Andrzej M. Kłonkowski

Non-monotonic variations of some parameters in vitreous R2OSiO2 and R2OAl2O3SiO2 systems

Abstract Vitreous silicates of the R2OSiO2 type in comparison with crystalline silicates of the same composition, as well as vitreous aluminosilicates of the R2OAl2O3SiO2 type (R = Li, Na, K, Rb, Cs) were investigated. Some physical parameters change non-systematically if the vitreous systems alkali atoms are consecutively replaced with increasing atomic mass. Among the parameters which behave non-systematically are density, packing density, and refractive index. Further, the vitreous and crystalline materials doped with 0.5 mol.% CuO were studied by means of optical and electron spin resonance (ESR) spectroscopy methods. Attention is also paid to variations of the total basicity of oxide ions and the basicity of non-bridging ions of this kind in the glasses. Measures of theses basicities such as the molar refractivity of O2− ions (RO2−) and normalized convalency of Cu2+-O bonding of π symmetry (Tπ) respectively, are presented. These two parameters, similar to the ligand field strength v max and ESR parameters of Cu2+ which depend on the basicity, change systematically.

Amino-Modified Silicate Xerogels Complexed with Cu(II) as Catalyst Precursors. Coordination State and Thermal Decomposition

The sol-gel process is a useful method for preparing two series of organically and co-ordinately modified xerogels of the types [CuNn]·N5−n·5xSiO4/2 (n < 4) and [Cu(N−N)n]·(N−N)2−n·2x SiO4/2(n ≤ 2), where N = NH2(CH2)3 SiO3/2, N−N = NH2(CH2)2NH·(CH2)3SiO3/2 and x = [SiO4/2]/[N] or [SiO4/2]/[N−N]. The amino groups in the materials are coordinately active and participate partly in the coordination sphere of Cu(II) ions. The composition of the coordination sphere can be varied with the SiO4/2 content and also as a result of the thermal decomposition of the organic residues at higher temperatures.Because the xerogel materials are considered to be catalyst precursors, this study is focused on their coordination and thermal properties. The prepared xerogels, such as silica, aminated silicates with N and N−N, as well as those entities complexed with Cu(II), were characterised by FT-IR spectroscopy. During gelation and thermal decomposition the materials were analysed by electron paramagnetic resonance (EPR) spectroscopy. The xerogels were additionally studied by UV-Vis absorption spectroscopy. The gaseous products of the thermal decomposition of these materials in an Ar atmosphere were investigated by the use of FT-IR spectroscopy coupled with TG and DTG thermal analysis. These data were complemented by temperature-programmed decomposition (TPDec) in a 2% O2 + 98% Ar stream coupled with quadrupole mass spectroscopy.

Improvement of emission intensity in luminescent materials based on the antenna effect

Abstract Ternary Eu(III) complexes with macrobicyclic and acyclic ligands+co-ligands were encapsulated in silica or methylated silicate xerogels. Additionally, deuterated reagent and solvent were used in the sol–gel procedure. This preparation method with moderate thermal treatment reduced the concentration of OH groups in the materials and simultaneously improved their photophysical properties, i.e. increased luminescence intensity and prolonged luminescence lifetime. The best results were obtained for the Eu(III) complex with a cryptand of the [biqO2·2·2]+1,10-phenanthroline type (where biqO2=3,3′-biisoquinoline-2,2′-dioxide) immobilized in methyl-modified silicate xerogel. The effective luminescence properties of this sample make it a promising candidate for use as a luminescent material.

The antenna effect of Eu(III) cryptate entrapped in xerogel matrices

Abstract The europium(III) complex with [biq.2.2] cryptand, where biq is 3,3′-biisoquino-line-2,2′-dioxide and complexes with additional secondary ligands such as 1,10-phenanthroline (phen) or triphenylphosphine oxide (TPPO) were entrapped by the sol-gel method in silica or silicate xerogel organically modified with methyl groups. The photophysical properties of such materials were studied. The luminescence behaviour of the complexes in the rigid matrix was studied by means of emission, excitation spectra and lifetime measurements. The results indicated that the Eu(III)-[biq.2.2] complex in the methylated silicate xerogel displayed a distinctly higher emission intensity and longer lifetime than in the silica matrix, whereas in the case of the complexes with the secondary ligands these changes were not so pronounced. It was also observed for the silica xerogel with Eu(III) complex that the emission intensity increased up to 110 °C with temperature.

Antenna effect in an oxide xerogel

Abstract Silica xerogel doped with [Eu⊂cryptand] 3+ was prepared by the sol-gel method from a hydrolyzed tetramethoxysilane solution containing [Eu⊂cryptand](CF 3 SO 3 ) 2 Br. UV-visible optical absorption spectra, fluorescence excitation and emission spectra, fluorescence lifetime as well as luminescence quantum yield were measured. Experiments were carried out in aqueous solution and in rigid silica xerogel at room temperature. It is shown that the excitation is centred on the ligand, but the metal ion takes part in the emission process. In other words, the antenna effect was observed in the Eu(III) cryptate studied in the solution and xerogel. The cryptate entrapped in the xerogel showed higher emission efficiency and longer lifetime than in solution.

Coordination environment of copper (II) during the sol–gel process of an aminated alkoxide

Copper(II) complexes with N-2-aminoethyl-3-aminopropyltnmethoxysilane (N – N) as an ethylenediamme analogue were analysed prior to the sol–gel process, during the reaction (N – N + tetramethoxysilane) with water and in the gel products, to determine the coordination environment of the central ion. The results of EPR, thermal decomposition and CuII adsorption studies are summarized in three identified models of the coordination sites in the gels. Partial conversion of the bis- to mono-[N – N] environment of CuII during the transition from the sol to the gel is observed. There is also EPR evidence of the existence of another copper(II) site, the coordination sphere of which was not identified.

Spectroscopic studies of Ln(III) complexes with polyoxometalates in solids, and aqueous and non-aqueous solutions

Chosen polyoxometalate (POM) anions and their lanthanide(III) complexes, LnPOM, have been synthesized and spectroscopically characterized in solid state, aqueous and non-aqueous solutions. POMs, such as Keggins, Dawsons and Andersons type, Na9EuW10O36, compositions that function as inorganic cryptands ([(Na)P5W30O110]14−-Preyssler anion, and [(Na)As4W40O140]27−), containing inorganic (Na

Spectral properties of bis-9-anthryl derivatives immobilised in silica xerogel

Abstract Three bis-9-anthryl derivatives of the type Ant - R - Ant , where Ant is anthryl group and R is receptor spacer consisting of such donor atoms as N or N and O, were encapsulated in silica xerogel by the sol–gel method. Our recent studies in methanol solution show that these materials could be used as fluorosensors in chemical recognition phases for optical chemical sensor. Optical absorption spectra of the bis-anthryl derivatives are nearly the same in the solution and silica matrix. However, the free species entrapped in silica exhibit fluorescence emission spectra with a long wavelength tail, which is probably due to the presence of excimers in the excited state and/or heterogeneous environment of the emission centres in the amorphous silica matrix. The studied bis-anthryl derivatives undergo photochemical degradation during UV irradiation.

Diffusion of Cu+ ions in binary phosphate glasses

Abstract The diffusion of Cu + ions into phosphate glasses with different modifiers MgO, CaO, SrO and BaO was studied by the fluorescence method. The peak of the emission spectra of Cu + ions was shifted to a longer wavelength as the ion radius of the modifier increased. The diffusion coefficient of Cu + ions was smallest for magnesium phosphate glasses, increasing with the increase of the ionic radius of the network modifier.

Transition metal complexes in aminated silicate xerogels with Ni and Co ions

Abstract Two series ( N and N – N ) of aminated silicate xerogels complexed with Ni 2+ and Co 2+ ions have been synthesized by a two-step reaction procedure: coordination and sol–gel process. The N series consists of unidentate ligands H 2 N (CH 2 ) 3 SiO 3/2 and the N – N series of bidentate ligands H 2 N (CH 2 ) 2 N H(CH 2 ) 3 SiO 3/2 . The coordination environments of the transition metal ions in the xerogels were analysed by UV–Vis absorption, luminescence, IR absorption and EPR spectroscopies. Moreover, the spectral data are complemented with thermoanalytical methods such as differential thermal analysis (DTA), differential thermogravimetry (DTG) and thermogravimetry (TG). The UV–Vis absorption and EPR spectra show that Ni and Co ions are in the +2 valence state in both xerogel series studied. For the Ni 2+ - and Co 2+ -doped xerogels the positions of the vibration bands related to the potential ligand groups and molecules (OH and H 2 O) are shifted according to the Irving–Williams order. In the case of Co 2+ , the tendency to transit from a tetrahedral to an octahedral environment increases with water and/or OH group content in the xerogels. When the temperature is increased, amino groups in the coordination sphere dissociate first and only then do amino groups not involved in coordination dissociate. The modified silicate xerogels can be considered as catalyst precursors.