A Series of Copper Complexes of a Dinucleating Bis(tetradentate) Nitrogen Ligand: Synthesis, Structural, Spectroscopic, Electrochemical, and Magnetic Characterization

Abstract

The dinucleating ligand "susan" [4,7-dimethyl-1,1,10,10-tetra(2-pyridylmethyl)-1,4,7,10-tetraazadecane] has been used for the synthesis of a series of dinuclear Cu II complexes with varying exogenous ligands: [(susan){Cu(MeCN)} 2 ]-(ClO 4 ) 4 , [(susan){CuCl} 2 ]Cl 2 , [(susan){CuBr} 2 ]Br 2 , [(susan){Cu(μ-OH)Cu}](ClO 4 ) 3 , and [(susan){Cu(μ-OH)Cu}](PF 6 ) 3 . In the solid state, the Cu II ions are trigonal-bipyramidally coordinated in [(susan){Cu(μ-OH)Cu}] 3+ , whereas they are in a square-pyramidal environment in the other complexes although mononuclear Cu II complexes are trigonal-bipyramidal. In solution, all complexes are trigonal-bipyramidal; only [(susan){Cu(MeCN)} 2 ] 4+ is distorted even in solution. The UV/Vis spectra exhibit unique charge-transfer (CT) transitions, which make them easy to iden-[a] 3571 [a] X = N5, Cl1, Br1, or O3. [b] Y = N45, Cl2, Br2, or O3. [c] As there are two half molecules in the asymmetric unit, there are two different Cu···Cu distances: Cu1···Cu1′, Cu2···Cu2′.

Molecular and Electronic Structures of a Series of Dinuclear CoII Complexes Varied by Exogeneous Ligands: Influence of π‐Bonding on Redox Potentials

“…In the analogous dinuclear Cu II complexes, the same trend has been observed. [58] A significant intermolecular interaction is only observed in the crystal structure of [(susan)-{Co II Cl} 2 ](ClO 4 ) 2 • 2MeOH. Two pyridine rings (pyridine with N4 and pyridine with N43 of the adjacent complex) form a π-πinteraction (Figure S2), which is not as well defined for [(susan)-{Co II Br} 2 ](ClO 4 ) 2 .…”

“…[46][47][48][49] One example is the ligand susan (susan = 4,7-dimethyl-1,1,10,10-tetra(2-pyridylmethyl)-1,4,7,10tetraazadecane), [46] that can be regarded as a dinucleating version of the ligand Me 2 -uns-penp [50][51][52] or of the family of tpabased ligands although one pyridine is formally substituted by one tert-amine (Scheme 1). Dinuclear iron [46][47][48][53][54][55][56][57] and copper [58] complexes of the ligand susan have already been investigated to mimic reactive intermediates in the catalytic cycles of dinuclear metalloenzymes and their reactivity. The ligand susan provides a flexible coordination that allows various bridging modes, [47,48] which can be interconverted on a fast time-scale [55] as it is required for an efficient catalysis.…”

A Dinucleating Ligand System with Varying Terminal Donors to Mimic Diiron Active Sites

“…In order to mimic the carboxylate-rich coordination in many diiron metalloenzymes, we synthesized the ligand H 4 julia. [45,46] The pyridine donors in susan/susan Me [45,47,48] reflect the coordi-nation environment in the plethora of diiron model complexes synthesized with tpa-based ligands. [49][50][51][52][53][54][55][56][57][58][59][60][61] On the other hand, the phenolates in H 4 hilde Me 2 [45] have been chosen to increase the electron density by the strong σ-and π-donating phenolate ligands that should facilitate the oxidation to high-valent species.…”

Reactivity Differences for the Oxidation of FeIIFeII to FeIII(µ‐O)FeIII Complexes Caused by Pyridyl versus 6‐Methyl‐Pyridyl Ligands

“…However, although these complexes exhibit low redox potentials for oxidation, the oxidations are ligand‐centered leading to coordinated phenoxyl radicals and the oxidized dinuclear complexes decay into mononuclear fragments , . Thus, we have developed a dinucleating bis(tetradentate) ligand system to coordinate a {Fe(µ‐O) 2 Fe} core (Schemeà) employing different terminal donors (carboxylates, phenolates, and pyridines) , , . The strong electron‐donating character of the bis‐µ‐oxo bridge should enable the oxidation to high‐valent species.…”