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The Relationship between the Structure and Magnetic Properties of Bioinspired Iron( ii/iii ) Complexes with Schiff‐Base‐Like Chelate Ligands, Part I: Complexes with Dianionic [N 4 ] Macrocycles
Author(s) -
Weber Birgit,
Käpplinger Indira,
Görls Helmar,
Jäger ErnstG.
Publication year - 2005
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.200400759
Subject(s) - chemistry , crystallography , spin crossover , antiferromagnetism , octahedron , magnetic susceptibility , ligand (biochemistry) , dabco , mössbauer spectroscopy , spin states , ground state , intermolecular force , spin transition , octane , stereochemistry , inorganic chemistry , molecule , crystal structure , biochemistry , physics , receptor , organic chemistry , quantum mechanics , condensed matter physics
The molecular structures and the spin ground‐state of the iron( ii/iii ) complexes Fe1 , Fe2 and Fe3 , which contain dianionic macrocyclic [N 4 ] ligands derived from substituted acetylacetaldehydes and 1,2‐diamines, have been investigated by X‐ray analysis and temperature‐dependent susceptibility measurements, respectively. The iron( II ) complexes Fe II 1 (which is dimeric by intermolecular coordination of one peripheral carbonyl group), Fe II 1MeOH , (Fe II L) 2 dabco (L = 1 , 2 , 3 ; dabco = 1,4‐diazabicyclo[2.2.2]octane) and the iron( III ) complex Fe III 1Cl are pentacoordinate and have an intermediate‐spin ground‐state at room temperature ( S = 1 for Fe II ; S = 3/2 for Fe III ). The intermediate‐spin state was confirmed by DFT‐MO calculations for Fe II 1MeOH and Fe III 1Cl and is also in agreement with the Mössbauer data of Fe II 1 and ESR measurements of Fe III 1Cl . The iron centre in Fe II 2 is nearly square‐planar and shows a strong decrease of the magnetic moment below T ≈ 250 K. This is probably due to an S = 0 to S = 1 spin‐crossover or, more likely, to intermolecular antiferromagnetic interactions (shortest Fe–Fe distance of 3.4 Å). A new pair of octahedral iron( ii/iii ) complexes with an N‐heterocyclic axial ligand, Fe II 3(Py) 2 /[ Fe III 3(Py) 2 ]PF 6 , could be crystallised. In contrast to the previously described pairs Fe II 1(Him) 2 / [ Fe III 1(Him) 2 ]PF 6 and Fe II 2Py 2 /[ Fe III 2Py 2 ]ClO 4 , the orientation of the planes of the axial ligands is nearly independent of the oxidation step of the central atom. Octahedral derivatives with biologically relevant anions as axial ligands have been crystallised for the first time, namely [BzEt 3 N][ Fe III 1(NCS) 2 ], [Et 4 N][ Fe III 2(CN) 2 ](H 2 O) 0.5 , Na[ Fe III 2(NO 2 ) 2 ](MeOH) 2 (H 2 O) 0.5 and [ Fe III 2(NO 2 )OH 2 ](MeOH). The latter shows a magnetic moment of μ eff ≈ 2.85 μ B at room temperature, which decreases to 1.85 μ B at lower temperature. This indicates an incomplete S = 1/2 to S = 3/2 spin‐crossover, which is probably due to the presence of H 2 O as a weak axial ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)