Sulfonamido tripods: Tuning redox potentials via ligand modifications

Abstract

A series of FeII–OH2 complexes were synthesized with ligands based on the tetradentate sulfonamido tripod N,N',N"-[2,2',2"-nitrilotris(ethane-2,1-diyl)]-tris-({R-Ph}-sulfonamido). These complexes differ by the substituent on the aryl rings and were fully characterized, including their molecular structures via X-ray diffraction methods. All the complexes were five-coordinate with trigonal bipyramidal geometry. A linear correlation was observed between the electronic effects of each ligand, given by the Hammett constants of the para-substituents, and the potential of the FeII/FeIII redox couple, which were determined using cyclic voltammetry. It was found that the range of redox potentials for the complexes spanned approximately 160 mV.

Modulating the Primary and Secondary Coordination Spheres within a Series of CoII—OH Complexes

“…This ligand system has been shown to stabilize metal-aqua complexes with Fe II and Co II ions. 19,42 Additionally, the [MST] 3− platform has been shown to facilitate binding of secondary metal ions, such as Ca 2+ , Sr 2+ , and Ba 2+ ions, through the sulfonamide oxygen atoms. 34,43 Several heterobimetallic complexes supported by the [MST] 3− ligand scaffold with two different transition metal ions bridged by a single hydroxide have also been isolated and characterized, including complexes with Fe II /Fe III , Mn II /Fe III , and Mn II /Mn III cores.…”

Terminal NiII−OH/−OH2 complexes in trigonal bipyramidal geometries derived from H2O

“…The preparation of NMe 4 [Ni II MST(OH 2 )] also followed a reported route from our group (Scheme 2) [38]. Green crystals of this salt suitable for X-ray diffraction were obtained by layering a CH 2 Cl 2 solution of the compound under pentane.…”

“…The solution effective magnetic moment was 3.2 μ B , supporting an S = 1 spin ground state [47]. The FTIR spectrum of NMe 4 [Ni II MST(OH 2 )], recorded as a Nujol mull, revealed a peak at 3241 cm −1 that is assigned to the O–H vibration from the aqua ligand [37,38]. …”

“…1B) is a sulfonamide-based tripodal ligand that can stabilize hydroxido or aqua ligands through intramolecular H-bonds involving the O–H group and the sulfonamido oxygen atoms [33–35]. In addition, the S=O and mesityl groups in [MST] 3− appear to be bulky enough to help prevent the hydroxido or aqua ligand from bridging [36–38]. …”

Effects of coordination sphere on unusually large zero field splitting and slow magnetic relaxation in trigonally symmetric molecules

“…2 25,26. They focused on using these to mimic active sites in biologically relevant proteins and enzymes such as nonheme iron-containing monooxygenases and secondary coordination spheres in metalloproteins 25,27,28. In the present work with 3d metals, the steric bulk of the mesityl substituents enforces trigonal monopyramidal geometry with an open axial position.…”