Cadmium(II) and calcium(II) complexes with N,O-bidentate ligands derived from pyrazinecarboxylic acid

The synthesis and characterization of cad- mium(II) and calcium(II) complexes with N , O -bidentate ligands derived from pyrazinecarboxylic acid (3-hydroxy- 2-quinoxalinecarboxylic acid HL 1 , pyrazine-2-carboxylic acid HL 2 ) are reported. Obtained compounds [Cd(L 1 ) 2 (H 2 O) 2 ](H 2 O) 2 ( 1 ), [Cd(L 2 ) 2 ] n ( 2 ) and [Ca(L 2 ) 2 (H 2 O) 4 ]( 3 ) were studied by elemental analyses, IR, Raman spectros- copy and thermogravimetric methods (TG, DTG, DSC). In addition, the molecular structure of complex 1 has been determined by X-ray single crystal diffraction. Thermal analysis reveals a decomposition process of 1 , 3 complexes in multiple stages. The data obtained from TG and DSC curves for 1 , 3 confirm not only the presence but also the nature of water (crystallization and coordination) and the stoichiometry of the studied metal complexes. The results of thermal studies are in good agreement with their crystal structures. Thermal behavior of complex 2 indicates a single complete decomposition process of the sample. In addition, complex 2 as a coordination polymer is the most stable all of them and the thermal stability of the obtained complexes can be ordered in the following sequence: 1 \ 3 2

Mimetics of manganese catalase as synthetic antioxidants

The coordination chemistry of manganese complexes with heteroaromatic ligands have received considerable attention in modern inorganic chemistry due to its wide range of applications. One of them is related with its potential biological role associated with prevention of oxidative stress injuries. Manganese complexes are one of the most versatile and interesting synthetic systems that can act as artificial mimics of manganese-containing metalloenzymes such as manganese catalase (Mn-CAT). Due to the potential use as catalytic scavengers of H2O2, numerous and diverse, very structurally interesting Mn compounds exhibiting CAT-like activity have been reported so far. In this short review, the relevant features of both, structural, as well as, functional mimics of manganese catalase and their CAT-like activity are presented and some insights into the role of the bridging ligands, endogenous bases, and first- and second-sphere effects on the catalysis are discussed

Thermal behavior of manganese(II) complexes with pyridine-2,3-dicarboxylic acid

In this study, we analyzed influence of the type of the syntheses used: hydrothermal and non-hydrothermal on pyridine-2,3-dicarboxylic acid (2,3pydcH 2 ) coordina- tion fashion. Two manganese(II) complexes: [Mn(H 2 O) 3 (2,3pydc)] n ( 1 ) and [Mn(H 2 O) 6 ][Mn(2,3pydcH) 3 ] 2 ( 2 ) were successfully synthesized from the non-hydrothermal reac- tion system containing organic ligand and different Mn(II) salts. The received complexes have been prepared and characterized by spectroscopic (IR, Raman), structural (X-ray single crystal), and thermogravimetric methods. The results of the crystal study give some evidence that ligand exhibits various topological structures and interest- ing properties. Pyridine-2,3-dicarboxylic acid acts as monodicarboxylate N,O-chelating anion (complex 2 )ora doubly deprotonated three-dentate- N , O , O 0 dicarboxylate ion (complex 1 ). In the [Mn(H 2 O) 6 ][Mn(2,3pydcH) 3 ] 2 the coordination geometry around Mn(1) ion can be considered as being distorted octahedron {MnN 3 O 3 }. The Mn(2) cat- ion possesses the same coordination polyhedron (octahe- dral). We have also analyzed influence of furnace atmosphere on the thermal behavior and the kind of final product. The sample of ( 1 ) decomposes in four stages in N 2 (368–1073 K) and the final residue is MnO 2 . The ther- mogram of ( 2 ) exhibits three main distinct decomposition steps (383–973 K). A residue of MnO is remained. In both air and nitrogen atmosphere, Mn(II) complexes ( 1 ) and ( 2 ) keep unchanged over all steps of decomposition. Only the final residues are different (Mn 2 O 3 are formed). The course of pyrolysis and molecular structure of the complexes lead to the same conclusion about the strength of metal–ligand bonds. On the basis of the above results, it is concluded that the thermal stability of the manganese(II) compounds is slightly different