Synergy of\nExperiment and Broadened Exploration of\nAb Initio Calculations for Understanding of Lanthanide–Pentacyanidocobaltate\nMolecular Nanomagnets and Their Optical Properties

We present a synergistic experimental–theoretical\nmethodology\nfor the investigation of lanthanide-based single-molecule magnets\n(SMMs), demonstrated using the example of novel heterometallic molecules\nincorporating Nd<sup>3+</sup>/Ce<sup>3+</sup> ions combined with three\ndifferent, rarely explored, penta­cyanidocobaltate(III) metalloligands,\n[Co<sup>III</sup>(CN)<sub>5</sub>(azido/nitrito-<i>N</i>/iodido)]<sup>3–</sup>. The theoretical part of our approach\nbroadens the exploration of <i>ab initio</i> calculations\nfor lanthanide(III) complexes toward the convenient simulations of\nsuch physical characteristics as directional dependences of Helmholtz\nenergy, magnetization, susceptibility, and their thermal and field\nevolution, as well as light absorption and emission bands. This work\nwas conducted using newly designed SlothPy software (https://slothpy.org). It is introduced\nas an open-source Python library for simulating various physical properties\nfrom first-principles based on results of electronic structure calculations\nobtained within popular quantum chemistry packages. The computational\nresults were confronted with spectroscopic and <i>ac</i>/<i>dc</i>-magnetic data, the latter analyzed using previously\ndesigned relACs software. The combination of experimental and computational\nmethods gave insight into phonon-assisted magnetic relaxation mechanisms,\ndisentangling them from the temperature-independent quantum tunneling\nof magnetization and emphasizing the role of local-mode processes.\nThis study provides an understanding of the changes in lanthanide(III)\nmagnetic anisotropy introduced with penta­cyanidocobaltates(III)\nmodifications, theoretically exploring also potential applications\nof reported compounds as anisotropy switches or optical thermometers.