α-Acylaminoantraquinones have not 9,10-, but 1,10-quinoid structure. Their characteristic feature is competition of two types of tautomerism - acylamino-acylimino and keto-enol, connected with the migration of hydrogen atom in acylamino group. For benzoylaminogroups the most characteristic structure is NHCOPh, and for acetylamino groups − N=C(OH)Ме. Both basic and excited states are responsible for tautomeric transformations. Excitation of molecules is accompanied by a shift of tautomeric equilibria.

Выделены в кристаллическом состоянии и определены кристаллическая и молекулярная структуры 2,3,5,6-тетраоксопиперазина (I), кристаллогидрата 2,3,5,6-тетраоксо-4-нитропиридината аммония (II), сокристаллизата 2,3,5,6-тетраоксо-4-нитропиридината диметиламмония и хлорида диметиламмония (III) и 2,6-диоксо-3,5-динитропиридината аммония (IV). Показано, что все гетероциклы плоские и не являются ароматическими, а состоят из двух сопряженных фрагментов, объединенных простыми связями С–С. В случае I в формировании кристаллической структуры большой вклад вносят короткие С···О-контакты (2.841–3.048 A), объединяющие молекулы в зигзагообразные двумерные цепи, в то время как в II–IV наиболее важными в образовании кристаллов являются водородные связи, формирующие трехмерные сетки.

2,3,5,6-Tetraoxopiperazine (I), ammonium 2,3,5,6-tetraoxo-4-nitropyridinate crystal hydrate (II), co-crystallized dimethylammonium 2,3,5,6-tetraoxo-4-nitropyridinate and dimethylammonium chloride (III), and ammonium 2,6-dioxo-3,5-dinitropyridinate (IV) were isolated in the crystalline state and studied by X-ray diffraction. All heterocycles are planar and nonaromatic. They consist of two conjugated moieties linked together by C-C single bonds. The short C...O contacts (2.841–3.048 Å), which link the molecules to form zigzag two-dimensional chains, make a considerable contribution to the formation of the crystal structure of I, whereas hydrogen bonds that form three-dimensional networks play the most important role in the formation of the crystals of II–IV.

We have isolated in crystalline state and studied with a set of spectral methods of investigation 8 complexes of manganese(II), nickel(II), copper(II) and cadmium(II) with some -carbonyl-containing arylhydrazones. On the basis of spectral characteristics (IR, electron spectroscopy) we defined the character of coordination and suggested the schemes of composition of coordination compounds.

Compounds widely known as 1,4-bis(alkylamino)-9,10-anthraquinones are in fact neither individual substances nor substituted 9,10-anthraquinones but equilibrium mixtures of tautomers. Their aminoimine tautomeric transformations follow the sequence 4,9-bis(alkylamino)-1,10-anthraquinones ↔ 9-alkylamino-4-(alkylimino)-10-hydroxy-1,4-dihydroanthracen-1-ones ↔ N 1 , N 10 -dialkyl-4,9-dihydroxy-1,10-dihydroanthracene-1,10-diimines.

Neutral [EuL(3)Phen] complexes were synthesized by the reaction of EuCl3 with heterocyclic diketones-1-(1,5-dimethyl-1H-pyrazol-4-yl)-4,4,4-trifluoro-1,3-butanedione and 4,4,5,5,6,6,6-heptafluoro-1-(1-methyl-1H-pyrazol-4-yl)-1,3-hexanedione-and 1,10-phenanthroline (Phen) in an aqueous alcohol solution in the presence of NaOH. The reaction of GdCl3 with the same diketones under analogous conditions, but without adding 1,10-phenanthroline, yielded [GdL3(H2O)(2)] complexes. The composition of the complexes was determined by elemental analysis, and their optical and luminescent properties were examined.

Based on the example of 1,4,5,8-tetraamino-9,10-anthraquinone, a method is described for establishing the tautomeric compositions and sequences of tautomeric transformations that occur in known samples of quinones. An analysis of electronic absorption spectra shows that this substance is a dynamic equilibrium mixture of 4,5,8,9-tetraamino-1,10-anthraquinone and the imines tautomeric to it. The tautomeric compositions of different samples of matter differ and can contain 1,4,8-triamino-5-hydroxy-9,10-anthraquinone-10-imine, 4,8,9-triamino-10-hydroxy-1,5-anthraquinone-5-imine, 5,8-diamino-4,9-dihy-droxy-1,10-antraquinonediimine, and 8,10-diamino-5,9-dihydroxy-1,4-antraquinonediimine. Tautomeric equilibrium shifts can accompany not only chemical reactions but physical processes as well, so any investigation of the properties of substances without establishing their tautomeric compositions would be incorrect.

3-amino-4-hydroxy benzenesulfonamide and its hydrochloride have been isolated in the crystalline state. Their crystal and molecular structures are determined by X-ray diffraction. The equilibrium between neutral tautomeric forms of the 3-amino-4-hydroxy benzenesulfonamide molecule is studied within the approximation of density functional theory (B3LYP/aug-cc-pVDZ). The constants of acid-base equilibrium of 3-amino-4-hydroxy benzenesulfonamide are deter-mined using spectrophotometry.

Using spectral (electron spectroscopy) and quantum-chemical (PPP, PМ3) methods we studied tautomeric and ionic forms 6-(2-methyl-5-oxo-1-phenyl-4,5-dihidro-1Н-imidazole-4-ilazo)-1-oxo-2,5-dihidro1Н-benzo[4,5]imidazo[1,2-c]pyrimidine-7-carboxxylic acid. Its primary existence as non-flat СН-azo tautomer has been shown.

Keto-enol and amine-imine tautomerism and equilibria with trans-conformers are characteristic of 1-(alkyl,aryl)amino-4-hydroxy-9,10-anthraquinones. Amino forms possess 1,10- and 1,4-, but not 9,10-quinoid structure. Various tautomeric and conformeric transformations are in competition. The outcome of this competition may be studied by the correlation analysis of electron absorption spectra but it would be possible to understand the causes of changes in the direction of the competing transformation only in the case when each action on the substance would be accompanied with establishing the corresponding alterations in its tautomeric composition.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Complexes of copper(II), nickel(II), and cobalt(II) chlorides and bromides with 2-phenyl-4-(piperidyl-1)-anthra[1,2-b]pyridine-7,12-dione (L-1) and 2-[phenyl-4-(octylamino)-anthra[1,2-b]pyridine-7,12-dione (L-2) were synthesized from neutral and acidic media. The molecular and crystal structure of 2-phenyl-4-(piperidyl-1)-anthra[1,2-b]pyridine-7,12-dionium hexabromodicuprate(II) (HL1)(2)[Cu2Br6] was determined by X-ray diffraction analysis. The spectral characteristics of L-1 and L-2 and their complexes are presented. Formation of their complexes in solutions was studied.

The fine structure of the πl,π*-absorption of hydroxyanthraquinones solutions in sulfuric acid arises due to the existence of the protonated forms as equilibrium mixtures of tautomers and conformers distinguished by the positions of the π-bonds, charges, and the number of intramolecular hydrogen bonds. Using quantum-chemical calculations and correlation analysis of the absorption spectra tautomers were identified of mono- and dications of 1,4,5-trihydroxyanthraquinone of 9,10-, 1,4-, and 1,10-isomeric structure. For 1,4,5,8-tetrahydroxyanthraquinone 9,10-, 1,4-, 1,10-, and 1,5-isomeric mono- and dications and their conformers were found.

Structure and amino-imine tautomerism of α-aminoanthraquinones, 1,5-and 1,8-diaminoanthraquinones, as well as 1,4,5-triamino-9,10-anthraquinones was studied. We found that in the study of properties of the compounds prone to tautomeric transformation the tautomeric composition should be taken into account.

The explanation of reasons of significant diferencies in electronic absorption spectra of 1-amino-anthraquinones in identical media was proposed. The results of quantum-chemical and correlational analysis indicate the possibility of existence of 1-amino-9,10- and 9-amino-1,10-anthraquinones. For each of them the tautomeric transformations to imines and trans-conformers without intermolecular H-bonds occur.

The reaction of Tb(NO3)3 · 6H2O with 1,3-bis(1,3-dimethyl-1H-pyrazol-4-yl)-1,3-propanedi-one (HL) and 1,10-phenanthroline (Phen) in the presence of NaOH in a water-alcohol medium afforded the neutral complex [Tb(L)3(Phen)] (I). The unstable adduct [Tb(L)3(Phen)] · 0.4 MeCN (II), whose structure is studied by X-ray diffraction analysis, is obtained from an acetonitrile solution. The crystals of compound II at 100 K are triclinic, a = 11.2508(13), b = 11.4246(14), c = 22.486(3) Å, α = 96.522(2)°, β = 91.578(2)°, γ = 110.073(2)°, V = 2690.3(5) Å3, space group P \(\bar 1\), Z= 2, R = 0.0433. The complex is characterized by the green luminescence (λexc = 380 nm, λem = 550 nm).

Chemistry of 9,10-anthraquinones is considered as chemistry of isomeric anthraquinones existing in dynamic equilibrium with each other. Diversity of electronic absorption spectra of the same compounds is determined by tautomeric transformations. Alizarin exists as equilibrium mixtures of tautomers and conformers having 9,10- and 2,9-quinoid structures. Qualitatively different compositions are inherent not only to samples of alizarin prepared or purified by different methods but also to different solvates of the same sample.