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Fluorescencepropertiesof 2 and 4
The ligand-assisted photoluminescence properties of the lanthanide compounds 2 and 4 were examined at room temperature.When excited at 335 nm, 2 emits red light, while 4 shows green light emission upon excitation at 334 nm.The photoluminescence spectra are shown in Fig.4.The characteristic emission bands of 2 at 584, 598, 622,and 693 nm are assigned to 5D0 → 7FJ (J =0,1,2, and 4) transitions,while the emission peaks of 4 at 495, 548, 590,and 625 nm can be attributed to 5D4→7FJ (J =6,5,4,and3) transitions,respectively.However,these characteristic emission bands indicate that the ligand-to-metal energy transfer is moderately eﬃcient under the experimental conditions[43].It is noted that the forbidden transition 5D0 → 7F0 was also observed in the europium compound 2.Moreover,the preferred transition,5D0→7F2 for europium-containing luminescent materials,is much more intense than the 5D0→7F1 transition in 2.It is well-known that the 5D0→7F2 transition induced by the electric dipole moment is hypersensitive to the environment of the Euion,while the 5D0→7F1 transition is a magnetic dipole transition which is fairly insensitive to the coordination environment of the Euion.The intensity ratio I(5D0→7F2)/I(5D0→7F1) is equal to 3.57,which indicates that Eu3+ ions are not at an inversion center [12a].This is in agreement with the result of the single crystal X-ray diﬀraction.

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4.Conclusion
The first examples of lanthanide coordination polymers
with bpdc and phen were self-assembled by hydrothermal
method.The bpdc ligands in these polymers adopt tetrad-
entate coordination modes in two bridging bidentate car-
boxylate groups.Coordination polymers 1–4 are
isostructural,and 1-D zigzag chains are composed of
Ln2(bpdc)3(phen)2(H2O)2 building blocks.The bond
lengths of Ln–O,Ln–N and Ln Ln separations show a
lanthanide contraction over the series.The thermal stabil-
ity of the frameworks can be attributed to the high coordi-
nation number of lanthanide ions,the strong metal–
carboxylate bonds and p–p interactions.Photolumines-
cence properties indicate that compound 2 and compound
4 emit characteristic fluorescence,respectively.