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The work continues the study on the peculiarities of the interaction of 1,3,7-trimethylxanthine (caffeine) compounds with polyoxometalates of molybdenum and tungsten with the artificial radical of 1,3,5- triphenylverdazyl (TFV). Using the example of a model reaction with the TFV radical, these compounds showed a special antiradical action. Based on the research results, it was found that the nature of the destruction of the radical when interacting with (HСaf)3[PМ12O40]∙6H2O (where М = Мо, W) differs from most known systems, which are characterized by a mechanism of disproportionation. The data obtained confirmed the previously made assumption about the chemical nature of these interactions. To establish the stoichiometry of the reaction between TFV and (HСaf)3[PW12O40], electrochemical studies were conducted which showed that the activity of the radical is restored after exceeding the concentration ratio of 12 : 1, respectively. The synergism of the components of the compound (HСaf)3[PW12O40] is shown: when TFV interacts with H3[PW12O40], the maximum cathode current characteristic of TFV occurs at a concentration ratio of 4 : 1, respectively, while caffeine has no antiradical effect at all. Previously obtained data from X-ray diffraction analysis of compounds (HСaf)3[PMo12O40]∙6H2O, (HСaf)3[PW12O40]∙6H2O prove that the orientation of protonated caffeine relative to polyoxamethalate-anion is possible due to hydrogen bonds =O…H–N=. This process can result in the delocalization of the charge over the entire O-enriched surface, by all twelve groups [О–Ме–О]-, which are part of the POM, making the latter active centers capable of interacting with TFV. Therefore, the data presented correlate with the previously obtained results of spectrophotometric analysis and X-ray diffraction data and confirm the previously made conclusions.

In the course of research on interaction of artificial radicals of triphenyl-verdazyl (TPV) and diphenyl picryl hydrazyl (DPPH) with complex compounds of 1,3,7-trimethylxanthine with anions of polyoxometalates of molybdenum and tungsten, an anti-radical action of the coordination compounds mentioned above was proved. During the interaction of these compounds with the TPV-radical, deactivation of the latter occurs. This is evidenced, firstly, by a decrease followed by vanishing of characteristic absorption maximum in the visible area of spectroscopy for the radical form -720 nm and, secondly, by disappearance on і,Е-curves of maxima of TPV-radical transition into the anionic form. Unequal decrease in absorption maxima of the cationic and anionic forms of TPV can give evidence of complicated nature of the interaction of the TPV-radical with the complex (Hcaf)3[PМе12O40]6H2O (where Ме = Мо, W). According to the spectroscopy data, compounds (Hcaf)3[PМо12O40]6H2O showed greater antiradical action compared to (Hcaf)3[PW 12O40]6H2O. That is, the antiradical effect of the complex compounds (Hcaf)3[PМо12O40]6H2O, (Hcaf)3[PW 12O40]6H2O was proved.Анотація В процесі досліджень взаємодії штучних радикалів 1,3,5-трифенілвердазил (ТФВ) та дифенілпікрілгідразил (ДФПГ) із комплексними сполуками 1,3,7-триметилксантинію з аніонами поліоксометалатів молібдену та вольфраму було доведено антирадикальну дію вказаних координаційних сполук. При взаємодії даних сполук із ТФВ-радикалом відбувається дезактивация останнього. Про це свідчить, по-перше, зниження, а потім і взагалі зникнення характерного максимуму поглинання у видимій області ЕСП для радикальної форми -720 нм, а по-друге, зникнення на і,Е-кривих максимуму переходу ТФВ-радикала у аніонну форму. Нерівномірне зростання максимумів поглинання катіонної та аніонної форм ТФВ може свідчити про складний характер взаємодії ТФВ-радикалу з комплексом (Hcaf)3[PМе12O40]6H2O (де Ме = Мо, W). За даними спектроскопії сполуки (Hcaf)3[PМо12O40]6H2O виявили більшу антирадикальну активність у порівнянні з (Hcaf)3[PW 12O40]6H2O.Аннотация В процессе исследований взаимодействия радикалов 1,3,5-трифенилвердазил и дифенилпикрилгидразил с комплексными соединениями 1,3,7-триметилксантиния с анионами полиоксометалатов молибдена и вольфрама было доказано антирадикальное действие указанных координационных соединений. При взаимодействии данных соединений с ТФВ-радикалом происходит дезактивация последнего. Об этом свидетельствует, во-первых, снижение, а затем и полное исчезновение характерного максимума поглощения в видимой области ЭСП для радикальной формы -720 нм, а во-вторых, исчезновение на і, Екривых максимума перехода ТФВ-радикала в анионную форму. Неравномерный рост максимумов поглощения катионной и анионной формам ТФВ может свидетельствовать о сложном характере взаимодействия ТФВ-радикала с комплексом (Hcaf)3[PМе12O40]6H2O (где Ме = Мо, W). По данным спектроскопии обнаружили, что соединения (Hcaf)3[PМе12O40] 6H2O проявляют большую антирадикальную активность по сравнению с (Hcaf)3[PW12O40]6...

Anion...π interactions are newly recognized weak supramolecular forces which are relevant to many types of electron-deficient aromatic substrates. Being less competitive with respect to conventional hydrogen bonding, anion...π interactions are only rarely considered as a crystal-structure-defining factor. Their significance dramatically increases for polyoxometalate (POM) species, which offer extended oxide surfaces for maintaining dense aromatic/inorganic stacks. The structures of tetrakis(caffeinium) μ12-silicato-tetracosa-μ2-oxido-dodecaoxidododecatungsten trihydrate, (C8H11N4O2)4[SiW12O40]·3H2O, (1), and tris(theobrominium) μ12-phosphato-tetracosa-μ2-oxido-dodecaoxidododecatungsten ethanol sesquisolvate, (C7H9N4O2)3[PW12O40]·1.5C2H5OH, (2), support the utility of anion...π interactions as a special kind of supramolecular synthon controlling the structures of ionic lattices. Both caffeinium [(HCaf)+ in (1)] and theobrominium cations [(HTbr)+ in (2)] reveal double stacking patterns at both axial sides of the aromatic frameworks, leading to the generation of anion...π...anion bridges. The latter provide the rare face-to-face linkage of the anions. In (1), every square face of the metal–oxide cuboctahedra accepts the interaction and the above bridges yield flat square nets, i.e. {(HCaf+)2[SiW12O40]4−} n . Two additional cations afford single stacks only and they terminate the connectivity. Salt (2) retains a two-dimensional (2D) motif of square nets, with anion...π...anion bridges involving two of the three (HTbr)+ cations. The remaining cations complete a fivefold anion...π environment of [PW12O40]3−, acting as terminal groups. This single anion...π interaction is influenced by the specific pairing of (HTbr)+ cations by double amide-to-amide hydrogen bonding. Nevertheless, invariable 2D patterns in (1) and (2) suggest the dominant role of anion...π interactions as the structure-governing factor, which is applicable to the construction of noncovalent linkages involving Keggin-type oxometalates.