In this paper we describe a simple colorimetric method for the sensitive and selective detection of Ba ²⁺ ions, using 11-mercaptoundecylphosphonic acid functionalized gold nanoparticles (AuNPs–MPA) in aqueous solution.

Chemical properties of geopolymers were evaluated from the reduction of fly ash particle size by grinding. X-ray diffraction determined that at early curing ages new crystalline phases appear in the matrix of the geopolymer and they remain for 28 days, with increases in intensities up to 60%. In Fourier transform infrared spectroscopy, displacements were identified in the main band of the geopolymers at higher wavenumbers, attributed to the greater rigidity in the structures of the aluminosilicate gel due to the increase of the reaction products in the geopolymers obtained through fly ashsubjected to previous grinding, which is observable in the geopolymers matrix. Results indicate that the reduction of fly ash particle size by grinding has an influence on the chemical properties of geopolymers.

3- and 4-pyridineboronic acids have been combined with trimesic and pyromellitic acids to give three molecular complexes of compositions [(3PBAH⁺)(H₂TMA⁻)] (1), [(3PBAH⁺)₂(H₂PMA²⁻)] (2), and [(4PBAH⁺)₂(H₂PMA²⁻)]·2H₂O (3) (3PBA = 3-pyridineboronic acid, 4PBA = 4-pyridineboronic acid, H₃TMA = trimesic acid, H₄PMA = pyromellitic acid). The products have been characterized by elemental analysis, infrared spectroscopy, single-crystal X-ray diffraction analysis and luminescence spectroscopy. The structural analysis revealed that the hydrogen bonding interactions of the resulting 2D and 3D assemblies involve at least one of the following charge-assisted synthons: –B(OH)₂⋯⁻OOCR, RCOOH⋯⁻OOCR or PyN⁺–H⋯⁻OOCR. The dimensions are enhanced by additional hydrogen bonds as well as π–π stacking interactions, which include B⋯π interactions in two crystal structures. Intermolecular close contacts have also been examined by Hirshfeld surface analysis, which by means of the associated 2D fingerprint plots enabled similarities and differences in the crystal structures to be revealed. Solid-state photoluminescence spectroscopy of compounds 1–3 revealed that variations of the π–π stacking in the molecular aggregates induced changes in the emission behavior.

New copper(I) compounds of compositions [Cu(HL)(PPh₃)₂]·H₂O (1) and [Cu(HL)POP]·CH₂Cl₂ (2), where HL = monoanion of pyridine-2,5-dicarboxylic acid, PPh₃ = triphenylphosphine and POP = bis [2-(diphenylphosphine)phenyl]ether), are documented. The complexes were characterized by elemental analysis, spectroscopic techniques (IR, ¹H/³¹P RMN and UV–VIS), cyclic voltammetry, and thermogravimetric analysis. Single-crystals for 1 and 2 enabled X-ray diffraction analysis, revealing distorted tetrahedral geometries for Cu(I) centers embedded in NOP₂ environments. The crystal structures are stabilized by O−H∙∙∙O, C−H∙∙∙O, C−H∙∙∙π and π∙∙∙π interactions that were analyzed by inspection of the Hirshfeld surfaces and fingerprint plots. Compounds 1 and 2 show interesting optical/electrochemical properties, which were studied experimentally in solution by UV–Vis spectroscopy and cyclic voltammetry, as well as theoretically using Time-Dependent Density Functional Theory (TD-DFT). Additionally, in combination with the ruthenium complex N719, their efficiency as co-sensitizers in dye-sensitized solar cells (DSSCs) was assessed, showing good activity.