Crystal structures and Raman spectroscopic study of croconate violet salts with alkaline earth ions

Deciphering the Thermal and Electrochemical Behaviors of Dual Redox-Active Iron Croconate Violet Coordination Complexes

“…The structure of 2 (H 2 O) 2 ·2H 2 O was determined by single-crystal X-ray diffraction (SCXRD) (see Table S1 for details on data collection and structure refinement). This solid was found to be isostructural with the already reported complexes K 2 M­( CV ) 2 (H 2 O) 2 ·2H 2 O (M = Co, Cu, Mg, and Zn − , ); the structures are essentially the same, with slight variations of M–O distances, as expected. The structure consists again of octahedrally coordinated iron ions bound to two CV ligands, but this time, each ligand interacts through two neighboring oxygen atoms in a chelating mode.…”

“…50,51 Below 1640 cm −1 , noticeable differences are also detected (Figure S9), but as both water deformation modes and combination of CO and CC vibration modes are expected in this region, a definitive attribution is not straightforward. 49,52,60 Eventually, the spectroscopic characterizations are in line with the XRD structure analysis. Polymorphs 1(H 2 O) 4 and 2(H 2 O) 2 •2H 2 O, although presenting very distinct complexing modes, could be obtained under very similar experimental conditions.…”

“…Eventually, in the low wavenumber region, bands associated with CO stretching modes are seen at 1706 and 1676 cm –1 for K 2 ( CV )· 2 H 2 O. , These bands are almost unchanged in 1 (H 2 O) 4 (1705 and 1680 cm –1 ) but become weaker for 2 (H 2 O) 2 ·2H 2 O (1706 and 1682 cm –1 ). This phenomenon has already been observed in the isostructural compounds made of Co and Cu and is considered to be a consequence of the formation of carbonyl–cation bonds. , Below 1640 cm –1 , noticeable differences are also detected (Figure S9), but as both water deformation modes and combination of CO and CC vibration modes are expected in this region, a definitive attribution is not straightforward. ,, …”

“…48 The coordination ability of the dianion towards transition metals and lanthanides has also been explored, notably by the group of Fabre [49][50][51] and de Oliviera and Machado. [52][53][54][55][56][57] It has been shown that both oxygen and nitrogen atoms can form coordination bonds with metallic cations. We focused our attention on iron, which has several advantages such as high abundancy, low cost and low toxicity when compared to other redox active cations found in standard positive electrode materials (Co, Ni).…”

“…Its disodium salt was reported back in the 1970s by Fatiadi and was found to present at least four accessible oxidation states (as solute) as deduced by cyclic voltammetry in organic solvents, in good consistency with its extended π system. − For this reason, its interest as both an anolyte and a posolyte for redox flow batteries has been recently evaluated . The coordination ability of the dianion toward transition metals and lanthanides has also been explored, notably by the group of Fabre − and de Oliviera and Machado. − It has been shown that both oxygen and nitrogen atoms can form coordination bonds with metallic cations.…”