Poly[diaquabis(μ4-fumarato-κ4 O 1:O 1′:O 4:O 4′)(μ4-fumarato-κ6 O 1:O 1,O 1′:O 4:O 4,O 4′)(μ2-fumaric acid-κ2 O 1:O 4)dipraseodymium(III)]

The title complex, [Pr2(C4H2O4)3(C4H4O4)(H2O)2]n, was synthesized by reaction of praseodymium(III) nitrate hexahydrate with fumaric acid in a water–ethanol (4:1) solution. The asymmetric unit comprises a Pr3+ cation, one and a half fumarate dianions (L 2−), one half-molecule of fumaric acid (H2L) and one coordinated water molecule. The carboxylate groups of the fumarate dianion and fumaric acid exhibit different coordination modes. In one fumarate dianion, two carboxylate groups are chelating with two Pr3+ cations, and the other two O atoms each coordinate a Pr3+ cation. Each O atom of the second fumarate dianion binds to a different Pr3+ cation. The fumaric acid employs one O atom at each end to bridge two Pr3+ cations. The Pr3+ cation is coordinated in a distorted tricapped trigonal–prismatic environment by eight O atoms of fumarate dianion or fumaric acid ligands and one water O atom. The PrO9 coordination polyhedra are edge-shared through one carboxylate O atom and two carboxylate groups, generating infinite praseodymium–oxygen chains, which are further connected by the ligands into a three-dimensional framework. The crystal structure is stabilized by O—H⋯O hydrogen-bond interactions between the coordinated water molecule and the carboxylate O atoms.

The title complex, [Pr 2 (C 4 H 2 O 4 ) 3 (C 4 H 4 O 4 )(H 2 O) 2 ] n , was synthesized by reaction of praseodymium(III) nitrate hexahydrate with fumaric acid in a water-ethanol (4:1) solution. The asymmetric unit comprises a Pr 3+ cation, one and a half fumarate dianions (L 2À ), one half-molecule of fumaric acid (H 2 L) and one coordinated water molecule. The carboxylate groups of the fumarate dianion and fumaric acid exhibit different coordination modes. In one fumarate dianion, two carboxylate groups are chelating with two Pr 3+ cations, and the other two O atoms each coordinate a Pr 3+ cation. Each O atom of the second fumarate dianion binds to a different Pr 3+ cation. The fumaric acid employs one O atom at each end to bridge two Pr 3+ cations. The Pr 3+ cation is coordinated in a distorted tricapped trigonal-prismatic environment by eight O atoms of fumarate dianion or fumaric acid ligands and one water O atom. The PrO 9 coordination polyhedra are edge-shared through one carboxylate O atom and two carboxylate groups, generating infinite praseodymium-oxygen chains, which are further connected by the ligands into a three-dimensional framework. The crystal structure is stabilized by O-HÁ Á ÁO hydrogen-bond interactions between the coordinated water molecule and the carboxylate O atoms.

Related literature
For the structural diversity and potential use as superconductors and magnetic materials of metal complexes of carboxylates, see: Kim et al. (2004); Ye et al. (2005). For applications of rare earth carboxylates, see: Baggio & Perec (2004); Seo et al. (2000).

Comment
Metal complexes of carboxylates have attracted much attention due to their wide range of structural diversities and potential use on superconductors and magnetic materials (Kim et al., 2004;Ye et al., 2005). What is more, a particularly attractive goal is the rare-earth carboxylates, because of their special application on the 4f-block elements and their unique f-f electronic transitions. (Seo et al., 2000;Baggio et al., 2004). In this paper, we report the title complex (scheme. 1), obtained by the reaction of praseodymium(III) nitrate hexahydrate with fumaric acid in a water-ethanol (4:1) solution.
The structure of the asymmetric unit of the title complex is shown in Fig. 1. It comprises a Pr 3+ cation, 1.5 fumarate dianions (L 2-), 0.5 fumaric acid (H 2 L) and one water ligand. The carboxylate groups of the fumarate dianion and fumaric acid exhibit different coordination modes. In one fumarate dianion, two carboxylate groups are chelating with two Pr 3+ cations, and other two O atoms(O4 and O4 iv ) are coordinated with Pr 3+ cation respectively. The other fumarate dianion bridges four Pr 3+ cations with monodentate mode, and the fumaric acid bridges two Pr 3+ cations with monodentate mode. In the crystallographic asymmetric unit, the Pr 3+ cation is sited within a distorted tricapped trigonal prism defined by nine O atoms derived from seven different bridging ligands and a coordinated water molecule. One of the carboxylate groups, derived from L 2-, is chelating, and the remaining six carboxylates coordinate in a monodentate mode. The Pr-O bond distances range from 2.4040 (15) to 2.7719 (16) Å. The O-Pr-O bond angles range from 72.35 (5) to 146.04 (5)°. The PrO 9 coordination polyhedra are edge-shared through one carboxylate O atoms (O4) and two carboxylate groups (O8-C4-O9 and O6-C1-O7) to generate infinite praseodymium-oxygen chains (Fig. 2). The chains are further connected by the ligands to form a three-dimensional framework. The crystal is stabilized by hydrogen bond interactions between the coordinated water and carboxylate O atoms.

Experimental
Fumaric acid (0.5 mmol, 0.058 g), Praseodymium(III) nitrate hexahydrate(0.3 mmol, 0.13 g) was dissolved in a water-ethanol(4:1) solution(10 ml). The mixture was transferred to a 20 ml Teflon-lined stainless steel autoclave, which was heated at 413 K for 96 h. The reactor was cooled to room temperature over a period of 24 h. Blue crystals were obtained after filtrated, washed with water and vacuum dried.

Refinement
Carbon-bound H atoms were included in the riding-model approximation, with C-H =0.93Å and with U iso (H) = 1.2U eq (C).
H atom bound to carboxyl-O atom was initially located in a difference map but was then fixed in the riding-model approx-supplementary materials sup-2 imation, with O-H = 0.82Å and with U iso (H) = 1.5 U eq (O). Water H atoms were tentatively located in difference Fourier maps and were refined with distance restraints of O-H = 0.82Å and H···H = 1.29 Å, and with U iso (H) = 1.5 U eq (O). Fig. 1. View of the local coordination of praseodymium(III) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i)x,1/2 -y,-1/2 + z; (ii)1 + x,y,z; (iii)1 + x,1/2 -y,-1/2 + z; (iv)1 -x,-y,1 -z; (v)2 -x,-y,1 -z.]  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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.3406 (