The monoclinic polymorph of catena-poly[[diaquamanganese(II)]-μ-oxalato-κ4O1,O2:O1′,O2′]

The title polymer, [Mn(C2O4)(H2O)(2)](n), was synthesized by the reaction of manganese( II) nitrate tetrahydrate with a proton-transfer compound, ( pipzH(2))( ox) ( where oxH(2) is oxalic acid and pipz is piperazine), in aqueous solution. The structure features a six-coordinate Mn2+ ion located on a twofold rotation axis, with a distorted octahedral geometry [ Mn-O = 2.1728 ( 8) - 2.1914 ( 9) angstrom]. The bond angles show that the two coordinated water molecules are arranged trans. One-dimensional linear chains are formed through bis-bidentate oxalate ligands bridging the Mn-II ions. These structural units are held together by O - H center dot center dot center dot O hydrogen bonds. A neutron diffraction study of [Mn(mu-ox)(D2O)(2)](n), using powdered samples, has been published recently in the same space group [ Sledzinska, Murasik & Fischer ( 1987). J. Phys. Solid State Phys. 20, 2247 2259]. However, it should be noted that an orthorhombic polymorph for the title polymer is also known [ Huizing, van Hal, Kwestroo, Langereis & van Loosdregt ( 1977). Mater. Res. Bull. 12, 605 - 611; Lethbridge, Congreve, Esslemont, Slawin & Lightfoot ( 2003). J. Solid State Chem. 172, 212 - 218]. The present single-crystal X-ray study deals with the monoclinic polymorph. This phase is isostructural with the Co-II analogue.