pair [M III(hino) 3] (M = Sb III, Bi III), type D′, with the bis-chelate, pseudo-6-coordinate complexes with one inert electron pair [M III(hino) 2X] (M = Sb III, X = Br), type E, with tris-chelate, 6-coordinate complexes with Δ and Λ isomers [M III(hino) 3] (M = Fe III), type E′ of bis-chelate, 6-coordinate complex [M IV(hino) 2X 2] (M = Ti IV, X = Cl), type F, with water-soluble alkali metal salts [M I(hino)] (M = K I), and type H, with tetrakis-chelate, 8-coordinate complexes [M IV(hino) 4](M = Zr IV, Hf IV). These structural features were compared with those of metal complexes with a related ligand, tropolone (Htrop). The antimicrobial activities of these complexes, evaluated in terms of minimum inhibitory concentration (MIC; μg mL −1) in two systems, were compared to elucidate the relationship between structure and antimicrobial activity.

Delving into the complex picture of Ti(IV)–citrate speciation in aqueous media: Synthetic, structural, and electrochemical considerations in mononuclear Ti(IV) complexes containing variably deprotonated citrate ligands

The aqueous reaction of TiCl 4 with citric acid at pH ∼ 4 (KOH), led to the surprising isolation of a species assembly K 3[Ti(C 6H 6O 7) 2(C 6H 5O 7)] · K 4[Ti(C 6H 5O 7) 2(C 6H 6O 7)] · 10H 2O ( 1). The same system at pH ∼ 3 (neocuproine), led to the crystalline material (C 14H 13N 2) 2[Ti(C 6H 6O 7) 3] · 5H 2O ( 2), while at pH 5.0 (NaOH), afforded Na 3[Ti(C 6H 6O 7) 2(C 6H 5O 7)] · 9H 2O ( 3). Analytical, spectroscopic and structural characterization of 1, 2 and 3 revealed their distinct nature exemplified by mononuclear complexes bearing variably deprotonated citrates bound to Ti(IV). Solid-state 13C MAS NMR spectroscopy in concert with solution 13C and 1H NMR on 3 provided ample evidence for the existence of bound citrates of distinct coordination mode to the metal ion. Cyclic voltammetry defined the electrochemical signature of complex 2, thereby projecting the physicochemical profile of the species formulated by the aforementioned properties. Comparison of cyclic voltammetric data on available discrete Ti(IV)–citrate species depicts the electrochemical profile and an E 1/2 value trend of the species in that binary system’s aqueous speciation, further substantiating the redox behavior of mononuclear Ti(IV)–citrate species in a pH-sensitive fashion. Collectively, the well-defined discrete species in 1– 3 reflect and corroborate a synthetically challenging yet complex pH-specific picture of the aqueous Ti(IV) chemistry with the physiological citric acid, and shed light on the pH-dependent speciation in the binary Ti(IV)–citrate system.

FT-IR spectra of alginic acid block fractions in three species of brown seaweeds

Sodium alginates obtained by alkaline extraction of Lessonia flavicans, Desmarestia ligulata and Desmarestia distans (Phaeophyta) from southern Chile were partially hydrolyzed with HCl. Each alginate gave three fractions that were characterized using FT-IR spectroscopy. The fractions soluble in 0.3 M HCl presented in the fingerprint region four vibrations at around 960, 911, 890 and 815 cm −1 that were assigned to heteropolymeric blocks. The fractions soluble at pH 2.85 showed bands at around 948, 888 and 820 cm −1 attributed to homopolymannuronic acid blocks, the first band is resolved in the second-derivative spectra into two bands at 951 and 936 cm −1. The fractions insoluble at pH 2.85 presented four bands at around 947, 903, 812 and 781 cm −1, which were assigned to homopolyguluronic acid blocks. For some samples, the second derivative FT-IR spectra showed new bands indicating the presence of other structures, in low proportions. Structures deduced by FT-IR spectroscopy were corroborated by solution 1H and 13C NMR spectroscopy. Two-dimensional spectra were collected to confirm the fine structure of the hetero- and homopolymeric fractions. A geometrically optimized model for the disaccharide α- l-gulopyranuronosyl-(1→4)-α- l-gulopyranuronic acid was calculated using density functional theory; good agreement was obtained between its corresponding calculated vibrations and the experimental bands assigned to homopolyguluronic acid blocks.

Conformational analysis of a helically distorted gold(I) macrocycle derived from xantphos: evidence for the aurophilic Au… Au interaction from NMR

Variable-temperature solution (1)H- and (31)P-NMR experiments are reported for [Au(2)(xantphos)(2)](NO(3))(2) gold(I) complex incorporating a 16-membered Au(2)P(4)C(8)O(2) macrocycle derived from the 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (xantphos) ligand. These NMR studies provide detailed structural information about its solution structure in comparison to the solid-state structure available from single crystal X-ray diffraction. Two-dimensional (1)H-NOESY spectroscopy at low temperatures allowed the full assignment of proton resonances, which are severely exchange-broadened at room temperature. The (1)H--(1)H spatial connectivities of the large number of non-equivalent protons unravel the complete stereochemistry of the gold(I) macrocycle in its symmetrically twisted conformation. Chemical exchange between particular proton pairs has allowed understanding the molecular dynamics and ruled out formation of coordination oligomers. Spectral analysis of the unique phosphorous AA'BB' spin system has revealed three-bond (31)P--(31)P scalar couplings mediated through the Au--Au bond, and has confirmed the existence of the aurophilic contact in low-temperature solutions. The solution (13)C and (31)P spectra are compared to the solid state (31)P-MAS and (13)C--CP/MAS spectra, where signal doubling effects due to the crystal packing have been discovered.

Structure of Co 2(CO) 6(dppm) and Co 2(CO) 5(CHCO 2Et)(dppm) (dppm = Ph 2PCH 2PPh 2) and exchange reaction with 13CO: An experimental and computational study

Crystal structures of Co 2(CO) 6(dppm) ( 1) and Co 2(CO) 5(CHCO 2Et)(dppm) ( 2) (dppm = Ph 2PCH 2PPh 2) show asymmetry with respect to the orientation of the phenyl groups in 1 and owing to the bridging ethoxycarbonylcarbene ligand in 2. The effect of this asymmetry was recognized in the solid-state 31P NMR spectra of 1 and 2 and in the solid-state and solution 13C NMR spectra of 2 as well, but not in the solid-state and solution 13C NMR spectra of 1. In CH 2Cl 2 solution under an atmosphere of 13CO, the CO ligands of both complexes exchange with 13CO. The overall rate of 13CO exchange at 10 °C was found to be k obs = 0.107 × 10 −3 s −1 for 1 and k obs = 0.243 × 10 −3 s −1 for 2. Two-layered ONIOM(B3LYP/6-31G(d):LSDA/LANL2MB) studies revealed fluxional behavior of 1 with rather small barriers of activation of the rearrangements. Four possible isomers have been computed for 2, close to each other energetically.

Light-stable and antimicrobial active silver(I) complexes composed of triphenylphosphine and amino acid ligands: Synthesis, crystal structure, and antimicrobial activity of silver(I) complexes constructed with hard and soft donor atoms ( n∞{[Ag(L)(PPh 3)] 2} with L = α-ala − or asn − and n = 1 or 2)

Three novel silver(I) complexes consisting of both hard Lewis bases (O and N atoms) and one soft Lewis base (P atom) (( dl-α-alaninato)(triphenylphosphine)silver(I) ( 1), ( dl-asparaginato) (triphenylphosphine)silver(I) ( 2) and ( l-asparaginato) (triphenylphosphine)silver(I) ( 3)) were prepared from stoichiometric reactions of amino acid–silver(I) complexes with PPh 3 in a 1:1 molar ratio in a mixed organic solvent. These silver(I) complexes were soluble in organic solvents but insoluble in water; they are also more light-stable as compared to the corresponding precursors, amino acid–silver(I) complexes. Their solid-state and solution structures were unequivocally characterized using elemental analysis, TG/DTA, FTIR, X-ray structure analysis, solution ( 1H, 13C, and 31P) NMR and solid-state 31P CPMAS NMR spectroscopy. The X-ray structure analysis of complexes 1 and 2 revealed that these complexes were dimers with an inversion center. Each silver(I) atom was coordinated in a distorted four-coordinate environment containing an AgNO 2P core. Complexes 1 and 2 formed 1D and 2D networks in the crystal through intermolecular hydrogen bonding networks that can be described as ∞{[Ag( dl-α-ala)(PPh 3)] 2 · 2H 2O} and 2 ∞{[Ag( dl-asn)(PPh 3)] 2 · 2H 2O · 2EtOH}, respectively. Complexes 1– 3 showed moderate to modest antimicrobial activities against selected bacteria and yeasts in a water-suspension system.

Tunable π-Interactions in Monomeric Organozinc Complexes: Solution and Solid-State Studies

A series of the calix[4]arene ligands, partially oxygen-depleted at the 1 and 3 positions via the Sonogashira cross-coupling reaction with several arylacetylenes, were prepared. Upon reaction with R2Zn (R = Me, Et, C6F5), the corresponding organozinc complexes were obtained. X-ray analysis showed weak π-interactions between the organozinc fragment and the triple bonds. In addition, the solution 13C NMR studies showed good correlation between the strength of these interactions and electron density at the acetylene group, with more electron-rich alkynes binding stronger to the Zn center. The latter was also supported by DFT calculations on a model compound. These results show that, albeit weak, π-interactions of organozinc compounds can be observed and fine-tuned in both solution and the solid state.

Synthesis and solution behavior of the trinuclear palladium(II) unsaturated carboxylate complexes triangle-Pd 3[μ-O 2CC(R′) = CHMe] 6 (R′ = Me, H): X-ray structure of palladium(II) tiglate (R′ = Me)

The first examples of binary palladium(II) derivatives of unsaturated carboxylic acids are reported. It was found that the interaction of Pd 3(μ-OAc) 6 with the α,β-unsaturated 1-methylcrotonic (tiglic) and crotonic acids leads to the corresponding carboxylates of composition Pd 3[μ-O 2CC(R′) = CHMe] 6, where R′ = Me ( 1) or H ( 2). The new compounds have been characterized by elemental analysis, solid and solution IR, 1H and 13C NMR, and ESI mass spectrometry. The crystal structure of 1 has been determined. This molecule displays a central Pd 3 cyclic core with Pd–Pd distances of 3.093–3.171 Å. Each Pd–Pd bond is bridged by a pair of carboxylate ligands, one above and the other below the Pd 3 plane, providing a square planar coordination for each Pd atom in an approximate D 3 h overall symmetry arrangement. Solution spectroscopic data show that the bridging η 1:η 1:μ 2 interaction of the carboxylates of 1 and 2 is readily displaced, with a change of the ligand to the terminal (η 1) coordination mode.

Zinc halide complexes of imidazolidine-2-thione and its derivatives: X-ray structures, solid state, solution NMR and antimicrobial activity studies

The preparation and characterization of zinc complexes of formula ZnL2X2 (X = Cl and Br), with L = 1,3-diazinane-2-thione (Diaz), 1,3-diazipane-2-thione (Diap), imidazolidine-2-thione (Imt) and its methyl and n-propyl substituted derivatives, are described. The complexes dichlorobis(1-methylimidazolidine-2-thione-S)-zinc(II) (1) and dichlorobis(1-propylimidazolidine-2-thione-S)-zinc(II) (2) have been characterized by single-crystal X-ray methods. Both complexes adopt distorted tetrahedral geometry. Only intramolecular hydrogen bonding interactions are observed in 1 and 2. Solution and solid state 13C NMR show a significant shift of the C=S carbon resonance of the ligands, while other resonances are relatively unaffected, indicating that most likely the solid state structure is maintained in solution. Antimicrobial activity studies of the free ligands and their complexes show that ligands exhibit substantial antibacterial activities compared to the complexes.

Complexations of Hg(CN) 2 with imidazolidine-2-thione and its derivatives: Solid state, solution NMR and antimicrobial activity studies

The preparation and characterization of new mercuric complexes of formula L 2Hg(CN) 2 with L being imidazolidine-2-thione (Imt) and its substituted derivatives, 1,3-diazinane-2-thione (Diaz), 1,3-diazipane-2-thione (Diap), are described. The solution and solid-state 13C NMR show a significant shift of the C S carbon resonance of the ligands, while the other resonances are relatively unaffected, indicating that most likely the solid-state structure is maintained in solution as well. The principal components of the 199Hg shielding tensors were determined from solid-state NMR data. Antimicrobial activity studies of the free ligands and their complexes show that ligands exhibit substantial antibacterial activities compare to their Hg(II) complexes.

GC‐MS and 13C NMR Investigation of Lead Zirconate Titanate Precursor Sols for Fiber Preparation

Different macroscopic properties of PZT fibers have been obtained when using acetic acid and methacrylic acid to modify the PZT precursor. In order to clarify the role of the acids the molecular structure of the acidified PZT precursors was investigated and compared by gas chromatography‐mass spectrometry, Fourier transform infrared, 13C nuclear magnetic resonance (NMR) spectroscopy (solution and solid state 13C NMR) and the reason for obtaining long PZT fibers is discussed. The results indicate that when methacrylic acid was used, long gel and ceramic fibers have been obtained because strongly co‐ordinating carboxylate groups of methacrylic acid were formed. Linear chains, like those of methacrylic acid propyl ester and methacrylic acetate, have been formed in the PZT precursor sols. In addition, after heat treatment the polymer decomposed quickly so that pure perovskite could be obtained at low temperature in the PZT fibers. When acetic acid was used short fibers were obtained. Acetic acid may act as chelate agent to form oxo acetate in the precursors; this oxo acetate nature also resulted in PZT fibers drawing. However, the longest gel and ceramic fibers have been prepared from precursors with methacrylic acid.