6-Amino-2-iminiumyl-4-oxo-1,2,3,4-tetrahydropyrimidin-5-aminium sulfate monohydrate

The title compound, C4H9N5O2+·SO4 2−·H2O, is the monohydrate of the commercially available compound `C4H7N5O·H2SO4·xH2O'. It is obtained by reprecipitation of C4H7N5O·H2SO4·xH2O from dilute sodium hydroxide solution with dilute sulfuric acid. The crystal structure of anhydrous 2,4,5-triamino-1,6-dihydropyrimidin-6-one sulfate is known, although called by the authors 5-amminium-6-amino-isocytosinium sulfate [Bieri et al. (1993). Private communication (refcode HACDEU). CCDC, Cambridge, England]. In the structure, the sulfate group is deprotonated, whereas one of the amino groups is protonated (R 2C—NH3 +) and one is rearranged to a protonated imine group (R 2C=NH2 +). This arrangement is very similar to the known crystal structure of the anhydrate. Several tautomeric forms of the investigated molecule are possible, which leads to questionable proton attributions. The measured data allowed the location of all hydrogen atoms from the residual electron density. In the crystal, ions and water molecules are linked into a three-dimensional network by N—H...O and O—H...O hydrogen bonds.

The crystal structure of a new polymorph of hexaaquanickel(II) bis(6-oxo-1,6-dihydropyridine-3-carboxylate)

In a new polymorph of the title salt, [Ni(H2O)6](C6H4NO3)2, the metal atom of the cationic complex lies on a symmetry centre and is coordinated by six water molecules to provide a quite regular octahedral coordination environment. These cations interact with 6-oxo-1,6-dihydropyridine-3-carboxylate anions through electrostatic interactions and by means of O—H...O and N—H...O hydrogen bonds involving the carboxylate, keto and protonated imine groups of the anion, and the coordinating water molecules from the cationic complex entity to generate a supramolecular three-dimensional architecture. The previously reported polymorph of this compound presents a network of hydrogen bonds, in which the organic anions establish mutual hydrogen-bonding interactions involving their keto and protonated imine groups.

Porous imine-based networks with protonated imine linkages for carbon dioxide separation from mixtures with nitrogen and methane

Porous imine-linked networks with protonated imine linkages and an ionic structure were synthesized. They exhibit good carbon dioxide uptakes and CO2/N2 as well as CO2/CH4 separation coefficients.

Proton transfers in the Strecker reaction revealed by DFT calculations

The Strecker reaction of acetaldehyde, NH3, and HCN to afford alanine was studied by DFT calculations for the first time, which involves two reaction stages. In the first reaction stage, the aminonitrile was formed. The rate-determining step is the deprotonation of the NH3 + group in MeCH(OH)-NH3 + to form 1-aminoethanol, which occurs with an activation energy barrier (ΔE ≠) of 9.6 kcal/mol. The stereochemistry (R or S) of the aminonitrile product is determined at the NH3 addition step to the carbonyl carbon of the aldehyde. While the addition of CN− to the carbon atom of the protonated imine 7 appears to scramble the stereochemistry, the water cluster above the imine plane reinforces the CN− to attack the imine group below the plane. The enforcement hinders the scrambling. In the second stage, the aminonitrile transforms to alanine, where an amide Me-CH(NH2)-C(=O)-NH2 is the key intermediate. The rate-determining step is the hydrolysis of the cyano group of N(amino)-protonated aminonitrile which occurs with an ΔE ≠ value of 34.7 kcal/mol. In the Strecker reaction, the proton transfer along the hydrogen bonds plays a crucial role.

Tris{2-methoxy-6-[(4-methylphenyl)iminiomethyl]phenolato-κ2O,O′}tris(thiocyanato-κN)cerium(III)

The asymmetric unit of the title compound, [Ce(NCS)3(C15H15NO2)3], contains three Schiff base 2-methoxy-6-[(4-methylphenyl)iminomethyl]phenol (HL) ligands and three independent thiocyanate ions that coordinate the cerium ionviatheir N atoms. The protonated imine N atoms are involved in an intramolecular hydrogen bond with the respective phenoxide group. The Ce(III) ion exhibits a coordination number of nine.