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Download fileExperimental and Theoretical Investigations of Magnetic Exchange Pathways in Structurally Diverse Iron(III) Schiff-Base Complexes
journal contribution
posted on 2015-09-08, 00:00 authored by Radovan Herchel, Ivan Nemec, Marek Machata, Zdeněk TrávníčekThe
synthesis, and the structural and magnetic properties, of the following
new iron(III) Schiff base complexes with the {O′,N,O″}-chelating
ligand H2L (2-hydroxyphenylsalicylaldimine) are reported:
K[FeL2]·H2O (1), (Pr3NH)[FeL2]·2CH3OH (2), [FeL(bpyO2) (CH3OH)][FeL2]·CH3OH (3), [Fe2L3(CH3OH)]·2CH3OH·H2O (4), and [{Fe2L2}(μ–OH)2{FeL(bpyO2)}2][BPh4]2·2H2O
(5), where Pr3NH+ represents the
tripropylammonium cation and bpyO2 stands for 2,2′-bipyridine-N-dioxide. A thorough density functional theory (DFT) study
of magnetic interactions (the isotropic exchange) at the B3LYP/def-TZVP
level of theory was employed, and calculations have revealed superexchange
pathways through intramolecular/intermolecular noncovalent contacts
(π–π stacking, C–H···O and
O–H···O hydrogen bonds, diamagnetic metal cations)
and/or covalent bonds ((μ-OPh, μ-OH) or bis(μ-OPh) bridging modes), which helped us to postulate trustworthy
spin Hamiltonians for magnetic analysis of experimental data. Within
the reported family of compounds 1–5, the mediators of the antiferromagnetic exchange can be sorted by
their increasing strength as follows: π–π stacking
(JDFT = −0.022 cm–1/Jmag = −0.025(4) cm–1 in 2) < C–H···O contacts and
π–π stacking (JDFT =
−0.19 cm–1/Jmag = −0.347(9)cm–1 in 1) <
O–H···O hydrogen bonds (JDFT = −0.53 cm–1/Jmag = −0.41(1) cm–1 in 3) < bis(μ-OPh) bridge (JDFT = −13.8 cm–1/Jmag = −12.3(9) cm–1 in 4) < (μ-OPh, μ-OH) bridge (JDFT = −18.0 cm–1/Jmag = −17.1(2) cm–1 in 5), where JDFT and Jmag are the isotropic exchange parameters derived
from DFT calculations, and analysis of the experimental magnetic data,
respectively. The good agreement between theoretically calculated
and experimentally derived isotropic exchange parameters suggests
that this procedure is applicable also for other chemical and structural
systems to interpret magnetic data properly.