Counteranion Modulated Crystal Growth and Function of One-Dimensional Homochiral Coordination Polymers: Morphology, Structures, and Magnetic Properties.

Abstract

Four pairs of enantiomeric dysprosium(III) phosphonates, namely, R- or S-[Dy3(pempH2)2(pempH)7]2(NO3)4·12H2O ( R-1 or S-1), R- or S-[Dy3(pempH)7(pempH2)2]Cl2·2H2O ( R-2 or S-2), R- or S-[Dy3(pempH)7(pempH2)2]Br2·2H2O ( R-3 or S-3), and R- or S-[Dy11(pempH2)6(pempH)27](CF3SO3)6·22H2O ( R-4 or S-4) are reported, where R- or S-pempH2 represent R- or S-(1-phenylethyl)amino] methylphosphonic acid. All show homochiral chain structures, charge-balanced by counteranions. A comparison of the crystal morphologies of the R-isomers reveals that the overall shapes are quite similar for the four compounds, but the aspect ratio changes remarkably following the sequence: R-1 < R-2 < R-3 < R-4. The sequence is in agreement with the decreasing interchain interactions related to different counteranions, which is rationalized by molecular simulations. The counteranions also influence the intrachain structures and the local coordination environments of the DyIII ions. As a result, compounds R-2 and R-3 exhibit distinct dual relaxation processes at zero dc field with the effective energy barriers for the slow- and fast-relaxation being 79.1 and 37.6 K for R-2, and 80.0 and 39.1 K for R-3, respectively. For compounds R-1 and R-4, however, slow magnetic relaxation is also observed at zero dc field but without the appearance of maxima down to 1.8 K.