Poly[tetra-n-butylammonium [(μ5-benzene-1,3,5-tricarboxylato)(μ4-benzene-1,3,5-tricarboxylato)-μ3-hydroxido-trizincate] 0.25-hydrate]

In the asymmetric unit of title coordination polymer, {(C16H36N)[Zn3(C9H3O6)2(OH)]·0.25H2O}n, there are three independent Zn2+ cations, two benzene-1,3,5-tricarboxylate ligands and a μ3-bridging hydroxide group, together with a tetra-n-butylammonium counter-cation and a partially occupied water molecule of solvation (occupancy 0.25). Each Zn ion is coordinated by three carboxylate O atoms and one O atom from the bridging hydroxide ion, displaying a slightly distorted tetrahedral stereochemistry [overall Zn—O range = 1.875 (3)–1.987 (2) Å]. An intramolecular hydrogen bond involving the hydroxide H atom and a carboxylate O-atom acceptor is also present in the complex unit. The bridging benzene-1,3,5-tricarboxylate anions generate a three-dimensional framework structure.

In the asymmetric unit of title coordination polymer, {(C 16 H 36 N)[Zn 3 (C 9 H 3 O 6 ) 2 (OH)]Á0.25H 2 O} n , there are three independent Zn 2+ cations, two benzene-1,3,5-tricarboxylate ligands and a 3 -bridging hydroxide group, together with a tetra-n-butylammonium counter-cation and a partially occupied water molecule of solvation (occupancy 0.25). Each Zn ion is coordinated by three carboxylate O atoms and one O atom from the bridging hydroxide ion, displaying a slightly distorted tetrahedral stereochemistry [overall Zn-O range = 1.875 (3)-1.987 (2) Å ]. An intramolecular hydrogen bond involving the hydroxide H atom and a carboxylate O-atom acceptor is also present in the complex unit. The bridging benzene-1,3,5-tricarboxylate anions generate a three-dimensional framework structure.

Related literature
For a related structure, see: Su et al. (2009).

Experimental
The reaction mixture of zinc nitrate hexahydrate (59.4 mg, 0.2 mmol), benzene-1,3,5-tricarboxylic acid (21.0 mg, 0.1 mmol), and 1 ml of aqueous tetra-n-butylammonium hydroxide solution (10%, w/w) in 12 ml of water was sealed in a 16 ml Teflon-lined stainless steel container and heated to 453 K for 3 days. After cooling to room temperature, colorless block crystals of the title complex were obtained.

Refinement
The hydrogen atoms on all C atoms were located in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.93-0.97 Å and U iso (H) = 1.2 or 1.5U eq (C). The hydrogen atom on the hydroxide group (O13) was found at a reasonable position in the difference-Fourier map and was constrained with U iso (H) = 1.2U eq (O)]. The partial water molecule of solvation (O1W) was refined with occupancy 0.25, while the attached hydrogen atoms could not be located.

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 > σ(F 2 ) is used only for calculating Rfactors(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.