Diaquabis[5-(2-pyridyl)tetrazolato-κ2 N 1,N 5]iron(II)

The title complex, [Fe(C6H4N5)2(H2O)2], was synthesized by the reaction of ferrous sulfate with 5-(2-pyridyl)-2H-tetrazole (HL). The FeII atom, located on a crystallographic center of inversion, is coordinated by four N-atom donors from two planar trans-related deprotonated L ligands and two O atoms from two axial water molecules in a distorted octahedral geometry. The FeII mononuclear units are further connected by intermolecular O—H⋯N and C—H⋯O hydrogen-bonding interactions, forming a three-dimensional framework.


Experimental
Crystal data [Fe(C 6
Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 (Rizk et al., 2005;Robin & Fromm, 2006). Hydrogen bonds, combining directionality, strength and selectivity, have been noted as the most versatile organizing force to assemble supramolecular structures (Kitagawa & Uemura, 2005). Due to their ability of providing multi-coordination sites as well as hydrogen bonding acceptors, tetrazole and its derivatives are receiving much attention in coordination and supramolecular chemistry (Mo et al., 2004;Song et al., 2008;Tao et al., 2008;Wang et al., 2003;Wen, 2008;Wu et al., 2007). Herein we report the crystal structure of an iron(II) In the title complex, the Fe II atom is located on a crystallographic center of inversion. It is six-coordinated by two O atoms from water molecules and four N-atom donors from two deprotonated N,N'-chelating L ligands binding via the pyridyl nitrogen and the tetrazole nitrogen in 1-position, in a transoid pseudo-octahedral geometry (Fig. 1).
Each Fe II mononuclear unit exhibits both proton donors (water molecules) and acceptors (uncoordinated N atoms on the tetrazole rings) and can therefore act as a good building unit for hydrogen bonded networks. As shown in Fig. 2 the O-H···N hydrogen bonds (Table 1)  Furthermore, the crystal structure of (I) also contains intermolecular C-H···O (Table 1) hydrogen-bonding interactions (Desiraju & Steiner, 1999), between the L ligands and the coordinated water molecules that interlink the twodimensional layers to form a three dimensional supramolecular framework.

Experimental
A solution of HL (0.05 mmol) in CH 3 OH (10 ml) in the presence of excess 2,6-dimethylpyridine (ca 0.05 ml for adjusting the pH value of the reaction system to basic conditions) was carefully layered on top of an aqueous solution (15 ml) of FeSO 4 (0.1 mmol) in a test tube. Yellow single crystals suitable for X-ray analysis appeared at the tube wall after ca one month at room temperature (yield ~30% based on HL). Elemental analysis calculated for (C 12 H 12 FeN 10 O 2 ): H 3.15, C 37.52, N 36.46%; found: H 3.08, C 37.37, N 36.68%.

Refinement
H atoms of the water molecules were located from the difference Fourier map and were allowed to ride on the O atom, with U iso (H) = 1.2 U eq (O). The remaining H atoms were included in calculated positions and treated in the subsequent refinement as riding atoms, with C-H = 0.93 (aromatic), and U iso (H) = 1.2 U eq (C).  Fig. 1. The molecular structure of the title complex. Displacement ellipsoids are drawn at the 30% probability level. Atoms labelled with the suffix A are generated by the symmetry operation (-x, -y + 1,-z + 2).  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 > σ(F 2 ) is used only for calculating Rfactors(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.