Structural Diversity in Neodymium Bipyrimidine Compounds with Near Infrared Luminescence: from Mono- and Binuclear Complexes to Metal-Organic Frameworks

Treatment of Nd(NO3)3 with 2,2′-bipyrimidine (bpm) afforded the mononuclear adduct [Nd(NO3)3(bpm)(MeOH)2] (1) after recrystallization from MeOH, while reactions of hydrated NdCl3 and various β-diketonates in the presence of bpm gave the binuclear compounds [{Nd(dbm)3(THF)}2(μ-bpm)] (2) and [{Nd(bta)3(MeOH)}2(μ-bpm)]·bpm (3·bpm) (Hdbm = dibenzoylmethane, Hbta = 4,4,4-trifluoro-1-phenyl-1,3-butanedione) and the one-dimensional coordination polymer [Nd(tta)3(μ-bpm)·MeOH]∞ (4·MeOH) (Htta = 2-thenoyltrifluoroacetone). The crystal structures of 2−4 demonstrate that the bpm molecule can act as a planar bridging ligand between two lanthanide ions as large as Nd3+. Luminescence measurements revealed that near-IR emission from neodymium can be obtained after excitation of either the bpm or the β-diketonate ligand, and that an energy transfer occurs from the β-diketonate group to the bpm molecule.