Size-dependent polymeric arrays of heterometallic Cs+–Ln3+ β-diketonates

Abstract

A series of alkali–lanthanide heterometallic systems such as Cs+–Ln3+ β-diketonate complexes [Ln(TFPB)4Cs]n (Ln = La (1), Pr (2), Eu (3), Y (4), Yb (5), Lu (6) and TFPB = 4,4,4-trifluoro-1-phenyl-1,3-butanedione) were prepared and structurally explored. The complexes exist only in polymeric forms while both monomeric and polymeric structures are found in the previously reported Na+–Ln3+ congeners. Tuning the sizes of the central rare earth ions from La3+ to Lu3+ results in three types of infinite Cs+–Ln3+ chains which are helical, two-step zigzag and single zigzag patterns. Nonetheless, the Na+–La3+ and Na+–Eu3+ complexes (1-Na and 3-Na) are isomorphous polymers. The size variation of the Ln3+ ions can also alter the degree of π interactions of the Cs+ ions with β-diketonate fragments and phenyl rings. Interestingly, multiple interactions are detected in the complexes with small rare earth ions (5 and 6). Photoluminescence measurements reveal much brighter red emission of 3 than that of 3-Na. It is assumed that the Cs+ ions have more appropriate size than the Na+ ions toward the binding with [Eu(TFPB)4]– anions via oxygen and fluorine atoms, alleviating the energy dissipation of the excited states.