Anion Driven [Cu^IIL₂]_n Frameworks: Crystal Structures, Guest-Encapsulation, Dielectric, and Possible Ferroelectric Properties

Employing a flexible phosphoramide ligand L, PhPO(NH 3 Py) 2 ( 3 Py = 3-pyridyl), four new Cu(II) cationic coordination assemblies 1, 1a, 2, and 3 of composition {[Cu 2 L 4 (H 2 O) 2 ]·(ClO 4 ) 4 ·(H 2 O) 5 ·(CH 3 OH)} ∞, {[Cu 3 L 6 (H 2 O) 3 ]·(ClO 4 ) 5 ·(NO 3 )·(H 2 O) 11 } ∞, {[Cu 4 L 8 (H 2 O) 5 ]·(NO 3 ) 8 ·L·(H 2 O) 9 }, and {[Cu 3 L 6 ]·(NO 3 ) 6 ·(H 2 O) 8 ·(CH 3 OH) 2 }, respectively, were synthesized. The compounds 1 and 1a having perchlorate and mixed perchlorate-nitrate anions, respectively, were obtained as noncentrosymmetric 1D-helical assemblies. However, 2 and 3 were obtained as discrete centrosymmetric assemblies of composition M 4 L 8 and M 3 L 6, respectively. Interestingly, 2 can encapsulate the hydrated potassium cation [K(H 2 O) 8 ] + in its intrinsic cavity. The ferroelectric measurements of 1 and 1a gave a well saturated ferroelectric hysteresis loop giving saturation polarization ( P s ) values of 1.8 and 0.55 μC/cm 2, 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 1a in comparison with that of 1 . Furthermore, the room temperature dielectric constant values of 118.7, 27.4, and 39.2 for 1, 1a, and 2, respectively, suggest that they are potential candidates for high-technique applications.