Slow relaxation in doped coordination polymers and dimers based on lanthanoids and anilato ligands

Abstract

In this work we report the synthesis, structure and magnetic properties of two lanthanoid based coordination polymers (CP) and two dimers prepared with two derivatives of the 2,5-dihydroxy-1,4-benzoquinone (C6O4X2)2− as ligands. Using the bromanilato ligand: (C6O4Br2)2− we have prepared the CP [Eu1.96Dy0.04(C6O4Br2)3(DMSO)6]·2DMSO (1) (DMSO = dimethylsulfoxide) and with the chlorocyananilato ligand: (C6O4(CN)Cl)2−) we have prepared one CP formulated as [Eu1.96Dy0.04(C6O4(CN)Cl)3(DMSO)6] (2) and two isostructural dimers: [Eu1.96Dy0.04(C6O4(CN)Cl)3(H2O)10]·6H2O (3) and [Eu2(C6O4(CN)Cl)3(H2O)10]·6H2O (4). Compounds 1, 2 and 3 are Eu(III) compounds doped with 2.0 % of Dy(III), whereas compound 4 is a pure phase of Eu(III). The X-ray structure of these CPs shows that compounds 1 and 2 present neutral (6,3)-2D networks with rectangular cavities in 1 and very distorted hexagonal cavities in 2, while 3 and 4 are isostructural and present a dimeric structure where the Ln(III) ions are connected by a bis-bidentate chlorocyananilato ligand. Each metal completes its nonacoordination environment with a terminal bidentate chlorocyananilato ligand and five water molecules in a slightly distorted capped square antiprismatic geometry. In addition, these coordination complexes have very interesting magnetic properties. Compounds 1 and 3 behave as single-molecule magnets (SMM) with energy barriers of 40.9 and 25.3 K, respectively. In contrast, compound 2 does not present any SMM behaviour.