Flávia C. Machado

A two-dimensional oxamate- and oxalate-bridged Cu(II)Mn(II) motif: crystal structure and magnetic properties of (Bu4N)2[Mn2{Cu(opba)}2ox].

A new compound of formula (Bu4N)2[Mn2{Cu(opba)}2ox] (1) [Bu4N(+) = tetra-n-butylammonium cation, H4opba = 1,2-phenylenebis(oxamic acid), and H2ox = oxalic acid] has been synthesized and magneto-structurally investigated. The reaction of manganese(II) acetate, [Cu(opba)](2-), and ox(2-) in dimethyl sulfoxide yielded single crystals of 1. The structure of 1 consists of heterobimetallic oxamato-bridged Cu(II)Mn(II) chains which are connected through bis-bidentate oxalate coordinated to the manganese(II) ions to afford anionic heterobimetallic layers of 6(3)-hcb net topology. The layers are interleaved by n-Bu4N(+) counterions. Each copper(II) ion in 1 is four-coordinate in a square planar environment defined by two amidate-nitrogen and two carboxylate-oxygen atoms from the two oxamate groups of the obpa ligand. The manganese(II) ion is six-coordinate in a somewhat distorted octahedral surrounding that is built by two oxalate-oxygen and four carbonyl-oxygen atoms from two [Cu(opba)](2-) units. The magnetic properties of 1 in the temperature range 1.9-300 K correspond to those expected for the coexistence of intralayer antiferromagnetic interactions of the type copper(II)-manganese(II) across oxamato and manganese(II)-manganese(II) through oxalato bridges plus a weak spin canting in the very low temperature domain. Simulation of the magnetic data through quantum Monte Carlo methodology reveals the magnitude of the intralayer magnetic interactions [J(CuMn) = -32.5(3) cm(-1), and J(MnMn) = -2.7(3) cm(-1)], their values being within the range of those previously observed in lower nuclearity systems.

2-D coordination polymers of copper and cobalt with 3,4-pyridinedicarboxylic acid: synthesis, characterization, and crystal structures

Two new complexes involving 3,4-pyridinedicarboxylic acid (3,4-H2pdc), copper(II) and cobalt(II) complexes, {[Cu(3,4-Hpdc)2(H2O)2]·2dmso}n (1) and {[Co(3,4-Hpdc)2(H2O)2]·2H2O·2dmso}n (2) (dmso = dimethylsulfoxide), have been synthesized by the diffusion method and characterized by elemental analysis, IR spectroscopy, thermal analysis, powder and single-crystal X-ray diffraction analysis, and electron paramagnetic resonance (EPR). In both compounds, the metal coordination sphere is composed of a trans-MO4N2 core and adopts a distorted octahedral geometry in accordance with X-ray diffraction and EPR results. 3,4-Hpdc− ligands bridge the metal centers giving two-dimensional (2-D) coordination polymers with four-connected uninodal nets of (4,4) topology. Graphical Abstract

Insights into the multi-equilibrium, superstructure system based on β-cyclodextrin and a highly water soluble guest.

Pentamidine isethionate (PNT) is an antiprotozoal active in many cases of leishmaniasis, despite the present limitations including high toxicity and parenteral administration. In the present work, a PNT encapsulation strategy into β-cyclodextrin cavity at 1:1 and 2:1 (βCD:PNT) molar ratios was used in order to improve the drugs physical and chemical properties. Combining thermodynamic and structural approaches such as isothermal titration calorimetry (ITC), electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance ((1)H NMR, and ROESY) the inclusion process and the thermodynamics parameters were identified. ITC and ESI-MS experimental data suggest the simultaneous formation of different supramolecular complexes in solution. Moreover, NMR data are in accordance with these results, suggesting a deep inclusion of PNT into the βCD cavity, through correlations observed in 2D ROESY contour maps. The systems were also characterized by FTIR, TG/DTA and SEM. These techniques indicate the formation of inclusion complex in the solid state. In vivo PNT activity was evaluated orally in mice. The inclusion complex showed a significant reduction of parasite load compared to free PNT.

A Co(II) 1D coordination polymer constructed from 1,3-bisbenzyl-2-oxoimidazoline-4,5-dicarboxylic acid: crystal structure and magnetic properties

A new complex involving 1,3-bisbenzyl-2-oxoimidazoline-4,5-dicarboxylic acid (H2L) and a cobalt(II) metal ion designated [Co(L)(H2O)2]n has been synthesized under solvothermal conditions and characterized by elemental analyses, IR spectra, thermogravimetric analysis, single crystal X-ray diffraction and magnetization. The new compound crystallizes as pink crystals in an orthorhombic system with space group Pbca. A unit cell with 8 asymmetric units is present, each containing a Co(II) center with distorted octahedral geometry and a coordination sphere consisting of one nitrogen and five oxygen ligands. Bridging carboxylate groups are responsible for the formation of a 1D polymer. Adjacent chains are connected through OH⋯O hydrogen bonds involving coordinated water molecules leading to the formation of supramolecular arrangement. Low-temperature electron paramagnetic resonance (EPR) measurements identified that Co ions are in the divalent charge state in orthorhombic or less symmetry in high-spin (HS) configuration with principal values of g tensor of g1 = 5.5(2), g2 = 3.0(2) and g3 = 2.0(1). Magnetic susceptibility measurements as a function of temperature were analyzed by the standard Curie–Weiss law including diamagnetic contributions. Magnetic data were consistently explained by HS configuration of Co2+ ions with very small contribution of anti-ferromagnetic coupling.

Study of the supramolecular interactions of carboxylic acids used as versatile ligands in coordination chemistry

Carboxylate ligands are very versatile because they can adopt different coordination modes towards metal cations, such as monodentate, bidentate-chelate, bidentate bridging and monoatomic bridging. Because of this versatility, these ligands have been widely used in coordination chemistry. In this study the three dimensional structure of the crystal arrangement of 2,5-thiophenedicarboxylic (H2TPD), trans-3-(3- pyridyl)acrylic (HPYA), and 4,4′-sulfonyldibenzoic (H2SFD) acids are determined in order to investigate their supramolecular properties for coordination polymers and metal-organic framework (MOF) constructions.

The zwitterionic structure of 2-hydroxy-4-[(2-hydroxybenzylidene)amino]benzoic acid

The title compound, C₁₄H₁₁NO₄, exists in the solid phase in the zwitterionic form, 2-{[(4-carboxy-3-hydroxyphenyl)iminiumyl]methyl}phenolate, with the H atom from the phenol group on the 2-hydroxybenzylidene ring transferred to the imine N atom, resulting in a strong intramolecular N-H∙∙∙O hydrogen bond between the iminium H atom and the phenolate O atom, forming a six-membered hydrogen-bonded ring. In addition, there is an intramolecular O-H∙∙∙O hydrogen bond between the carboxylic acid group and the adjacent hydroxy group of the other ring, and an intermolecular C-H∙∙∙O contact involving the phenol group and the C-H group adjacent to the imine bond, connecting the molecules into a two-dimensional network in the (103) plane. π-π stacking interactions result in a three-dimensional network. This study is important because it provides crystallographic evidence, supported by IR data, for the iminium zwitterionic form of Schiff bases.

Dipotassium tetra­aqua­bis­[3,5-bis­(dicyano­methyl­ene)cyclo­pentane-1,2,4-trionato(1−)-κN]cobaltate(II)

The title structure, K2[Co(C11N4O3)2(H2O)4], is isotypic with K2[Fe(C11N4O3)2(H2O)4]. The CoII atom is in a distorted octahedral CoN2O4 geometry, forming a dianionic mononuclear entity. Each dianionic unit is associated with two potassium cations and interacts with adjacent units through O—H⋯N and O—H⋯O hydrogen bonds.