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(C₆H₄NO₂)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, <b>I_M</b> (Eu³⁺ core) and <b>III_M</b> (Tb³⁺ core), crystallize in the monoclinic space group <i>C</i>₂<i>_h</i>⁶ - <i>C</i>2/<i>c</i> (No. 15) and the other two compounds, <b>II_H</b> (Eu³⁺ core) and <b>IV_H</b> (Tb³⁺ core), in the enantiomorphic hexagonal space group <i>D</i>₆³ - <i>P</i>6₅22 (No. 179). Both <b>I_M</b> and <b>II_H</b> (or both <b>III_M</b> and <b>IV_H</b>) 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 <b>I_M</b> (or <b>III_M</b>) can be reconstructed into <b>II_H</b> (or <b>IV_H</b>) 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 <b>II_H</b> and <b>IV_H</b> reveals the absolute configuration of parallel helical assemblies. Their optical and magnetic data show the salient features of topospecific chirality over those racemic counterparts.