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Quantitative Estimation of Ising‐Type Magnetic Anisotropy in a Family of C 3 ‐Symmetric Co II Complexes
Author(s) -
Mondal Amit Kumar,
Jover Jesús,
Ruiz Eliseo,
Konar Sanjit
Publication year - 2017
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.201702108
Subject(s) - ising model , chemistry , magnetic anisotropy , anisotropy , isostructural , intermolecular force , crystallography , relaxation (psychology) , condensed matter physics , ab initio , ab initio quantum chemistry methods , magnetic field , diamagnetism , computational chemistry , magnetization , physics , molecule , crystal structure , quantum mechanics , psychology , social psychology , organic chemistry
In this paper, the influence of the structural and chemical effects on the Ising‐type magnetic anisotropy of pentacoordinate Co II complexes has been investigated by using a combined experimental and theoretical approach. For this, a deliberate design and synthesis of four pentacoordinate Co II complexes [Co(tpa)Cl] ⋅ ClO 4 ( 1 ), [Co(tpa)Br] ⋅ ClO 4 ( 2 ), [Co(tbta)Cl] ⋅ (ClO 4 ) ⋅ (MeCN) 2 ⋅ (H 2 O) ( 3 ) and [Co(tbta)Br] ⋅ ClO 4 ( 4 ) by using the tripodal ligands tris(2‐methylpyridyl)amine (tpa) and tris[(1‐benzyl‐1 H ‐1,2,3‐triazole‐4‐yl)methyl]amine) (tbta) have been carried out. Detailed dc and ac measurements show the existence of field‐induced slow magnetic relaxation behavior of Co II centers with Ising‐type magnetic anisotropy. A quantitative estimation of the zero‐field splitting (ZFS) parameters has been effectively achieved by using detailed ab initio theory calculations. Computational studies reveal that the wavefunction of all the studied complexes has a very strong multiconfigurational character that stabilizes the largest m s =±3/2 components of the quartet state and hence produce a large negative contribution to the ZFS parameters. The difference in the magnitudes of the Ising‐type anisotropy can be explained through ligand field theory considerations, that is, D is larger and negative in the case of weak equatorial σ‐donating and strong apical π‐donating ligands. To elucidate the role of intermolecular interactions in the magnetic relaxation behavior between adjacent Co II centers, a diamagnetic isostructural Zn II analog ( 5 ) was synthesized and the magnetic dilution experiment was performed.