Structural and solution chemistries of five-coordinate copper(II) complexes

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1. Five-coordinate Cu(II) ternary complexes containing some kinds of Linear triamines as terdentate and. amino acids and diamines as bidentate have been synthesized and characterized by means of X-ray single crystal analyses and spectral measurements. Stabilities of the five-coordinate species were also investigated by potentiometric titrations.2. The ternary complexes containing N,N,N', N", N"-pentamethyldiethylenetriamine (pmdt) and L-valine (L-val) and alpha-aminoisobutyric acid (aiba), [Cu(pmdt)(L-val)]CLO_4 and Cu(pmdt)(aiba)]CLO_4, were approximately regular trigonal bipyramidal with trigonal factors of 81 and 94%. The ternary complex with 2,2'-dipicolylamine (dpa) and L phenylalanine (L-phe), [Cu(dpa)(L-phe)]CLO_4, was slightly distorted square pyramidal, and there was no intramolecular aromatic ring stacking between the pyridyl group of dpa and the phenyl group of L-phe, while the intermolecular stacking was observed. The ternary complexes containing N,N- dimethyl-N'-(2-pyridyhnethyl)ethylene diamine (p yen) and an amino acid exhibited also square pyramidal spectra. Some complexes with dpa and an amino acid showed unique spectral behavior : the spectrum in solid state is significantly different from that in solution.3. The stability constant of the ternary five-coordinate complexes containing dpa and pyen as a terdentate ligand and an aromatic amino acid as a bidentate was significantly large compared with those with alkyl- and hydroxyalkyl-substituted amino acids, indicating a hydrophobic intramolecular interaction between the pyridine ring of dpa and pyen and the aromatic sidechains of the amino acids.