Synthesis and crystal structure of new lanthanide coordination polymers with Pyridine-2, 6-dicarboxylic acid

Reactions between Ln(NO₃)₃ aq (Ln = La (1), Ce (2), Pr (3) and Nd(4)), pyridine-2, 6-dicarboxylic acid (2, 6-pdc), and sodium nitroprusside Na₂[Fe(CN)₅NO] lead to three-dimensional network structures: {[Ln₂(2, 6-pdc)₂(H₂O)₈][Fe(CN)₅NO]·4H₂O}_n (Ln = La (1), Ce (2), Pr (3) and Nd(4)). The complexes 1 and 2 crystallize in the monoclinic space group Cc while complexes 3 and 4 crystallize in the monoclinic space group I2. The Ln(III) ion is nine-coordinate by four oxygen atoms of three 2, 6-pdc ligands, four oxygen of water and one nitrogen atom of 2, 6-pdc. Ln(III) ions are bridged by 2, 6-pdc ligands via bridging/chelating-bridging pentadentate coordination to form 3-D framework structures. Hydrogen bonds provide additional stabilization of the crystal structures. The magnetic properties of 2-4 have been investigated.