Crystal structure and properties of a copper(II) complex of an 18-memberedmacrocyclic ligand with N,N '-dicarboxylic acid arms

CuL . 5H(2)O (H2L = 1,15-diaza-3,4; 12,13-dibenzo-5,8,11-trioxacyclo-octade cane-N,N'-diacetic acid) crystallized from water. Its crystal structure was determined by X-ray diffraction analysis and refined in space group Pnma, a = 20.1784(11), b = 15.8745(9), c = 8.9266(5) Angstrom, V = 2859.4(3) Angs trom(3), Z = 4, lambda(MoK alpha) = 0.71073, R-w = 0.0294 for 1822 observed reflection [I > 2 sigma (I)]. The copper atom is surrounded by two nitroge n atoms, two oxygen atoms from the carboxyl groups in the ligand and one ox ygen atom from a coordinated water to form a distorted square pyramidal arr angement. The three ether oxygen atoms in the cycle have no contact with th e copper ion. The stability constant for the 1:1 complex of copper(II) and protonation co nstants for the ligand have been determined by potentiometric titration in water (I = 0.1, KNO3) at 25 degrees C. Electronic spectra, conductivity mea surements, thermal analysis, and the EPR of the complex are discussed in te rms of the crystal structure.