Anion Driven [Cu^IIL₂]_<i>n</i> Frameworks: Crystal Structures, Guest-Encapsulation, Dielectric, and Possible Ferroelectric Properties

Employing a flexible phosphoramide ligand L, PhPO­(NH³Py)₂ (³Py = 3-pyridyl), four new Cu­(II) cationic coordination assemblies <b>1</b>, <b>1a</b>, <b>2</b>, and <b>3</b> of composition {[Cu₂L₄(H₂O)₂]·(ClO₄)₄·(H₂O)₅·(CH₃OH)}_∞, {[Cu₃L₆(H₂O)₃]·(ClO₄)₅·(NO₃)·(H₂O)₁₁}_∞, {[Cu₄L₈(H₂O)₅]·(NO₃)₈·L·(H₂O)₉}, and {[Cu₃L₆]·(NO₃)₆·(H₂O)₈·(CH₃OH)₂}, respectively, were synthesized. The compounds <b>1</b> and <b>1a</b> having perchlorate and mixed perchlorate-nitrate anions, respectively, were obtained as noncentrosymmetric 1D-helical assemblies. However, <b>2</b> and <b>3</b> were obtained as discrete centrosymmetric assemblies of composition M₄L₈ and M₃L₆, respectively. Interestingly, <b>2</b> can encapsulate the hydrated potassium cation [K­(H₂O)₈]⁺ in its intrinsic cavity. The ferroelectric measurements of <b>1</b> and <b>1a</b> gave a well saturated ferroelectric hysteresis loop giving saturation polarization (<i>P</i>_s) values of 1.8 and 0.55 μC/cm², respectively. This indicates that the presence of nitrate anion in the packing structure has an effect in altering the asymmetry of the system, which causes a change of polarization in <b>1a</b> in comparison with that of <b>1</b>. Furthermore, the room temperature dielectric constant values of 118.7, 27.4, and 39.2 for <b>1</b>, <b>1a</b>, and <b>2</b>, respectively, suggest that they are potential candidates for high-technique applications