Isonicotinamide (INA) co-crystallizes with carbamazepine (CBZ), as do nicotinamide (NA) and benzamide. The structure of CBZ-INA form II is solved from powder and is shown to be isostructural with CBZ-NA. However picolinamide (PA), despite its similarity to the other pyridine carboxamides in the homologous series, does not appear to form a co-crystal with CBZ. We compare and contrast the use of computed crystal energy landscapes and binary and ternary phase diagrams to explain this behavior. Two 1:1 co-crystal structures of CBZ and INA were predicted to have lower or comparable lattice energies than the sum of the pure component lattice energies. These structures corresponded to the known co-crystal structures. On the other hand, lattice energies of predicted CBZ-PA co-crystal structures were less stable than the pure component lattice energies, implying that CBZ and PA would not form a co-crystal. This is consistent with the experimental evidence. Examination of the hypothetical crystal structures for CBZ-INA and for CBZ-PA explains this in terms of intermolecular hydrogen-bonding capability. Thus computed crystal energy landscapes are more reliable than simple crystal engineering concepts in understanding co-crystal formation, and can provide a useful complement to experimental co-crystal screening.
Activation of mannuronic acid esters leads to a conformational mixture of alpha-anomeric triflates, in which the equatorial triflate ((1)C(4) chair) is formed preferentially. This unexpected intermediate clearly opposes the anomeric effect and is mainly stabilized by the electron-withdrawing carboxylate function at C-5. Because the anomeric center carries a significant positive charge, the (1)C(4) mannopyranosyl chair approximates the favored (3)H(4) half-chair oxacarbenium ion conformation. The excellent beta-selectivity in glycosylations of mannuronates is postulated to originate from the cooperative action of the triflate counterion and the (stereo)electronic effects governing oxacarbenium ion stabilization in the transition state leading to the 1,2-cis product.
Synthesis of poly(pyrazolyl)borate anionic ligands composed of 3,5-dimethyl-and 3,5-diphenylpyrazoles and their bis(ligand) high-spin cobalt(II) complexes are described. The molecular structures of [dihydrobis(3,5-diphenylpyrazolyl)borato][hydrobis(3,5-dimethylpyrazolyl)(3,5-diphenylpyrazolyl)-borato]cobalt(II) and bis[dihydro(3,5-dimethylpyrazolyl)(3,5-diphenylpyrazolyl)borato]cobalt(II) complexes were established by X-ray crystallography. The cobalt center is hexacoordinate in the former with five Co−N 2 (pyrazolyl) bonds and
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.