Modulating the Primary and Secondary Coordination Spheres within a Series of Co^II—OH Complexes

Abstract

The interplay between the primary and secondary coordination spheres is crucial to determining the properties of transition metal complexes. To examine these effects, a series of trigonal bipyramidal Co–OH complexes have been prepared with tripodal ligands that control both coordination spheres. The ligands contain combination of either urea or sulfonamide groups that control the primary coordination sphere through anionic donors in the trigonal plane and the secondary coordination sphere through intramolecular hydrogen bonds. Variations in the anion donor strengths were evaluated using electronic absorbance spectroscopy and a qualitative ligand field analysis to find that deprotonated urea donors are stronger field ligands than deprotonated sulfonamides. Structural variations were found in the CoII–O bond lengths that range from 1.953(4) to 2.051(3) Å; this range in bond lengths were attributed to the differences in the intramolecular hydrogen bonds that surround the hydroxido ligand. A similar trend was observed between the hydrogen bonding networks and the vibrations of the O–H bonds. Attempts to isolate the corresponding CoIII–OH complexes were hampered by their instability at room temperature.

Manganese–Hydroxido Complexes Supported by a Urea/Phosphinic Amide Tripodal Ligand

“…18 Central to the syntheses is the diurea compound, 1,1′-((2aminoethyl)azanediyl)bis(ethane-2,1-diyl))bis(3-( tert- butyl)urea which is combined in the final step with diphenylphosphinic chloride in THF and excess Et 3 N. Precipitation of the ammonium chloride salt was observed immediately, and H 5 pout was isolated as a white solid in 85% yield after purification.…”

“…Similar structural results were found in Co–OH complexes and emphasized the structural effects of the H-bonds within the secondary coordination sphere. 18 Notice also potassium ion does not interact with the Mn–OH unit in the lattice of K[Mn III H 2 pout(OH)]; it only interact with the carbonyl groups of the ureas which are pointed away from the hydroxido ligand (Figure 3D). …”

“…3,7–17 However, there are fewer examples that utilize a mixture of H-bond donors/acceptors to target a specific type of M–L unit. 18–21 …”

“…31–34 Recently, hybrid tripods were introduced that contain both urea and sulfonamido groups to vary the intramolecular H-bonding network that surrounds Co–OH units (Figure 1C). 18 These studies showed that deprotonated sulfonamido ligands are useful H-bond acceptors; however, they do not provide a sufficient primary coordination sphere to stabilize monomeric M–OH complexes with oxidation states greater than 3+.…”

Mononuclear complexes of a tridentate redox-active ligand with sulfonamido groups: structure, properties, and reactivity

“…1 ), which we and others have shown can produce metal complexes with diverse structures and functions. 29 – 41 For this study, we have incorporated sterically encumbering triisopropylbenzene groups to support the formation of a coordinatively unsaturated monomeric Fe II complex. We demonstrated that the metal center remains accessible to endogenous ligands by producing bipyridine adducts whose oxidative properties we have also defined.…”