Abstract
Three new binucleating ligands have been synthesized in which two tridentate PY2 units (PY2=bis[2-(2-pyridyl)ethyl]amine) are connected by carbon chains containing either an olefin linkage or a phenyl substituent. These three ligands are:
N,
N,
N′,
N′-tetrakis[2-(2-pyridyl)ethyl]-1,4-diamino-
cis-2-butene (C4PY2) (
3),
N,
N,
N′,
N′-tetrakis[2-(2-pyridyl)ethyl]-1,4-diamino-
trans-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
2O (
8) were isolated as tetrachloride derivatives in the solid state. Analysis of the diffuse transmittance d–d and powder EPR spectra of
6–
8 indicates a trigonal bipyramidal (tbp) copper ion geometry for these complexes in the solid state. In DMSO:H
2O (5:2) solution all three complexes exhibit similar d–d spectra characteristic of square pyramidal copper(II) and exist predominantly as an intramolecular, dihydroxy bridged species. This ‘closed’ dihydroxy bridged species is in equilibrium with an ‘open’ species in which no exogenous bridging groups are present. The ‘open’–‘closed’ equilibrium is shifted by the addition of H
+ or OH
− and has been studied by electronic spectroscopy, electron paramagnetic resonance (EPR) and electrochemical techniques.