Polymorph selective growth of sodium tetrakis(2-pyridinecarboxylato) lanthanides and their structure sensitive properties

Four new single crystals of sodium tetrakis(2-pyridinecarboxylato)Ln(III), where Ln is europium and terbium, with general formulas of Na[Ln(C ₆H₄NO₂)₄] · 2H₂O were prepared from a reaction of solvent-mediated polymorph selection. All the crystal structures were determined by using temperature-dependent single crystal X-ray diffraction at 100(2) and 298(2) K. No phase transition was observed within this temperature range. Two isostructural compounds, I_M (Eu³⁺ core) and III_M (Tb³⁺ core), crystallize in the monoclinic space group C_2h⁶ - C2/c (No. 15) and the other two compounds, II_H (Eu³⁺ core) and IV_H (Tb³⁺ core), in the enantiomorphic hexagonal space group D ₆³ - P6₅22 (No. 179). Both I_M and II_H (or both III_M and IV_H) are homeotypic. Each structure consists of an extensive network of organo-lanthanide complex and has extremely long-ranged interlayer distances, about 10 Å. The parallel interlayer in I_M (or III_M) can be reconstructed into II_H (or IV_II) via 6-fold angularly step-staggered packing. Such a phenomenon of crystal packing strongly depends not only on the nature of the applied solvent system but also on long-range ordering of the organo-lanthanides. Transmission electron microscopy analysis of II_H and IV_H reveals the absolute configuration of parallel helical assemblies. Their optical and magnetic data show the salient features of topospecific chirality over those racemic counterparts.