1- pyrazole derivatives, hydrogen bonding

The same effect is observed for the substituted pyridyl-pyrazole and -imidazole systems. While 2-(pyrazol-l-yl)pyridine 24 gives a low spin iron(II) complex a continuous spin transition is observed centred just above room temperature in solid salts of [Fe (31)3]2+ and just below in solution [39]. Spin crossover occurs in the [Fe N6]2+ derivative of 2-(pyridin-2-yl)benzimidazole 32 (Dq(Ni2+)=1050 cm"1) but not in that of the 6-methyl-pyridyl system 33 (Dq(Ni2+)=1000 cm"1). Although the transition in salts of [Fe 323]2+ is strongly influenced by the nature of the anion and the extent of hydration, suggesting an influence of hydrogen-bonding, in all instances it is continuous [40]. 

A study of aminomethylene derivatives of ketones, thiones and selenones including pyrrole, furan or pyrazole as the heterocyclic ring showed them to form intermolecular hydrogen bonds with phenol76. 

The aminopyrazole derivative (31) is indicated72 by H NMR and infrared spectroscopies to have two intramolecular hydrogen bonds the first with the nitro group on the aniline moiety, and the second with the C=0 group of the ester on the pyrazole ring, as depicted in the structure 31. 

The synthesis of cahx[4]arene dimelamines with different functionalities and their self-assembly with barbituric and cyanuric acid to hydrogen-bonded nanostructures have been published <05OBC3727> Unique ionophores of penta-crown ethers have been prepared by the reaction of l,3,5-triacryloylhexahydro-l,3,5-triazine (TAHTA) with diaza 18-crown-6 followed by Michael addition, and their binding capabilities towards alkali metal cations studied <05SL2257>. New silver complexes of polydentate ligands including a derivative of pyrazol-l-yl-l,3,5-triazine have been reported <05EJ14370>. 

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