Coordination Polyhedron Of Central Atom Research Articles

Synthesis of coordination compounds via dehalogenation of zinc bromoacetate in presence of some amines

The dehalogenation reactions of pure zinc bromoacetate and its mixtures with hexamethylenetetramine, 2,2′-bipyridine, 1,10-phenanthroline were studied in water solutions. Due to the decomposition of hexamethylenetetramine during reaction, the cadmium bromoacetate–hexamethylenetetramine system was also studied. The four new coordination compounds, catena-[bis(μ 2-α-hydroxyacetato-κ 3 O 1, O 2: O 1′)-zinc], catena[μ 2-1-(8-carboxylateethyl)-1,3,5,7-tetra-aza-adamantan-1-ium- N, O′]-dibromo-cadmium, dibromo-(2,2′-bipyridine- N, N′)-zinc, dibromo-(1,10-phenanthroline- N, N′)-zinc were synthesised and characterised by elemental and thermal analysis, IR and UV–vis spectroscopy, and X-ray crystallography. All compounds are air stable and well soluble in water. The zinc hydroxyacetate creates two-dimensional 4-c uninodal net. The zinc atoms are four and six coordinated and the cadmium atom is five coordinated. The coordination polyhedra of central atoms can be described as octahedron and trapezoidal pyramid for Zn and Cd polymers, respectively, and as trigonal pyramid for ZnBr 2 complexes. The bond valences considerations show that the chelating amines are bonded almost two times stronger to the central atoms than the chelating carboxylate groups. In the structures of polymeric compounds exist O–H⋯O, C–H⋯O, C–H⋯N and C–H⋯Br hydrogen bonds. The IR spectra show typical vibrations for chelating amine molecules. The thermal decomposition of studied compounds proceeds via multiple steps with gradual evolution of ligands.

Coordination behaviour of 2,2′-bipyridine towards the dichloroacetates of zinc and cadmium

The coordiantion compounds [Zn(C10H8N2)(Cl2HCCOO)(H2O)3]−·[Zn(C10H8N2)(Cl2HCCOO)3]+ and [Cd(C10H8N2)2(Cl2CHCOO)2] were synthesised and characterised by elemental and thermal analysis, IR and UV–VIS spectroscopy, and X-ray crystallography. The complexes are air stable and well-soluble in water. The zinc atoms are five and six coordinated and the cadmium atom is six coordinated. The coordination polyhedra of central atoms can be described as trapezoidal pyramid and octahedron in zinc compound and as rectangular bipyramid strongly distorted towards skew trapezoidal bipyramid in cadmium compound. In both compounds all dichloroacetate groups are monodentate. The bond valences considerations show that all 2,2′-bipyridine molecules are bonded almost 2 times stronger than carboxylate groups. In the structure of zinc compound exist O–H···O hydrogen bonds and in both structures can be found weak C–H···O hydrogen bonds. Additionally, both compounds are pile-stacked by π···π interactions. The IR spectra show typical vibrations for chelating 2,2′-bipyridine molecules and terminal monodentate carboxylate groups. The thermal decomposition studies show zinc compound decomposes in 4 steps and cadmium compound decomposes in 5 steps with formation of oxides as a final products. The ligands decompose gradually, first dichloroacetates and next 2,2′-bipyridine.

Coordination polymer of lanthanum: synthesis, properties and crystal structure of [La(4,4′-bipyridine)(CCl2HCOO)3(H2O)] n

A new mixed ligand complex of general formula [La(H2O)(4,4′-bpy)(CCl2HCOO)3] n has been synthesized and characterized by elemental and thermal analysis, IR spectroscopy and conductivity studies. The crystal and molecular structure was determined. The lanthanum atom is ten coordinate by four oxygen atoms from two chelating tridentate dichloroacetate substituents, two oxygen atoms from two bidentate bridging dichloroacetate groups, two oxygen atoms from two bridging tridentate dichloroacetate substituent, one oxygen atom of water molecule and one nitrogen atom from 4,4′-bipyridyl substituent. The coordination polyhedron of central atom can be described as tetradecahedron. The molecules are built up by O–H ··· N hydrogen bonds to a two-dimensional network.