Intramolecular vibrations relax a molecular magnet

CASSCF plus lattice dynamics on [(tpaPh)Fe]− show acoustic phonons are silent; intramolecular modes modulate D far more than rotations.

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Are acoustic phonons active in dilute-crystal relaxation of this SMM?

No; intramolecular modes modulate anisotropy far more than rotations.

Which molecule was the benchmark?

[(tpaPh)Fe]−, with H3tpaPh = tris((5-phenyl-1H-pyrrol-2-yl)methyl)amine.

What axial D and E/D were computed?

D = −27.5 cm−1 with a vanishing E/D ratio.

What electronic method gave D?

CASSCF with def2-TZVP on Fe/N and def2-SVP on C/H.

What spin multiplet is lowest?

An S = 2 manifold split by spin–orbit coupling.

What coordination geometry enforces anisotropy?

Trigonal pyramidal N4 with a stiff Fe2+ ligand cage.

What crystal symmetry was used?

P1 with two inversion-related SMMs; one molecule represents the crystal.

Where do Fe/N motions show up in the DOS?

A large amplitude below 500 cm−1, plus maxima near 250 and 1300 cm−1.

What extra design rule do the authors emphasize?

Include lattice dynamics, not only spin Hamiltonian engineering.

What class of magnets is being analyzed?

Mononuclear single-molecule magnets.

At high temperature, which motions should dominate?

Only internal displacements are expected to be operative.