A. Matos Beja

One-step synthesis of dipyrromethanes in water

In this communication we describe the first results of an efficient synthesis of β-free-dipyrromethanes in water. This new method affords very pure products in moderate to high yields, using a cheap, non-toxic, environment friendly solvent, in a one-step procedure from pyrrole and carbonyl compounds, needing little or no work up procedures.

Erythritol: Crystal growth from the melt

The structural changes occurring on erythritol as it is cooled from the melt to low temperature, and then heated up to the melting point have been investigated by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM), X-ray powder diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). By DSC, it was possible to set up the conditions to obtain an amorphous solid, a crystalline solid, or a mixture of both materials in different proportions. Two crystalline forms have been identified: a stable and a metastable one with melting points of 117 and 104 degrees C, respectively. The fusion curve decomposition of the stable form revealed the existence of three conformational structures. The main paths of the crystallization from the melt were followed by PLTM. The texture and colour changes allowed the characterization of the different phases and transitions in which they are involved on cooling as well as on heating processes. The type of crystallization front and its velocity were also followed by microscopic observation. These observations, together with the data provided by PXRD, allowed elucidating the transition of the metastable form into the stable one. The structural changes occurring upon the cooling and subsequent heating processes, namely those arising from intermolecular hydrogen bonds, were also accompanied by infrared spectroscopy. Particular attention was given to the spectral changes occurring in the OH stretching region.

Pyrrolidine-based amino alcohols: novel ligands for the enantioselective alkylation of benzaldehyde

A series of easily obtained pyrrolidine-based -amino alcohols derived from tartaric acid and primary amines was synthesized and used as chiral ligands in the enantioselective alkylation of benzaldehyde. Using diethylzinc, 1-phenyl-1-propanol was obtained with enantiomeric excesses of up to 80% when (3S,4S)-N-(1-naphthylmethyl)-3,4-dihydroxypyrrolidine was used. The nature of the N-substituent on the ligand, as well as the reaction temperature proved to significantly influence reaction product distribution as well as the enantiomeric excess of the chiral alcohol.

Conformation of cationic N,N-di­methyl­glycine in di­methyl­glycinium tri­fluoro­acetate

In the title compound, C(4)H(10)NO(2)(+).C(2)F(3)O(2)(-), the main N-C-COOH skeleton of the protonated amino acid is nearly planar. The C=O/C-N and C=O/O-H bonds are syn and the two methyl groups are gauche to the methylene H atoms. The conformation of the cation in the crystal is compared to that given by ab initio calculations (Hartree-Fock, self-consistent field molecular-orbital theory). The trifluoroacetate anion has the typical staggered conformation with usual bond distances and angles. The cation and anion form dimers through a strong O-H.O hydrogen bond which are further interconnected in infinite zigzag chains running parallel to the a axis by N-H.O bonds. Weaker C-H.O interactions involving the methyl groups and the carboxy O atoms of the cation occur between the chains.

Crystal structure of tetrakis (μ-betaine-O,O′) dichloro-dicopper(II) dichloride tetrahydrated

Abstract[Cu2(bet)4Cl2]Cl2·4H2O (bet = betaine: IUPAC name: trimethylammonioacetate) is monoclinic, space group P21/c, a = 11.0510(10) Å, b = 14.7140(4) Å, c = 11.1620(15) Å, β = 107.40(2)°. The dinuclear copper(II) cation [Cu2(bet)4Cl2]2+ is counterbalanced by two naked Cl− ions. The copper(II) ions have a square bipyramidal environment with oxygen atoms from the acetato groups in the basal planes and a chlorine and a copper atom occupying the apical positions. The metal atoms are μ2-bridged by four acetato groups and the molecular symmetry is close to C2h. The two symmetry-independent chelating betaine molecules are present in their zwitterionic, neutral form.

Crystal and Molecular Structure of dl-Serine Hydrochloride Studied by X-Ray Diffraction, Low-Temperature Fourier Transform Infrared Spectroscopy and DFT(B3LYP) Calculations

The structure of dl-serine.HCl was studied by three complementary techniques. Experimental Fourier transform infrared (FT-IR) spectra of pure NH/OH polycrystalline dl-serine.HCl [HO-CH2-CH(NH3+)-COOH.Cl(-)] and the respective deuterated derivatives [ND/ODAlcohol/Acid (<10% and ca. 60% D)] were recorded in the region 4000-400 cm(-1) in the temperature range 300-10 K and interpreted. The assignments were confirmed by comparison with the vibrational spectra of crystalline dl- and l-serine zwitterions [HO-CH 2-CH(NH3+)-COO(-)]. Further insight into the structure of the title compound was provided by theoretical DFT(B3LYP)/6-311++G(d,p) calculations of the infrared spectra and energies of 13 different conformers. Potential energy distributions resulting from normal co-ordinate analysis were calculated for the most stable conformer ( I) in its hydrogenated and deuterated modification. Frequencies of several vibrational modes were used in the estimation of enthalpies of individual H-bonds present in the crystal, using empirical correlations between enthalpy and the frequency shift that occurs as a result of the establishment of the H-bonds. X-ray crystallography data for dl-serine.HCl were recorded for the first time and, together with the experimental vibrational spectra and the theoretical calculations, allowed a detailed characterization of its molecular structure.

Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxyl-ate.

In the title compound, C9H13NO2, there are two independent molecules per asymmetric unit. The molecules are very similar and almost planar, with the ethoxycarbonyl group anti to the pyrrole N atom. The two independent molecules are joined into dimeric units by strong hydrogen bonds between NH groups and carbonyl O atoms.

Synthesis, structure, thermal and non-linear optical properties of L-argininium hydrogen selenite

L-Argininium hydrogen selenite (C(6)H(15)N(4)O(2)HSeO(3)) is a new semiorganic compound of the hydrogen selenite family with non-linear optical properties. The crystal lattice is monoclinic with unit-cell parameters a = 22.493 (5), b = 5.1624 (13), c = 9.730 (4) A, beta = 95.68 (3) degrees, V = 1124.3 (6) A(3), Z = 4, space group C2. Second-harmonic generation measurements performed on powder samples, using a Q-switched Nd:Yag laser (lambda = 1064 nm), showed the second-harmonic power to be about twice that of urea. Differential scanning calorimetry measurements revealed the existence of a phase transition with onset at 289 K.

Two anilinium salts: anilinium hydrogenphosphite and anilinium hydrogenoxalate hemihydrate

In the title compounds, C(6)H(5)NH(3)(+).H(2)PO(3)(-) and C(6)H(5)NH(3)(+).C(2)HO(4)(-).0.5H(2)O, the NH(3)(+) groups of the anilinium ion are ordered at room temperature. The rotation of these groups along the N-C(aryl) bond, which is often observed at room temperature in other anilinium compounds, is prevented by hydrogen bonds between the NH(3)(+) group and the anions. In both compounds, the geometry of the cation is significantly distorted from D(6h) to a symmetry close to C(2v). The angle ipso to the substituent is significantly larger than 120 degrees, as expected from the sigma-electron-withdrawing character of the NH(3)(+) group.

N,N'-Diphenylguanidinium Hydrogenselenite Monohydrate

In the crystal structure of the title compound, C 13 H 14 N 3 + .HSeO 3 - .H 2 O, the phenyl rings lie syn to the unsubstituted N atom of the cation and the geometry of the guanidinium group is close to that expected for a central C sp 2 atom. The crystal packing is stabilized by an extensive network of hydrogen bonds. The anion is an acceptor of the N-H guanidinium groups and the water molecule forms a four-membered hydrogenbonded ring with the anion.