21 research outputs found
Chalcogen SāāāS Bonding in Supramolecular Assemblies of Cadmium(II) Coordination Polymers with Pyridine-Based Ligands
Two cadmium(II) coordination polymers, with thiocyanate and pyridine-based ligands e.g., 3- acetamidopyridine (3-Acpy) and niazid (nicotinic acid hydrazide, nia), namely one- dimensional {; ; [Cd(SCN)2(3-Acpy)]}; ; n (1) and two- dimensional {; ; [Cd(SCN)2(nia)]}; ; n (2), are prepared in the mixture of water and ethanol. The adjacent cadmium(II) ions in 1 are bridged by two N, S-thiocyanate ions and an N, O-bridging 3-Acpy molecule, forming infinite one- dimensional polymeric chains, which are assembled by the intermolecular NāHāāāS hydrogen bonds in one direction and by the intermolecular SāāāS chalcogen bonds in another direction. Within the coordination network of 2, the adjacent cadmium(II) ions are bridged by N, S-thiocyanate ions in one direction and by N, O, Nā-chelating and bridging nia molecules in another direction. The coordination networks of 2 are assembled by the intermolecular NāHāāāS and NāHāāāN hydrogen bonds and SāāāS chalcogen bonds. Being the only supramolecular interactions responsible for assembling the polymer chains of 1 in the particular direction, the chalcogen SāāāS bonds are more significant in the structure of 1, whilst the chalcogen SāāāS bonds which act in cooperation with the NāHāāāS and NāHāāāN hydrogen bonds are of less significance in the structure of 2
Synthesis and Adsorbing Properties of Tabular (001) Calcite Crystals
One of the most common crystal habits of the thermodynamically stable polymorph of calcium carbonate, calcite, is the rhombohedral one, which exposes (10.4) faces. When calcite is precipitated in the presence of Li+ ions, dominantly (00.1) faces appear together with the (10.4), thus generating truncated rhombohedrons. This well-known phenomenon is explored in this work, with the aim of obtaining calcite crystals with smooth (00.1) faces. In order to achieve this objective, the formation of calcite was examined in precipitation systems with different c(Ca2+)/c(Li+) ratios and by performing an initial high-power sonication. At the optimal conditions, a precipitate consisting of thin, tabular (00.1) calcite crystals and very low content of incorporated Li+ has been obtained. The adsorption properties of the tabular crystals, in which the energetically unstable (00.1) faces represent almost all of the exposed surface, were tested with model dye molecules, calcein and crystal violet, and compared to predominantly rhombohedral crystals. It was found that the (00.1) crystals showed a lower adsorption capability when compared to the (10.4) crystals for calcein, while the adsorption of crystal violet was similar for both crystal morphologies. The obtained results open new routes for the usage of calcite as adsorbing substrates and are relevant for the understanding of biomineralization processes in which the (00.1) faces often interact with organic macromolecules
Effect of pH and Type of Stirring on the Spontaneous Precipitation of CaCO3 at Identical Initial Supersaturation, Ionic Strength and a(Ca2+)/a(CO32ā) Ratio
CaCO3 precipitation is physical-chemical basis of biomineral formation of hard tissue (shells, skeletons) in marine calcifying organisms (=biomineralization). Processes controlling biomineralization are still not fully clarified, so the study of influence of pH on basic processes of CaCO3 precipitation should contribute to better understanding of biomineralization under climate change. This paper reports on the effect of initial pH (pH0) and type of stirring (mechanical and magnetical) on spontaneous precipitation and phase composition, size and morphology of spontaneously precipitated CaCO3 formed at the identical initial supersaturation, ionic strength and a(Ca2+)/a(CO3 2-) ratio. The initial pH varied in a range 8.50 ā¤ pH0 ā¤ 10.50 and included values relevant for mimicking the conditions related to biomineralization in marine organisms. In all systems two CaCO3 polymorphs were found: calcite and/or vaterite. The increase of pH0 favoured the formation of rhombohedral calcite no matter the type of stirring. This was exclusively influenced by the systemsā pH0 (other relevant initial parameters were identical). Furthermore, increase of pH0 caused change of vaterite morphology from cauliflower-like spheroids to regular spherulites. The mechanically stirred systems produced larger calcite and vaterite particles and higher content of calcite
Role of Hydrodynamics, Li+ Addition and Transformation Kinetics on the Formation of Plate-Like {001}; Calcite Crystals
Plate-like calcite crystals with expressed unstable {; ; ; 001}; ; ; planes are interesting research model for investigations of interfacial interactions of different additive molecules, but also the crystal growth mechanisms. The aim of this study is to reproducibly prepare a significant amount of well- defined plate-like calcite crystals and to investigate the critical experimental parameters. Thus, in precipitation system c(NaHCO3) = c(CaCl2) = 0.1 mol dmā3, the influence of hydrodynamic parameters (mode of mixing of the reaction components) and a presence of lithium ions Li+ within a wide range of concentrations, 0.0 mol dmā3 < c(Li+) < 1.0 mol dmā3, have been studied. In addition, the kinetics of the solution mediated transformation of the initially formed metastable polymorph, vaterite, were followed in order to reproducibly describe the formation of stable calcite with expressed unstable morphology. The results indicate that the plate-like calcite is formed predominantly when the ultrasound irradiation is applied at c(Li+) ā„ 0.3 mol dmā3. On the other hand, when the magnetic and mechanical stirring are applied at higher Li+ concentrations, truncated rhombohedral crystals in a mixture with plate-like crystals are obtained. It was also found that the Li+ addition significantly prolonged the transformation, mainly by inhibiting the crystal growth of calcite
Mechanochemical synthesis of calcium oxalate
Ova studija prikazuje mehanokemijsku sintezu kalcijeva oksalata u planetarnom kugliÄnom mlinu, bez i uz prisutnost otapala. DosadaÅ”nja istraživanja su uglavnom bila usmjerena na otopinsku sintezu kalcijeva oksalata. U ovom radu opisujemo drugaÄiji pristup, koji Äe donijeti nova saznanja o sintezi kristala kalcijeva oksalata, a koje su uzrokovane utjecajem mehaniÄke energije. Cilj istraživanja je sinteza, identifikacija i karakterizacija pojedine oksalatne hidratne faze sintetizirane iz kalcijevih soli (klorida, nitrata i sulfata). Ispitivan je utjecaj brzine mljevenja i praÄena je reakcija u ovisnosti o vremenu sinteze. Strukturalna i termiÄka svojstva uzoraka ispitana su FTIR spektroskopijom i termogravimetrijskom analizom (TGA). MorfoloÅ”ke karakteristike kalcijeva oksalata te raspodjela veliÄine Äestica odreÄene su optiÄkom mikroskopijom i dinamiÄkim rasprÅ”enjem svjetlosti (DLS)