Anion receptors containing coordinatively unsaturated metal ions: copper(II) complexes with cyclam derivatives

The two coordinatively unsaturated complexes [[Cu(cyclam)].sup.2+] (cyclam: 1,4,8,11-tetraazacyclotetradecane, 1) and [[Cu([Bn.sub.4]cyclam)].sup.2+] (Bn4cyclam: 1,4,8,11-tetrabenzyl-1,4,8,11- tetraazacyclotetradecane, 2) in an MeCN solution uptake an anion [X.sup.-] (halide, pseudohalide) to give square pyramidal ternary complexes, whose stability has been determined through spectrophotometric titration experiments. The formation of a five-cordinate complex is favored by the trans-1 configuration of the [[Cu([Bn.sub.4]cyclam)].sup.2+] receptor, but it is contrasted by the severe steric repulsions exerted by the benzyl substituents on the macrocyclic framework. No significant repulsive effects have been observed in anion binding to the [[Cu(cyclam)].sup.2+] receptor, exhibiting a trans-111 configuration. The existence of a linear relationship between the magnitude of the red shift experienced by the d-d absorption band on anion binding and log K values is discussed. Key words: tetraamine macrocycles, anion recognition, five-coordinate complexes, spectroscopic properties/thermodynamic quantities linear relationships. Les complexes coordinativement insatures [[Cu(cyclam)].sup.2+] (cyclam : 1,4,8,11-tetraazacyclotetradecane, 1) et [[Cu([Bn.sub.4]cyclam)].sup.2+] (Bn4cyclam : 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane, 2) dans une solution de MeCN solution se fixent a un anion X(halogenure, pseudo-halogenure) pour former des complexes ternaires pyramidaux a base carree dont la stabilite a ete determinee a l'aide d'experiences de titrage spectrophotometriques. La formation d'un complexe pentacoordonne est favorisee par la conformation trans-1 du recepteur [[Cu([[Bn.sub.4]cyclam)].sup.2+] mais elle est genee par les fortes repulsions steriques exercees par les substituants benzyles sur la structure macrocyclique. Aucun effet repulsif significatif n'a ete observe au niveau de la liaison de l'anion au recepteur [[Cu(cyclam)].sup.2+], qui presentait une conformation trans-111. L'existence d'une relation lineaire entre la magnitude du decalage vers le rouge que subit la bande d'absorption d-d au niveau de la liaison anionique et les valeurs de log K est analysee. [Traduit par la Redaction] Mots-cles : tetraamines macrocycliques, reconnaissance anionique, complexes pentacoordonnes, relations lineaires entre proprietes spectroscopiques et quantites thermodynamiques.
Introduction Classical coordination chemistry, that involving metal ions, originated from the studies of Alfred Werner on the ammonia complexes with substitutionally inert metal ions ([Co.sup.III], [Cr.sup.III], [Pt.sup.IV]) and dates back [...]