Thermodynamic and fluorescence emission studies on chemosensors containing anthracene fluorophores.: Crystal structure of {[CuL1Cl]Cl}2•2H2O [L1 = N-(3-aminopropyl)-N′-3-(anthracen-9-ylmethyl)aminopropylethane-1,2-diamine]

The co-ordination capabilities toward hydrogen ions, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ of the novel receptor 2,6,9,13-tetraaza[14](9,10)anthracenophane (L) and of its open-chain counterpart N-(3-aminopropyl)-N'-3-(anthracen-9-ylmethyl)aminopropylethane-1,2-diamine (L-1) is described. Stepwise protonation constants of the cyclic receptor (L) are lower than those of the open-chain receptor (L-1). Quenching effects of the fluorescence emission occur upon first and second deprotonation of L and upon second deprotonation of L-1. Stability constants of the Co2+, Ni2+, Cu2+ Zn2+ and Cd2+ complexes follow the Irving-Williams trend and are intermediate between those of triethylenetetraamine with terminal primary amino groups and those of the alpha,omega-dibenzylated receptor 1,12-dibenzyl-1,5,8,12-tetraazaciclododecane. Luminescence studies show that complexation of Cu2+ and Ni2+ by L-1 yield CHEQ effects (chelation enhanced quenching) while complexation of Zn2+ and Cd2+ produce CHEF effects (chelation enhanced fluorescence). The magnitude of these effects depends on the strength of the co-ordination. Crystals of {[(CuLCl)-Cl-1]Cl}(2) ., 2H(2)O are triclinic, space group P (1) over bar, with a = 13.307(1), b = 13.305(1), c = 16.538(2) Angstrom, alpha = 104.94(1), beta = 111.67(1), gamma = 102.76(1)degrees R-1 = 0.0885, wR(2) = 0.2667. The crystal structure of {[(CuLCl)-Cl-1]Cl}(2). 2H(2)O shows a very strongly axially distorted square pyramidal co-ordination geometry in which the Cu2+ cation is co-ordinated by all the nitrogen donors of the receptor and a chloride ion disposed at the apical position of the square pyramid. The asymmetric unit is formed by two slightly different [(CuLCl)-Cl-1](+) cations with an arrangement that shows pi-stacking of their anthracene sub-units.