Structural investigations on the hydrolysis and condensation behavior of pure and chemically modified alkoxides. 2. Germanium alkoxides

Structural investigations on the hydrolysis and condensation behavior of germanium alkoxides were for the first time performed by means of X-ray absorption fine structure and Raman spectroscopy. The studies reveal that germanium alkoxides are monomeric in nature and undergo very fast hydrolysis and condensation reactions upon water addition. However, the chelation of germanium alkoxides by acetylacetone does not take place even 48 h after mixing, and any change in hydrolysis and condensation behavior is not observed after acetylacetone addition. When mixed with prehydrolyzed silicon alkoxide, the structures of germanium alkoxides are not modified. Both Si and Ge precursors are insensitive to the presence of each other in the reaction solution even after 48 h of aging. The addition of water to this mixture catalyzes the hydrolysis and condensation reactions very fast and leads to the formation of Ge-O-Ge (and consequently Si-O-Si) homocondensation products.     

Structural studies on the hydrolysis products of Ti,Nb and Zr alkoxides

Raman scattering was used to identify the vibrational modes of amorphous hydrolysis products of metal alkoxides and the corresponding sintered materials. These results were combined with X-ray diffraction data to identify the various isopoly complex groups which occurred in such materials.     

Preparation and structural investigations of fluorinated tungsten(vi) alkoxides

The preparation and characterization of compounds of composition Cl_6-xW(OCH₂CF₃)_x (x = 1−6) and X₄W[OC(CH₃) (CF₃)₂]₂ (X = Cl,F) together with ¹⁹F NMR spectra are reported. An X-ray structure analysis of Cl₄W[OC(CH₃)(CF₃)₂]₂ shows a W-O-C angle of 173.6°, which is unusually large for metal alkoxides, and a short W-O distance of 181.9 pm. A discussion on structural aspects and a comparison with related tungsten-nitrogen compounds are presented. Cl₄W[OC(CH₃) (CF₃)₂]₂ is monoclinic, space group C2/m, with a = 820.3(2), b = 1059.2(2), c = 1071.6(2) pm, β = 99.72(2)°, Z = 2 and was refined to R = 0.031 for 848 observed reflections.     

Structural studies of lanthanide ion complexes of pure gold, pure silver and mixed metal (gold-silver) dicyanides

Crystal structures of four lanthanide complexes of La[Au(CN)2](3).3H2O, La[Ag(CN)2](3).3H2O, La[Ag(0.83)Au(0.17)(CN)2](3).3H2O, and La[Ag(0.39)Au(0.61)(CN)2](3).3H2O are reported. Studies reveal that all the structures reported are isostructural. All systems were found to be in the hexagonal crystal system, space group P6(3)/mcm. The metal-metal distance for the pure gold system is 3.332 (1) A versus 3.359(1) A for the pure silver system. The mixed-metal systems have shown no distinct differences in the location of the metal atoms, with the La[Ag(0.83)Au(0.17)(CN)2](3).3H2O complex having a metal-metal Ag-Au separation of 3.346(1) A, and 3.344(1) A for the La[Ag(0.39)Au(0.61)(CN)2](3).3H2O complex. The crystal structures of the pure and mixed La complexes have been solved to provide evidence of Ag-Au heterometallic interactions and as a basis for understanding the interesting optical properties of the systems.     

Structural investigations of mixed metal compounds; the stereochemistry of two dilithium-tris(olefin)nickel(0) complexes

The structures of bis(lithium-N,N,N′,N′-tetramethylethylenediamine) (all-trans-1,5,9-cyclododecatrienenickel) (I) and tris(N,N,N′,N′,-tetramethyl-2-butene-1,4-diamine)dilithiumnickel (II) have been determined from single cyrstal X-ray data measured by counter methods. Crystals of I belong to the orthorhombic space group Pbca with a 13.776(2), b 14.090(2), c 58.374(6) », Z = 16 and d_c 1.10 g cm^-3. Compound II crystallizes in the monoclinic space group C2/c with a 22.960(2), b 8.9860(3), c 15.1984(6) », β 109.015(5)°, Z = 4 and d_c 1.12 g cm^-3. Refinement of I (II) coverged with R = 0.097 (0.037) for the 4281 (2424) reflections with I > 2σ(I).Two unique and essentially identical molecules not having crystallographic symmetry were found for I while molecules of II possess crystallographic C₂ symmetry, the two fold axis passing through the Ni atom and bisecting one olefinic CC bond. The trigonal bipyramidal geometry of the Ni atoms, the centers of three olefinic double bonds in the trigonal plane and Li atoms in apical positions, is distorted in I but nearly exact in II. The NiC (olefinic) bond lengths average 1.99(3) and 2.000(3) » in I and II respectively. The shorter bond distances to the Ni a toms formed by the three-coordinate Li atoms in I, average 2.400(6) », compared to those formed by the four-coordinate Li atoms in II, 2.561(3) », may be due to Ni → Li d_π → pπ backbonding in I. The LiNiLi angles are (average) 164(2)° in I and 178.9(1)° in II. The strength of the Ni olefin interactions in these compounds is most clearly shown by the long mean CC distances (1.452(9) ») and 40(2)° bending back of the olefinic substituents from the Ni atom in II.     

Swelling and scattering investigations on chemically cross-linked poly(vinyl alcohol) hydrogels

Swelling and scattering measurements are reported from chemically cross-linked polyvinyl alcohol) hydrogels and the corresponding semi-dilute polymer solutions. The mixing free energy in the swollen network is found to be significantly smaller than that of the corresponding polymer solution at identical concentration. Static light scattering and small-angle neutron scattering measurements indicate the presence of large-scale static structures in the solution. Reasonable agreement is found between the osmotic moduli obtained from light scattering measurements and macroscopic osmotic observations.     

Structural investigations on diorgano- and triorganotin(IV) derivatives of [meso-tetra(4-sulfonatophenyl)porphine] metal chlorides

Several new complexes of organotin(IV) moieties with MCl_n[meso-tetra(4-sulfonatophenyl)porphine], (R₂Sn)₂MCl_n[meso-tetra(4-sulfonatophenyl)-porphinate]s and (R₃Sn)₄MCl_n [meso-tetra(4-sulfonatophenyl)porphinate]s, [M = Fe(III), Mn(III): n = 1, R = Me, n-Bu; Ph; M = Sn(IV): n = 2, R = Me, n-Bu] have been synthesized and their solid state configuration investigated by infrared (IR) and Mössbauer spectroscopy, and by ¹H and ¹³C NMR in D₂O.The electron density on the metal ion coordinated inside the porphyrin ring is not influenced by the organotin(IV) moieties bonded to the oxygen atoms of the side chain sulfonatophenyl groups, as it has been inferred on the basis of Mössbauer spectroscopy and, in particular, from the invariance of the isomer shift of the Fe(III) and Sn(IV) atoms coordinated into the porphyrin square plane of the newly synthesized complexes, with respect to the same atoms in the free ligand.As far as the coordination polyhedra around the peripheral tin atoms are concerned, infrared spectra and experimental Mössbauer data would suggest octahedral and trigonal bipyramidal environments around tin, in polymeric configurations obtained, respectively, in the diorganotin derivatives through chelating or bridging sulfonate groups coordinating in the square plane, and in triorganotin(IV) complexes through bridging sulfonate oxygen atoms in axial positions.The structures of the (Me₃Sn)₄Sn(IV)Cl₂[meso-tetra(4-sulfonatophenyl)porphinate] and of the two model systems, Me₃Sn(PS)(HPS) and Me₂Sn(PS)₂ [HPS = phenylsulfonic acid], have been studied by a two layer ONIOM method, using the hybrid DFT B3LYP functional for the higher layer, including the significant tin environment. This approach allowed us to support the structural hypotheses inferred by the IR and Mössbauer spectroscopy analysis and to obtain detailed geometrical information of the tin environment in the compounds investigated.¹H and ¹³C NMR data suggested retention of the geometry around the tin(IV) atom in D₂O solution.     

Sorption and desorption of Fe(III) on natural and chemically modified zeolite

The Fe(III) uptake from aqueous solutions by natural and chemically modified zeolites was investigated using a gradual radioexchange method and AAS technique. The leachability of Fe(III) from loaded zeolites was studied too. The Fe-uptake reached the value of 60 mg·g⁻¹ for the zeolite chemically treated with 6 mol·l⁻¹ solution of NaOH and it is more than twelve times higher than that of the raw zeolite. The leachability of the loaded zeolite samples in water and alkaline solution was up 5%. The leachability of the same zeolites in acid solution depended on the concentration of modifying solution. The leachability at pH=2.6 in the range 2–20% at pH=1.9 was many times higher. The results of the radioexchange and AAS methods were compared.     

Spectral and electrochemical investigations on some condensation products of copper(II)-amino acid complexes

Summary Condensation products of several copper(II) amino acid complexes with formaldehyde or acetaldehyde have been prepared together with ethene-bridged copper(II) amino acid complexes. Structures were deduced from analytical and spectral data. Electronic spectral, e.s.r. and electrochemical behaviour at neutral and various low pH conditions were examined. Spectra of the unbridged complexes indicate the formation of [CuL]⁺ type species at pHca. 5, whereas the bridged complexes are stable at pH 3. The electrochemical behaviour of each complex is identical except for the doubly bridged complex. These results are explained in terms of a three-step electrode mechanism. The data show that the planarity of the complexes increases from unbridged, to bridged, to doubly bridged structures.     

General route for the synthesis of terminal phosphanylphosphido complexes of Zr(IV) and Hf(IV): Structural investigations of the first zirconium complex with a phosphanylphosphido ligand

Reactions of R₂P-P(SiMe₃)Li with [Cp₂MCl₂] (M = Zr, Hf) in hydrocarbons yield the related terminal phosphanylphosphido complexes [Cp₂M(Cl){(Me₃Si)P-PR₂-κP¹}] (R = ⁱPr and ^tBu). The solid state structures of [Cp₂M(Cl){P(SiMe₃)-PⁱPr₂-κP¹}] (M = Zr, Hf) were established by single crystal X-ray diffraction studies. The phosphido-P atoms adopt almost planar geometries and the phosphanyl P atoms adopt pyramidal geometries. The reaction of a mixture of (Me₃Si)₂PLi and Ph₂P-P(SiMe₃)Li with [CpZrCl₃] in toluene yields the dinuclear complex [Cp₂Zr₂Cl₅(Ph₂PPPSiMe₃)(Li THF DME)].     

Structural investigations in the series of spiro(thia)chromans

A comparative assessment was made of the reactivity of carbonyl-containing spirohydrochromans in their reaction with hydrogen sulfide under the conditions of acid catalysis. The special features of the structure of one of the obtained condensed spiro(thia)chromans are examined on the basis of the results from x-ray crystallographic analysis, the¹³C NMR spectra, and quantum-chemical calculations. N. G. Chernyshevskii Saratov State University, Saratov 410026, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1340–1345, October, 1998.     

Transition metal compounds of the purinic isomer allopurinol. Part 1

Summary The synthesis, spectral and magnetic properties of a series of new compounds of Co^II, Ni^II and Cu^II with the purinic isomer allopurinol (L) are reported. The counterions employed were Cl^–, Br^–, NO ₃ ^– , SO ₄ ^2– , ClO ₄ ^– and MeCO ₂ ^– . The metal:ligand stoichiometries found for the compounds range from 11 to 13. Allopurinol exhibits two classes of coordination behaviour: neutral monodentate (M^II=Co, Ni and Cu; X^–=Cl or Br) and monoanionic bidentate for the compound [CuL(OH)]_n. The latter was obtained when the counterion used in the syntheses was NO ₃ ^– , SO ₄ ^2– , ClO ₄ ^– or MeCO ₂ ^– . The coordination behaviour of theN-pyrazolic ring atoms may relate to the interaction mode of this heterocyclic fragment with the xanthine oxidase metalloenzyme.     

Ta3AlC2 and Ta4AlC3--single-crystal investigations of two new ternary carbides of tantalum synthesized by the molten metal technique

Single crystals of the new ternary carbides Ta4AlC3 and Ta3AlC2 were synthesized from molten aluminum and characterized XRD, EDX, and WDX measurements. Crystal structures were refined for the first time on the basis of single-crystal data. Both compounds crystallize in a hexagonal structure with space group P63/mmc and Z = 2. The lattice constants are a = 3.1131(3) A and c = 24.122(3) A for Ta4AlC3 and a = 3.0930(6) A and c = 19.159(4) A for Ta3AlC2. The crystal structures can be explained with a building block system consisting of two types of partial structures. The intermetallic part with a composition TaAl is a two layer cutting of a hexagonal closest packing. The carbide partial structure is a fragment of the binary carbide TaC (NaCl type). It consists of three (Ta4AlC3) or two layers (Ta3AlC2) of CTa6-octahedra linked via common corners and edges. Both compounds are members of the series (TaC)nTaAl. The crystal quality of Ta3AlC2 is improved by using a Al/Sn melt for crystal growth leading to small quantities of Sn in the crystal: Ta3Al1-xSnxC2, x approximately 0.04. On the basis of reliable data a detailed discussion of structural parameters is possible. According to the building principle structure models can be developed for the whole series (MX)nMM' including coordinates for all atoms.     

Preparation, characterization, and Zn(2+) adsorption behavior of chemically modified MCM-41 with 5-mercapto-1-methyltetrazole

A mesoporous silica (MCM-41) has been chemically modified with 5-mercapto-1-methyltetrazole using the homogeneous route. This synthetic route involved the reaction of 5-mercapto-1-methyltetrazole with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material (MTTZ-MCM-41) has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry, and elemental analysis. The solid was employed as a Zn(II) adsorbent from aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration, addition of ethanol, presence of other metals in the medium) has been studied using batch and column techniques. Flame atomic absorption spectrometry was used to determine the Zn(II) concentration in the filtrate or in the eluted solution after the adsorption process. Results obtained indicate that under the optimum conditions (pH 8 and 2 h stirring time), the maximum adsorption value for Zn(II) was 1.59+/-0.01 mmol/g, whereas the adsorption capacity of the unmodified mesoporous silica was about 0.010+/-0.001 mmol/g. On the other hand, the Zn(II) adsorption on the MTTZ-MCM-41 was independent of the presence of ethanol and other metals (Cu(II), Mn(II), Ca(II), and Mg(II)) in the medium. Finally, experiments carried out in order to study the regeneration capacity of the MTTZ-MCM-41 revealed that the adsorption capacity of this material was maintained after 3 cycles of the adsorption/desorption process.     

Thermochemical and structural investigations on alkali metal chlorides-iron(III)-chloride systems

The pseudobinary systems ACl?FeCl₃ (A=Na, K, Rb, Cs) were reinvestigated by means of differential thermal analysis and X-ray powder diffraction. The existence of the compounds AFeCl₄ (A=Na?Cs) and Cs₃Fe₂Cl₉ could be confirmed; Cs₃Fe₂Cl₉ is a stable compound which decomposes to CsCl and CsFeCl₄ above 270°C. Additionally, two Rb-compounds—Rb₃FeCl₆ and Rb₃Fe₂Cl₉—were found, which decompose, when heated, in the solid state. Rb₃Fe₂Cl₉ is isotypic with the analogous Cs-compound; Rb₃FeCl₆ has the Cs₃BiCl₆ structure. Cs₃FeCl₆ is isotypic with Cs₃CrCl₆, a recently found orthorhombic variant of the elpasolite type.     

In-situ spectroscopic investigations of the redox behavior of poly(indole-5-carboxylic-acid) modified electrodes in acidic aqueous solutions

The oxidation of electrochemically grown poly(indole-5-carboxylic-acid) (P5CO2H) and its spectroscopic properties have been studied by in-situ spectroelectrochemical techniques. The purpose of this paper is to characterize the different modifications on the P5CO2H backbone, induced by the electrochemical oxidation in aqueous acidic solution. We have identified, on the basis of Raman spectra, the vibrational modes associated with neutral and oxidized segments of polymer. It was shown that at least three chemically and optically different species (perhaps other products too) are produced in different potential regimes upon oxidation of this polymer. The results obtained also indicate that the molecular properties of this conducting polymer are better revealed by in-situ resonant spectra than by ex-situ infrared and Raman studies.     

Transition metal compatibilization of poly(vinylamine) and poly(ethylene imine)

Poly(vinylamine), PVA, complexes with cobalt chloride hexahydrate exhibit a 45 °C enhancement in the glass‐transition temperature per mol % of the d‐block metal cation. Poly(ethylene imine), PEI, complexes with CoCl₂(H₂O)₆ exhibit a 20 °C enhancement in T_g per mol % Co²⁺. Since the basicities of primary and secondary amines are comparable (i.e., pK_b,PVA ≈ 3.34 vs. pK_b,PEI ≈ 3.27) and the rates at which each polymeric ligand displaces waters of hydration in the coordination sphere of Co²⁺ are similar, transition metal compatibilization is operative in blends of both polymers with CoCl₂(H₂O)₆. These two polymers are immiscible in the absence of the inorganic component. Infrared spectroscopy suggests that nitrogen lone pairs in PVA and PEI coordinate to Co²⁺. The stress–strain response of a 75/25 blend of PVA and PEI with 2 mol % Co²⁺ reveals a decrease in elastic modulus from 4.4 × 10⁹ N/m² to 5.7 × 10⁷ N/m², a decrease in fracture stress from 3.7 × 10⁷ N/m² to 2.0 × 10⁶ N/m², and an increase in ultimate strain from 1.3 to 12% relative to the 75/25 immiscible polymer–polymer blend. A plausible explanation for this effect is based on the fact that cobalt chloride hexahydrate compatibilizes both polymers by forming a coordination bridge between nitrogen lone pairs in dissimilar chains. Hence, poly(ethylene imine), which is very weak with a T_g near −40 °C, is integrated into a homogeneous structure with poly(vinylamine) and the mechanical properties of the individual polymers are averaged in the compatibilized ternary complex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 552–561, 2000     

The synthesis and characterization of C60 chemically modified poly(N-vinylcarbazole)

Addition of C₆₀ moiety, a powerful electron acceptor to poly(N-vinylcarbazole) (PVK) by chemical reaction modifies considerably the physical and chemical properties of PVK. The characterization techniques employed are UV-visible, IR, DSC, TGA, ESR, ¹³C-NMR spectroscopy, scanning electron microscopy, XRD, and cyclic voltammetry. The fullerenated PVK, which has a visibly earthy yellow cast when compared with the unreacted polymer, has a new structure in the UV-vis absorption spectrum with the active range extending from about 280 to 870 nm, its apparent temperature sensitivity is intriguing, and an unusual temperature dependence for the ESR spectrum is observed. Considerable difference of electronic structure between pure PVK and C₆₀-PVK copolymer is indicated. The thermal stability and oxidation-reduction activation of pure PVK are enhanced by C₆₀-chemical modification. © 1996 John Wiley & Sons, Inc.     

DSC investigations on condensation polymers—I. Analysis of the curing process

Curing reactions in thermosetting resins and resin-composite systems have been examined using differential scanning calorimetry. In particular, phenol-formaldehyde and melamine-formaldehyde systems have been investigated using small pressure-sealed capsules. Curing exotherms obtained from a single temperature scan have been analysed to give reaction kinetic parameters associated with the overall cure process. The reproducibility of the derived parameters, their variation with scan speed and the absolute values of reaction rate constants obtained, are discussed. The kinetic values are shown to be reasonably reliable when used to calculate extents of cure resulting from thermal curing cycles.     

Low-temperature magnetic behavior of perovskite compounds PbFe(1/2)Ta(1/2)O3 and PbFe(1/2)Nb(1/2)O3

The isostructural perovskite compounds PbFe(1/2)Ta(1/2)O3 and PbFe(1/2)Nb(1/2)O3 have been known for long time, and they are part of the important class of materials called multiferroic, where ferroelasticity, ferroelectricity, and ferromagnetism coexist. In the literature regarding PbFe(1/2)Ta(1/2)O3 and PbFe(1/2)Nb(1/2)O3, an "anomaly" of their low-temperature magnetic behavior has not always been reported. Moreover, both the origin of this behavior, and the cause for which it was not always observed, were never completely explained. In this paper, the magnetic behavior of the two compounds at low temperature has been extensively studied and explained as the occurring of a spin-glasslike transition.