metal-organic papers m178 Harrison et al.  [Cu(C 2 H 8 N 2 ) 2 (H 2 O) 2 ](C 7 H 4 NO 4 ) 2 doi:10.1107/S1600536806052901 Acta Cryst. (2007). E63, m178–m180 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 Diaquabis(ethylenediamine)copper(II) bis(4-nitrobenzoate) William T. A. Harrison, a * Alexandra M. Z. Slawin, b Raj Pal Sharma, c * Bhavna Sharma c and Shekar Bhama c a Department of Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, Scotland, b Department of Chemistry, University of St Andrews, Fife KY16 9ST, Scotland, and c Panjab University, Department of Chemistry, Chandigarh 160 014, India Correspondence e-mail: w.harrison@abdn.ac.uk, rpsharma@yahoo.co.in, rpsharma@yahoo.co.in , rpsharma@yahoo.co.in Key indicators Single-crystal X-ray study T = 93 K Mean (C–C) = 0.004 A ˚ R factor = 0.034 wR factor = 0.077 Data-to-parameter ratio = 12.5 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. Received 27 October 2006 Accepted 6 December 2006 # 2007 International Union of Crystallography All rights reserved In the title compound, [Cu(C 2 H 8 N 2 ) 2 (H 2 O) 2 ](C 7 H 4 NO 4 ) 2 , the component complex cations and organic anions interact by way of N—HO and O—HO hydrogen bonds, leading to a layered structure. The Cu atom has site symmetry 1. Comment The title compound, (I), was prepared as part of our ongoing studies of second-sphere hydrogen-bonding interactions in compounds containing cationic metal complexes and organic counter-anions (Sharma, Bala et al., 2006; Sharma, Sharma et al., 2006). The geometrical parameters for the component species in (I) fall within their expected ranges (Allen et al., 1987). The well known [Cu(C 2 N 2 H 8 ) 2 (H 2 O) 2 ] 2+ complex cation in (I) is built up from a central copper(II) ion (site symmetry 1) chelated by two ethylenediamine molecules to form an approximate CuN 4 square. The Jahn–Teller distorted copper coordination is completed by two trans water molecules (Table 1). The Cu—N and Cu—O bond lengths in (I) are very similar to the equivalent values observed for the same complex cation in its bis(naphthalene-2-sulfonate) (Sharma et al., 2005) and bis(4-fluorobenzoate) (Liu et al., 2004) salts. The 4-nitrobenzoate anion in (I) is almost planar, the dihedral angles between the mean plane of the C3–C8 benzene ring and the planes of its attached C9/O2/O3 carboxylate and N3/O4/O5 nitro groups being 2.14 (17) and 1.9 (2)  , respectively. The carboxylate C—O bond lengths are almost equal, suggesting charge delocalization. As well as electrostatic forces, the component species in (I) interact by way of O—HO and N—HO hydrogen bonds (Table 2). Firstly, adjacent complex cations are linked into chains propagating along [100] by way of translation-related pairs of N1—H1O1 i bonds (see Table 2 for symmetry code). A bridging carboxylate atom O3 also helps to consolidate the chains (Fig. 2). Then, adjacent cations and anions form a distinctive bridged chain propagating along [010] (Fig. 3), where each carboxylate group in the chain accepts no fewer than four hydrogen bonds from its two adjoining cations.