Improving the emission quantum yield in dinuclear Eu(III) and Tb(III) complexes with 2-fluorobenzoate.

The reaction of Ln(NO3)2·6H2O salts (Ln = Eu and Tb) with an excess of 2-fluorobenzoic acid (H-2FBz) in ethanol/water mixture allows the isolation of dinuclear compounds of formula [Ln2(-2FBz)4(2FBz)2(H-2FBz)2(H2O)2] (Ln...

Behavior of beryllium halides and triflate in acetonitrile solutions

The solution behavior of beryllium halides and triflate in acetonitrile was studied by NMR, IR and Raman spectroscopy. Thereby mononuclear units [(MeCN)2BeX2] (X = Cl, Br, I, OTf) were identified as dominant species in these solutions. The solid state structure of [(MeCN)2Be(OTf)2] has been determined by X-ray diffraction. If only one equivalent of MeCN is used the dinuclear compounds [(MeCN)BeX2]2 (X = Cl, Br, I) are formed. Partial halide and triflate dissociation into the monomeric complexes as well as the formation of hetero-halide complexes [(MeCN)2BeClBr], [(MeCN)2BeClI] and [(MeCN)2BeBrI] was observed.

Selective Formation, Reactivity, Redox and Magnetic Properties of MnIII and FeIII Dinuclear Complexes with Shortened Salen-Type Schiff Base Ligands

The reactivity of the shortened salen-type ligands H3salmp, H2salmen and H2sal(p-X)ben with variable para-substituent on the central aromatic ring (X = tBu, Me, H, F, Cl, CF3, NO2) towards the trivalent metal ions manganese(III) and iron(III) is presented. The selective formation of the dinuclear complexes [M2(μ-salmp)2], M = Mn (1a), Fe (2a), [M2(μ-salmen)2(μ-OR)2)], R = Et, Me, H and M = Mn (3a–c) or Fe (4a–c), and (M2(μ-sal[p-X]ben)2(μ-OMe)2), X = tBu, Me, H, F, Cl, CF3, NO2 and M = Mn (5a–g) or Fe (6a–g), could be identified by reaction of the Schiff bases with metal salts and the base NEt3, and their characterization through elemental analysis, infrared spectroscopy, mass spectrometry and single-crystal X-ray diffraction of 2a·2AcOEt, 2a·2CH3CN and 3c·2DMF was performed. In the case of iron(III) and H3salmp, when using NaOH as a base instead of NEt3, the dinuclear complexes [Fe2(μ-salmp)(μ-OR)(salim)2], R = Me, H (2b,c) could be isolated and spectroscopically characterized, including the crystal structure of 2b·1.5H2O, which showed that rupture of one salmp3− to two coordinated salim− ligands and release of one salH molecule occurred. The same hydrolytic tendency could be identified with sal(p-X)ben ligands in the case of iron(III) also by using NEt3 or upon standing in solution, while manganese(III) did not promote such a C–N bond breakage. Cyclic voltammetry studies were performed for 3b, 4b, 5a and 6a, revealing that the iron(III) complexes can be irreversibly reduced to the mixed-valence FeIIFeIII and FeII2 dinuclear species, while the manganese(III) derivatives can be reversibly oxidized to either the mixed-valence MnIIIMnIV or to the MnIV2 dinuclear species. The super-exchange interaction between the metal centers, mediated by the bridging ligands, resulted in being antiferromagnetic (AFM) for the selected dinuclear compounds 3b, 4b, 5a, 5e,5f, 6a and 6e. The coupling constants J (–2JŜ1·Ŝ2 formalism) had values around −13 cm−1 for manganese(III) compounds, among the largest AFM coupling constants reported so far for dinuclear MnIII2 derivatives, while values between −3 and −10 cm−1 were obtained for iron(III) compounds.

Redox-Modulations of Photophysical and Single-molecule Magnet Properties in Ytterbium Complexes Involving Extended-TTF Triads

The reaction between the 2,2’-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate triad (H2SQ) and the metallo-precursor [Yb(hfac)3]⋅2H2O led to the formation of a dinuclear coordination complex of formula [Yb2(hfac)6(H2SQ)]⋅0.5CH2Cl2 (H2SQ-Yb). After chemical oxidation of H2SQ in 2,2’-cyclohexa-2,5-diene-1,4-diylidenebis(4,7-di-tert-butyl-1,3-benzodithiole-5,6-dione (Q), the latter triad reacted with the [Yb(hfac)3]⋅2H2O precursor to give the dinuclear complex of formula [Yb2(hfac)6(Q)] (Q-Yb). Both dinuclear compounds have been characterized by X-ray diffraction, DFT optimized structure and electronic absorption spectra. They behaved as field-induced Single-Molecule Magnets (SMMs) nevertheless the chemical oxidation of the semiquinone to quinone moieties accelerated by a factor of five the relaxation time of the magnetization of Q-Yb compared to the one for H2SQ-Yb. The H2SQ triad efficiently sensitized the YbIII luminescence while the chemical oxidation of H2SQ into Q induced strong modification of the absorption properties and thus a quenching of the YbIII luminescence for Q-Yb. In other words, both magnetic modulation and luminescence quenching are reached by the oxidation of the protonated semiquinone into quinone.

Luminescent properties of a 3,5-diphenylpyrazole bridged Pt(ii) dimer

We report the synthesis, electrochemistry, photophysics and electroluminescence of a highly luminescent pyrazolate-bridged platinum(ii) complex. Light-emitting electrochemical cells (LEECs) of this dimer complex were among the brightest and most efficient LEECs from dinuclear compounds to date.

Discrete mononuclear and dinuclear compounds containing a MoO22+ core and 4-aminobenzhydrazone ligands: synthesis, structure and organic-solvent-free epoxidation activity

New aroylhydrazone molybdenum(vi) complexes have been synthesized, characterized and used as (pre)catalysts for epoxidation of cyclooctene using aqueous TBHP as the oxidant.

Synthesis, APPI Mass-Spectrometric Characterization, and Polymerization Studies of Group 4 Dinuclear Bis(ansa-metallocene) Complexes

New ligand platforms of the type p- or m-Ph{-CR(3,6-tBu2Flu)(Cp)}2 (para-, R = Me (2a), H (2b); meta-, R = Me (2c)) were synthesized via nucleophilic addition of the 3,6-tBu2-fluorenyl-anion onto the parent phenylene-bridged difulvenes (1a–c). The corresponding discrete homodinuclear zirconium and hafnium bis(dichloro ansa-metallocene) complexes, Ph[{-CR(3,6-tBu2Flu)(Cp)}MCl2]2 (p-, R = Me (3a-Zr2, 3a-Hf2), R = H (3b-Zr2); m-, R = Me (3c-Zr2), were prepared by salt metathesis reactions. An attempt to generate in situ a heterodinuclear complex 3a-Zr-Hf was also undertaken. For the first time, Atmospheric Pressure PhotoIonization (APPI) mass-spectrometric data were obtained for all dinuclear compounds and found to be in excellent agreement with the simulated ones. Preliminary studies on the catalytic performances of these dinuclear complexes, upon activation with MAO, in ethylene homopolymerization and ethylene/1-hexene copolymerization revealed a few differences as compared to those of the monometallic analogues. In particular, slightly lower molecular weights and a greater formation of short methyl and ethyl branches were obtained with the dinuclear systems.