Bis(2-carboxybenzoato-κO 1)bis[1-cyclopropyl-6-fluoro-4-oxo-7-(piperazin-4-ium-1-yl)-1,4-dihydroquinoline-3-carboxylato-κ2 O 3,O 4]manganese(II) dihydrate

The title compound, [Mn(C17H18FN3O3)2(C8H5O4)2]·2H2O or [Mn(cfH)2(1,2-Hbdc)2]·2H2O (cfH = ciprofloxacin = 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid, 1,2-bdc = benzene-1,2-dicarboxylate), has been prepared under hydrothermal conditions. The Mn2+ atom, located on an inversion centre, exhibits a distorted octahedral geometry, coordinated by four O atoms from two symmetry-related zwitterionic ciprofloxacin ligands in the equatorial positions and two O atoms of two 1,2-Hbdc ligands in the axial positions. The complex molecules are linked into a two-dimensional network through N—H⋯O and OW—H⋯O hydrogen bonds. A strong intramolecular hydrogen bond between the carboxyl/carboxylate groups of the 1,2-Hbdc anion is also present. The layers are further extended through off-set aromatic π–π stacking interactions of cfH groups [centroid–centroid distance of 3.657 (2) Å] into the final three-dimensional supramolecular arrays.


Related literature
For background to the antibiotic drug ciprofloxacin, see: Turel (2002); Xiao et al. (2005). The mechanisms of action of the quinolone antibacterial agents are either their inhibition of DNA gyrase (Topoisomerase II) or their interaction with the DNA molecule via a metal complex intermediate, see : Chulvi et al. (1991); Ruiz et al. (1993); Wallis et al. (1995). For related structures, see: Fabbiani & Dittrich (2008); Wang et al. (2009).

Experimental
Crystal data [Mn(C 17
The Ciprofloxacin and its deprotonated anions can show a number of different coordinating or bridging modes. The title complex consists of a Mn 2+ atom lying on an inversion center, two Ciprofloxacin ligands, two 1,2-benzenedicarboxylate ligands (1,2-bdc) and a water molecule (Fig. 1). The Ciprofloxacin ligand acts as chelating bidentate and the Mn(II) atom is coordinated by four oxygen atoms from two different Ciprofloxacin ligands and two oxygen atoms from two 1,2-bdc ligands. The N-H···O and OW-H···O hydrogen bonds link the discrete molecules into two-dimensional arrays (Table   1). These two-dimensional layers are further extended through off-set aromatic π-π stacking interplanar of cfH groups (centroid distance of 3.657 Å) into the final three-dimensional supramolecular arrays (Fig. 2).

Experimental
A mixture of Mn(OAc) 2 .4H 2 O (0.5 mmol), ciprofloxacin hydrochloride (0.25 mmol), 1,2-KHbdc (0.5 mmol), and water (7 ml) was stirred for 30 min in air (solution pH = 4.0), then transferred and sealed in an 18 ml Teflon-lined autoclave, which was heated at 110 °C for 96 h. After slow cooling to room temperature, yellow block crystals were filtered off, washed with distilled water, and dried at ambient temperature.

Refinement
The structure was solved by direct methods and successive Fourier difference synthesis. The H atoms bonded to C or N atoms were positioned geometrically and refined using a riding model [aromatic C-H = 0.93 Å, aliphatic C-H = 0.97 -0.98 Å and N-H = 0.90 Å, U iso (H) = 1.2U eq (C) and U iso (H) = 1.2U eq (N)]. The H atoms bonded to OW atoms were located in a difference Fourier maps and refined with OW-H = 0.84 Å and U iso (H) = 1.3U eq (OW). Fig. 1. ORTEP drawing of 1 with thermal ellipsoids at 30% probability. Symmetry code (i):x, -y, -z+1. Fig. 2. Perspective view of the three-dimensional supramolecular network in 1. The hydrogen bonds are indicated by pink dotted lines while the aromatic π-π stacking interaction is indicated by a green dotted line.

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.