Two new neutral monoperoxidovanadium(V) complexes [VO(O2)(L)(pa)]·xH2O have been synthesized: [VO(O2)(pic)(pa)]·H2O (1) and [VO(O2)(Hquin)(pa)]·2H2O (2) [pic: pyridine-2-carboxylato(1–) or picolinato(1–), Hquin: pyridine-2,3-dicarboxylato(1–) or quinolinato(1–), and pa: picolinamide]. The solid state structures of 1 and 2 feature a typical distorted pentagonal bipyramid coordination polyhedron around the central vanadium atoms. The bidentate anionic ligands are coordinated in two equatorial positions, while the bidentate picolinamide molecule is bound via the aromatic nitrogen and the carboxamide oxygen in one equatorial and one apical position. The experimental geometric parameters were used for a detailed study of intermolecular interactions between the pic–pic and pa–pa aromatic rings in 1. Interestingly, no π–π interactions were observed between the pyridine rings of Hquin or pa in 2, however, the less common anion–π solid-state interactions were found between the pic ligands in 1 and pca [pca = pyrazinecarboxylato(1–)] ligands in the already published structure of the related complex [VO(O2)(pca)(pa)]·H2O (3). The presence of anion–π and π–π interactions in 1 and 3 was confirmed by DFT computations performed on their solid-state structures. Computational results suggested a direct analogy between anion–π and π–π interactions, both being of predominantly electrostatic character.
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