Maxim K. Lesnikov

Polymeric Lithium(I) Diaquabarbiturate: Crystal Structure

The lithium(I) catena-diaquabarbiturate complex [Li(H2O)2(HBA–O,O′)]n (I), where Н2ВА is barbituric acid, has been structurally characterized by X-ray diffraction (CIF file CCDC no. 1447689), and its thermal decomposition and IR spectrum have been studied. Crystals of complex I are monoclinic, a = 6.4306(7) Å, b = 16.720(1) Å, c = 7.1732(8) Å, β = 108.253(4)°, V = 732.5(1) Å3, space group P21/c, and Z = 4. One independent μ2-bridging HBA– ligand is coordinated to two Li(I) ions via the two oxygen atoms of C4(6)=O carbonyl groups. Each Li+ ion is linked with two μ2-HBA– ions and two terminal water molecules at tetrahedron vertices. μ2-HBA– ions link tetrahedra into a chain. The structure is stabilized by multiple hydrogen bonds and π–π-interaction between HBA–. The shift of ν(C=O) vibration bands in the IR spectrum of complex I in comparison with Н2ВА towards lower frequencies agrees with the coordination of HBA– via oxygen atoms. The dehydration of complex I occurs in two stages in the regions of 100–150 and 150–240°C.

Crystal Structure and Properties of Levofloxacinium 2-Thiobarbiturate Trihydrate

The structure of levofloxacinium 2-thiobarbiturate trihydrate LevoH2+Htba–·3H2O (I) (LevoH is levofloxacin, H2tba is 2-thiobarbituric acid) is determined (CIF file CCDC No. 1547466); its thermal decomposition and IR spectrum are studied. The crystals of I are triclinic: a = 8.670(1) Å, b = 9.605(1) Å, c = 15.786(2) Å, α = 89.144(5)°, β = 88.279(5)°, γ = 76.068(5)°, V = 1275.4(3) Å3, space group P1, Z = 2. The unit cell of I contains two LevoH2+ ions, two Htba– ions, and six H2O molecules. The absolute structure of the crystal and the configuration of the chiral center in a levofloxacin molecule S are determined. Experiments for generating the second optical harmonics gave a positive result. Intermolecular hydrogen bonds (HBs) N–H···O and O–H···O in I form a bilayer system along the ab diagonal with hydrophilic moieties within a layer and hydrophobic moieties directed outward. The structure is stabilized by multiple HBs and the π–π interaction between the Htba–and LevoH2+ ions and between the LevoH2+ ions.

Structure of Hydrates of Metal Complexes with Barbituric Acids

Data on the synthesis and structure of metal complexes with barbituric (H2ba), thiobarbituric (H2tba) and 1,3-diethyl-2-thiobarbituric (HDetba) acids, which include a different number of coordinated water molecules, are summarized. Depending on the conditions, compounds of the composition [M(H2O)n−kLm]∙pH2O (Mm+ – metal ion; L− = Hba−, Htba− и Detba−; k≥0, p≥0) crystallize from the aqueous solution. The formation of neutral complexes of [M(H2O)n−kLm]∙pH2O containing different amounts of coordinated water molecules (n-k) occurs in the case of L− ligands with potentially different dentateness and/or bridging coordination. Crystallization of several hydrates [M(H2O)n−kLm]∙pH2O is also expected if water molecules can be both terminal and bridged ligands in them, and central ions, for example, of alkaline earth metals, easily form different coordination polyhedra. Synthesis of new hydrates can significantly expand the range of available compounds, including potentially useful functional properties.

Bis(μ3-barbiturato−O,O,O′)-(μ2-aqua)- aqua-barium(II): crystal structure, spectroscopic and thermal properties

Abstract A polymeric coordination compound, [Ba(H2O) 2(Hba)2] (1) (H2ba – barbituric acid, C4H4N2O3), was obtained. The structure of 1 was solved using powder X-ray diffraction methods. The Ba2+ ion in 1 formed a three-capped trigonal prism. The BaO9 polyhedra, connected with each other by the edges and faces, formed a chain. Several 4- and 12-membered cycles due to the bridging μ2-H2O and bridging μ3-Hba– also formed implementing a 3-D polymer structure. The structures of 1 and other thiobarbiturate complexes were compared. The replacement of a S atom by an O atom in the heterocyclic ligand Htba− (thiobarbiturate ion) of the compound Ba(H2O)2(Htba)2 resulted in changes of the coordination number Ba(II) and supramolecular structure. The intermolecular hydrogen bonds O–H⋯O and N–H⋯O formed a 3-D net where pronounced 2-D layers of Hba– ions could be found. A new topological net in 1 was observed. The IR and thermal stability were investigated.