Volume 24, Issue 71 p. 18988-18997
Full Paper

Light-Induced Spin Transitions in Copper-Nitroxide-Based Switchable Molecular Magnets: Insights from Periodic DFT+U Calculations

Dr. Rocío Sánchez-de-Armas

Dr. Rocío Sánchez-de-Armas

Departamento de Química Física, Universidad de Sevilla, 41012 Spain

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Dr. Norge Cruz Hernández

Dr. Norge Cruz Hernández

Departamento de Física Aplicada I, Escuela Politécnica Superior, Universidad de Sevilla, 41011 Spain

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Dr. Carmen J. Calzado

Corresponding Author

Dr. Carmen J. Calzado

Departamento de Química Física, Universidad de Sevilla, 41012 Spain

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First published: 07 September 2018
Citations: 4

Graphical Abstract

Spinning around: The density of states (DOS) of Cu(hfac)2LPr gives insights on the states potentially accessible by electronic transitions in the UV/Vis range that could be involved in the photoswitching process, mainly, LMCT processes between the nitronyl-nitroxide and the Cu 3d bands. The similarities found in the DOS for the three considered compounds suggest the possibility of light-induced spin switching for other members of the breathing crystal family.

Abstract

The electronic structure and magnetic interactions of three members of the breathing crystal Cu(hfac)2LR family (hfac=hexafluoroacetylacetonato, LR=pyrazole-substituted nitronyl nitroxides with R=Me, Et, Pr, iPr, Bu ), mainly Cu(hfac)2LPr (1), Cu(hfac)2LBu0.5 C8H18 (2) and Cu(hfac)2LBu0.5 C8H10 (3), have been analyzed by means of periodic plane-wave based DFT+U calculations. These CuII-nitroxide based molecular magnets display thermally and optically induced switchable behavior and light-induced excited spin state trapping phenomena. The calculations confirm the presence of temperature-dependent exchange interaction within the spin triads formed by the nitroxide-copper(II)-nitroxide units, in line with the changes observed in the effective magnetic moment. Moreover, they quantify the interchain interaction mediated by the terminal nitroxide group of two spin triads in neighboring polymer chains. This interaction competes with the exchange interaction within the spin triads at high temperature, and introduces 1D exchange channels that do not coincide with the polymeric chains. The density of states reveal that the low-lying conduction states potentially involved in the UV/Vis transitions are located on the nitroxide radicals, the hfac groups and the Cu atoms. Then, the density of states is almost independent of the solvent and the R group. This suggests the possibility of light-induced spin switching for other members of this family. The 500 nm band of the low-temperature phase can be ascribed to a ligand-to-metal charge transfer transition between the nitroxide and Cu bands.

Conflict of interest

The authors declare no conflict of interest.