catena-Poly[[bis(ethylenediamine)copper(II)]-μ-sulfato]

In the title compound, [Cu(SO4)(C2H8N2)2]n, the Cu, S and two O atoms lie on a mirror plane. The Cu atom is in a distorted octahedral environment and the ethylenediamine ligand is in a gauche conformation. The sulfate dianion is bridging, forming a one-dimensional chain. A two-dimensional net parallel to (001) is generated by N—H⋯O hydrogen bonding between the chains.

In the title compound, [Cu(SO 4 )(C 2 H 8 N 2 ) 2 ] n , the Cu, S and two O atoms lie on a mirror plane. The Cu atom is in a distorted octahedral environment and the ethylenediamine ligand is in a gauche conformation. The sulfate dianion is bridging, forming a one-dimensional chain. A two-dimensional net parallel to (001) is generated by N-HÁ Á ÁO hydrogen bonding between the chains.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: VM2026).

catena-Poly[[bis(ethylenediamine)copper(II)]--sulfato]
M. Lutz, S. Smeets and P. Parois Comment Ethylenediamine (en) complexes of transition metals belong to the most studied compounds in inorganic chemistry. In the case of copper sulfate the tris(ethylenediamine) complex is known at room temperature (Cullen & Lingafelter, 1970) as well as at 120 K after a solid-solid phase transition (Bertini et al., 1979). These crystal structures show the copper in an octahedral geometry and the sulfate is not coordinated to the metal but hydrogen bonded to the amine groups.
Here, we report the crystal structure of the bis(ethylenediamine) complex of copper sulfate (I), in which the sulfate is bridging two copper centers. The compound thus forms a polymeric chain by coordination, which runs in the direction of the c axis (Fig. 1). The copper, the sulfur and two O atoms are in special positions on the crystallographic mirror plane of the orthorhombic space group Cmca. Bridging sulfate ions are very common in copper complexes. For example, in [Cu(en)(H 2 O) 2 ]SO 4 , the sulfate is a bridging ligand and a one-dimensional chain is formed by coordination (Healy et al., 1978;Manriquez et al., 1996;Taylor et al., 2006).
As expected, the ethylenediamine ligand is in a gauche conformation (Table 1) and the copper is in a distorted octahedral environment. The nitrogen atoms form the equatorial plane with Cu-N distances (2.0173 (8) and 2.0226 (8) Å), which are shorter than in the room temperature structure of the tris(ethylenediamine) complex (2.150 (2) Å). The two axial positions are occupied by oxygen atoms of sulfate anions with much longer distances than in the equatorial plane. This can be explained by the Jahn-Teller effect in Cu(II) compounds. The Cu-O distances (2.3575 (9) and 2.4673 (9) Å) also differ significantly compared to each other. Such differences are not uncommon with copper complexes of weakly coordinating anions like sulfate (Castro et al., 2002), nitrate (Plater et al., 2008), perchlorate (Bernhardt et al., 2001) or trifluoromethanesulfonate (Liu et al., 2007).
The coordinated NH 2 groups act as hydrogen bond donors and the non-coordinated sulfate O-atoms act as acceptors (Table 2). Two hydrogen bonds are formed within the coordination polymer via H1N and H4N. Two hydrogen bonds via H2N and H3N are between the chains resulting in a two-dimensional net in the b,c-plane (Figures 2 and 3). This two-dimensional motif is also reflected in the plate shaped crystal habitus, where the a-direction has the smallest dimension.
Experimental 2.04 g of copper sulfate pentahydrate (8.17 mmol) were dissolved in 150 ml of water and brought to boiling temperature.
Then 2 ml of ethylenediamine (37 mmol) were added dropwise. The resulting deep blue solution was concentrated at 333 K and atmospheric pressure. In the concentrated solution, crystals appeared after 2 days of evaporation at room temperature.

Refinement
An anisotropic mosaic model was used in the intensity integration with hkl = (0,0,1) as anisotropic vector (Duisenberg, 1983). Hydrogen atoms were located in difference Fourier maps. N-H hydrogen atoms were refined freely with isotropic supplementary materials sup-2 displacement parameters. C-H hydrogen atoms were refined using a riding model with C-H = 0.99 Å and with U iso (H) = 1.2 times U eq (C). Fig. 1. : Displacement ellipsoid plot of (I), drawn at the 50% probability level. Only three units of the polymeric chain are shown. View along the b axis. Symmetry operations i: -x, 0.5 -y, z -1/2; ii: -x, 0.5 -y, z + 1/2; iii: -x, y, z.

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 > 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.