Filling in the Gaps: the Last Unreported Mononuclear Lanthanide tris-Acethylacetonates with 1,10-Phenanthroline for Revealing Structural Trends and Studying the Dynamic Magnetic Properties

Abstract

We prepared and studied the last of previously unknown members of square antiprismatic lanthanide tris(acethylacetonate) complexes with 1,10-phenanthroline, namely [Ln(acac)3(phen)] ones formed by Nd3+ (Nd), Ho3+ (Ho) and Tm3+ (Tm) ions. The optimized synthetic technique which allows preparing 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 covalence of Ln-O(acac) bonds and the decrease in the flexibility of coordination geometry were revealed. In particular, change in the crystal packing on going from complexes of La and Ce to those formed by Pr-Lu was confirmed. Within the latter sub-series, the increase in symmetry of coordination polyhedron along with the increase in volume fraction of crystal voids takes place. Complex Nd is new representative of 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 Raman mechanism and quantum tunneling of magnetization. Supported by thorough literature survey of Nd-based SMMs, these findings allow assuming the overall efficiency of square antiprismatic coordination environments to further enhance the SMM performance of Nd(III) complexes.