pH-dependent absorption and emission properties of a ReI complex working as a carboxylate ligand for Cu2+

The fac-Re(CO)(3)(bipy-COOH)Cl complex (bipy = 2,2'-bipyridine) bears a carboxylic function in the 5-position of the bipy ligand: due to the kinetic inertness of the Re-1 center, the complex behaves as a R-COOH carboxylic acid. In aqueous solutions, it coordinates Cu2+, according to pH-dependent equilibria, to give the dimeric species Cu[fac-Re-1(CO)(3)(bipy-COO)Cl](2) and {Cu[fac-Re(CO)(3)(bipy-COO)Cl](2) (OH)(2)}(2-), whose formation constants have been determined by means of potentiometric titration experiments. The fac-Re(CO)(3)(bipy-R)Cl core is luminescent, and interestingly, its emitting properties are pH-dependent. In particular, its luminescence intensity increases with the formation of the {Cu[fac-Re(CO)(3)(bipy-COO)CI](2)(OH)(2)}(2-) species, visually signaling the formation of this hydroxo-containing multicenter complex. (C) 2003 Elsevier Science B.V. All rights reserved.