Potentiometric, spectrophotometric and ES-mass spectroscopic studies of the formation of binary and ternary species between Cu2+, a pyrazole bridged N2S-bismacrocycle and exogenous ligands

The protonation and stability constants of the binary Cu2+ complexes with 1 ,1'-[(1H-pyrazole-3.5-diyl) bis(methylene)]bis(octahydro-1H-1,4-triazonine) were determined by potentiometric titrations at 25 degrees and l = 0.5 M ( KNO3). The results show that a series of mononuclear [Cu(LHn)] (n = 1, 0, - 1, -2) and dinuclear species [Cu-2(LHm)] (m = 0, -1, -2, -3) are formed. St ructures are proposed for them based on their absorption spectra and result s previously obtained from X-ray diffraction studies. Complex [Cu-2(LH-1)]( 3+), in which the pyrazole bridging group is deprotonated, is especially in teresting since it is able to bind exogenous ligands Z such as N-3(-) pyraz ole and 1H,1'H-4,4'-methanediyl-bis-pyrazole (bispyr) to give ternary speci es [Cu-2(LH-1)Z] and [[Cu-2(LH-1)](2)Z], the stabilities of which have been measured by spectrophotometric titrations. Iii the case of bispyr the exis tence of the tetranuclear complex [[Cu-2(LH-1)](2)(bispyr)](2+) has been pr oven by ES-MS. (C) 1998 Elsevier Science Ltd. All rights reserved.