COPPER-COMPLEXES BEARING PENDANT, PROTONATABLE NONCOORDINATING GROUPS- SYNTHESIS, CHARACTERIZATION, AND PROTONATION CHEMISTRY

We have derivatized the pendant amine of methyl-3,7-diaza-2,9-nonanedi oato)chlorocopper(II) with 3-pyridinecarboxaldehyde and 4-pyridinecarb oxaldehyde. These new complexes, along with the starting material, com prise a set of copper complexes with chemically identical inner coordi nation spheres that provide protonatable nitrogen attached to the liga nd framework. The 3-pyridinecarboxaldehyde adduct has been characteriz ed by X-ray crystallography. This complex crystallized in the space gr oup P2(1)/n with a = 12.025(8) Angstrom, b = 12.304(5) Angstrom c = 13 .311(8) Angstrom, beta = 94.76(5)degrees, V = 1962(1) Angstrom(3), and Z = 4 (R, R-W = 0.049; 0.045). pH-dependent changes in the electronic spectroscopy and electrochemistry of these complexes have been observ ed. The parent complex undergoes a similar to 300 cm(-1) shift in lamb da(max) and a +140 mV shift in midpoint potential on going from high p H to low pH, while the pyridinecarboxaldehyde Schiff-base derivatives undergo smaller changes (78 and 110 cm(-1) and 104 and 100 mV, respect ively). The origins of the shift in lambda(max) are investigated spect roscopically. A number of explanations for these shifts can be ruled o ut, including metal complex dimerization and axial coordination to the metal complexes. The data tend to support the suggestion that the spe ctroscopic shifts are largely due to the electrostatic influence of th e pendant charge on the transition metal chromophore.