Diaquabis{[1-hydroxy-2-(1H-imidazol-3-ium-1-yl)ethane-1,1-diyl]bis(hydrogen phosphonato)}manganese(II)

In the title compound, [Mn(C5H9N2O7P2)2(H2O)2], the MnII atom (site symmetry ) is coordinated by four phosphonate O atoms from a pair of partially deprotonated 1-hydroxy-2-(imidazol-3-yl)ethane-1,1-bisphophonic acid ligands (imhedpH3 −) and two water molecules, resulting in a slightly distorted trans-MnO6 octahedral geometry for the metal ion. In the ligands, the imidazole units are protonated and two of the hydroxy O atoms of the phosphonate groups are deprotonated and chelate the MnII, thus forming the neutral molecule of the title compound. The two protonated O atoms within the phosphonate groups of one imhedpH3 − ligand act as hydrogen-bond acceptors for a bifurcated hydrogen bond originating from the coordinated water molecule. The phosphonate units of neigboring molecules are connected with their equivalents in neighboring molecules via two types of inversion-symmetric hydrogen-bonding arrangements with four and two strong O—H⋯O hydrogen bonds, respectively. The two interactions connect molecules into infinite chains along [111] and [110], in combination forming a tightly hydrogen-bonded three-dimensional supramolecular network. This network is further stabilized by additional hydrogen bonds between the protonated imidazole units and one of the coordinated P—O O atoms and by additional O—H⋯O hydrogen bonds between the water molecules and the P=O O atoms of neigboring molecules.

In the title compound, [Mn(C 5 H 9 N 2 O 7 P 2 ) 2 (H 2 O) 2 ], the Mn II atom (site symmetry 1) is coordinated by four phosphonate O atoms from a pair of partially deprotonated 1-hydroxy-2-(imidazol-3-yl)ethane-1,1-bisphophonic acid ligands (imhedpH 3 À ) and two water molecules, resulting in a slightly distorted trans-MnO 6 octahedral geometry for the metal ion. In the ligands, the imidazole units are protonated and two of the hydroxy O atoms of the phosphonate groups are deprotonated and chelate the Mn II , thus forming the neutral molecule of the title compound. The two protonated O atoms within the phosphonate groups of one imhedpH 3 À ligand act as hydrogen-bond acceptors for a bifurcated hydrogen bond originating from the coordinated water molecule. The phosphonate units of neigboring molecules are connected with their equivalents in neighboring molecules via two types of inversion-symmetric hydrogen-bonding arrangements with four and two strong O-HÁ Á ÁO hydrogen bonds, respectively. The two interactions connect molecules into infinite chains along [111] and [110], in combination forming a tightly hydrogen-bonded three-dimensional supramolecular network. This network is further stabilized by additional hydrogen bonds between the protonated imidazole units and one of the coordinated P-O O atoms and by additional O-HÁ Á ÁO hydrogen bonds between the water molecules and the P O O atoms of neigboring molecules.

Related literature
For a review of the structures and applications of lanthanide phosphonates, see: Mao (2007). For other complexes based on the imhedpH 4 ligand, see: Cao et al. (2007Cao et al. ( , 2008. For the structures and properties of some metal organophosphonates, see: Rao et al. (2004); Yang et al. (2009).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: ZL2255).

Comment
Organophosphonic acids have attracted much attention in the field of organic-inorganic hybrid materials because of their flexible coordination modes and strong coordination ability (Mao 2007;Rao et. al. 2008;Yang et al. 2009). Compared to other organophosphonic acid derivatives, there are only few complexes of metal-organic compounds with 1-hydroxy-2-(imidazol-3-yl)ethane-1,1-bisphophonic acid (imhedpH 4 ) and its anions as the ligand (Cao et al. 2007;Cao et al. 2008).
Herein, we thus report the synthesis and structure of the title compound, a manganese complex of the monoanion of the aformentioned acid.
The title compound crystallizes in the triclinic system with the space group P1. The Mn II ion adopts a slightly distorted octahedral geometry and is located on a crystallographic inversion center. Two pairs of phosphonate oxygen atoms (O1, O4, O1 i , O4 i ; symmetry code: i, -x, -y, -z) from two equivalent imhedpH 3 ligands define the equatorial plane, while two equivalent water molecules (O8 and O8  These two protonated O atoms O3 and O6 act as a hydrogen bond acceptors for a bifurcated H bond from the coordinated water molecule (O8, see Table 1 for numerical values).
The phosphonate units are connected with their equivalents in neighboring molecules via two types of inversion symmetric hydrogen bonding arrangements (Fig. 2 and in combination to a tightly hydrogen bonded three-dimensional supramolecular network (Fig. 3). This network is further stabilized by additional hydrogen bonds between the protonated imidazole units towards one of the coordinated P-O oxygen atoms (O4) and by additional O-H···O hydrogen bonds between the water molecule and P═O oxygen atoms (O2) of neigboring molecules (Table 1).

Experimental
The title compound was prepared by the hydrothermal reaction of a mixture of MnSO 4 (0.

Refinement
All non-hydrogen atoms were found in Fourier maps and were refined anisotropically. Hydrogen atoms attached to C and N atoms were positioned geometrically with bond distances of 0.95 or 0.99 Å for C-H and 0.88 Å for N-H. Water and hydroxy H atoms were located in a difference Fourier map and refined with distance restraints on all O-H bond lengths with distances of 0.85 (1) Å, and the H···H distance within the water molecule was restrained to 1.55 (2) Å. The isotropic displacement parameters of H atoms are related to the non-H atom to which they are bonded, viz. U iso (H) = 1.2 U eq (parent).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.