A Family of Lanthanoid Dimers with Nitroanilato Bridges

Abstract

Abstract:The first complexes with lanthanoid ions and the nitroanilato ligand have been synthesized (nitroanilate dianion = [C 6 O 4 (NO 2 ) 2 ] 2− = dianion of the 3,6-dinitro-2,5-dihydroxo-1,4-dibenzoquinone ligand). This family of dimers can be formulated as [Ln 2 (C 6 O 4 (NO 2 ) 2 ) 3 (H 2 O) 10 ]·6H 2 O with Ln(III) = Sm (1), Gd (2), Tb (3), Dy (4), Ho (5), and Er (6). The X-ray structure of this family of isostructural complexes shows that they all present a dimeric structure where the Ln 3+ ions are connected by a bis-bidentate nitroanilato ligand. Each metal completes its nonacoordination environment with a terminal bidentate nitroanilato ligand and five water molecules in a slightly distorted tri-capped trigonal prismatic geometry. The magnetic properties of this family show the expected contributions of the lanthanoid ions without any noticeable magnetic interaction through the nitroanilato ligand. The compounds present luminesce of the nitroanilato ligand superimposed with a weaker emission from the lanthanide ion in compound 5 (Ho).

Tuning the Structure and Properties of Lanthanoid Coordination Polymers with an Asymmetric Anilato Ligand

“…The observed behaviour indicates that compounds 2-4 are essentially paramagnetic and, therefore, also indicates that the chlorocyananilato bridge gives rise to very weak (if any) magnetic coupling, in agreement with the observed behaviour when the anilato-type ligands connect transition metals [27,29,30] or Ln(III) ions [33,36,37]. The observed χ m T values at room temperature are close to those calculated for 3 H 4 (in compounds 2 and 3) or 2 F 7/2 ground multiplets (in compound 4) [44].…”

“…This transition can be excited with light by direct population of the 1 S state, using short wavelengths (UV excitation) [39]. However, the optical properties of the chromophores may vary after crystallization [37] and, therefore, the measurements in solution may not be representative of our compounds. Accordingly, we have measured, as a reference, the chlorocyananilato ligand as its potassium salt K 2 (C 6 O 4 (CN)Cl), in the same conditions as for the crystals of compounds 2-4.…”

“…Interestingly, this ligand shows luminescent properties in solid state [40] and in solution [39], as well as in the two Al(III) complexes. Given these above-mentioned results: (i) the luminescence of the nitranilato derivative with Ho(III) [37], (ii) the intrinsic luminescence of the chlorocyananilato ligand [39,40], (iii) the luminescence shown by many Ln(III) ions, (iv) the above-mentioned ability of anilato ligands to form 2D lattices with all the Ln(III) ions [31,33,36] (Tables 1-3), and (v) the capacity shown by some coordinating solvents to modify these 2D lattices [35,36], we have initiated a detailed study to prepare and characterize the complete series of compounds with Ln(III) ions and the ligand chlorocyananilato. Furthermore, we have decided to use different solvents as H 2 O, DMF, and DMSO, since these solvents have a high ability to coordinate to the Ln(III) ions [41], and are therefore expected to modulate not only the luminescent properties, but also the structure of the resulting compounds, as has been very recently demonstrated by some of us [36] …”

“…In this ligand, the two NO 2 groups are tilted with respect to the anilato plane, giving rise to a large steric effect that precludes the formation of the (6,3)-lattices observed when X = H, Cl and Br. Thus, for nitranilato, all the attempts to obtain the 2D lattice led to a series of nitranilato-bridged dimers, formulated as [Ln 2 (C 6 O 4 (NO 2 ) 2 ) 3 (H 2 O) 10 ]·6H 2 O (Ln(III) = Sm, Eu, Gd, Tb, Dy, Ho and Er) (Table 4) [33,37]. The Ho(III) derivative of this series shows luminescence, due to the nitroanilato ligand, being superimposed with a weaker emission from the lanthanide ion [37].…”

“…Thus, for nitranilato, all the attempts to obtain the 2D lattice led to a series of nitranilato-bridged dimers, formulated as [Ln 2 (C 6 O 4 (NO 2 ) 2 ) 3 (H 2 O) 10 ]·6H 2 O (Ln(III) = Sm, Eu, Gd, Tb, Dy, Ho and Er) (Table 4) [33,37]. The Ho(III) derivative of this series shows luminescence, due to the nitroanilato ligand, being superimposed with a weaker emission from the lanthanide ion [37]. Attempts to combine larger or smaller Ln(III) ions with nitranilato have been unsuccessful to date.…”