THE FAVORED UNS-CIS GEOMETRY IN OCTAHEDRAL NICKEL(II) COMPLEXES CONTAINING LINEAR TETRADENTATE EDDA-TYPE LIGANDS FORMING 6-MEMBERED RINGS - CRYSTAL-STRUCTURE OF UNS-CIS-[NI(1,3-PDDA)(H2O)(2)]

Two paramagnetic octahedral nickel(II) complexes containing the tetradentate 1,3-propanediamine-N,N'-diacetate (1,3-pdda) or ethylenediamine-N,N'-di-3-propionate (eddp) anions and water in the remaining two coordination positions were prepared and characterized. In both cases, only one (uns-cis) of the three geometrical isomers, was found to dominate. The 1,3-pdda and eddp ligands prefer the uns-cis configuration, indicating that six-membered chelate rings have a profound effect on the distribution of geometrical isomers. The infrared and electronic absorption spectra of these complexes are discussed in comparison with those of an edda-Ni(II) complex (edda = ethylenediamine-N,N'-diacetate ion) of known s-cis configuration. The electronic absorption spectra have been treated in terms of 0(k) symmetry but the splitting of the T-3(2g)(0(h)) bands of the complexes indicates that the tetragonal field is enhanced. The splitting patterns are assigned with the D-4h model: B-3(1g) --> B-3(2g) and B-3(1g) (3)E(g). The magnetic measurements are also reported for the complexes studied. The uns-cis-[Ni(1,3-pdda) (H2O)(2)] complex crystallizes in the space group P2(1)2(1)2(1) of the orthorhombic crystal system with a = 15.982(4), b = 8.502(2), c = 8.032(2) (Angstrom) and Z = 4. The six-membered diamine ring assumes the stable 'chair' conformation. The five-membered glycinate rings show a relatively small puckering resembling an 'envelope' conformation.