Magnetic, electrochemical and spectroscopic properties of iron(iii) amine–bis(phenolate) halide complexes

Abstract

Eight new iron(III) amine-bis(phenolate) complexes are reported. The reaction of anhydrous FeX(3) salts (where X = Cl or Br) with the diprotonated tripodal tetradentate ligands 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L1, 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L2, and 2-methoxyethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L3, 2-methoxyethylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L4 produces the trigonal bipyramidal iron(III) complexes, L1FeCl (1a), L1FeBr (1b), L2FeCl (2a), L2FeBr (2b), L3FeCl (3a), L3FeBr (3b), L4FeCl (4a), and L4FeBr (4b). All complexes have been characterized using electronic absorption spectroscopy, cyclic voltammetry and room temperature magnetic measurements. Variable temperature magnetic data were acquired for complexes 2b, 3a and 4b. Variable temperature Mössbauer spectra were obtained for 2b, 3a and 4b. Single crystal X-ray molecular structures have been determined for proligand H(2)L4 and complexes 1b, 2b, and 4b.

Synthesis<span> and </span>structural<span> characterization of a novel amine-bis(phenolate)ligand</span>

“…1), is shown with selected bond lengths and angles collected in the corresponding figure caption, and relevant experimental parameters are presented in Table 1. This ligand exhibits intramolecular hydrogen bonding between phenol and amine functional groups, as has been observed for related amine bis(phenols) [1][2][3][4]. Heavy atom (O…N) interatomic distances are consistent with the presence of hydrogen bonds, and are within the range of those reported for similar amine bis(phenolate) ligands.…”

Iron(III) Contrast Agent Candidates for MRI: a Survey of the Structure–Effect Relationship in the Last 15 ­Years of Studies

“…In the literature, data are often provided for a pure complex at a given pH, whereas other reports relate to complexes formed in situ. [77] All of these issues in fact lead, in practice, to difficulty in comparing the presented values. Moreover, these measurements are additionally affected by the presence of proteins and other electrolytes.…”

“…Because aminophenols are good π-donors, their iron(III) complexes are relatively weak Lewis acids and therefore exhibit lower affinity to ROS. [77] Additionally, according to Martell, the basic character of the alkylamine moiety is one of the factors maintaining the third oxidation state and lowering the redox potential of the chelated iron. [62] Finally, the hydrophobic, aromatic surroundings in the close neighborhood of the central atom do not attract any polar species.…”

Amino-phenol complexes of Fe(III) as promising T1 accelerators

“…This gap leads to high relaxivities, not yet reported for iron compounds, but could also be a pitfall. Kozak showed the irreversible character of the redox processes for Fe(III)-N,O,N complexes, which is more likely connected with ligand electron transfer (Dean et al, 2012). On the other hand, Schmitt showed instability seen on MS spectra for respective Mn-salan complexes (Schmitt et al, 2002) which was not observed in our models.…”

“…Successful bioactivation of N,O,N-aminobis(phenol) ligands (Kuz´nik et al, 2012) is currently being investigated for real iron complexes in steps. Aminophenol complexes, both with N,O,N-motifs and those based on a salan skeleton, exhibit poor redox activity which can additionally be tuned by the character of the ligand (Dean et al, 2012;Schmitt et al, 2002). Therefore, we investigated naphthalene derivatives, triphenol and diphenolpyridine systems as interesting T 1 accelerators of water protons.…”