POTENTIOMETRIC STUDY OF THE FORMATION OF HYDROXO COMPLEXES OF [CU(TERPY)]2+ - SYNTHESIS AND CRYSTAL-STRUCTURE OF [CU(TERPY) (H2O)](CF3SO3)2

Two complexes of formula [Cu(terpy)(H2O)](CF3SO3)2 (1) and [Cu(terpy)(OH)]BPh4 (2) (terpy = 2,2':6',2"-terpyridine and BPh4 = tetraphenylborate anion) have been synthesized and characterized by spectroscopic techniques. The x-ray crystal structure of (1) has been determined by x-rav diffraction. The structure is made up of [Cu(terpy)(H2O)]2+ mononuclear cations plus semi-coordinated CF3SO3- anions. The coordination geometry around the copper atom is approximately elongated tetragonal octahedral. The oxygen atom of water and the three nitrogen atoms of terpy occupy the equatorial sites whereas the apical ones are filled by trifluoromethanesulphonate oxygen atoms. The formation of hydroxo complexes of [Cu(terpy)(H2O)]2+ has been investigated bv potentiometry in aqueous solutions and the constants of the Equilibria (1) and (2) [Cu[(terpy)(H2O)]2+ half arrow right over half arrow left K1 [Cu(terpy)(OH)]+ + H+ (1) 2[Cu(terpy)(H2O)]2+ half arrow right over half arrow left K2 [Cu2(terpy)2(OH)]3+ + H+ + H2O (2) have been determined at 25-degrees-C and 0.1 mol dm-3 NaNO3: log K1 = - 8.106(1) and log K2 = - 6.96(2). The influence of tridentate N-donor ligands (L(n-)) on the acidity of the coordinated water molecule of [Cu(L)(H2O)](2-n)+ complexes is analyzed and discussed in the light of reported thermodynamic and structural data.