(2,2′-Bipyridine-6,6′-dicarboxylato-κ3 N,N′,O 6)(6′-carboxy-2,2′-bipyridine-6-carboxylato-κ3 N,N′,O 6)rhodium(III)

The RhIII ion in the title compound, [Rh(C12H6N2O4)(C12H7N2O4)], is coordinated by four N atoms and two O atoms from two chelating ligands L and HL (H2L = 2,2′-bipyridine-6,6′-dicarboxylic acid) to form a distorted octahedral geometry. Face-to-face π-stacking interactions are observed between inversion-related pyridine rings, with a centroid-to-centroid distance of 3.581 (1) Å [the perpendicular distance between the rings is 3.3980 (7) Å]. Intermolecular O—H⋯O hydrogen bonds link adjacent molecules into one-dimensional supramolecular chains along the c axis, while several intermolecular C—H⋯O interactions are also observed.


Related literature
For structures and photophysical properties of Ln III (Ln is a lanthanide) complexes with the title ligand, see: Bü nzli et al. (2000). For Rh complexes with pyridyl triazole ligands, see: Burke et al. (2004). For an Mn-Rh coordination polymer with the 2-methylpyrazine-5-carboxylic acid ligand, see : Chapman et al. (2002). For a catena-poly diaqua Cd II complex with the title ligand, see: Knight et al. (2006). For a review reporting the properties of coordination polymer networks via O and N atoms, see: Robin & Fromm (2006). For the structures and thermal properties of five Ln complexes with the title ligand, see: Wang et al. (2010). For a related Ni II complex with the title ligand, see: Wang et al. (2009).
The structure of the title compound ( Fig. 1) shows that the six-coordinated Rh III atom is surrounded by four N atoms and two O atoms from the two chelated ligands to form a distorted octahedral geometry. The Rh-N bond lengths are in the range of 1.9529 (13)-2.0808 (14) Å and the Rh-O bond lengths are 2.0226 (12) and 2.0316 (13) Å (Table 1), which are comparable to other distances reported in Rh III complexes (Burke et al., 2004;Chapman et al., 2002). The coordinated bipyridine fragments are nearly coplanar [see torsion angles of 2.1 (2) and 1.8 (2)° in Table 1].
The one-dimensional chain structure of the title compound via hydrogen bonds is illustrated in Fig. 2. The hydrogenbond donor O4 is connected to the acceptor O7 from the adjacent molecule to form one-dimensional infinite chains along the c-axis (O4-H4···O7 i = 1.64 Å, i = x, -y + 1/2, z -1/2, Table 2). Several intermolecular C-H···O interactions contribute to stabilize the crystal structure.

Experimental
The title compound was obtained by the reaction of the mixture of RhCl 3 and 2,2′-dipyridine-6,6′-dicarboxylic acid in a molar ratio of 1:3 and 10 ml of water under hydrothermal conditions (at 433 K for 3 d and cooled to room temperature with a 3°C h -1 rate). The orange block crystals were washed with water (yield: 40%).

Figure 1
The structure of the title compound with 50% probability displacement ellipsoids.

Figure 2
The one-dimensional chain structure of the title compound via hydrogen bonds along the c-axis.