879683-44-0Relevant articles and documents
Structural and zeolitic features of a series of heterometallic supramolecular porous architectures based on tetrahedral {M(C2O 4)4}4- primary building units
Imaz, Inhar,Bravic, Georges,Sutter, Jean-Pascal
, p. 2681 - 2687 (2005)
The utilization of tetrahedral pre-formed coordination compounds {M(C 2O4)4}4- (M = ZrIV, UIV; C2O42- = oxalate) permitted the efficient construction of rare examples of heteronuclear supramolecular nano-porous architectures. A series of metal-organic coordination frameworks prepared by association of these building units with either Mn2+, Cd2+, or Mg2+ have been structurally characterized and are described. Their 3-D chemical scaffold is based on the primary tetrahedral building unit but their pore sizes and topologies could be varied through the M2+ metal ion involved in the assembling process, and the anionic tetrahedral moiety. These structures display channels with apertures up to 12 A × 8 A which are emptied of solvates at mild temperatures without affecting the chemical scaffold, the integrity of which is maintained up to 250-300°C. A certain degree of flexibility of the coordination polymers upon guest release is suggested by the temperature dependence of the powder X-ray patterns and N2 sorption experiments, but reversible and selective sorption of small molecules has been observed substantiating that these open-frameworks behave like sponges. The Royal Society of Chemistry 2005.
Mechanistic Insight into Caffeine-Oxalic Cocrystal Dissociation in Formulations: Role of Excipients
Duggirala, Naga Kiran,Vyas, Amber,Krzyzaniak, Joseph F.,Arora, Kapildev K.,Suryanarayanan, Raj
, p. 3879 - 3887 (2017/11/15)
Caffeine-oxalic acid cocrystal, widely reported to be stable under high humidity, dissociated in the presence of numerous pharmaceutical excipients. In cocrystal-excipient binary systems, the water mediated dissociation reaction occurred under pharmaceutically relevant storage conditions. Powder X-ray diffractometry was used to identify the dissociated products obtained as a consequence of coformer-excipient interaction. The proposed cocrystal dissociation mechanism involved water sorption, dissolution of cocrystal and excipient in the sorbed water, proton transfer from oxalic acid to the excipient, and formation of metal salts and caffeine hydrate. In compressed tablets with magnesium stearate, the cocrystal dissociation was readily discerned from the appearance of peaks attributable to caffeine hydrate and stearic acid. Neutral excipients provide an avenue to circumvent the risk of water mediated cocrystal dissociation.
On the synthesis and optical absorption studies of nano-size magnesium oxide powder
Kumar, Ashok,Kumar, Jitendra
, p. 2764 - 2772 (2009/03/12)
Magnesium oxide (MgO) nano-size powder is synthesized using magnesium nitrate hexahydrate and oxalic acid as precursors with ethanol as a solvent. The process involves gel formation, drying at 100 °C for 24 h to form magnesium oxalate dihydrate [α-MgC2O4 · 2H 2O] and its decomposition at 500, 600, 800, and 1000 °C for 2 h to yield MgO powder (average crystallite size ～6.5-73.5 nm). The sol-gel products at various stages of synthesis are characterized for their thermal behaviour, phase, microstructure, optical absorption, and presence of hydroxyl and other groups like o = C = O, C = O, C-C, etc. MgO powder is shown to possess an f.c.c. (NaCl-type) structure with lattice parameter increasing with decrease in crystallite size (tav); typical value being ～4.222(2) A? for tav～6.5nm as against the bulk value of 4.211 A?. Infrared absorption has shown MgO to be highly reactive with water. Also, a variety of F- and M-defect centres found in MgO produce energy levels within the band gap (7.8 eV), which make it attractive for application in plasma displays for increasing secondary electron emission and reducing flickering effects. The possible application of the intermediate sol-gel products, viz., α-MgC2O4 · 2H2O and anhydrous magnesium oxalate (MgC2O4) in understanding the plants and ESR dosimetry, respectively, has also been suggested.
