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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.

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This version is available at https://strathprints.strath.ac.uk/56947/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.1 To whom correspondence should be addressed. E-mail: antonio.evora@uc.pt Tel.: Co-crystals of diflunisal and isomeric pyridinecarboxamides a thermodynamics and crystal engineering contribution +351239854450 ABSTRACTDiflunisal is an anti-inflammatory non-steroidal drug, class II of the Biopharmaceutical Classification System, that has recently been the subject of renewed interest due to its potential use in the oral therapy of familial amyloid polyneuropathy. In this work, a thermodynamic based approach is used to investigate binary mixtures (diflunisal + picolinamide) and (diflunisal + isonicotinamide) in order to identify solid forms potentially useful to improve the biopharmaceutical performance of this active pharmaceutical ingredient.Special emphasis is put on the research of co-crystals and on the influence of structural changes in the pyridinecarboxamide co-former molecules on co-crystal formation with diflunisal. The thermodynamic based methodology described by ter Horst et al. in 2010 indicates that the formation of co-crystals is thermodynamically feasible for both systems. The binary solid-liquid phase diagrams are built and allow identifying unequivocally the formation of co-crystals of diflunisal with each of the two isomers and also their stoichiometry: 1:1, (diflunisal:co-former) in the case of pyridine-2-carboxamide, picolinamide, and 2