Filling Tricompartmental Ligands with GdIII and ZnII Ions: Some Structural and MRI Studies

Abstract

Here we report the synthesis and characterization of a mononuclear gadolinium complex (Gd) and two heteronuclear Zn-Gd complexes (ZnGd and Zn2Gd), which contain two similar three-armed ligands that display an external compartment suitable for lanthanoid ions, and two internal compartments adequate for zinc (II) ions [H3L′ = (2-(3-formyl-2-hydroxy-5-methyl phenyl)-1,3-bis[4 -(3-formyl-2-hydroxy-5-methylphenyl)-3-azabut-3-enyl]-1,3-imidazolidine; H3L = 2-(5-bromo-2-hydroxy-3-methoxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxy-3-methoxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine]. The synthetic methods used were varied, but the use of a metalloligand, [Zn2(L)AcO], as starting material was the key factor to obtain the heterotrinuclear complex Zn2Gd. The structure of the precursor dinuclear zinc complex is mostly preserved in this complex, since it is based on a compact [Zn2Ln(L)(OH)(H2O)]3+ residue, with a µ3-OH bridge between the three metal centers, which are almost forming an isosceles triangle. The asymmetric spatial arrangement of other ancillary ligands leads to chirality, what contrasts with the totally symmetric mononuclear gadolinium complex Gd. These features were confirmed by the crystal structures of both complexes. Despite the presence of the bulky compartmental Schiff base ligand, the chiral heterotrinuclear complex forms an intricate network which is predominately expanded in two dimensions, through varied H-bonds that connect not only the ancillary ligands, but also the nitrate counterions and some solvated molecules. In addition, some preliminary magnetic resonance imaging (MRI) studies have been made to determine the relaxivities of the three gadolinium complexes, with apparently improved T1 and T2 relaxivities with increasing zinc nuclearity, since both transversal and longitudinal relaxivities appear to enhance in the sequence Gd < ZnGd < Zn2Gd.

New Heterotrinuclear CuIILnIIICuII (Ln = Ho, Er) Compounds with the Schiff Base: Syntheses, Structural Characterization, Thermal and Magnetic Properties

“…In recent years, much progress in the synthesis and investigation of heteronuclear 3d-4f Schiff base coordination compounds has been observed [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Their crystal structures and properties are determined by several factors, e.g., type of the metal ions, metal-to-ligand stoichiometry, the nature and position of the ligands, methods of synthesis (a stepwise reaction or one-pot reaction, Figure 1), type of solvents, kind of coligands, etc.…”

“…The salen-type Schiff bases are ligands obtained from salicylaldehyde or its derivatives and different diamines. They usually consist of rigid aromatic rings and flexible aliphatic chains [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In the coordination compounds formed by them, 3d and 4f metal ions are captured simultaneously and linked together through two O phenol atoms.…”