This project deals with the synthesis of new metal complexes with pyrazole ligands, and the study of their behaviour as anion receptors. The metal fragments will be chosen so as to permit an orientation of the pyrazole ligands in such a geometry that the N-H bonds of several of them can participate in hydrogen bond interactions with the external anion. Moreover, metal fragments with one or two positive charges will be chosen so that the electrostatic attraction adds to the hydrogen bonds thus leading to a stronger receptor-anion interaction. The cationic receptors will be prepared as their salts with the anion tetrakis (3,5-bis(trifluoromethyl) phenyl)borate, with which the interaction of the receptor is expected to be negligible, thus eliminating the problem of the competition between the external anion and the counterion.
The interaction of the new receptors with different simple anions in solvents of different polarity will be studied. The anion-receptor association constants will be obtained from the variation of the 1H NMR chemical shift of the pyrazole N-H hydrogens in response to the addition of increasing amounts of anions to solutions of the receptor. The effect on the mentioned constants of the different substituents on the pyrazole ring will be evaluated. Also, the solid state structure of some receptor-anion adducts will be determined by means of X-ray diffraction in order to know the detailed geometries resulting from the interaction. The suitability of the new receptors as anion sensors will be assessed, in particular (for the receptors featuring carbonyl ligands), as IR sensors, of which no precedent is known.
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