The influence of the counterion in the behavior of a trans-diacetate dysprosium complex with a semirigid macrocycle

Introduction. After studying the magnetic properties of [Dy(L)(OAc)₂]NO₃·2H₂O (L = 2E,6E,9E,13E-3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane-2,6,9,13-tetraene), its single-molecule magnet behavior under an optimal field of 2000 Oe was revealed. Furthermore, luminescence measurements indicated that the ratio between the integrated intensity of the macrocyclic Schiff base and that of the Dy^{3+ 4}F_9/2 → ⁶H_13/2 transition can define a secondary luminescent thermometer, with a maximum relative thermal sensitivity value of 2.3% K⁻¹. In view of these interesting properties, we changed the counterion from nitrate to tetraphenylborate to see its influence.

Synthesis and methods. Here, we present the result of the synthesis and characterization of the dysprosium complex [DyL(OAc)₂]BPh₄. It was obtained by a template synthesis of 2,6-pyridinedicarboxaldehyde, dysprosium acetate tetrahydrate and ethylenediamine, and a subsequent reaction with sodium tetraphenylborate. Single crystals of the compound were obtained via the recrystallization of the solid in dichloromethane with an Et₂O layer in the fridge. Then, it was characterized by elemental analysis, IR spectroscopy and single X-ray diffraction techniques.

Results. Two slightly different moieties of [DyL(OAc)₂]⁺ are present in the unit cell, alongside tetraphenylborate anions, but no other species are present. Thus, the crystal packing lacks classic H bonds, whereas many C-H···O and C-H···π interactions are present in the crystal packing scheme. This cationic complex shows a decacoordinate metal center, almost forming a distorted tetradecahedron. The characterization of this Dy^III complex allows us to compare its properties with those of other closely related species.

Conclusion. The presence of such a hydrophobic counterion strongly influences the crystal packing of this species, but is does not have such an intense impact on other features, mostly related to the [DyL(OAc)₂]⁺ cation.