SYNTHESIS, CHARACTERIZATION AND STRUCTURAL DETERMINATION OF SOME TRANSITION METAL FLUORIDE CHELATES

Abstract

Nitrogen donor ligands have been found to cause d-block metal fluorides to dissolve in water ethanol and methanol. From some of these solutions metal fluoride hydrate complexes were isolated. The work had been concentrated on fluorides of metals that have a role in enzymes; copper, zinc, nickel and cobalt. A large number of fluoride complexes have been made and some of them produced crystals suitable for the X-ray analysis. The X-ray and infrared studies indicated that the structures were stabilized by extensive fluoride hydrogen bonding interactions involving ligand or lattice molecules. In some fluoride complexes, the fluoride hydrogen bonds were very strong. The X-ray structure determination of [Ni(im)6]F2.5H2O (1a) (im = imidazole) revealed the presence of octahedral configuration around nickel. This complex presents a rare example of a complex with lattice water hydrogen bonded to lattice fluoride. Both the intra and inter-molecular hydrogen bonds were observed in the structure of [Ni(im)6]F2.5H2O (1a). The lattice fluorides are connected by short hydrogen bonds to lattice waters. Moreover intra-molecular hydrogen bonds connect the lattice water to NH group of imidazole. The intermolecular hydrogen bonds between lattice fluoride and NH group of imidazole and between lattice water of one molecule and lattice fluoride of other molecule also exists and stabilizes the crystal. In [Ni(dmen)2F2].8H2O (1b) (dmen = 1,1,N,N-dimethylethane-1,2-diamine) nickel has some what distorted octahedral geometry, in which it is coordinated to two fluorides and two 1,1,N,N-dimethylethane-1,2-diamine ligands (dmen). The fluoride ligands are trans to each other and occupy axial positions. This is an example of molecular complex. xi The two hydrogen bonds of apical fluorides are R(F---O) = 2.6104(11) and 2.6798(12) Å which are among the short F---HO hydrogen bonds between lattice water and fluoride ligand in a neutral complex. The X-ray crystal structure analysis of [Co(im)6]SiF6 (2a) (im = imidazole) provided a rare example of complex where SiF62ionpresentascounter ion. SiF62indicates regular octahedral geometry with all FSiF bond angles of 90.82(4) and 89.18(3)°. Each fluoride ion of hexafluorosilicate moiety is hydrogen bonded to two nitrogen atoms of coordinated imidazole with NH---F = 2.9345(12) Å. The SiF62anion join [Co(im)6]2+ cations through hydrogen bonds forming infinitely extended chains. A complex of cobalt and 1,10-phenanthroline [Co(phen)3]F2.2H2O (2c) was prepared. The X-ray analysis revealed weak hydrogen bonds between lattice fluoride and lattice waters. There are also strong hydrogen bonds between lattice waters with R(O2---O1) = 2.780(2) Å. This distance is significantly shorter than sum of their Vander Waal’s radii (3.04 Å). The crystal structure of [Co(bpy)2(CO)3]F.8H2O (2d) (bpy = 2,2 ́-bipyridine) showed that the cobalt has distorted octahedral environment. The complex has been synthesized without adding any carbonate. The source of carbonate could be air CO2, dissolved and get trapped in lattice during slow evaporation. OH---O and OH---F hydrogen bonds generate a one dimensional chain. The R (O---F) bond length in this complex is within the range of short lattice fluoride lattice water hydrogen bond distances. Two isostructural complexes [Co(dmen)2F2].2H2O (2b) and [Zn(dmen)2F2].2H2O (3) (dmen = 1,1,N,N-dimethylethan-1,2-diamine) were prepared. Their X-ray analysis revealed that coordinated fluorides occupied apical positions in both complexes. Lattice waters are strongly hydrogen bonded to apical fluorides. These F---HOH hydrogen bonds extend through the lattice and stabilize the complex. A relatively weak intramolecular hydrogen bond exists between axial fluorides and NH groups. The linear chain complex [Cu(isna)4SiF6].9H2O (4) (isna = isonicotinamide) was prepared by reacting copper fluoride in methanol water mixture with isonicotinamide (isna). The X-ray structure of the complex [Cu(isna)4SiF6].9H2O (4) revealed the presence of chains built up by [Cu(isna)4]2+ and SiF62- ions, attached to each other via CuFSi bonds. The coordination geometry around the copper is tetragonally distorted octahedral. The two axial copper to fluoride bonds are slightly elongated due to John Teller’ s distortion in octahedral Cu(II) complexes. Geometry around SiF62is almost regular octahedral. Each fluoride of coordinated SiF62- is hydrogen bonded to two ring nitrogen atoms belonging to ligand isonicotinamide with R(N--- F) = 2.838(3) Å. Water molecule O(2) in lattice form four hydrogen bonds in tetrahedral geometry, one with amide nitrogen, second with carbonyl oxygen and two with water molecules.