New unsymmetrical μ -phenoxo bridged binuclear copper(II) complexes

A series of binuclear Cu II complexes [Cu 2 XL] n + having two copper(II) ions bridged by different motifs (X = OH − , MeCO 2 − , or Cl − ) have been prepared using the ligands: H 2 L 1 = 4-methyl-2-[ N -(2-{dimethylamino}ethyl- N ′-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H 2 L 2 = 4-nitro-2-[ N -(2-{dimethylamino}ethyl- N ′-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H 2 L 3 = 4-methyl-2-[ N -(2-{diethylamino}ethyl- N ′-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol and H 2 L 4 = 4-nitro-2-[ N -(2-{diethylamino}ethyl- N ′-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol. The complexes have been characterized by spectroscopic, analytical, magnetic and electrochemical measurements. Cryomagnetic investigations (80–300 K) revealed anti-ferromagnetic exchange between the Cu II ions (−2 J in the range −50 to −182 cm −1 ). The strength of anti-ferromagnetic coupling lies in the order: OAc > OH > Cl. Cyclic voltammetry revealed the presence of two redox couples, assigned to Cu II /Cu II /Cu II /Cu I /Cu I /Cu I . The first reduction potential is sensitive to electronic effects from the aromatic ring substituents and steric effect on the donor nitrogens (side arm) of the ligand systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43853/1/11243_2004_Article_5102817.pd

Synthesis of flexible ligands for assembling two metals in close proximity. Magnetic, electrochemical and spectral properties of binuclear copper (II) complexes with different exogenous bridging motifs

Binuclear Cu II complexes having new flexible heptadentate ligands 2,6-bis{[bis(3,3′- N , N -dimethylaminopropyl)amino]methyl}-4-bromophenol [HL 1 ], 2,6-bis(3,3′- N , N -dimethylaminopropyl)amino]methyl}-4-methylphenol [HL 2 ], and 2,6-bis{[bis(3,3′- N , N -dimethylaminopropyl)amino]methyl}-4-methoxyphenol [HL 3 ], capable of assembling two copper ions in close proximity have been synthesized. Comparisons of the charge-transfer (CT) features, observed in electronic spectra of these complexes, are correlated with the electronic effect on the aromatic ring of the ligand systems. Cyclic voltammetry has revealed the existence of two reduction couples, The first is sensitive to the electronic effects of aromatic ring substituents of the ligand system, shifting to more positive potentials when more electrophilic groups replace the existing substituents. The conproportionation constants ( k con ) for the mixed valent Cu I Cu II complexes have been determined electrochemically. The magnetic susceptibilities of the complexes have been measured over the 70–300 K range and the exchange coupling parameter (−2 J ) determined by a least squares fit of the data which indicates an antiferromagnetic spin exchange (−2 J = 94–172 cm −1 ) between the Cu II ions with bridging units in the order: N 3 ≈ NO 2 > OAc > OH.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43852/1/11243_2004_Article_5095478.pd

A novel discrete dinuclear copper(II)–gadolinium(III) complex derived from a Schiff base ligand [Cu(salbn)Gd(NO 3 ) 3 ·H 2 O] (salbn): N , N ′-butylenebis(salicylideaminato)

The synthesis, X-ray and e.p.r. spectral studies of a 3d–4f couple are described here. The crystal structure of [Cu(salbn)Gd(NO 3 ) 3 ·H 2 O], (2) , salbn = N , N ′-butylenebis(salicylideaminato), has been determined by X-ray crystallography. Compound (2) crystallizes in the monoclinic system, space group p21/n, with a = 9.025(1), b = 22.912(1), c = 12.790(1) Å, β = 99.36(1), Z = 4. The deviations of the four coordinating atoms (O(1)O(2)N(1) and N(2) of salbn and the copper atom is displaced from the plane in spite of the lack of any apical ligand. The gadolinium(III) ion is nine-coordinated by the two oxygen atoms of the salbn moiety, three bidentate nitrate ions and one water molecule. The geometry of Gd III can be described as a square antiprism, in which compound Cu II and Gd III are bridged by the two phenolic oxygens of salbn. The Cu II –Gd III distance is 3.269(1) Å. The bridging core CuO2Gd is a butterfly shape. Significant distortion was observed for the complex having the larger diamino string. The title compound exhibits seven e.s.r. transitions with | D | = 0.0467 cm −1 , which demonstrates the existence of zero field splitting. This outcome indicates that compound (2) consists of a perfectly isolated dinuclear Cu–Gd core and steric bulk alters the dihedral angle in the Cu–O–Gd bridge.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43854/1/11243_2004_Article_5115383.pd

Synthesis, spectral, electrochemical and magnetic properties of new asymmetric dicopper(II) complexes bearing chemically distinct coordination sites

Two new unsymmetrical binucleating ligands, 2-[bis(3- N, N -dimethylaminopropyl)-aminomethyl]-6-[prolin-1-yl)methyl]-4-bromophenol [H 2 L 1 ] and 2-[bis(3- N, N -dimethylaminopropyl)aminomethyl]-6-[prolin-1-yl)methyl]-4-methylphenol [H 2 L 2 ], and their dicopper(II) complexes with different exogenous bridging motifs (OAc, Br and Cl) have been prepared and characterized by spectral, electrochemical, magnetic and e.p.r. studies. Electrochemical studies indicate the presence of two irreversible reduction peaks in the cathodic region. Variable temperature magnetic susceptibility studies of the complexes show that the extent of antiferromagnetic coupling increases in the order: OAc − < Cl − < Br − . Broad isotropic or axial symmetric spectral features are observed in powder e.p.r. spectra of the complexes at 77 K. A comparison of the electrochemical and magnetic behaviour of the complexes derived from the ligands is discussed on the basis of an exogenous bridge as well as the substituent at the para position of the phenolic ring.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43855/1/11243_2004_Article_5272793.pd

Synthesis and conformational analysis of redox-active ferrocenyl-calixarenes

International audienceA novel synthetic approach toward redox-active calixarene-based receptors is described wherein ferrocene fragments have been introduced at the lower rim through anion-binding urea or amide connections. A thorough 1H NMR investigation on a series of calixarene-ferrocene receptors was performed in order to estimate their hydrogen bonding-driven self-association properties and improve our understanding of the correlation between molecular structures and redox properties

Redox control of molecular motions in bipyridinium appended calixarenes.

International audienceA series of redox-responsive architectures featuring two bipyridinium units introduced onto the lower rim of a calixarene skeleton has been synthesized. The redox-triggered intramolecular dimerization of the reduced bipyridiniums has been investigated by electrochemistry, spectroelectrochemistry and by theoretical chemistry. The spectroscopic signature of the intramolecular dimers was found to evolve significantly with the size of the alkyl linker introduced between the calixarene skeleton and the bipyridinium units. On account of experimental data supported by theoretical calculations, these differences have been attributed to the extent of the orbital overlap in the π-dimerized species, involving either four or only two of the pyridine rings of the bipyridinium radical cations stacked in eclipsed or staggered conformations, respectively

Conformational analysis and anion binding properties of ferrocenyl- calixarene receptors

International audienceNovel synthetic approaches toward redox active calixarene-based receptors is described wherein ferrocene fragments have been introduced at the lower rim through anion-binding urea or amide connections. A thorough 1H NMR investigation on macrocycles was performed in order to estimate their hydrogen bonding-driven self-association properties and improve our understanding of the correlation between molecular structures and redox properties. The anion binding properties of these artificial receptors have also been revealed by NMR spectroscopy and thoroughly investigated by electrochemical methods. We especially assessed the importance of the urea-phosphate bonds in the observed electrochemical response upon studying receptors wherein the ferrocene reporters and binding fragments are intimately associated or fully disconnected through a long alkyl chain. The experimental results clearly showed the utmost importance of ion pairing effects in the electrochemical recognition process accounting for most of the transduction signal in organic apolar media

Viologen-based redox-switchable anion-binding receptors

International audienceA series of viologen-based receptors have been synthesized and their anion-binding properties have been investigated by-NMR, UV-visible spectroscopy, electrochemistry and X-ray diffraction analyses. Linking two positively charged viologens through a propyl chain promotes a remarkable chelate-like binding of chlorides revealed by 1H-NMR spectroscopy. Of all the anionic species investigated, only fluoride is detectable by the naked eye and by electrochemical methods. The reduction-triggered formation of a π-dimer from two viologen-based cation radicals was also investigated by electrochemical and spectroelectrochemical methods and by theoretical calculations