Crystal structure analyses of some addition compounds of glycine

Abstract

Abstract The crystal structure of three addition compounds of glycine, viz., bisglycine barium(II) dichloride monohydrate, (NH3 +CH2COO−)2Ba++Cl2 − · H2O; bisglycine strontium(II) dichloride trihydrate, (NH3 +CH2COO−)2Sr++Cl2 − · 3H2O;and bisglycine manganese(II) dichloride, (NH3+CH2COO−)2Mn++Cl2 −, hereafter refered as GlycBa, GtycSr and GlycMn, respectively, were solved by single-crystal x-ray diffraction methods and refined to R values of 0.034, 0.058 and 0.074, respectively, using visually estimated and counter measured intensity data. GlycBa and GlycSr crystallize in the orthorhombic system of space group Pbcn, with four formula units per unit cell of dimensions a = 8.31, b = 14.84 and c = 9.32 Å; and a = 16.42, b = 9.35 and c = 8.26 Å, respectively, and GlycMn crystallizes in the triclinic system of space group P[unk], with one formula unit per unit cell of dimensions a = 4.97, b = 7.92 and c = 6.98 Å, α = 107.4, β = 115.9 and γ = 87.0°. The glycine molecule is almost planar except for the nitrogen atom, which deviates by 0.145, 0.113 and 0.677 Å. The conformation of the glycine molecule is synplanar with conformation angle of 5.8, 6.7 and 29.2° and the molecule exists in zwitterion configuration in these structures. Nitrogen, chlorine and water-oxygen atoms take part in the hydrogen-bond formation and only one of the carboxyl-oxygen atoms is acceptor of an hydrogen bond in GlycBa and GlycSr whereas both the carboxyl-oxygen atoms are acceptors of hydrogen bonds in GlycMn. The average values of N…O, N…Cl, OCl and O…O bonds are 2.86, 3.21, 3.23 and 2.84 Å, respectively. The coordination number is 9 in GlycBa and GlycSr and is 6 in GlycMn. Oxygen and chlorine atoms are coordinated to the metal ion in GlycBa and GlycMn and chlorine atoms do not enter into coordination with the metal ion in GlycSr. The coordination polyhedron around Ba ion can be visualized as a distorted antiprism with an extra atom and around Sr ion as a distorted antiprism with an extra atom or as a distorted regular prism and around Mn ion as an octahedron. Glycine residue acts as a bidentate, forming four-membered chelate rings with metal ions in GlycBa and GlycSr and acts as an unidentate in GlycMn.