Poly[[aqua-μ3-picolinato-μ2-picolinato-dipicolinatopotassium(I)terbium(III)] 2.5-hydrate]

In the title compound, [KTb(C6H4NO2)4(H2O)]·2.5H2O, each Tb3+ centre is coordinated by four N and five O atoms from five distinct picolinate ligands in a geometry resembling a highly distorted tricapped trigonal prism. One of the ligands establishes a skew bridge between neighbouring Tb3+ centres, leading to the formation of one-dimensional anionic polymeric chains, {[(C6H4NO2)4Tb]−}n, running along the direction [010]. Each K+ cation is seven-coordinated by six O atoms from one anionic polymeric chain and one water molecule [K⋯O 2.676 (3)–3.208 (4) Å]. The uncoordinated water molecules are involved in O—H⋯O hydrogen bonding.

In the title compound, [KTb(C 6 H 4 NO 2 ) 4 (H 2 O)]Á2.5H 2 O, each Tb 3+ centre is coordinated by four N and five O atoms from five distinct picolinate ligands in a geometry resembling a highly distorted tricapped trigonal prism. One of the ligands establishes a skew bridge between neighbouring Tb 3+ centres, leading to the formation of one-dimensional anionic polymeric chains, {[(C 6 H 4 NO 2 ) 4 Tb] À } n , running along the direction [010]. Each K + cation is seven-coordinated by six O atoms from one anionic polymeric chain and one water molecule [KÁ Á ÁO 2.676 (3)-3.208 (4) Å ]. The uncoordinated water molecules are involved in O-HÁ Á ÁO hydrogen bonding.

Related literature
For recent research on metal-organic frameworks (MOFs) or coordination polymers from our research group, see: Shi et al.

S1. Comment
In the last years research on multidimensional Metal-Organic Frameworks (MOFs), or coordination polymers, has received a remarkable interest as consequence of the their fascinating structural architectures which, in many cases, are also associated with interesting potential applications (e.g., gas storage, separation, catalysis, guest exchange, magnetic or optical sensors). Following our ongoing research focused on the preparation and structural characterization of these interesting compounds (for recent examples see: Shi et al., 2008;Cunha-Silva et al., 2007;Paz & Klinowski, 2007;Soares-Santos et al., 2006;Paz et al., 2005), we report in this short communication the crystalline structure of the title compound, K 2 [Tb 2 (pic) 6 (µ-pic) 2 ].7(H 2 O) [where picstands for the picolinate anion, C 6 H 4 NO 2 -].
The crystalline structure of the title compound contains a single crystallographically independent Tb 3+ site, Tb1, which is coordinated to four N and five O-donor atoms belonging to five distinct picolinate anionic (pic -) ligands, with a nine- 150.65 (10)°, respectively (see Figure 1 and Table 1).
As usually found in related compounds (see for example: Soares-Santos et al., 2006;Sendor et al., 2003;Starynowicz, 1993;Jian-Fang et al., 1996), all picligands are coordinated to the Tb 3+ metal centre via the typical N,O-chelation mode ( Figure 1). Furthermore, one picestablishes a skew-bridge (through the O7 atom; Figure 1) with a neighbouring Tb 3+ , thus completing the nine-coordination environment of the lanthanide centre and leading to the formation of the onedimensional (one-dimensional) anionic coordination polymer (chain), [Tb 2 (pic) 6 (µ-pic) 2 ] n 2n-, running along the [010] direction ( Figure 2). The skew-bridge is also responsible for the zigzag distribution of the Tb 3+ centres along the aforementioned crystallographic direction, imposing an intermetallic Tb1···Tb1 i distance of 6.4375 (4) Å [symmetry code: (i) 1 + x-y, 1 -y, -z]. Adjacent polymers close pack along the [001] direction of the unit cell with an arrangement resembling a layered-like structure. The water molecules of crystallization and the potassion cations are housed in the interchain empty spaces ( Figure 2c with the K + cations being omitted for clarity).

S2. Experimental
Starting materials were purchased from commercial sources and were used as received without further purification. The title compound has been prepared by adding an aqueous solution (5 ml) of TbCl 3 .6H 2 O (1 mmol, 373 mg) to a solution of picolinic acid (Hpic, 4 mmol, 492 mg) and KOH (4 mmol, 220 mg) in distilled water (20 ml, pH = 6.8). After stirring the mixture for 1 h, an aqueous solution (5 ml) of tetrabutylammonium chloride hydrate ( n Bu 4 NCl.nH 2 O, 4 mmol, 1.12 g) supporting information was added drop wise. The resulting mixture was heated and the formed white precipitate was collected by vacuum filtering. Colourless crystals suitable for single-crystal X-ray analysis were obtained from the mother solution after three days.

S3. Refinement
Hydrogen atoms attached to carbon were located at their idealized positions and were included in the refinement in riding-motion approximation with isotropic displacement parameters fixed at 1.2 times U eq of the carbon atom to which they are attached. The five crystallographically unique water molecules of crystallization were directly located from difference Fourier maps and refined successfully using anisotropic displacement parameters. All H atoms associated with the water molecules were geometrically positioned (and not refined) with O-H distances in the range 0.85-0.89 Å and U iso fixed at 1.5 times U eq of the oxygen atom to which they are attached. direction of the unit cell (K + cations and H-atoms were omitted for clarity).

Poly[[aqua-µ 3 -picolinato-µ 2 -picolinato-dipicolinatopotassium(I)terbium(III)] 2.5-hydrate]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.004 Δρ max = 1.00 e Å −3 Δρ min = −0.70 e Å −3 Absolute structure: Flack (1983) Absolute structure parameter: −0.020 (15) Special details Experimental. Please see the details in the main paper Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.