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Light‐Induced Spin Transitions in Copper‐Nitroxide‐Based Switchable Molecular Magnets: Insights from Periodic DFT+U Calculations
Author(s) -
SánchezdeArmas Rocío,
Cruz Hernández Norge,
Calzado Carmen J.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201803962
Subject(s) - nitroxide mediated radical polymerization , chemistry , crystallography , exchange interaction , spin (aerodynamics) , density functional theory , spin transition , excited state , antiferromagnetism , ferromagnetism , chemical physics , condensed matter physics , computational chemistry , polymer , polymerization , atomic physics , physics , radical polymerization , organic chemistry , thermodynamics
The electronic structure and magnetic interactions of three members of the breathing crystal Cu(hfac) 2 L R family (hfac=hexafluoroacetylacetonato, L R =pyrazole‐substituted nitronyl nitroxides with R=Me, Et, Pr, i Pr, Bu ), mainly Cu(hfac) 2 L Pr ( 1 ), Cu(hfac) 2 L Bu ⋅ 0.5 C 8 H 18 ( 2 ) and Cu(hfac) 2 L Bu ⋅ 0.5 C 8 H 10 ( 3 ), have been analyzed by means of periodic plane‐wave based DFT+U calculations. These Cu II ‐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.