supplementary materials

Aromatic dicarboxylate ligands such as phthalate (phth) and substituted phthalatehave been used in the construction of polymeric metal complexes because they can act as a bis-monodentate, bis-bidentate and combined modes of coordination to form short bridges via one carboxylato end or long bridges via the benzene ring and lead to a great variety of structures (Biagini Cingi et al., 1978; Guo and Guo, 2007; Wang et al., 2009; Ma et al., 2004; Baca et al., 2003, 2004; Yang et al., 2003; Fu et al., 2006). We have used the 4-nitrophthalate dianion as a ligand, and have obtained the title novel five-coordinate 4-nitrophthalate-copper complex, (I), which forms a three-dimensional supramolecular network through O—H···O hydrogen bonding.

The asymmetric unit in the structure of (I) comprises one Cu atom, one complete 4-nitrophthate dianion and two non-equivalent water molecules, and is shown in Fig. 1 in a symmetry-expanded view, which displays the full coordination of the Cu atom. Selected geometric parameters are given in Table 1.

The Cu atom exhibits an approximate square pyramidal environment (the τ value being 0.171, Addison et al., 1984), with atoms O1, O4ⁱ (see Fig. 1 for symmetry codes) of two non-equivalent 4-nitrophthalate dianions and O7 and O8 atoms of coordinated water molecules in a planar arrangement, with the mean Cu–O(eq) bond distance being 1.961 (3) Å, which is comparable to that reported for poly[(µ₃-methylmalonato-O,O',O'',O''')-aqua-\ copper(II)] (Pasan, et al., 2007). The apical position is occupied by O3ⁱⁱ atom [Cu1–O3ⁱⁱ = 2.263 (3) Å]. The Cu atom is shifted by 0.0889 (5) A° toward the apical position. There is an additional weak Cu–O2 contact in (I), with a Cu···O distance of 2.821 (3) Å.

In the present structure, monodentate, bidentate 1,3-bridging bonding and 1,6-bridging bonding modes via the benzene ring are present (Fig. 2). The O1 atom binds in a monodentate fashion, while the O3 and O4 atoms display both monodentate and bidentate 1,3-bridge bonding to link two Cu atoms. The O1 and O3 (or O4) atoms adopt a 1,6-bridging bonding mode via the benzene ring to connect with two other Cu atoms.

The Cu atoms are further interconnected by three O atoms from three 4-nitrophthalate dianions into a two-dimensional layer in the ab plane. The mean planes of the carboxylate groups of O1/C1/O2 and the benzene ring make a dihedral angle of 72.4 (5)°, and the value of a dihedral angle for the carboxylate groups of O3/C8/O4 is 14.5 (5)°; the two C—O bond distances (O1—C1 and O2—C1) of the monodentate carboxylate group are 1.278 (5) and 1.241 (5) Å, respectively, and the two C—O bond distances (O3—C4 and O4—C4) of the 1,3-bridging bonding carboxylate group are 1.253 (5) and 1.266 (6) Å, respectively. These indicate that the mesomeric effect for the 1,3-bridging bonding carboxylate group is somewhat greater than that of the monodentate carboxylate group.

The two water molecules within the coordination sphere of the Cu atom, and the nitro group (O5/N1/O6) in the present structure engage in distinct hydrogen bonding interactions (see Table 2). Within each layer, the non-coordinated O2 atom is involved in forming strong O8—H8B···O2ⁱⁱ (Brown, 1976) and weak O7—H7A···O2^v hydrogen bonds. These play an important role in the propagation of the two-dimensional layer structure, due to the formation of different hydrogen bonded ring graph set motifs (Bernstein et al., 1995), such as an S(8), and two 10-membered R₂²(10) motifs (Fig.3). The neighbouring layers are linked together via weak O7—H7B···O6^vi hydrogen bonding interactions. These also result in the aryl rings of the 4-nitrophthalato ligands stacking weakly in an offset fashion along the c direction with centroid to centroid distances in the range 4.55 (4)Å - 4.97 (2)%A. Thus, the three-dimensional connectivity of the structure is achieved.