The miracle of self-assembly: a journey of the {LnF} core in the world of lanthanides.

This work presents a unique example of the self-assembly of {LnF} clusters composed of Ln cations and F and CFCOO anions. The crystal structures of new fluorotrifluoroacetate compounds with the general formula , where A = Na and Ln = Pr(), Eu (IIa), Tb(iii), Dy(iv) and Tm(v); A = Na and HO and Ln = Eu (IIb); or A = K and Ln = Yb(vi); tfa = CFCOO (trifluoroacetate anion); L = Htfa (CFCOOH, trifluoroacetic acid) and HO, determined by the single-crystal XRD method revealed that they were constructed from the complex anion and alkali metal (or alkali metal and hydroxonium) cations and included solvate molecules in some cases. The core of the anion presented a rhombododecahedral unit of six lanthanide atoms linked by bridging fluoride and trifluoroacetate anions. The nature of the counterion led to the formation of compounds with different dimensions: from 1D for potassium cations and 2D for sodium cations to 3D for sodium and hydroxonium cations. The {LnF} clusters were obtained for a wide range of lanthanides, with Pr and Yb being the end members; thus, the existence of heterometallic compounds was presumed. At a temperature of 100 °C, the new compounds started to release solvent molecules, whereas the core was stable up to 270-300 °C according to the TG-MS data. Substances IIb, III and IV revealed metal-centered luminescence and could be used for the development of new optoelectronic materials.