The Effect of Ligand Charge on the Coordination Geometry of an Fe(III) Ion:  Five- and Six-Coordinate Fe(III) Complexes of Tris(2-benzimidazolylmethyl)amine

Abstract

By using the tripodal tetradentate ligand tris(2-benzimidazolylmethyl)amine (H(3)ntb), which can have several charge states depending on the number of secondary amine protons, mononuclear octahedral and dinuclear trigonal bipyramidal Fe(III) complexes were prepared. The reaction of mononuclear octahedral [Fe(III)(H(3)ntb)Cl(2)]ClO(4), 1, with 3 equiv of sec-butylamine in methanol led to the formation of mononuclear cis-dimethoxo octahedral Fe(III)(H(2)ntb)(OMe)(2), 2. One equivalent of the sec-butylamine was used to generate the monoanionic H(2)ntb(-) ligand where one of the three amines in the benzimidazolyl groups was deprotonated. The remaining 2 equiv were used to generate two methoxides that were coordinated to the octahedral Fe(III) ion in a cis fashion as demonstrated by the chlorides in 1. Reaction of 1 with excess (7 equiv) sec-butylamine generated the doubly deprotonated dianionic Hntb(2-) that stabilized the dinuclear mu-oxo Fe(III)(2)O(Hntb)(2), 3, adopting a five-coordinate trigonal bipyramidal geometry. The magnetic data for 3 are consistent with the antiferromagnetically coupled Fe(III) (S = 5/2) sites with the coupling constant J = -127 cm(-1).

Iron(III) Complexes with the Ligand N′,N′‐Bis[(2‐pyridyl)methyl]ethylenediamine (uns‐penp) and Its Amide Derivative N‐Acetyl‐N′,N′‐bis[(2‐pyridyl)methyl]ethylenediamine (acetyl‐uns‐penp)

“…Such dinuclear complexes are thermodynamically favoured in the presence of water and many examples have been reported in the literature. [62][63][64][65][66][67][68][69][70][71][72] With regard to previous results it is possible that the carboxamido group of the ligand already undergoes a very weak interaction with the metal centre and is not truly sp 2 hybridised, however is not yet deprotonated. [13] Furthermore, two weak transitions occur at 580 and 920 nm which are typical for catecholateiron()-CT transitions and indicate the presence of a low concentration of the desired mononuclear substrate adduct.…”

Asymmetrically Dibridged Diiron(III) Complexes with Aminebis(phenoxide)‐Based Ligands for a Magnetostructural Study

“…Accordingly, the Fe(1)-O(40) bond length is shorter for 3 [1.912(2) Å] than the corresponding Fe III -O bonds in 1 and 2 and falls in the range of bond lengths previously determined for terminally bound methoxides in structurally characterised Fe III complexes. [13] The phenolates O (15) The asymmetric unit of 4 consists of two discrete crystallographically independent dinuclear monoanions and two triethylammonium monocations as well as two solvent molecules of crystallisation. The metrical parameters for the two crystallographically independent molecules in the anion observed for 4 are very similar and only one ORTEP diagram is shown ( Figure 2); selected bond lengths and angles are summarised in Table 2 ).…”

Crystal structure of bis[1,3-bis(benzimidazol-2-yl)benzene]- dichlorocadmium(II), Cd(C20H14N4)2Cl2

“…The most feasible strategy used to design and construct such complexes is to select suitable polyfunctional ligands and the metal centers that enable the control of the structure [7]. Benzimidazole, having two potential coordinating N-donor atoms, can coordinate metal ions in diverse modes and provide potential identified sites of hydrogen bonds and p···p stacking interactions to form high dimensional frameworks [8], as in the neutral ligands 2,2-bibenzimidazole [9], tris(2-benzimidazolylmethyl)amine [10], and 1,3,5-tri(2-benzimidazolyl)benzene [11]. As for the metal centers, compounds of the d 10 transition metals such as Cd(II) and Zn(II) have been found to be significant high transparency in the UV region and fluorescence potency not only in the solution but also in the solid state [12].…”