The triclinic form of di-μ-aqua-bis[diaquabis(thiocyanato-κN)iron(II)]–1,4-bis(4H-1,2,4-triazol-4-yl)benzene (1/3)

In the title compound, [Fe2(NCS)4(H2O)6]·3C10H8N6, the centrosymmetric dinuclear complex contains two FeII ions bridged by two aqua ligand O atoms, forming a four-membered ring. The slightly distorted octahedral coordination environment of the two FeII ions is completed by two monodentate aqua ligands and two thiocyanate ligands. One of the 1,4-bis(4H-1,2,4-triazol-4-yl)benzene molecules lies across an inversion center. In the crystal, O—H⋯N hydrogen bonds connect the components, forming a two-dimensional network parallel to (011). In addition, π–π stacking interactions involving the benzene and triazole rings, with centroid–centroid distances in the range 3.502 (5)—3.787 (6) Å, connect the two-dimensional hydrogen-bonded network into a three-dimensional network.


Pan Yang, Bin Ding and Gui-Xiang Du Comment
The diiron unit, with a carboxylate-rich coordination environment, continues to attract considerable attention due to the enzyme catalysis activity, which occurs in related multicompent dioxygen dependent enzymes, including toluene monooxy-genase (Sazinsky et al., 2004) and the R2 subunit of ribonucleotide reductase (Stubbe & Van der Donk, 1998;Nordlund & Eklund, 1993). With the development of compounds that contain the diiron center, the structure of a series of Fe2(II,II) (MacMurdo et al., 2000), Fe2(III,III) (Zheng et al., 1999) and Fe2(III,IV) (Hsu et al., 1999) complexes with a central Fe 2 O 2 four-membered ring have been obtained. Compared to the chelating to iron atoms with carboxylic oxygen atoms, it is rarely reported that the four-membered center includes both aqua oxygen atoms. In order to explore further details of the coordinated environment of the diiron system, the title complex was synthesized and its crystal structure is presented herein.
The molecular structure of the title complex is shown in Fig. 1. The dinuclear complex structure comprises two Fe II ions related by a crystallographic inversion center and bridged by two aqua oxygen atoms to form a four-membered core. Both Fe II ions are in a slightly distorted octahedral coordination environment. The separation between the Fe II ions is 3.487 (1) Å, compared to 3.0430 (7) Å reported previously (Yoon et al., 2004) possibly owing to the absence of the carboxylate ligands in the title compound. Moreover, the Fe···Fe distance is comparatively different from that of diiron compounds containing higher valences of iron (MacMurdo et al., 2000;Zheng et al., 1999;Hsu et al., 1999). In the crystal, O-H···N hydrogen bonds connect the components of the structure to form a two-dimensional network parallel to (011) (see Fig. 2).
In addition, π···π stacking interactions involving the benzene and triazole rings with centroid to centroid distances in the range 3.502 (5)-3.787 (6) Å connect the two-dimensional hydrogen-bonded network into a three-dimensional network.

Figure 2
The two-dimensional layered structure of the title complex. Purple Dashed lines indicate donor acceptor distances of the hydrogen bonds. H atoms are not shown.

Di-µ-aqua-bis[diaquabis(thiocyanato-κN)iron(II)]-1,4-bis(4H-1,2,4-triazol-4-yl)benzene (1/3)
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.