Solvent-Induced Polymorphism of Iron(II) Spin Crossover Complexes

Two new mononuclear iron(II) compounds (1) and (2) of the general formula [Fe(L) $_{2}$](BF$_{4}$)$_{2}$·nCH$_{3}$CN (L = 4-(2-bromoethyn-1-yl)-2,6-bis(pyrazol-1-yl)pyridine, n = 1 for (1) and n = 2 for compound (2)), were synthesized. The room temperature crystallization afforded concomitant formation of two different solvent analogues: compound (1) exhibiting triclinic P-1 and compound (2) monoclinic C2/c symmetry. Single-crystal X-ray studies confirmed the presence of the LS (low-spin) state for both compounds at 180 K and of the HS (high-spin) state for compound (2) at 293 K, in full agreement with the magnetic investigations for both solvent polymorphs. Compound (1) exhibits spin transition above 293 K followed by subsequent solvent liberation, while the spin transition of (2) takes already place at 237 K. After complete solvent removal from the crystal lattice, compound (1d) (the desolvated polymorph derived from (1)) exhibits spin transition centered at 342 K accompanied by a thermal hysteresis loop, while the analogous compound (2d) (the desolvated derivate of compound (2)) remains blocked in the HS state over all the investigated temperature range

A versatile Diels-Alder approach to functionalized hydroanthraquinones

The synthesis of highly substituted hydroanthraquinone derivatives with up to three stereogenic centres via a Diels-Alder reaction, starting from easily accessible 2-substituted naphthoquinones, is described. The [4+2]-cycloaddition is applicable for a broad range of substrates, runs under mild conditions and results in high yields. The highly regioselective outcome of the reactions is enabled by a benzoyl substituent at C2 of the dienophiles. The obtained hydroanthraquinones can be further modified and represent ideal substrates for follow-up intramolecular coupling reactions to create unique bicyclo[3.3.1] or -[3.2.2]nonane ring systems which are important natural product skeletons.Peer reviewe

Selectivity control towards CO versus H2_2 for photo-driven CO2_2 reduction with a novel Co(II) catalyst

Developing efficient catalysts for reducing carbon dioxide, a highly stable combustion waste product, is a relevant task to lower the atmospheric concentration of this greenhouse gas by upcycling. Selectivity towards CO$_2$-reduction products is highly desirable, although it can be challenging to achieve since the metal-hydrides formation is sometimes favored and leads to H$_2$ evolution. In this work, we designed a cobalt-based catalyst, and we present herein its physicochemical properties. Moreover, we tailored a fully earth-abundant photocatalytic system to achieve specifically CO$_2$ reduction, optimizing efficiency and selectivity. By changing the conditions, we enhanced the turnover number (TON) of CO production from only 0.5 to more than 60 and the selectivity from 6% to 97% after four hours of irradiation at 420 nm. Further efficiency enhancement was achieved by adding 1,1,1,3,3,3-hexafluoropropan-2-ol, producing CO with a TON up to 230, although at the expense of selectivity (54%)

Towards stable and efficient electrolytes for room-temperature rechargeable calcium batteries

Rechargeable calcium (Ca) batteries have the prospect of highenergy and low-cost. However, the development of Ca batteries is hindered due to the lack of efficient electrolytes. Herein, we report novel calcium tetrakis(hexafluoroisopropyloxy)borate Ca[B(hfip)₄]₂ based electrolytes exhibiting reversible Ca deposition at room temperature, a high oxidative stability up to 4.5 V and high ionic conductivity >8 mS cm¯¹. This finding opens a new approach towards room-temperature rechargeable calcium batteries

A designed and potentially decadentate ligand for use in lanthanide(III) catalysed biomass transformations: targeting diastereoselective trans-4,5-diaminocyclopentenone derivatives

The goal of this study was to design a ligand system which can accommodate single lanthanide(III)-ions and investigate the properties of the resulting complexes. The complexes of all the accesible lanthanides and yttrium with the new ligand LH6 = N,N′-dimethyl-N,N′-ethylene-bis(5-bromo-3-(1H-benzimidazol-2-yl)hydrazineylidene)-2-hydroxybenzylamine) were obtained in high yield at room temperature under aerobic reaction conditions. The corresponding compounds were characterised using X-ray diffraction, FT-IR, elemental analysis and the optical properties of all complexes were investigated using UV-vis and fluorescence spectroscopy. The air stable complexes efficiently transform biomass furfural to trans-4,5-cyclopentenones in high yield

2,1,3-Benzoselenadiazole as Mono- and Bidentate N-Donor for Heteroleptic Cu(I) Complexes: Synthesis, Characterization and Photophysical Properties

Mono- and binuclear Cu(I) complexes were isolated employing 2,1,3-benzoselenadiazole (BSeD) as the N-donor ligand, and triphenylphosphine or bis[(2-diphenylphosphino)phenyl] ether (DPEphos) as P-donors. Then, $^{77}$Se NMR was measured for the free ligand and the corresponding Cu(I) derivatives, and the related signal was downshifted by 12.86 ppm in the case of [Cu(BSeD)(PPh$_{3}$)$_{2}$(ClO$_{4}$)], and around 15 ppm for the binuclear species. The structure of [Cu(BSeD)(PPh$_{3}$)$_{2}$(ClO$_{4}$)] and [Cu2(μ2-BSeD)(DPEphos)2(ClO4)2] was confirmed by single-crystal X-ray diffraction. The geometry of the Cu(I) complexes was optimized through DFT calculations, and the nature of the Cu···O interaction was investigated through AIM analysis. The three Cu(I) complexes were characterized by intense absorption under 400 nm and, after being excited with blue irradiation, [Cu(BSeD)(PPh$_{3}$)$_{2}$(ClO$_{4}$)] and [Cu2(μ2-BSeD)(PPh$_{3}$)$_{2}$(ClO$_{4}$)$_2$] exhibited weak red emissions centered at 700 nm. The lifetimes comprised between 121 and 159 μs support the involvement of triplet excited states in the emission process. The photoluminescent properties of [Cu(BSeD)(PPh$_{3}$)$_{2}$(ClO$_{4}$)] were supported by TDDFT computations, and the emission was predicted at 710 nm and ascribed to a metal-to-ligand charge transfer ($^3$MLCT) process, in agreement with the experimental data

Scope of tetrazolo[1,5-a] quinoxalines in CuAAC reactions for the synthesis of triazoloquinoxalines, imidazoloquinoxalines, and rhenium complexes thereof

The conversion of tetrazolo[1,5-a]quinoxalines to 1,2,3-triazoloquinoxalines and triazoloimidazoquinoxalines under typical conditions of a CuAAC reaction has been investigated. Derivatives of the novel compound class of triazoloimidazoquinoxalines (TIQ) and rhenium(I) triazoloquinoxaline complexes as well as a new TIQ rhenium complex were synthesized. As a result, a small 1,2,3-triazoloquinoxaline library was obtained and the method could be expanded towards 4-substituted tetrazoloquinoxalines. The compatibility of various aliphatic and aromatic alkynes towards the reaction was investigated and the denitrogenative annulation towards imidazoloquinoxalines could be observed as a competing reaction depending on the alkyne concentration and the substitutions at the quinoxaline

Reaching strong absorption up to 700 nm with new benzo[ g ]quinoxaline-based heteroleptic copper( i ) complexes for light-harvesting applications

Heteroleptic copper(I) complexes, with a diimine as a chromophoric unit and a bulky diphosphine as an ancillary ligand, have the advantage of a reduced pseudo Jahn–Teller effect in their excited state over the corresponding homoleptic bis(diimine) complexes. Nevertheless, their lowest absorption lies generally between 350 to 500 nm. Aiming at a strong absorption in the visible by stable heteroleptic Cu(I) complexes, we designed a novel diimine based on 4-(benzo[g]quinoxal-2′-yl)-1,2,3-triazole derivatives. The large π-conjugation of the benzoquinoxaline moiety shifted bathochromically the absorption with regard to other diimine-based Cu(I) complexes. Adding another Cu(I) core broadened the absorption and extended it to considerably longer wavelengths. Moreover, by fine-tuning the structure of the dichelating ligand, we achieved a panchromatic absorption up to 700 nm with a high molar extinction coefficient of 8000 M$^{-1}$ cm$^{-1}$ at maximum (λ = 570 nm), making this compound attractive for light-harvesting antennae