A organic-inorganic hybrid complex,Er4O2[C5H3(COO)2N]5(phen)2(H2O)2,has been hydrothermally synthesized from pyRIdine-2,5-dicarboxylic acid,Er(NO3)3,1,10-phenanthroline and so on,and characterized by TG,IR spectrum and X-ray crystallography.The data show it belong to monoclinic crystal system,P2(1)/c space group,with a=9.2357(1),b=55.3842(8),c=11.9419(2),β=94.5470(1)°,V=6089.20(2)((A)3),Z=4,Dc=2.093g·cm-3,F(000)=3648.0,Goof=1.075,Final R indices [Ⅰ>2sigma(Ⅰ)]:R1=0.0572,wR2=0.0958.The title complex exhibits a novel 1D polymeric structure with Erbium(Ⅲ) centers and bridged by pyridine-2,5-dicarboxylic ligands and bridging oxygen atoms.The Erbium(Ⅲ) coordination number is eight.From Fig.1,we can see it is a tetranuclear Erbium(Ⅲ) coordination complex and the four nuclears were bridged by a pyridine-2,5-dicarboxylic anion,which exist a triple bond oxygen like O1.Neighboring two Erbium(Ⅲ) (such as Er1 and Er2 or Er3 and Er4) were linked by a bridging oxygen atoms like O21 and O22,and two carboxyls connected them came into being a 22-member-ring.Otherwise the complex exists five kinds of coordination modes for pyddine-2,5-dicarboxylic ligands.Fig.2 shows One-dimensional Chain structure and the adjacent 1D chains form a 2D samdwich structure through π…π stacking between two phenanthroline.Furthermore,the ionic radii of metal cations in the compound play an essential role in arrangement of pyridine-2,5-dicarboxylic anions and phenanthroline in the structure.In addition,a 3D supramoleeular framework is formed through hydrogen bonding interaction between 2D layers structure and free water.