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Source of material 2-Pyridinecarboxylic acid (1 mmol, 0.1231 g) was dissolved in 15 ml 95 %ethanol. To this solution, Gd(NO 3 ) 3 ·6H 2 O(0.5 mmol, 0.2257 g) was added and refluxed at 333 Kf or 0.5 hour. Then 0.027 ml (0.25 mmol) diethylenetriamine was added under continuous stirring. The resulting suspension was added dropwise 0.01 mol · l −1 HNO 3 until pellucid. The mixture was refluxed at 348 Kfor 12 hours with stirring, then cooled. After filtration, the filtrate was left to stand at room temperature. Slow evaporation afforded pink block-like crystals. Experimental detailsThe aromatic Ha toms were positioned geometrically and included in the refinement using ariding model [d(C-H) =0.93 Å U iso (H) =1.2 U eq (C)]. The water Hatoms were located from different maps and their positions were refined isotropically, with O-Hdistances fixed by 0.85(2) Å and d(H···H) =1.30(2) Å,their displacement parameters were set to 1.5 U eq(O). DiscussionRare earth metal complexes are of growing importance because of their chemical [1], biochemical and medicinal applications [2]. Rare earths ions may be one of the strongest cut reagents of nucleic acids [3]. It was also reported that pyridinecarboxamide complexes provide anti-tumor activity [4,5]. Study on these kinds of compounds will be useful to develop new drugs with biological functions. The title complex has ao ne-dimensional polymeric structure. The asymmetric unit consists of two pyridinecarboxylate ,three waterm olecules and one nitrate. The gadolinium(III) atom, whichisinadistorted tetragonal-prismatic environment, is coordinated by N1, N2, O1, O2, O3, O4 from two different pyridinecarboxylate ligands and O2W, O3W from two water molecules. The bidentate carboxylic groups of carboxyl pyridine ligands chelated one gadolinium(III) center and simultaneously bridge the other one. The flexible 2-carboxyl pyridine ligands interconnect the gadolinium(III) atoms to form one-dimensional zigzag chains. There are also afree water molecule and one nitrate anion out of the coordination sphere. The conformations are stabilized by H-bonds such as O−H···O, with bond lengths of ca. 2.6 -3.2 Å.All oxygen atoms of water molecules, two oxygen atoms of nitrate and one oxygen atom of carboxyl take part at hydrogen bonding.

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