Dysprosium-based complexes with a flat pentadentate donor: a magnetic and ab initio study

Abstract

The reactivity of dysprosium(III) nitrate towards the reported pentadentate N3O2 Schiff base H2L (2,6-bis(2-hydroxyphenyliminomethyl)pyridine) has been investigated. This reactivity depends to a large extend on the operational pH of the medium and, accordingly, two different complexes, [Dy(HL)(NO3)2]·H2O (1·H2O) and [Dy(L)(NO3)(EtOH)(H2O)]·2H2O (2·2H2O) were isolated. Besides, reaction of H2L with dysprosium chloride in methanol yields [Dy(HL')2)][Dy(L)(Cl2)] (3), where H2L' (6 (2 hydroxyphenyliminomethyl)-2-methoxyhydroxymethyl)pyridine) is an N2O2 hemiacetal donor derived from the partial hydrolysis of the H2L ligand, and subsequent addition of the methanol solvent to the carbonyl group. Single crystal X-ray diffraction studies of 1·Py·0.5CH3OH·0.5H2O, 2·2H2O and 3 show that the Schiff base acts in all cases as a nearly flat pentadentate donor, and that this behavior is independent of the degree of deprotonation of the phenolic oxygen atoms (monodeprotonated or bisdeprotonated). Therefore, 1·Py·0.5CH3OH·0.5H2O, 2·2H2O and 3 constitute the first lanthanoid complexes of H2L to be crystallographically characterized. Complexes 1·Py·0.5CH3OH·0.5H2O and 2·2H2O show DyN3O6 cores, with distorted geometries closer to spherical tricapped trigonal prism or spherical capped square antiprism for 1·Py·0.5CH3OH·0.5H2O and 2·2H2O, respectively. In the case of 3, the cation [Dy(HL')2)]+ shows a dysprosium ion in an N4O4 square antiprism environment, while the [Dy(L)(Cl2)]- unit shows a DyN3O2Cl2 core with distorted pentagonal bipyramidal geometry. Moreover, attempts to dilute 1·H2O with yttrium yielded single crystals of (Et3NH)[Dy0.09Y0.91(L)(NO3)2] (4), where the Schiff base shows the same pentadentate chelate coordination mode. Studies on the behavior of 1·H2O, 2·2H2O and 3 as potential single molecular magnets show that 2·2H2O and 3 are field-induced SIMs, while 1·H2O does not exhibit frequency-dependent peaks of the out of phase susceptibility even in the presence of an external dc magnetic field. Nevertheless, diluted sample 4 is a SIM at zero dc field. Ab initio calculations support these magnetic results.