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)]
Dj. Radanovic et al., 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)], Inorganica Chimica Acta, 237(1-2), 1995, pp. 151-157
Two paramagnetic octahedral nickel(II) complexes containing the tetrad
entate 1,3-propanediamine-N,N'-diacetate (1,3-pdda) or ethylenediamine
-N,N'-di-3-propionate (eddp) anions and water in the remaining two coo
rdination positions were prepared and characterized. In both cases, on
ly one (uns-cis) of the three geometrical isomers, was found to domina
te. The 1,3-pdda and eddp ligands prefer the uns-cis configuration, in
dicating that six-membered chelate rings have a profound effect on the
distribution of geometrical isomers. The infrared and electronic abso
rption spectra of these complexes are discussed in comparison with tho
se of an edda-Ni(II) complex (edda = ethylenediamine-N,N'-diacetate io
n) of known s-cis configuration. The electronic absorption spectra hav
e 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 i
s 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) (H2
O)(2)] complex crystallizes in the space group P2(1)2(1)2(1) of the or
thorhombic 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 sta
ble 'chair' conformation. The five-membered glycinate rings show a rel
atively small puckering resembling an 'envelope' conformation.