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Factors Influencing the Structural and Magnetic Properties of Octahedral Cobalt(II) and Iron(II) Complexes of Terdentate N 3 Schiff Base Ligands
Author(s) -
Handel Robyn W.,
Willms Holger,
Jameson Geoffrey B.,
Berry Kevin J.,
Moubaraki Boujemaa,
Murray Keith S.,
Brooker Sally
Publication year - 2010
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.201000288
Subject(s) - chemistry , cobalt , octahedron , schiff base , pyridine , crystallography , moiety , methylene , alkyl , chelation , ethylene , stereochemistry , medicinal chemistry , crystal structure , inorganic chemistry , organic chemistry , catalysis
The influence of the length of the linking alkyl spacer and of the presence of either a proton or a methyl group, in four related terdentate N 3 Schiff base ligands, on the structures and properties of the resulting iron(II) and cobalt(II) complexes has been investigated. The four ligands were prepared in situ by condensation of 2‐(2‐aminoethyl)pyridine or 2‐(aminomethyl)pyridine with 2‐acetylpyridine ( L1 vs. L3 ) or 2‐formylpyridine ( L2 vs. L4 ). Hence they comprised a mixture of a relatively rigid chelate with a 2‐iminopyridyl moiety, comparable to bipyridine coordination, and a more flexible chelate containing the –(CH 2 ) n – spacer. Four iron(II) complexes, [Fe( L1 ) 2 ](BF 4 ) 2 ( 1 ), [Fe( L2 ) 2 ](BF 4 ) 2 ( 2 ), [Fe( L3 ) 2 ](BF 4 ) 2 ( 3 ), [Fe( L4 ) 2 ](BF 4 ) 2 ( 4 ), were obtained whereas only in the case of the two ethylene (i.e. not methylene) spaced ligands could pure cobalt(II) complexes, [Co( L1 ) 2 ](BF 4 ) 2 ( 5 ), [Co( L2 ) 2 ](BF 4 ) 2 ( 6 ), be obtained. The 1 H NMR spectra confirmed that in MeCN 1 – 4 are diamagnetic whereas 5 and 6 are paramagnetic. X‐ray structure determinations of the ethylene‐linked complexes, 1 , 5 and 6 , revealed distorted octahedral geometries due to chelate ring restrictions. The M–N distances were typical for high‐spin cobalt(II) ( 5 and 6 ) and for low‐spin iron(II) ( 1 ). The magnetic data on 5 and 6 are typical of those expected for distorted octahedral high‐spin d 7 species; fitting attempts have yielded zero‐field splitting and low symmetry ligand field parameters. A metal‐centred M 2+/3+ redox wave and ligand‐based reduction processes were observed for 1 – 6 in MeCN. The metal‐centred redox potential (Fe: 1 0.59, 2 0.68, 3 0.58, 4 0.70 V; Co: 5 0.03, 6 0.09 V vs. Fc/Fc + ) was influenced much more strongly by the presence of the proton vs. methyl group (Fe: shift of 0.09–0.12 V, Co: shift of 0.06 V) than by the bridging methylene vs. ethylene group (Fe: shift of 0.01–0.02 V).