Synthesis,crystal structures and properties of three new lanthanide 2,6-pyridinedicarboxylate complexes with zero-dimensional structure

Three new lanthanide dipicolinate complexes with zero-dimensional structure have been synthesized by mild hydrothermal method. In these complexes the lanthanide is surrounded by three dipicolinate groups in the usual tridentate mode. For two of them, (CN₃H₆)₃La(C₇H₃NO₄)₃] · 3H₂O I and (C₄N₂H₁₂)_1.5Ce(C₇H₃NO₄)₃] · 7H₂O II, the dipicolinate groups are wholly unprotonated. The resulting molecular entity is three-times negatively charged and the balance charge is insured by the presence of guanidinium or piperazinium ions for the first and second, respectively. For the third complex, Eu(C₇H₄NO₄)₃]₂ · 2.5H₂O III, one hydrogen atom remains globally on each dipicolinate and so the molecular entities are neutral. For the latter complex, the resulting molecular entities are connected into chains through strong hydrogen bonding. Thermogravimetric analyses and luminescent behaviour of complex III have been carried out.