catena-Poly[[bis(pyridine-κN)zinc]-μ-5-carboxybenzene-1,3-dicarboxylato-κ2 O 1:O 3]

The title one-dimensional coordination polymer, [Zn(C9H4O6)(C5H5N)2]n or [Zn(HBTC)(py)2]n, (I), where BTC is benzene-1,3,5-tricarboxylate and py is pyridine, is a solvent-free polymorph of [Zn(HBTC)(py)2]·2C2H5OH [Yaghi et al. (1997 ▶). Chem. Mater. 9, 1074–1076]. Differences in the spatial arrangements and supramolecular packing of the [Zn(HBTC)(py)2]n chains in the two structures are described. The chain in (I) extends parallel to [100] and is severely puckered, with a Zn⋯Zn distance of 8.3599 (3) Å and a Zn⋯Zn⋯Zn angle of 107.516 (3)°, as a result of hydrogen-bonding interactions of the types O—H⋯O and C—H⋯O. There is no evidence for π–π interactions in (I). The differences between the solvent-free and solvent-containing structures can be accounted for by the absence of the ethanol solvent molecule and the use of the converging pair of O atoms in the bis-monodentate bridging HBTC2− ligand in (I).

The title one-dimensional coordination polymer, [Zn(C 9 H 4 O 6 )(C 5 H 5 N) 2 ] n or [Zn(HBTC)(py) 2 ] n , (I), where BTC is benzene-1,3,5-tricarboxylate and py is pyridine, is a solvent-free polymorph of [Zn(HBTC)(py) 2 ]Á2C 2 H 5 OH [Yaghi et al. (1997). Chem. Mater. 9, 1074-1076]. Differences in the spatial arrangements and supramolecular packing of the [Zn(HBTC)(py) 2 ] n chains in the two structures are described. The chain in (I) extends parallel to [100] and is severely puckered, with a ZnÁ Á ÁZn distance of 8.3599 (3) Å and a ZnÁ Á ÁZnÁ Á ÁZn angle of 107.516 (3) , as a result of hydrogenbonding interactions of the types O-HÁ Á ÁO and C-HÁ Á ÁO. There is no evidence forinteractions in (I). The differences between the solvent-free and solvent-containing structures can be accounted for by the absence of the ethanol solvent molecule and the use of the converging pair of O atoms in the bis-monodentate bridging HBTC 2À ligand in (I).

Related literature
For the ethanol monosolvate of (I), see: Yaghi et al. (1997). For a review on supramolecular isomerism in coordination compounds, see: Zhang et al. (2009).

Experimental
Crystal data [Zn(C 9 Table 1 Hydrogen-bond geometry (Å , ).  (Yaghi et al., 1997). It is clear that the two isomers result from differences in the synthesis method. In order to synthesize I, a simple solution route was adopted, whereas the crystals of [Zn(HBTC)(py) 2 ].2C 2 H 5 OH have only been synthesized when poly(ethyleneoxide) (PEO) gel is used as the reaction medium in the presence of C 2 H 5 OH as solvent (Yaghi et al., 1997). The absence or presence of the C 2 H 5 OH solvent molecules results in different spatial arrangements and supramolecular packing in the two isomers.
While the two supramolecular isomers are built up of the same structural building motifs, i.e. a tetrahedral Zn(II) ion, two monodentate pyr molecules and a bridging HBTC 2anion, the architecture of the one-dimensional chains of the two isomers notably differs. In the case of I, an asymmetric unit comprises a tetrahedral Zn(II) ion ( Fig. 1), coordinated by two N atoms (N1 and N2) from two crystallographically independent pyr molecules and two O atoms (O1 and O2) from two distinct carboxylato groups of the HBTC 2anion. The HBTC 2ligand in structure I adopts a bis-monodentate bridging mode (µ 2 -η 1 :η 1 :η 0 :η 0 :η 0 :η 0 ) ( respectively. The presence of the C 2 H 5 OH solvent molecule in the vicinity of the two coordinating carboxylato groups in the [Zn(HBTC)(py) 2 ].2C 2 H 5 OH isomer ostensibly forces the coordinating atoms to be the diverging pair of O atoms (equivalent to O3 and O6 in I), rather than the converging pair as in I.
A larger degree of puckering in I compared to that of the previously reported isomer imparts an immense influence on the corresponding supramolecular interactions and packing. While there are no π-π interactions in I, which is in contrast to the [Zn(HBTC)(py) 2 ].2C 2 H 5 OH case, an acidic proton of the bridging HBTC 2anion is involved in the hydrogen bonding interactions with the O atom of the HBTC 2anion from the adjacent chain (Fig. 3). Weak C-H···O hydrogen bonding interactions further link these one-dimensional chains into a dense, three-dimensional supramolecular structure.

Experimental
A small fraction of pyridine (0.50 ml, 6.18 mmol; 99.8% Sigma-Aldrich) was gradually added to a 2.50 ml of a 0.   View of the one-dimensional chain of I. Hydrogen atoms are omitted for clarity.

Figure 3
View of supramolecular packing in I, directed primarily by the O-H···O hydrogen bonding interactions (dotted lines).