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Lanthanide Tetrazolate Complexes Combining Single‐Molecule Magnet and Luminescence Properties: The Effect of the Replacement of Tetrazolate N 3 by β‐Diketonate Ligands on the Anisotropy Energy Barrier
Author(s) -
Jiménez JuanRamón,
DíazOrtega Ismael F.,
Ruiz Eliseo,
Aravena Daniel,
Pope Simon J. A.,
Colacio Enrique,
Herrera Juan Manuel
Publication year - 2016
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.201601457
Subject(s) - crystallography , chemistry , ligand (biochemistry) , lanthanide , luminescence , molecule , phenanthroline , coordination sphere , magnetic susceptibility , magnetic anisotropy , ion , stereochemistry , crystal structure , magnetization , materials science , magnetic field , receptor , biochemistry , optoelectronics , organic chemistry , physics , quantum mechanics
Three new sets of mononuclear Ln III complexes of general formulas [LnL 3 ] ⋅ CH 3 OH [Ln III =Yb ( 1 ), Er ( 2 ), Dy ( 3 ), Gd ( 4 ), and Eu ( 5 )], [LnL 2 (tmh)(CH 3 OH)] ⋅ n H 2 O ⋅ m CH 3 OH [Ln III =Yb ( 1 b ), Er ( 2 b ), Dy ( 3 b ), Gd ( 4 b )], and [LnL 2 (tta)(CH 3 OH)] ⋅ CH 3 OH [Ln III =Yb ( 1 c ), Er ( 2 c ), Dy ( 3 c ), Gd ( 4 c )] were prepared by the reaction of Ln(CF 3 SO 3 ) ⋅ n H 2 O salts with the tridentate ligand 2‐(tetrazol‐5‐yl)‐1,10‐phenanthroline (HL) and, for the last two sets, additionally with the β‐diketonate ligands 2,2,6,6‐tetramethylheptanoate (tmh) and 2‐thenoyltrifluoroacetonate (tta), respectively. In the [LnL 3 ] ⋅ CH 3 OH complexes the Ln III ions are coordinated to three phenanthroline tetrazolate ligands with an LnN 9 coordination sphere. Dynamic ac magnetic measurements on 1 – 3 reveal that these complexes only exhibit single‐molecule magnet (SMM) behavior when an external dc magnetic field is applied, with U eff values of 11.7 K ( 1 ), 16.0 K ( 2 ), and 20.2 K ( 3 ). When the tridentate phenanthroline tetrazolate ligand is replaced by one molecule of methanol and the β‐diketonate ligand tmh ( 1 b – 3 b ) or tta ( 1 c – 3 c ), a significant increase in U eff occurs and, in the case of the Dy III complexes 3 b and 3 c , out‐of‐phase χ′′ signals below 15 and 10 K, respectively, are observed in zero dc magnetic field. CASSCF+RASSI ab initio calculations performed on the Dy III complexes support the experimental results. Thus, for 3 the ground Kramers’ doublet is far from being axial and the first excited state is found to be very close in energy to the ground state, so the relaxation barrier in this case is almost negligible. Conversely, for 3 b and 3 c , the ground Kramers’ doublet is axial with a small quantum tunneling of the magnetization, and the energy difference between the ground and first Kramers’ doublets is much higher, which allows these compounds to behave as SMMs at zero field. Moreover, these calculations support the larger U eff observed for 3 b compared to 3 c . Additionally, the solid‐state photophysical properties of 1 , 2 , 4 , and 5 show that the phenanthroline tetrazolate ligand can act as an effective antenna to sensitize the characteristic Yb III , Er III , and Eu III emissions through an energy‐transfer process.