Generation and Stabilization ofD6h andC2v Valence Tautomeric Structures of the Rhodizonate Dianion in Hydrogen-Bonded Host Lattices

Rhodizonate Metal Complexes with a 2D Chairlike M6 Metal–Organic Framework: [M(C6O6)(bpym)(H2O)]⋅n H2O

“…Notably, the CC bond lengths—1.501(7) Å in 1 , 1.492(3) Å in 2 —between two nonbonded CO groups are close to being single bond in character, and they are also larger than other CC bond lengths—1.453(7)–1.468(7) Å in 1 and 1.443(3)–1.481(3) Å in 2 —for a C 2 molecular symmetry (Figure 4). This result implies that when C 6 O 6 2− acts as a bridging ligand, the π‐electron delocalization in the six‐membered ring of dianion is less extensive than that of its free ion in rhodizonate salts 7–9. The nonplanar molecular geometry in C 6 O 6 2− seems to be in accordance with this theoretical prediction 2.…”

“…The measured dimensions of the C 6 O 6 2− species in 1 and 2 conform nearly to a C 2 molecular symmetry, which corresponds to a diketone character (Figure 4). The mean deviations of carbon atoms from planarity are 0.071 and 0.054 Å for 1 and 2 , respectively, which are obviously larger than those of 0.020 and 0.010 Å in the inclusion compounds incorporating tetra‐ n ‐butylammonium rhodizonate and urea derivatives 9. Moreover, the deviations of most oxygen atoms (see the numbers shown in Figure 4) in C 6 O 6 2− are larger than 0.1 Å, thus indicating a nonplanar molecular geometry.…”

“…Conversely, owing to their relative instability, structural information on complexes by using deltate and rhodizonate as the building ligands is obscure 6–10. Thus far, just a few rhodizonate salts of K 2 C 6 O 6 ,8 Rb 2 C 6 O 6 10 and some inclusion compounds of urea and thiourea9 have been structurally well characterized. For example, rhodizonate conforms to nonplanar D 3 d and C 2 molecular geometries coexisting in K 2 C 6 O 6 , a D 6 h geometry in Rb 2 C 6 O 6 , [ n Bu 4 N] + 2 C 6 O 6 2− ⋅4 PhNHCONH 2 and [ n Bu 4 N] + 2 C 6 O 6 2− ⋅2 m ‐OHC 6 H 4 NHCONH 2 ⋅2 H 2 O, and a planar C 2 v molecular geometry in [ n Bu 4 N] + 2 C 6 O 6 2− ⋅2 NH 2 CONHCH 2 CH 2 NHCONH 2 ⋅3 H 2 O 9.…”

“…Thus far, just a few rhodizonate salts of K 2 C 6 O 6 ,8 Rb 2 C 6 O 6 10 and some inclusion compounds of urea and thiourea9 have been structurally well characterized. For example, rhodizonate conforms to nonplanar D 3 d and C 2 molecular geometries coexisting in K 2 C 6 O 6 , a D 6 h geometry in Rb 2 C 6 O 6 , [ n Bu 4 N] + 2 C 6 O 6 2− ⋅4 PhNHCONH 2 and [ n Bu 4 N] + 2 C 6 O 6 2− ⋅2 m ‐OHC 6 H 4 NHCONH 2 ⋅2 H 2 O, and a planar C 2 v molecular geometry in [ n Bu 4 N] + 2 C 6 O 6 2− ⋅2 NH 2 CONHCH 2 CH 2 NHCONH 2 ⋅3 H 2 O 9. To the best of our knowledge, the crystal structure of a rhodizonate transition‐metal complex, unfortunately, has not yet been reported.…”

μ‐Rhodizonato‐1κO,1:2κO′,2κO′′‐tetra(triphenylphosphine)disilver(I): A Molecular Complex with the [C6O6]2– Ligand Template

“…The C–C and C–O distances typically vary considerably within the respective anion. Only one structure shows equal bond lengths over the whole anion, implying an increased degree of charge delocalization 10b. Lastly, the formal dihydrate was structurally characterized while the water‐free rhodizonic acid has withstood all attempts to grow single crystals 9c…”