Screening of pyrazinamide polymorphs was carried out by crystallization from solvents differing in polarity and hydrogen bonding ability and also by sublimation and lyophilization. Pure samples of polymorphs α, δ, and γ could be prepared, and mixtures of the β form with one of the other polymorphs were also produced. These forms were fully characterized by infrared spectroscopy and two main profiles registered in the N−H stretching vibration region, clearly distinguishing polymorphs encompassing a dimeric pirazinamide unit, α, β, and δ, and where the dimer does not exist, the γ one. The thermal behavior of pyrazinamide polymorphs was also investigated using differential scanning calorimetry (DSC) and polarized light thermal microscopy, supported by powder X-ray diffraction and infrared spectroscopy. The α, β, and δ forms give rise on heating to the γ form, in endothermic transitions, with some superheating being observed. Also, the DSC peaks display an irregular shape. These observations suggest kinetic hindering of the solid−solid transitions. An endothermic phase transition of the δ form to the α one was observed only for samples seeded with this latter polymorph. The relative stability of the four pyrazinamide polymorphs was derived from the experimental observations.

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The magnetic and powder neutron diffraction data indicate a complex magnetic structure of Mn 5 Si 3. This compound has the hexagonal D8 8 crystal structure at room temperature. The Mn atoms occupy two nonequivalent sublattices. Two phase transitions, at 60 and 106 K, are observed. The first one is between a non-collinear AF1 and a collinear AF2 magnetic structure, the second one is between the collinear AF2 structure and a paramagnetic state. At 106 K the crystal structure changes from the hexagonal to the or-thorhombic one. The values of the Mn magnetic moment in both structures were calculated by different ab initio methods. The results of the calculations are compared with the values of the Mn magnetic moment determined experimentally in this work and presented in the previous ones.

The effective 'one-pot' microwave-assisted synthesis of several substituted 5,10,15,20-tetraarylporphyrins is reported. The microwave-assisted insertion of five different transition metals into the 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin and 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin core was also achieved with high yields. In addition to their simplicity, both these straightforward, experimental protocols were also characterized by extremely short reaction times and quite small quantities of solvents employed.

A screening of naproxen cocrystals with coformers picolinamide, nicotinamide, isonicotinamide, and pyrazinamide is performed by the Kofler contact method and mechanochemistry. The solids obtained by mechanochemistry are characterized by differential scanning calorimetry, DSC, polarized light thermomicroscopy, PLTM, infrared spectroscopy, FTIR, and X-ray powder diffraction, XRPD. No cocrystal could be prepared under the experimental conditions investigated between naproxen and pyrazinamide, which bears two aromatic nitrogen atoms, ortho and meta to the amide group. For the o-, m-, and p-pyridinecarboxamide isomers, regardless of the aromatic nitrogen position, the coformer interacts with naproxen to give rise to new cocrystals: naproxen:picolinamide, naproxen 2 :nicotinamide, and naproxen:isonicotinamide. A supramolecular acid:aromatic nitrogen heterosynthon is found in all these cocrystals. The structure of the new naproxen:isonicotinamide compound was solved by single-crystal X-ray diffraction, SXD. As nicotinamide has FDA/GRAS status the naproxen:nicotinamide (2:1) cocrystal is of special relevance.