catena-Poly[iron(II)-bis{μ-5-carboxy-2-[(1H-1,2,4-triazol-1-yl)methyl]-1H-imidazole-4-carboxylato}]

In the title coordination polymer, [Fe(C8H6N5O4)2]n {or [FeL 2]n,where HL = 2-[(1H-1,2,4-triazol-1-yl) methyl]-1H-imidazole-4,5-dicarboxylic acid)}, the FeII ion, located on an inversion centre, is six-coordinated by two O atoms and four N atoms from two L − ligands in a distorted octahedral geometry [Fe—O = 2.1452 (13), Fe—N = 2.1316 (14) and 2.2484 (15) Å]. There is an intramolecular O—H⋯O hydrogen bond in each L − ligand. Being an effective tridentate bridging ligand, the deprotonated L − anions link two FeII atoms, yielding a chain-like polymer propagating along [100]. In the crystal, these polymer chains are linked via N—H⋯N hydrogen bonds, forming a two-dimensional network.

We report herein on the crystal structure of the title one-dimensional coordination polymer.
As shown in Fig. 1, the asymmetric unit of the title coordination polymer contains half a Fe II ion, located on an inversion centre, and a deprotonated Lligand. The local coordination geometry around the Fe II centre can be described as distorted octahedral. The equatorial plane is formed by two imidazole N atoms (N4 and N4d) and two carboxylate O atoms (O1 and O1d) from two Lligands, while the axial positions are occupied by two triazolate N atoms (N3b and N3c). The cis bond angles around each Fe II centre are in the range 78.11 (5)° to 101.89 (5)°.
Two Fe II centers are linked together by two identical Lligands through triazolate N-donors, imidazole N-donors and carboxylate O-donors into a 14-membered box-like macrocycle with the Fe1···Fe1 ii separation being 7.179 Å. The symmetrically related triazolyl rings are parallel to one another, and the shortest distance between atoms is 3.662 Å, indicating a weak π-π interaction. Being an effective tridentate bridging ligand, the deprotonated Lanions link two Fe II centers to yield a one-dimensional chain-like polymer propagating along [100].
In the crystal the one-dimensional polymer chains are linked by classical N-H···N hydrogen bonds, involving the uncoordinated triazolate N atoms and the imidazole N atoms, resulting in the formation of a two-dimensional supramolecular network propagating in the bc-plane (Table 1 and Fig. 2).

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.