Two new complexes belonging to the family [Fe(II)(L)2(NCX)2] have been synthesized and structurally characterized. Complexation of the ligand L(O) = 2,5-di(2-pyridyl)-1,3,4-oxadiazole results in the formation of two derivatives of [Fe(II)(L(O))2(NCS)2] (1) with the common s-trans and the rarely observed s-cis conformation. No thermal spin crossover (SCO) was observed for the amorphous bulk material of the mixture. Using the new ligand L(Se) = 2,5-di(2-pyridyl)-1,3,4-selenadiazole, compound [Fe(II)(L(Se))2(NCS)2]·1.4DCM·0.6MeOH (2·1.4DCM·0.6MeOH) was structurally characterized by single crystal X-ray diffraction. Bulk material of [Fe(II)(L(Se))2(NCS)2]·MeOH (2·MeOH) exhibits a thermally induced SCO with small hysteresis [T(1/2)(↓) = 91 K, T(1/2)(↑) = 96 K]. LIESST and reflectivity studies have been performed on the SCO complexes [Fe(II)(L(S))2(NCS)2], [Fe(II)(L(S))2(NCSe)2], [Fe(II)(L(S))2(NCBH3)2]·H2O [L(S) = 2,5-di(2-pyridyl)-1,3,4-thiadiazole], and 2·MeOH. All complexes belong to the T0 = 90 K line [T(LIESST) = T0 - 0.3T(1/2)]. [Fe(II)(L(S))2(NCS)2], that exhibits a two-stepped thermal SCO process, has been found to also exhibit two well-separated T(LIESST) temperatures [T(LIESST, 1) = 44 K; T(LIESST, 2) = 53 K].

The coordination behaviour of 3,5-di(2-pyridyl)-1,2,4-oxadiazole (LЈ) has been studied and compared with that of the

The importance of electrical energystorage systems (EES), for a successful integration of intermittent renewable energy sources into the electrical grid is beyond dispute. [1][2][3][4] For mobile applications, lithium ion batteries (LIBs) with high energy density prevail. [2,5,6] Although many efforts focus on alternative chemical systems (e.g., multivalent Al, Mg, and Ca), it is hard to imagine that LIBs will disappear in the near future. [4,7] Yet, for large scale stationary EES, there is no such prevailing technology. Although other alternatives, like pumped hydro or fuel cells are available, batteries are amongst the most promising technologies for this purpose. [1,3,8] With the energy density being slightly less relevant, other redox active materials could be employed in large scale EES, i.e., redox-flow batteries (RFBs) with their very long cycle life and decoupled capacity, power and energy output. [2,9,10] Their benchmark is the allvanadium redox-flow battery (VRFB) with V II /V III and V IV / V V redox couples, [2] as well as a 15 000-20 000 charge/discharge cycles lifetime and an acceptable energy density of 25-35 Wh L −1 installed in up to 60 MWh capacity EES. [2,6] However, probably due to the high cost, a commercial breakthrough still has to come. [2,6,9] Considering abundancy and cost, few elements are suitable as redox active material in sustainable batteries. [4,11] Manganese is one of them and, therefore, finds application in LIB-cathode active materials (e.g., LiMn 2 O 4 or Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 ) or in cathode materials of primary batteries (MnO 2 ). [5,12] However, to the best of our knowledge, only one battery system exclusively using manganese compounds at both electrodes is described, [13] i.e., Mn(acac) 3 acetonitrile (MeCN) solutions with the Mn II /Mn III couple at the negative and the Mn III /Mn IV couple at the positive electrode. Yet, with E cell of 1.1 V the system does not exploit the large potential range advantage of a non-aqueous electrolyte. Already the aqueous standard potential difference ΔE 0 of Mn 0 /Mn II and Mn II /Mn III redox couples amounts to an impressive 2.69 V. In addition, the Mn volumetric specific capacity is 7034.7 Ah L −1 (two-electron-process). It clearly exceeds that of zinc (5853.8 Ah L −1 ), which in the zinc A new all-Manganese flow battery (all-MFB) as a non-aqueous hybrid redox-flow battery is reported. The discharged active material [Cat] 2 [Mn II Cl 4 ] (Cat = organic cation) utilized in both half-cells supports a long cycle life. The reversible oxidation of [Mn II Cl 4 ] 2− to [Mn III Cl 5 ] 2− at the positive electrode and manganese metal deposition from [Mn II Cl 4 ] 2− at the negative electrode give a cell voltage of 2.59 V. Suitable electrolytes are prepared and optimized, followed by a characterization in static battery cells and in a pumped flow-cell. Several electrode materials, solvents, and membranes are tested for their feasibility in the all-MFB. An electrolyte consisting of [EMP] 2 [MnCl 4 ] and some solvent γ-butyrolactone is cycle...