Computational approach to the study of thermal spin crossover phenomena

Abstract

The key parameters associated to the thermally induced spin crossover process have been calculated for a series of Fe(II) complexes with mono-, bi-, and tridentate ligands. Combination of density functional theory calculations for the geometries and for normal vibrational modes, and highly correlated wave function methods for the energies, allows us to accurately compute the entropy variation associated to the spin transition and the zero-point corrected energy difference between the low-and high-spin states. From these values, the transition temperature, T 1/2 , is estimated for different compounds.

On the zeroth‐order hamiltonian for CASPT2 calculations of spin crossover compounds

“…[13] to extract the thermodynamic magnitudes from experimental data, the computational details, and an introduction to the IPEA parameter. We must note here that the seven compounds used as a dataset in this article are the same that we used in this recent manuscript, with chemical formulae: Fe(phen) 2 (NCS) 2 (1), [16] [Fe(abpt) 2 (NCS) 2 ] (2), [17] [Fe(abpt) 2 (NCSe) 2 ] (3), [17] Fe(bapbpy)(NCS) 2 (4), [18] Fe(HB(pz) 3 ) 2 (5), [19] Fe[H 2 B(pz) 2 ] 2 (bipy) (6), [20] and [Fe(1-bpp)][BF 4 ] 2 (7). [21] Those compounds have a common structural characteristic, they display a FeN 6 core, probably the largest family of inorganic SCO materials (see Fig.…”

Density functional plus dynamical mean-field theory of the spin-crossover moleculeFe(phen)2(NCS)2

“…25,26 Diffusion Quantum Monte-Carlo method has also been applied to charged spin-crossover molecules, although direct comparisons to experiments are not currently feasible for charged systems. 27,28 Very recently a detailed quantum chemical calculation based on CASPT2 methods reported an energy splitting of 0.17eV, 29 indicating the importance of correlations in this system.…”

From Mononuclear to Dinuclear: Magnetic Properties of Transition Metal Complexes

“…There is ample evidence that the CAS(9,12) and the basis set specified in the computational information are su ciently large to give close to converged estimates of the optimal CASPT2 distances [175,185,186,214,220].…”

“…Hence, we opt for an indirect comparison with experiment via the transition temperature of the thermal spin crossover T 1/2 [193,195,216]. Following the procedure outlined in previous studies [84,215,[217][218][219][220], we calculated T 1/2 by adding the zero-point energy to the electronic energy of both states and look for the temperature at which the T S product is equal to the enthalpy. The entropy change is dominated by the vibrational contribution but has a small constant contribution due to the di↵erent spin multiplicity of the LS and HS states of 9.13 J/K 1 mol 1 (0.76 cm 1 /K).…”