Anion Driven [CuIIL2]n 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 1, 1a, 2, and 3 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 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 M4L8 and M3L6, respectively. Interestingly, 2 can encapsulate the hydrated potassium cation [K­(H2O)8]+ in its intrinsic cavity. The ferroelectric measurements of 1 and 1a gave a well saturated ferroelectric hysteresis loop giving saturation polarization (Ps) 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 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.