Carboxamido Nitrogens Are Good Donors for Fe(III):  Syntheses, Structures, and Properties of Two Low-Spin Nonmacrocyclic Iron(III) Complexes with Tetracarboxamido-N Coordination

Abstract

Two nonmacrocyclic ligands with pyridine and carboxamide nitrogens as donors readily form bis complexes of the type [FeIIIL2]+ in which the Fe(III) centers exhibit preference for coordination to carboxamido nitrogens over pyridine nitrogens. These Fe(III) complexes with deprotonated carboxamido nitrogens are very stable in water.

Change in the Spin State of an FeIII Center upon One N‐to‐O Switch in the Coordination of a 2,6‐Pyridinedicarboxamido Unit: The Effect of Methyl Thioether and Methyl Ether Appendages at the Ligand Periphery

“…Ligands with the 2,6-pyridinedicarboxamide moiety (P stands for the peptide functionality in all abbreviations) pyridine groups (structure iii, Figure 2). [5] The Fe III centers in both of these complexes are low spin, much like the Fe Ϫ , reported by Mukherjee and co-workers. [11] The failure of the pendant pyridine units to bind to the Fe III centers in these complexes is not related to any steric effect, since Py 3 PH 2 gives rise to many [Co(Py 3 P)(L)] ϩ/0 complexes.…”

“…As a result of this Nto-O donor switch around the Fe III center in 1, the complex is high spin, which is in contrast to other similar bis complexes with two bound 2,6-pyridinedicarboxamido units (FeN 6 chromophore and all low spin). [5,11] In order to further substantiate our hypothesis that the steric repulsion among the pendant thioether groups in 1 is responsible for this N-to-O donor switch, we have also synthesized the bis Fe III complex of the tridentate ligand PyPOMeH 2 . The pendant ether groups in (Et 4 N)[Fe(PyPOMe) 2 ] (2) give rise to steric hindrance around the Fe III center much like the crowding in 1.…”

“…[5,6,9,11,15] Recent work in this laboratory has afforded a variety of Fe III complexes based on this tridentate moiety in the first coordination sphere. [5,6,10] For example, coordination of the pentadentate ligand POPyH 4 to Fe III (H represents dissociable amide protons) results in high-spin, seven-coordinate, pentagonal bipyramidal complexes with the entire ligand in the basal plane and with two exogenous axial ligands (structure i, Figure 2). [6] In contrast, the Fe III complex of the similar pentadentate ligand PyPSH 4 is high spin, five-coordinate with a distorted trigonal bipyramidal geometry due to the steric bulk of the thiolato sulfur (structure ii, Figure 2).…”

“…[11] The failure of the pendant pyridine units to bind to the Fe III centers in these complexes is not related to any steric effect, since Py 3 PH 2 gives rise to many [Co(Py 3 P)(L)] ϩ/0 complexes. [16] We believe that formation of the bis complex [Fe(Py 3 P) 2 It is also interesting to note that due to the steric repulsion among the pendant thioether groups in 1, one of the carboxamido groups employs the carbonyl oxygen instead of the carboxamido nitrogen, as a donor atom, resulting in an FeN 5 O chromophore. As a result of this Nto-O donor switch around the Fe III center in 1, the complex is high spin, which is in contrast to other similar bis complexes with two bound 2,6-pyridinedicarboxamido units (FeN 6 chromophore and all low spin).…”

TTF salts of optically pure cobalt pyridine amidates; detection of soluble assemblies with stoichiometry corresponding to the solid state

“…We have analysed the crystal structures of previously reported achiral compounds of this type and note that in several cases extended structures with different topologies are present; 1D chains 19,22 and ribbons 23 , 2D layers 23 and 0D Similarly there is no extended coordination structure but close contacts are observed between the potassium counterions and the stereogenic methyl groups of the neighbouring complex e.g. K(1) -H(86C) = 2.817 Å.…”