Dicopper(II) complexes with flexible binucleating ligands containing two tridentate coordination sites

Three new binucleating ligands have been synthesized in which two tridentat e PY2 units (PY2 = bis[2-(2-pyridyl)ethyl]amine) are connected by carbon ch ains containing either an olefin linkage or a phenyl substituent. These thr ee ligands are: N,N,N',N'-tetrakis[2-(2-pyridyl)ethyl]- 1.4-diamino-cis-2-b utene (C4PY2) (3), N,:N,N',N'-tetrakis[2-(2-pyridyl)ethyl]-1,4-diamino-tran s-2-butene (T4PY2) (4) and N,N,N',N'-tetrakis[2-(2-pyridyl)ethyl]2-phenyl-1 ,3-diaminopropane (P3PY2) (5). The corresponding dicopper(II) complexes: Cu -2(C4PY2)Cl-4. MeOH (6), Cu-2(T4PY2)Cl-4 (7) and Cu-2(P3PY2)Cl-4. 2H(2)O (8 ) were isolated as tetrachloride derivatives in the solid state. Analysis o f the diffuse transmittance d-d and powder EPR spectra of 6-8 indicates a t rigonal bipyramidal (tbp) copper ion geometry for these complexes in the so lid state. In DMSO:H2O (5:2) solution all three complexes exhibit similar d -d spectra characteristic of square pyramidal copper(II) and exist predomin antly as an intramolecular, dihydroxy bridged species. This 'closed' dihydr oxy bridged species is in equilibrium with an 'open' species in which no ex ogenous bridging groups are present. The 'open'-'closed' equilibrium is shi fted by the addition of H+ or OH- and has been studied by electronic spectr oscopy, electron paramagnetic resonance (EPR) and electrochemical technique s. (C) 2001 Elsevier Science B.V. All rights reserved.