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A Comprehensive Study on Triplesalen‐Based [Mn III 6 Fe III ] 3+ and [Mn III 6 Fe II ] 2+ Complexes: Redox‐Induced Variation of Molecular Magnetic Properties
Author(s) -
Hoeke Veronika,
Krickemeyer Erich,
Heidemeier Maik,
Theil Hubert,
Stammler Anja,
Bögge Hartmut,
Weyhermüller Thomas,
Schnack Jürgen,
Glaser Thorsten
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201300400
Subject(s) - chemistry , dication , crystallography , ligand (biochemistry) , absorption spectroscopy , manganese , mössbauer spectroscopy , ion , biochemistry , physics , receptor , organic chemistry , quantum mechanics
The synthesis and structural, mass spectrometric, FT‐IR, Mössbauer, and UV/Vis spectroscopic, electrochemical, and DC and AC magnetic properties of three [Mn III 6 Fe III ] 3+ (short for [{(talen t Bu 2)Mn III 3 } 2 {Fe III (CN) 6 }] 3+ ) compounds {[Mn III 6 Fe III (MeOH) 6 ]Cl 3 · 11MeOH · H 2 O ( 1a ), [Mn III 6 Fe III (MeOH) 6 ]Cl 3 · 3MeOH · H 2 O ( 1b ), and [Mn III 6 Fe III (MeOH) 6 ](PF 6 ) 2 (OAc) · 11MeOH ( 3 )} and the one‐electron reduced congener [Mn III 6 Fe II (MeOH) 4 ](BPh 4 ) 2 · 3MeOH · toluene ( 2 ) are presented. The half‐wave potential of the Fe III /Fe II couple in [Mn III 6 Fe III/II ] 3+/2+ is E 1/2 = –0.06 V versus Fc/Fc + . The overall molecular structures of the complexes resemble those of the already published [Mn III 6 M c ] 3+ compounds (M c = Cr III , Co III , Mn III , Fe III ). The [Mn III 6 Fe II ] 2+ dication, however, exhibits shorter Mn–N C≡N bonds than the tricationic [Mn III 6 M c ] 3+ complexes, as well as a higher degree of aromaticity of the central benzene ring of the triplesalen ligand. The electronic absorption spectrum of [Mn III 6 Fe II ] 2+ differs considerably from the superimposable spectra of tricationic [Mn III 6 M c ] 3+ complexes in exhibiting lower‐energy ligand field transitions due to stronger π‐donation of the surrounding ligands and weaker absorption features in the 27000–35000 cm –1 region, due to a weaker keto‐enamine character of the central phloroglucinol unit. AC susceptibility measurements indicate single‐molecule magnet (SMM) behavior for 1a and 3 . Analysis of the DC magnetic data ( μ eff vs. T , VTVH) of these compounds by a full‐matrix diagonalization of the spin‐Hamiltonian including isotropic exchange, zero‐field splitting with full consideration of the relative orientation of the D ‐tensors, and Zeeman interaction reveals J Mn,Mn = –1.00 to –1.15 cm –1 ( Ĥ ex = –2 J ij Ŝ i ·Ŝ j ), J Fe,Mn = +0.50 to +0.80 cm –1 , and D Mn = –3.5 cm –1 . These values are similar to those previously found for [Mn III 6 Fe III ][Fe III (CN) 6 ]. For 2 , the simulations indicate very weak antiferromagnetic Mn III –Mn III interactions within the trinuclear triplesalen subunits ( J Mn,Mn (1) = –0.20 cm –1 ) as well as across the central diamagnetic Fe II ion ( J Mn,Mn (2, cis ) = –0.06 cm –1 , J Mn,Mn (2, trans ) = –0.18 cm –1 ), whereas D Mn = –3.5 cm –1 . The J Mn,Mn (1) coupling in 2 is much less antiferromagnetic than in the tricationic [Mn III 6 M c ] 3+ compounds; this is interpreted in terms of a stronger ferromagnetic contribution to the exchange interaction due to more efficient spin‐polarization through the central benzene ring, the aromatic nature of which is more pronounced.