Filling in the gaps: the last unreported mononuclear lanthanide tris-acetylacetonates with 1,10-phenanthroline for revealing structural trends and studying the dynamic magnetic properties

Abstract

We prepared and studied the last unreported members of square antiprismatic lanthanide tris-acetylacetonate complexes with 1,10-phenanthroline, namely, [Ln(acac)₃(phen)], formed by Nd³⁺ (Nd), Ho³⁺ (Ho) and Tm³⁺ (Tm) ions. An optimized synthetic technique, which allows for the preparation of single phase complexes of both light and heavy lanthanides, was proposed for the first time. For the entire [Ln(acac)₃(phen)] series, structural trends arising from the increase in the covalency of Ln–O(acac) bonds and the decrease in the flexibility of the coordination geometry were revealed. In particular, a change in the crystal packing from the La and Ce complexes to those formed by Pr–Lu was confirmed. Within the Pr–Lu sub-series, an increase in the symmetry of the coordination polyhedron, along with an increase in the volume fraction of crystal voids, takes place. Complex Nd is a new representative of the scarcely studied Nd-based single-molecule magnets, SMMs. The slowdown of demagnetization in Nd is achieved under non-zero magnetic fields and proceeds via the combination of the Raman mechanism and quantum tunneling of magnetization. Supported by a thorough literature survey of Nd-based SMMs, these findings allow assuming that square antiprismatic coordination environments are effective in enhancing the SMM performance of Nd(III) complexes.