A multinuclear ( 1 H, 13 C, 17 O, 51 V) 1D and 2D NMR study of the complexation of L-lactic acid with vanadium(V) and hydrogen peroxide shows that four peroxo complexes are formed in aqueous solution in the pH range 1−7. Two isomeric 2:2:1 (metal:ligand:peroxo) complexes, together with a 2:2:2 species, are found over the entire pH range. At pH [a]

The kinetically inert chromium(III) tris-(8-hydroxyquinolinate), Crq3, has been synthesized, crystallized from 90% methanol-water, and characterized by MALDI-TOF mass spectrometry, thermogravimetry, FTIR, NMR spectroscopy, and X-ray powder diffraction. It is formed as a methanol solvate, but the solvent can be removed by heating. Large paramagnetic shifts and spectral broadening in (1)H NMR spectra indicate electron delocalization between the metal and the ligand. DFT calculations show it is present as the meridional isomer, with the HOMO largely based on one of the metal 3d orbitals and the LUMO essentially localized on the ligands. Cyclic voltammetry (CV) in acetonitrile solutions shows four oxidation peaks and two, less intense reduction waves on the first scan. The HOMO energy determined from the first oxidation peak is fairly close to that obtained by DFT, in agreement with this being mainly metal based. Although the number of peaks decreases on subsequent CV scans, the complex shows markedly enhanced electrochemical stability compared with aluminium(III) tris-(8-hydroxyquinolinate). Solution UV/visible absorption and solid diffuse reflectance spectra have a weak, long wavelength band, assigned to the metal based d-d transition, in addition to the normal, ligand based bands seen in metal quinolates. The energy of the lowest energy band is identical to the HOMO-LUMO separation obtained by cyclic voltammetry, in agreement with the above description. The compound is only weakly luminescent, in contrast to many other metal quinolates, due to the lowest energy transition being metal rather than ligand based. The potential of this compound as an electron transporting/hole blocking layer in optoelectronic devices is indicated.

M. MADALENA CALDEIRA, M. Lufsa RAMOS, NUNO C. OLIVEIRA, and VICTOR M. S. GIL. Can. J. Chem. 65,2434Chem. 65, (1987. A proton, carbon-13, and vanadium-5 1 nuclear magnetic resonance study is reported on the number, stoichiometry, geometry, and relative stability of the complexes that form when vanadate(V) solutions are mixed with each one of the following organic a-hydroxyacids in the pH range -2.5--7:glycolic, lactic, chloro-3-and phenyl-3-lactic, mandelic, glyceric, and malic acids. The predominant complexes have 1:l composition (almost certainly in a polymeric structure) in contrast with the 1:2 (meta1:ligand) stoichiometry of the corresponding Mo(V1) and W(V1) complexes. Chem. 65, 2434Chem. 65, (1987. On rapporte une ktude par rCsonance magnktique nuclkaire du 'H, du I3C et du 5 1~ sur le nombre, la stoechiomktrie, la giomktrie et la stabilite relative des complexes qui se foment lorsqu'on mklange, a des pH allant de 2,5 a 7, des solutions de vanadate(V) avec l'un des acides a-hydroxylks suivants : acides glycolique, lactique, chloro-3 et phCnyl-3 lactiques, mandilique, glyckrique et malique. Les complexes qui se foment d'une faqon priponderante ont une composition 1 : 1 (presque certainement dans une structure polymkrique); ces rksultats sont en opposition avec ceux obtenus avec le Mo(V1) et le W(V1) dont les complexes sont de composition 1 : 2 (metal : ligand).[Traduit par la revue]

No abstract

We report the polymorphic behaviour, in melt cooling experiments, of racemic betaxolol, a low aqueous solubility selective b 1-adrenergic antagonist drug with a flexible molecular structure. A multidisciplinary approach is employed, using thermal analysis (differential scanning calorimetry, polarised light thermomicroscopy), spectroscopic methods (infrared spectroscopy, magic angle spinning 1 H NMR) and X-ray powder diffraction. A glass phase is obtained, T g *-10°C, on cooling the melt, unless the cooling rate is B0.5°C min-1 , while a new metastable form, polymorph II, T fus = 33°C, is generated in subsequent heating runs in a two step process. Although either partial crystallisation from the melt in the first step or the formation of an intermediate, metastable, low ordered phase may explain these observations, our results favour the second hypothesis. The stable polymorph I, T fus = 69°C, which crystallizes on further heating after form II melting, has also been obtained either from polymorph II or from the molten phase, on standing at 25°C. The racemic betaxolol crystalline phases are found to exhibit some degree of disorder.