Novel eight-coordinated Cd(II) complexes with two homologous pyridine alcohols. Crystal structure, spectroscopic and thermal properties

Supramolecular architectures in metal(II) (Cd/Zn) halide/nitrate complexes of cytosine/5-fluorocytosine

Three new metal(II)-cytosine (Cy)/5-fluorocytosine (5FC) complexes, namely bis(4-amino-1,2-dihydropyrimidin-2-one-κN³)diiodidocadmium(II) or bis(cytosine)diiodidocadmium(II), [CdI₂(C₄H₅N₃O)₂], (I), bis(4-amino-1,2-dihydropyrimidin-2-one-κN³)bis(nitrato-κ²O,O')cadmium(II) or bis(cytosine)bis(nitrato)cadmium(II), [Cd(NO₃)₂(C₄H₅N₃O)₂], (II), and (6-amino-5-fluoro-1,2-dihydropyrimidin-2-one-κN³)aquadibromidozinc(II)-6-amino-5-fluoro-1,2-dihydropyrimidin-2-one (1/1) or (6-amino-5-fluorocytosine)aquadibromidozinc(II)-4-amino-5-fluorocytosine (1/1), [ZnBr₂(C₄H₅FN₃O)(H₂O)]·C₄H₅FN₃O, (III), have been synthesized and characterized by single-crystal X-ray diffraction. In complex (I), the Cd^II ion is coordinated to two iodide ions and the endocyclic N atoms of the two cytosine molecules, leading to a distorted tetrahedral geometry. The structure is isotypic with [CdBr₂(C₄H₅N₃O)₂] [Muthiah et al. (2001). Acta Cryst. E57, m558-m560]. In compound (II), each of the two cytosine molecules coordinates to the Cd^II ion in a bidentate chelating mode via the endocyclic N atom and the O atom. Each of the two nitrate ions also coordinates in a bidentate chelating mode, forming a bicapped distorted octahedral geometry around cadmium. The typical interligand N-H...O hydrogen bond involving two cytosine molecules is also present. In compound (III), one zinc-coordinated 5FC ligand is cocrystallized with another uncoordinated 5FC molecule. The Zn^II atom coordinates to the N(1) atom (systematic numbering) of 5FC, displacing the proton to the N(3) position. This N(3)-H tautomer of 5FC mimics N(3)-protonated cytosine in forming a base pair (via three hydrogen bonds) with 5FC in the lattice, generating two fused R₂²(8) motifs. The distorted tetrahedral geometry around zinc is completed by two bromide ions and a water molecule. The coordinated and nonccordinated 5FCs are stacked over one another along the a-axis direction, forming the rungs of a ladder motif, whereas Zn-Br bonds and N-H...Br hydrogen bonds form the rails of the ladder. The coordinated water molecules bridge the two types of 5FC molecules via O-H...O hydrogen bonds. The cytosine molecules are coordinated directly to the metal ion in each of the complexes and are hydrogen bonded to the bromide, iodide or nitrate ions. In compound (III), the uncoordinated 5FC molecule pairs with the coordinated 5FC ligand through three hydrogen bonds. The crystal structures are further stabilized by N-H...O, N-H...N, O-H...O, N-H...I and N-H...Br hydrogen bonds, and stacking interactions.

Effective catalytic disproportionation of aqueous H2O2 with di- and mono-nuclear manganese(II) complexes containing pyridine alcohol ligands

The two novel manganese(II) complexes with 2-hydroxymethylpyridine (2-CH2OHpy) {[Mn2(μ-Cl)2(2-CH2OHpy)4]Cl2·2H2O (1)} and 2-hydroxyethylpyridine (2-(CH2)2OHpy) {[Mn(2-(CH2)2OHpy)2(NCS)2] (2)} were synthesized and characterized by means of X-ray diffraction, IR, EPR, HF EPR spectroscopy, magnetic and TG/DTG data. The complexes show catalase-like activity in neutral aqueous solution since they were able to disproportionate H2O2 to harmless H2O and O2. Both complexes act as true catalysts since they reverted to their original form after depleting all the H2O2, as suggested by the operando resonant inelastic X-ray spectroscopy (RIXS) measurements.

Eight- and six-coordinated Mn(II) complexes of heteroaromatic alcohol and aldehyde: crystal structure, spectral, magnetic, thermal and antibacterial activity studies

Crystal, molecular and electronic structure of new manganese(II) compounds: [Mn(2-CH2OHpy)2(NO3)2] (1), [Mn(4-CHO-5-MeIm)2(NO3)2] (2) and [Mn(4-CHO-5-MeIm)2Cl2] (3), where 2-hydroxymethylpyridine (2-CH2OHpy) and 5(4)-carbaldehyde-4(5)-methylimidazole (5(4)-CHO-4(5)-MeIm), have been characterised using X-ray, spectroscopic, magnetic and TG/DTG data. In compounds 1 and 2, the Mn(II) ion is eight-coordinated forming distorted pseudo-dodecahedron, that is rather unusual for the manganese(II) complexes, whereas in 3 the Mn(II) ion environment is a distorted octahedron. The high coordination number (CN=8) of 1 and 2 results from bidentate character of the nitrate ligands. The X-band EPR spectra of compounds 2 and 3 exhibit fine structure signals resulting from zero-field splitting (ZFS) of the spin states for high spin d(5) Mn(II), whereas for 1 the broad isotropic signals were observed. The estimation of ZFS for individual Mn(II) ions was carried out for all compounds using DFT calculations. The free ligands and their manganese(II) complexes have been tested in vitro against gram-positive and gram-negative bacteria in order to assess their antimicrobial properties.

Two novel lead(II) complexes of 2-(hydroxymethyl)pyridine: a threefold diamondoid supramolecular network based on Pb4O4 cores and a two-dimensional (4,4) network based on Pb2O2 units

Reactions of 2-(hydroxymethyl)pyridine (Hhmp) with PbCl2 and Pb(NO3)2 at room temperature led to the formation of two novel compounds, namely tetrakis[μ3-(pyridin-2-yl)methanolato]-tetrahedro-tetrakis[chloridolead(II)], [Pb4(C6H6NO)4Cl4], (I), and poly[(μ2-nitrato)[μ2-(pyridin-2-yl)methanolato]lead(II)], [Pb(C6H6NO)(NO3)]n, (II). Compound (I) exhibits a tetranuclear Pb4O4 cubane structure, which is connected through π-π stacking interactions between the pyridine groups of the (pyridin-2-yl)methanolate (hmp(-)) ligands and through C-H···Cl interactions to form an interesting threefold diamondoid network. Compound (II) possesses two-dimensional (4,4)-sql topology based on a Pb2O2 unit, which is further extended into a three-dimensional supramolecular network through π-π stacking interactions between adjacent pyridine rings and through C-H···O interactions between the pyridine C atoms of the hmp(-) ligands and the nitrate anions.