supplementary materials

The chemistry of metal complexes containing paramagnetic metal ions and exhibiting extended structures is at the forefront of modern research, due to these compounds' potential applications in molecular magnetism (Field et al., 2006; Rueff et al., 2002; Zeng et al., 2005). The most useful strategy by which to construct such extended one dimensional systems is to employ appropriate bridging ligands, carboxylate for example, capable of binding metal centers through direct bond formation, promoting magnetic interactions. Pyridine-2,6-dicarboxylate (2,6-pdc²⁻), which has been used as a ligand in homoleptic coordination polymers and coordination complexes, is a suitable building block for two-dimensional arrays (Zhao et al., 2003; Gao et al., 2006). There are a few examples of manganese complexes of 2,6-pdc (Ma, Chen, Chen et al., 2003; Ma, Chen, Liu et al., 2003; Okabe & Oya, 2000; Wei et al., 2005), although many crystal structures of complexes of 2,6-pdc with divalent ions such as Co^II, Ni^II and Cu^II (Ghosh et al., 2004; Ghosh et al., 2005) have been determined. The reactants we have used are different from those reported previously in the literature in an attempt to obtain a compound analogous to the title complex (I) (Wei et al., 2005). Its crystal structure is presented here. It should be noted that, compound (I) crystallizes in the monoclinic space group C2/c, while the P-1 space group was previously reported (Wei et al., 2005).

The hydrothermal reaction of Mn(NO₃)₂, 2,6-pdc and 5-bromo-2,4'-bipyridine (5-Br-2,4'-bpy) did not lead to the expected manganese system with coordinated bpy ligands, but to the unexpected formation of (I). Attempts were made to obtain compound (I) under the same conditions in the absence of bpy ligand. The collected crystals were in poor quality and not suitable for X-ray crystallography.

The crystallographically independent unit and atomic numbering of (I) are shown in Fig. 1, and selected bond distances and angles are given in Table 1. A half of (I) is crystallographically independent with a 2-fold axis through O1w. The asymmetric unit consists of one (O2w) and half water (half O1w), one Mn atom and one 2,6-pdc group. The coordination around the Mn atom is pentagonal-bipyramidal. All water molecules are coordinated with metal atoms: O1w atom as a bridge is connected to two neighbouring Mn atoms, while Ow2 atom is coordinated with Mn atom as terminal ligand. The equatorial belt is formed by one N atom (N1) and four O atoms (O2, O2ⁱⁱ, O3, O1w), and the axial positions are occupied by O3 atom and O2w atom [symmetry codes: (ii)-x,-y, −z + 2]. The Mn—O bond lengths fall in the ranges 2.122 (2)–2.4944 (16) Å, and Mn—N bond length is 2.292 (2) Å. These values are consistent with the corresponding distances in the literature (Wei et al., 2005).

In complex (I), the Mn atom is coordinated by four different O atoms of three trans 2,6-pdc ligands, so the complex is extended along c-axis, resulting in the formation of one-dimensional supramolecular chains (Fig.2). The water O1w is connected to the atom O1ⁱ by O1w—H1···O1ⁱ within one-dimensional chain[symmetrycodes: (i)-x,y,-z + 3/2]. The water O2w is hydrogen bonded to O4ⁱⁱⁱ and O^iv of two neighboring chains through O2w—H2b···O4ⁱⁱⁱ and O2w—H2a···O4^iv [symmetry codes: (iii)-x + 1/2,y − 1/2, −z + 3/2; (iv)x,-y,z + 1/2], forming cyclic hydrogen bonded net. Thus, the complex is further assembled into two-dimensional layer by hydrogen-bonding interaction along b-axis. Adjacent sheets cross each other to give a square hydrogen bonded network, in which are filled 2,6-pdc ligand from neighboring chains (Fig.3). The hydrogen bonding interaction plays an important role in stabilizing the crystal structure.