Mononuclear and polynuclear complexes containing f ions

Abstract

Dinuclear and tetranuclear uranyl(VI) complexes ((UO 2) 2(L A)·2H 2O and (UO 2) 4(LB)· nS, n=2; S=H 2O, dmf, dmso), where H 4L A and H 8L B are the Schiff bases obtained by condensation of 1,4-bis- [bis(2-aminoethyl)aminomethyl]benzene with salicylaldehyde or 2,3-dihydroxybenzaldehyde, respectively, have been prepared by template procedure or by reaction of the preformed ligands with uranyl(VI) salts. The ligands and the complexes have been characterized by physicochemical data, particularly by IR and NMR spectroscopy. Their properties have been compared with those of the similar mono-, homo- and heterodinuclear complexes containing uranyl(VI) and/or lanthanide(III) ions with the potentially heptadentate compartmental Schiff bases H 4L c and H 4L D, derived by condensation of 2,3-dihydroxybenzaldehyde with 1,5-diamino-3-azapentane and 1,5-diamino-3-thiapentane, respectively. The X-ray structure of the dinuclear uranyl complex (UO 2) 2(L A)·dmso·C 6H 6 has been determined by X-ray diffractometry and compared with that of UO 2(H 2L c)·dmf, (UO 2) 2(L c)(dmf) and (UO 2) 2(L c)(dmso). The crystals of (UO 2) 2(L A)·dmso·C 6H 6 grown from a dmso/C 6H 6 solution are triclinic, space group P 1 with a=13.459(4), b=13.179(3), c=11.418(4) Å, α=75.80(4), β=108.30(4)m γ=116.77(5)°, U=1704(1) Å 3, D c=1.38 g cm −3 for Z=1. The asymmetric unit is half of the molecule, this being centrosymmetric. The structure was refined to the final R of 4.9%. The compound forms a centro-symmetric binuclear complex as the benzene ring, bridging the two macroacyclic coordination moieties, is centered on inversion point 1 2 , 0, 1 2 The uranium atom is in the usual, slightly distorted, bipyramidal pentagonal configuration; the quasi linear (175°) uranyl UO 2 2+ ion is equatorially coordinated by the O 2N 3 donor set of the Schiff base ligand forming an irregular puckered pentagon. Selected bond distances for this compound are: UO (uranyl) 1.77 (mean), UO (ligand) 2.22 (mean) and UN 2.61 Å (mean). The two uranium atoms displace 1.20 Å above and below the central benzene ring plane and are 12.686(1) Å apart (the shortest intermolecular U···U distance is 6.954(1) Å. One dmso and one benzene molecule are present, as clathrate solvents, in disordered positions and do not present any type of interaction with the remaining cell content.