Characterization of the two geometrical isomers of (1,3-propanediamine-N,N′-diacetato-N,N′-di-3-propionato)-nickelate(II). X-ray structure of the binuclear complex trans(O5)-[Ni2(1,3-pddadp)(H2O)4]·4H2O and octahedral distortion of edta-type chelates

Abstract Nickel(II) complexes with the hexadentate ligand 1,3-propanediamine- N , N ′-diacetate- N , N ′-di-3-propionate (1,3-pddadp) have been prepared, chromatographically separated into the two geometrical isomers, trans (O 5 )-Na 2 [Ni(1,3-pddadp)]·2H 2 O ( 1 ) and trans (O 5 O 6 )-Na 2 [Ni(1,3-pddadp)]·3H 2 O ( 2 ), and characterized. The trans (O 5 ) configuration of compound 1 was found to dominate and this geometry was verified crystallographically in the binuclear complex [Ni 2 (1,3-pddadp)(H 2 O) 4 ]·4H 2 O ( 1 ). The complex crystallizes in the triclinic P 1 space group. The structure converged to R =0.0521 for 5210 reflections. The conformations of the chelate rings are those usually observed for these kinds of chelates [a six-membered diamine (T) ring in a twist-boat conformation, the two β-alaninate (G 1 and G 2 ) rings in an envelope - like conformation, and the two glycinate rings, R 1 in a twist and R 2 in an envelope conformation]. The structural data correlating an octahedral distortion are discussed with reference to those of related complexes. The IR and electronic absorption spectra are discussed in comparison with those of similar complexes.