Luminescence and light-driven energy and electron transfer from an exceptionally long-lived excited state of a non-innocent chromium(III) complex

Photoactive metal complexes employing Earth-abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non-innocence to tune the luminescence and photochemistry of the excited state of the [CrN6] chromophore [Cr(tpe)2]3+ with close to octahedral symmetry (tpe=1,1,1-tris(pyrid-2-yl)ethane). [Cr(tpe)2]3+ exhibits the longest luminescence lifetime (τ=4500 μs) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Φ=8.2 % at room temperature in fluid solution. Furthermore, the tpe ligands in [Cr(tpe)2]3+ are redox non-innocent, leading to reversible reductive chemistry. The excited state redox potential and lifetime of [Cr(tpe)2]3+ surpass those of the classical photosensitizer [Ru(bpy)3]2+ (bpy=2,2′-bipyridine) enabling energy transfer (to oxygen) and photoredox processes (with azulene and tri(n-butyl)amine)

Assessing the reactivity of sodium alkyl-magnesiates towards quinoxaline : single electron transfer (SET) vs. nucleophilic alkylation processes

By exploring the reactivity of sodium butyl-magnesiate (1) supported by the bulky chelating silyl(bisamido) ligand {Ph2Si(NAr*)2}(2-) (Ar* = 2,6-iPr2-C6H3) towards Quinoxaline (Qx), the ability of this bimetallic system to effectively promote SET processes has been disclosed. Thus 1 executes the single-electron reduction of Qx affording complex (2) whose structure in the solid state contains two quinaxolyl radical anions Qx˙ stabilised within a dimeric magnesiate framework. Combining multinuclear NMR and EPR measurements with DFT calculations, new insights into the constitution of 2 in solution and its magnetic behaviour have been gained. Further evidence on the SET reactivity of 1 was found when it was reacted with nitroxyl radical TEMPO which furnished contacted ion pair sodium magnesiate [(Ph2Si(NAr*)2)Mg(TEMPO(-))Na(THF)3] (4) where both metals are connected by an alkoxide bridge, resulting from reduction of TEMPO. The role that the different ligands present in 1 can play in these new SET reactions has also been assessed. Using an amination approach, the Bu group in 1 can be replaced by the more basic amide TMP allowing the isolation of (3) which was characterised by multinuclear NMR and X-ray crystallography. (1)H NMR monitoring of the reaction of 3 with Qx showed its conversion to 2, leaving the hydrogen atoms of the heterocycle untouched. Contrastingly, using sodium homoalkyl magnesiate [NaMg(CH2SiMe3)3] (5) led to the chemoselective C2 alkylation of this heterocycle, suggesting that the presence of the steric stabiliser {Ph2Si(NAr*)2}(2-) on the mixed-metal reagent is required in order to facilitate the Qx reduction

Synthesis, Structural, and Magnetic Characterization of a Mixed 3d/4f 12-Metallacrown-4 Family of Complexes

A new family of complexes (tBu4N){[LnIII(O2CBut)4][12-MC-Mn(III)N(shi)-4]}·5CH2Cl2 (Ln = Gd (1) and Tb (2)), (tBu4N)2{[YIII(O2CBut)4][12-MC-Mn(III)N(shi)-4]}(ClO4) (3); where shiH3 = salicylhydroxamic acid; ButCO2− = pivalate ions; tBu4N = tetrabutylammonium and ClO4− = perchlorate ions, has been isolated. The reaction of salicylhydroxamic acid with Mn(O2CBut)2·2H2O, Ln(NO3)3·xH2O, tBu4NClO4 in the presence of morpholine (C4H9NO) led to the isolation of compounds 1–3. The complexes belong to the 12-MC-4 family of Metallacrowns (MCs) possessing a central {Mn4IIILnIII(µ-NO)4}11+ core with the four MnIII atoms occupying the periphery positions, while the formed [Mn–N–O] repeating unit, assists in the accommodation of the LnIII atom in the center of the ring. Peripheral ligation is provided by four η1:η1:μ pivalate ions. Direct current magnetic susceptibility (dc) measurements revealed the presence of predominant antiferromagnetic exchange interactions within the metal centers. A 1-J fitting model was used in order to quantify the MnIII–MnIII interactions and fitting of the data, for the diamagnetic YIII analogue, gave J = −3.74 cm−1 and gMn(III) = 2.07. Fitting of the {Mn4Gd} compound using a 2-J model, counting additionally for the MnIII–GdIII interactions, revealed values of J1 = −3.52 cm−1, J2 = −0.45 cm−1, and gMn(III) = 1.99

Three Novel Thiazole-Arm Containing 1,3,4-Oxadiazole-Based [HS-HS] Fe(II) Dinuclear Complexes

Novel synthesis of 2,5-bis[(1,3-thiazol-2-ylmethyl)amino]methyl-1,3,4-oxadiazole (LThiazole) is reported, along with the preparation of three new dinuclear Fe(II) complexes with different counterions [FeII2(μ2-LThiazole)2](BF4)4·2CH3CN (1), [FeII2(μ2-LThiazole)2](ClO4)4 (2) and [FeII2(μ2-LThiazole)2](CF3SO3)4·2CH3CN (3). The obtained complexes were characterized by single-crystal X-ray crystallography, SQUID magnetometry and IR spectroscopy. The structure of the crystalline material was determined at 120 K for 1 and 3. The magnetic properties of all three complexes (1–3) were measured between 2–300 K and clearly show that all three complexes stay in the high-spin state over the measured temperature range

First Cobalt(II) Spin Crossover Compound with N4S2-Donorset

Herein we report the synthesis and characterization of a novel bis-tridentate 1,3,4-thiadiazole ligand (L = 2,5-bis[(2-pyridylmethyl)thio]methyl-1,3,4-thiadiazole). Two new mononuclear complexes of the type [MII(L)2](ClO4)2 (with M = FeII (C1) and CoII (C2)) have been synthesized, containing the new ligand (L). In both complexes the metal centers are coordinated by an N4S2-donorset and each of the two ligands is donating to the metal ion with just one of the tridentate pockets. The iron(II) complex (C1) is in the low spin [LS] state below room temperature and shows an increase in the magnetic moment only above 300 K. In contrast, the cobalt(II) complex (C2) shows a gradual spin crossover (SCO) with T1/2 = 175 K. To our knowledge, this is the first cobalt(II) SCO complex with an N4S2-coordination

Triggering of Valence Tautomeric Transitions in Dioxolene-Based Cobalt Complexes Influenced by Ligand Substituents, Co-ligands, and Anions

We report the multistep synthesis of the 1,1′-(piperazine-1,4-diyl)bis(N,N-bis(pyridin-2-ylmethyl)methanamine)(Ltpbap) octadentate ligand, which, in combination with the known 3,5-di-tert-butylcatechol (3,5-dbcat), allowed the preparation of two di-nuclear cobalt complexes [Co2(Ltpbap)(3,5-dbcat)2](SO4)·5.5MeOH·2H2O (3a) and [Co2(Ltpbap)(3,5-dbcat)2 ](ClO4)2·1.5H2O (3b). We also report the synthesis of two mono-nuclear cobalt complexes [Co(3,5-dbsq)(3,5-dbcat)(4-Mepip)2] (1) with 4-Mepip being 4-methylpiperidine and (Hpip)[Co(tbcat)2(pip)2]·CH3CN (2) where Hpip denotes a piperidinium cation and tbcat is the tetra-bromocatechol ligand. The obtained complexes were characterized by single-crystal X-ray crystallography, SQUID magnetometry, and IR spectroscopy. The structure of the crystalline material in all the cases was determined at 173 K. The magnetic properties of all complexes were measured between 2 and 380 K. The magnetic data clearly show that mono-nuclear complex 1 and di-nuclear complex 3a exhibit valence tautomerism with onset around 300 K and 370 K, respectively, whereas the other two complexes 2 and 3b remain unchanged over the measured temperature range

Triggering of Valence Tautomeric Transitions in Dioxolene-Based Cobalt Complexes Influenced by Ligand Substituents, Co-ligands, and Anions

We report the multistep synthesis of the 1,1′-(piperazine-1,4-diyl)bis(N,N-bis(pyridin-2-ylmethyl)methanamine)(Ltpbap) octadentate ligand, which, in combination with the known 3,5-di-tert-butylcatechol (3,5-dbcat), allowed the preparation of two di-nuclear cobalt complexes [Co2(Ltpbap)(3,5-dbcat)2](SO4)·5.5MeOH·2H2O (3a) and [Co2(Ltpbap)(3,5-dbcat)2 ](ClO4)2·1.5H2O (3b). We also report the synthesis of two mono-nuclear cobalt complexes [Co(3,5-dbsq)(3,5-dbcat)(4-Mepip)2] (1) with 4-Mepip being 4-methylpiperidine and (Hpip)[Co(tbcat)2(pip)2]·CH3CN (2) where Hpip denotes a piperidinium cation and tbcat is the tetra-bromocatechol ligand. The obtained complexes were characterized by single-crystal X-ray crystallography, SQUID magnetometry, and IR spectroscopy. The structure of the crystalline material in all the cases was determined at 173 K. The magnetic properties of all complexes were measured between 2 and 380 K. The magnetic data clearly show that mono-nuclear complex 1 and di-nuclear complex 3a exhibit valence tautomerism with onset around 300 K and 370 K, respectively, whereas the other two complexes 2 and 3b remain unchanged over the measured temperature range

Luminescent Cadmium(II)-Based 12-MC-4 Metallacrown Complex with 2-Methylmercaptobenzohydroxamic Acid Ligand

We reported herein the synthesis, structure determination and emission properties of a cubic molecular Cd(II) coordination cluster whose faces are composed of 12-MC-4 metallacrown units built up from Cd2+ and 2-methylmercaptobenzohydroxamic acid (LmmbHA), resulting in [CdII14(LmmbHA)12(µ6−O)(DMF)10](ClO4)2·3H2O. The polynuclear complex obtained was characterised by single crystal X-ray diffraction at 193 K. The bulk sample was also analysed by elemental analysis. UV-Vis and emission spectra of the complex were measured in chloroform, as well as the emission spectra of the ligand for comparison. The results of the emission studies revealed that both the ligand and the complex are weakly emissive

Sodium congener of the classical lithium methylchromate dimer: synthetic, x-ray crystallographic, and magnetic studies of Me8Cr2[Na(OEt2)](4)

One of the milestone structures in the development of transition-metal complexes with metal metal bonds of multiple bond order was the lithium methylchromate dimer Me8Cr2[Li(donor)](4) (donor = THF or Et2O). Using a simple salt metathesis reaction mixing this compound with sodium tert-butoxide, the sodium congener Me8Cr2-[Na(OEt2)]4 has been synthesized as a green crystalline compound and isolated in 51% yield. Its solid-state structure was determined by single-crystal X-ray diffraction. Exhibiting exact crystallographic C-4h symmetry, this heavier alkali-metal chromate structure is also dimeric, formally comprising a (Me8Cr4)(4-) tetranionic core with four peripheral Na+ cations carrying supporting ether ligands. Its salient feature is the long Cr center dot center dot center dot Cr distance of 3.263(2) angstrom, which is remarkably elongated compared to that in the lithium THF-solvated congener [1.968(2) angstrom]. With respect to the methyl C atoms, the Cr coordination is distorted-square-planar. Each Na interacts with four methyl C atoms, and there are also some short Na center dot center dot center dot H(C) contacts. Unlike for lithium chromate, no NMR spectroscopic data could be obtained for sodium chromate. The paramagnetic character of sodium chromate was confirmed by variable-temperature magnetization measurements, which indicated antiferromagnetic behavior