CRYSTAL STRUCTURE OF { [ La 2 ( CNCH 2 COO ) 6 ( H 2 O ) 4 ] H 2 O } n COMPLEX

Abstract. The lanthanum(III) cyanoacetate complex of formula {[La2(CNCH2COO)6 (H2O)4]∙H2O}n (1), has been prepared and characterized by X-ray diffraction analysis. Compound crystallizes in the triclinic centrosymmetric space group P-1 (No.2), a=8.997(5) Å, b=9.251(5) Å, c=9.728(5) Å, α=67.849(5)°, β=84.224(5)°, γ=81.351(5)°. Single-crystal X-ray diffraction study reveals that crystals of 1 exhibits one-dimensional coordination polymer structure, which is composed of cyanoacetate bridged lanthanum (III) ions. The O9 coordination surrounding of La cation is completed by oxygen atoms of six carboxylate ligands that are coordinated in the bidentate bridging and tridentate-chelating bridging mode and two water molecules. The cations are bridged in a polymeric chain by four exo-bidentate cyanoacetate ligands or through μ2-O function of two other chelato-bridgind cyanoacetate ligands. The La∙∙∙La separation along the polymer is equal to 4.754(3) Å and 4.608(2) Å.


Introduction
The synthesis of functional rare-earth coordination polymers with various N-and / or O-donor ligands has attracted increasing interest, due to their various topologies [1][2][3] and potential applications as optical, electronic and magnetic materials [4][5][6][7].
The carboxylate ligands are attractive candidates for construction of the polymeric networks due to their versatile functions as bridges or terminal groups, which lead to generation of dimers [8,9], 1D chains [10], 2D-layers [11], and 3D-polymeric structures [12].
However, investigation of lanthanide complexes with cyanoacetic acid anion as ligand is very scarce [13,14].Our previous investigations of 3d and 4f metal complexes with cyanoacetate anions have demonstrated that copper(II) ion has {O 4 (carbox.)N (CN) } coordination node, while neodymium(III) ion -{O 7 (carbox.)O 2 (H ² O) }, respectively [15,16].The study of magnetic properties of gadolinium(III) cyanoacetate complex has shown that external magnetic fi eld induces two slow relaxation processes, while heat capacity and direct current susceptibility measurements at very low temperatures has indicated strong single ion anisotropy, due to the Kramer's doublet of the ground state [17].
In continuation of our research on the use of cyanoacetic acid with both O-and N-potential donor atoms as a ligand for 4f cations [16,17] and d-block transition metal [15], we have synthesized and structurally characterized the {[La 2 (CNCH 2 COO) 6 (H 2 O) 4 ]•H 2 O} n compound by single crystal X-ray method.

Physical measurements
IR spectrum of polycrystalline sample was recorded on Perkin Elmer spectrum 100 FT IR Spectrometer in the range of 4000-400 cm -1 .

X-ray crystallography
The X-ray data for 1 were collected at room temperature on an Oxford Diffraction Xcalibur diffractometer equipped with CCD area detector and a graphite monochromator utilizing MoKα radiation.The crystals were placed at 40 mm from the CCD detector.The data were processed using the CrysAlis package of Oxford Diffraction [19].The fi nal unit cell dimensions were obtained and refi ned on an entire data set.The structures were solved by direct methods using SHELX-97 program package [20] and refi ned with full-matrix least squares method with anisotropic thermal parameters for the non-hydrogen atoms.The C(sp 2 )-bound H atoms were placed in calculated positions and were treated using a riding model approximation with Uiso(H) = 1.2Ueq(C), while the hydrogen atoms of water molecules were refi ned with isotropic displacement parameter Uiso (H) = 1.5Ueq(O) using DFIX restrain instruction.The fi gures were produced using MERCURY [21].The X-ray data and details of the refi nement for 1 are summarized in Table 1, the selected geometric parameters are given in Table 2 and the hydrogen-bonding geometry is given in Table 3

Results and discussion
The reaction of lanthanum(III) oxide with cyanoacetic acid in a molar ratio of 1:3 in water solution leads to polymeric complex with the composition {[La 2 (CNCH 2 COO) 6 (H 2 O) 4 ]H 2 O} n (1).The complex is a colorless, air hygroscopic crystalline solid, readily dissolves in water, but is insoluble in organic solvents, such as methanol, acetone and acetonitrile.The IR spectrum shows the absorption band at 2265 cm -1 , which is characteristic to the (C≡N) vibrations of the ligand.
In the crystal, the parallel polymer chains run along a crystallographic axis and are united into a threedimensional network through a system of hydrogen bonds involving water molecules and nitrogen atoms of cyanoacetic ligands (Figure 2).

Conclusions
The lanthanum(III) cyanoacetate polymer of formula {[La 2 (CNCH 2 COO) 6 (H 2 O) 4 ]•2H 2 O} n (1) has been synthesized and characterized by single-crystal X-ray diffraction.The complex was found to be isostructural to Nd analog.The cyano-group of the ligand is not coordinated to the lanthanide ion.

and structure refi nement data for 1.
. CCDC 1032624 contains the crystallographic data for 1.These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.