Tris(1,10-phenanthroline)cadmium 3,3′-dicarboxy-4,4′-diazenediyldibenzoate–4,4′-diazenediyldiphthalic acid–methanol (1/0.5/1)

In the title compoud, [Cd(C12H8N2)3](C16H8N2O8)·0.5C16H10N2O8·CH3OH, the CdII atom has a distorted octahedral coordination formed by six N atoms from three separate phenanthroline ligands. One of the 4,4′-diazenediyldiphthalic acid molecules is arranged around an inversion center and possesses two –COOH groups, while the other is partially deprotonated and is a dianion for charge balance. It can be noted that, in the undeprotonated acid, the –COOH groups are disordered over two positions by rotation around the C—C bond linking the –COOH group to the phenyl ring. Surprisingly, the H atom is not involved in the disorder. In the dianion, the remaining H atom is located between the two COO groups. These deprotonated and undeprotonated molecules are linked by O—H⋯O hydrogen bonds, forming a chain developing parallel to the [111] direction. The methanol solvent molecule is highly disordered; it was not considered in the final model by elimination of its contribution from the intensity data.

In the title compoud, [Cd(C 12 H 8 N 2 ) 3 ](C 16 H 8 N 2 O 8 )Á0.5C 16 H 10 -N 2 O 8 ÁCH 3 OH, the Cd II atom has a distorted octahedral coordination formed by six N atoms from three separate phenanthroline ligands. One of the 4,4 0 -diazenediyldiphthalic acid molecules is arranged around an inversion center and possesses two -COOH groups, while the other is partially deprotonated and is a dianion for charge balance. It can be noted that, in the undeprotonated acid, the -COOH groups are disordered over two positions by rotation around the C-C bond linking the -COOH group to the phenyl ring. Surprisingly, the H atom is not involved in the disorder. In the dianion, the remaining H atom is located between the two COO groups. These deprotonated and undeprotonated molecules are linked by O-HÁ Á ÁO hydrogen bonds, forming a chain developing parallel to the [111] direction. The methanol solvent molecule is highly disordered; it was not considered in the final model by elimination of its contribution from the intensity data.

Comment
In the past decade, much progress has been achieved in the synthesis and structural characterization of metal-organic frameworks(MOFs) due to their potential applications (Yaghi et al., 2003;Kitagawa et al., 2004). Generally, the multidentate organic ligands containing coordination sites of O donors are widely used as building blocks in the construction of MOFs (Banerjee et al., 2008;Liu, Huang et al., 2011). On the other hand, 1, 10-Phenanthroline, one of those ligands, has usually been used to construct a great variety of structurally interesting entities, such as monomers (Breneman & Parker, 1993;Liu, Jia & Wang, 2011;Liu, 2011). Herein, we are interested in self-assemblies of Cd(II) ion with H 4 L and phenanthroline, which led to the preparation of the title compound.
In the asymmetric unit of title compound, there are one Cd(II) ion, three phen ligands, one deprotonated H 2 L, a half undeprotonated H 4 L ligand and one methanol molecule. As shown in Fig. 1. The Cd(II) atom is six-coordinated in a slightly distorted octahedral geometry defined by six N atoms from three different phen ligands. Interestingly, one of the (4,4'diazenediyldiphthalic acid) is arranged around inversion center and possess two COOH groups, while the other is partially deprotonated and it is a dianion for balancing the charge. The Cd-N bond distances range from 2.329 (3) to 2.366 (3)Å. The N4-Cd1-N5 and N1-Cd1-N5 bond angles are 90.58 (9) and 93.19 (9)°, respectively. From the above values, it appears that the three phen ligands are nearly perpendicular to each other.
In H 2 L, the acidic H atom is nearly engaged in a bridging O···H···O interactions (Table 1) Table 1). The disordered methanol molecule is located in the void. The Cd(II) complexes are antiparallel to the above chains. The above hydrogen bonds could participate to the stabilization of the title complex.
Then, the reaction mixture was stirred for 15 days at room temperature. Crystals of (I) were obtained at room temperature.

Refinement
The occupancy of the COOH group was determined by fixing the sum of the occupancy to 1 and by using overall isotropic thermal parameter for O atoms and restraining the C-O distances by using the SAME instruction. The ratio was found to be equal to 0.65/0.35. Once the occupancy has been determined, the occupancy factors were fixed and the Uiso for the O atoms was refined freely then anisotropic thermal parameters were introduced. supplementary materials sup-2 All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.93 Å, and U iso (H) = 1.2U eq (C).
All H atoms attached to the COOH groups were found in difference Fourier maps, and then they were refined freely with U iso (H) = 1.2U eq (C). In the last cycles of refinement they were treated as riding on their parent O atoms.
The unit cell contains a certain amount of methanol molecules. However, these molecules appear to be highly disordered and it was difficult to model their positions and distribution reliably. Therefore, the SQUEEZE function of PLATON (van der Sluis & Spek, 1990;Spek, 2003) was used to eliminate the contribution of the electron density in the solvent region from the intensity data, and the solvent-free model was emplyed from the final refinement.

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 > 2sigma(F 2 ) is used only for calculating R-factors(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.