Tetrakis(picolinato-κ2 N,O)zirconium(IV) dihydrate

In the title compound, [Zr(C6H4NO2)4]·2H2O, the ZrIV atom is located on a crystallographic fourfold rotoinversion axis () and is coordinated by four picolinate anions with Zr—O and Zr—N distances of 2.120 (2) and 2.393 (2) Å, respectively. An approximate square-antiprismatic coordination polyhedron of the N,O-coordination ligand atoms is formed, with a distortion towards dodecahedral geometry. The crystal packing is stabilized by intermolecular π–π interactions between adjacent picolinate rings [centroid–centroid distances = 3.271 (1) and 3.640 (2) Å], as well as O—H⋯O hydrogen bonds between the solvent molecules and the coordinated ligands, thereby linking the molecules into a supramolecular three-dimensional network.

In the title compound, [Zr(C 6 H 4 NO 2 ) 4 ]Á2H 2 O, the Zr IV atom is located on a crystallographic fourfold rotoinversion axis (4) and is coordinated by four picolinate anions with Zr-O and Zr-N distances of 2.120 (2) and 2.393 (2) Å , respectively. An approximate square-antiprismatic coordination polyhedron of the N,O-coordination ligand atoms is formed, with a distortion towards dodecahedral geometry. The crystal packing is stabilized by intermolecularinteractions between adjacent picolinate rings [centroid-centroid distances = 3.271 (1) and 3.640 (2) Å ], as well as O-HÁ Á ÁO hydrogen bonds between the solvent molecules and the coordinated ligands, thereby linking the molecules into a supramolecular threedimensional network.
The title compound, [Zr(C 6 H 4 NO 2 ) 4 ].2H 2 O, with C 6 H 4 NO 2 as picolinic acid, crystallizes in the form of colourless cubic crystals in the tetragonal P4 2 /n space group. The Zr IV atom, located on a crystallographic fourfold rotoinversion axis (4), is coordinated to four picolinic acid ligands (Fig. 1). The assymetric unit contains half a solvent molecule located on a twofold axis. The Zr-O and Zr-N bond lengths are 2.120 (2) Å and 2.393 (2) Å, respectively, with a N-Zr-O bite angle of 69.79 (7) °. The coordination polyhedron around the metal centre is an approximate square antiprism of the N,O-coordination ligand atoms, with a distortion towards dodecahedral geometry. The crystal packing is stabilized by intermolecular π-π interactions ( Fig. 2), between adjacent picolinato rings, with interplanar and centroid-to-centroid distances of 3.271 (1) Å and 3.640 (2) Å, respectively. Further stabilization of the crystal structure is afforded by O-H···O hydrogen bonding (Fig.   3) between the carbonyl group of the picolinato ligands and the solvent water molecules. All of these interactions serve to link the molecules into a supramolecular three-dimensional network.

Experimental
Chemicals were purchased from Sigma-Aldrich and used as received. ZrCl 4 (103.3 mg, 0.463 mmol) and picolinic acid (PicA) (175.2 mg, 1.423 mmol) was separately dissolved in DMF (2.5 ml ea) and heated to 60 °C. The PicA solution was added drop-wise to the zirconium solution and stirred at 60 °C for 30 minutes. The reaction solution was removed from heating, covered and left to stand for crystallization. White cubic crystals, suitable for single-crystal X-ray diffraction, formed after 30 days (yield: 178 mg, 86%).

Refinement
The aromatic H atoms were placed in geometrically idealized positions (C-H = 0.95 Å) and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C). The hydrogen atoms of the solvent water molecule were located on the Fourier difference map and refined isotropically. The highest residual electron density was located 0.74 Å from O1.
supplementary materials sup-2 Figures   Fig. 1. Representation of the title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius. Fig. 2. Graphical illustration of π-π interaction and stacking between different PicA-ligands of neighboring molecules to form a three-dimensional network (displacement ellipsoids are drawn at the 50% probability level). Hydrogen atoms and solvent water molecules omitted for clarity.

Fig. 3. Graphical illustration of Zr(PicA) 4 indicating O-H···O hydrogen bonding interaction
as observed between the solvent molecules and the free carbonyl oxygen atoms from neighboring molecules (displacement ellipsoids are drawn at the 50% probability level).

Special details
Experimental. The intensity data were collected on a Bruker X8 ApexII 4 K Kappa CCD diffractometer using an exposure time of 40 s/frame. A total of 1709 frames were collected with a frame width of 0.5° covering up to θ = 28.40° with 99.5% completeness accomplished.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.